Electronic Poster Session - Pulse Sequences & Reconstruction A
  Parallel MRI & B1 Mapping 3344-3367
  Endogenous Contrast Applications & B0 Field Correction 3368-3391
  Image Analysis & Motion Correction 3392-3415
  Parametric Mapping - T1, T2, T2*, T1rho/Elastography & Motion Correction 3416-3439
  Susceptibility & RF Pulses 3440-3463
  Electromagnetic Property Imaging & Parallel Transmit 3464-3487
     

Parallel MRI & B1 Mapping
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  13:30 - 14:30

  Computer #  
3344.   25 Highly accelerated parallel imaging using variable density spiral acquisition and spatial adaptive CORNOL reconstruction
Sheng Fang1, Wenchuan Wu2, and Hua Guo2
1Institute of nuclear and new energy technology, Tsinghua University, Beijing, China, 2Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China

 
A highly accelerated parallel imaging technique based on variable density spiral (VDS) acquisition and spatial adaptive CORNOL reconstruction is proposed. With an optimized undersampling and a reconstruction tailored for VDS, the proposed method can make the full use of MR image features by exploiting both the incoherence of aliasing artifacts and the coherence of image structures. The simulation and in vivo VDS experiments results demonstrate that this method can achieve a very high reduction factor while maintaining high SNR and well-preserved image structure

 
3345.   26 Reconstruction of undersampled radial PatLoc imaging using Total Generalized Variation
Florian Knoll1, Gerrit Schultz2, Kristian Bredies3, Daniel Gallichan2, Maxim Zaitsev2, Jürgen Hennig2, and Rudolf Stollberger1
1Institute of Medical Engineering, Graz University of Technology, Graz, Styria, Austria, 2Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 3Institute of Mathematics and Scientific Computing, University of Graz, Graz, Austria

 
This work presents a new iterative reconstruction method for undersampled radial PatLoc imaging based on the Total Generalized Variation (TGV). Results from numerical simulations and in-vivo PatLoc measurements with as few as 16 radial projections for the reconstruction of a 256x256 matrix are presented, which demonstrate significant improvements in image quality.

 
3346.   27 Autocalibrated Parallel MR Spectroscopic Imaging without Extra Autocalibrating k-space Lines
Michael Abram Ohliger1, Simon Hu1, Peder E. Z. Larson1, Robert Bok1, Peter Shin1, James Tropp2, Lucas Carvajal1, Sarah J. Nelson1, John Kurhanewicz1, and Daniel Vigneron1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States, 2General Electric Healthcare, Fremont, CA, United States

 
Autocallibrated parallel MR strategies generally rely on a densely sampled center of k-space to obtain coil array reference information. This dense sampling can be a large burden when applied to spectroscopic imaging. We present a new strategy for MR spectroscopic imaging with parallel reconstruction that eliminates the need for extra auto-calibrating lines. Combining spatial and spectral undersampling, select chemical species alias to unused portions of the spectrum, and can be used as sensitivity references. For an undersampling factor of 3, 38% fewer phase encode lines are acquired. Theoretical background, numerical simulations, and in vivo examples are presented using hyperpolarized 13C.

 
3347.   28 Correlation Imaging for Multi-Scan Acceleration in Clinical MRI
Yu Li1, Feng Huang2, Wei Lin2, Randy Duensing2, and Charles L. Dumoulin1
1Imaging Research Center, Radiology Department, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, United States, 2Invivo Diagnostic Imaging, Philips HealthCare, Gainesville, Florida, United States

 
Parallel imaging provides a generic solution to accelerating single-scan MRI. However, a clinical MRI protocol needs a series of MRI scans for acquiring a number of images with different contrast and geometry. In the presented work, we propose a new high-speed MRI framework, correlation imaging, that can accelerate multi-scan MRI by combining multi-channel acceleration mechanisms underlying parallel imaging and the shared information of a multi-scan acquisition. In a three-scan anatomical MRI protocol, we demonstrated that correlation imaging optimized for multi-scan MRI outperforms conventional parallel imaging techniques optimized for single-scan MRI.

 
3348.   29 Reconstruction of TOF Images from Undersampled k-Data Using SENSE, GRAPPA, CS, CS-SENSE, SPIRiT, and L1-SPIRiT
Jerome Yerly1,2, Michel Louis Lauzon2,3, and Richard Frayne2,3
1Electrical and Computer Engineering, University of Calgary, Calgary, AB, Canada, 2Seaman Family MR Research Centre, Foothills Medical Centre, Calgary, AB, Canada, 3Departments of Radiology and Clinical Neurosciences, University of Calgary, Calgary, AB, Canada

 
Recent advances in image reconstruction from sparsely sampled k-space data, such as CS and parallel MR imaging, provide potential solutions to enable visualization of small cerebral vessels without increasing the total acquisition time. In this study, we investigated and compared SENSE, GRAPPA, CS, SPIRiT, CS-SENSE, and L1-SPIRiT techniques to accelerate time-of-flight 3-T MR imaging. The reconstructions involving an L1-norm regularization procedure (i.e., CS, CS-SENSE, and L1-SPIRiT) resulted in lower aliasing interference, but also less conspicuous small cerebral vessels due to blurring. The auto-calibrating techniques (i.e., GRAPPA, SPIRiT, and L1-SPIRiT) exhibited less sensitivity artifacts and most reliably depicted small vessels.

 
3349.   30 A multi-kernel approach for reducing inter-slice image ghosting in simultaneous multi-slice EPI
Kawin Setsompop1,2, and Lawrence L Wald1,3
1Dept. of Radiology, A. A. Martinos Center for Biomedical Imaging, MGH, Charlestown, Massachusetts, United States, 2Harvard Medical School, Boston, MA, United States, 3Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, United States

 
Simultaneous multi-slice EPI using parallel imaging allows for an increase in sampling rate of fMRI and reduced acquisition time in diffusion imaging. Nonetheless, the unaliasing problem is difficult for closely spaced simultaneously excited slices. A blipped-CAIPI acquisition scheme was introduced to mitigate this issue by creating an inter-slice image shift to increase the distance between aliased voxels. In this work, we show that spatially varying field inhomogeneities and eddy currents can cause significant aliasing artifact in the form of inter-slice ghost leakage which is particularly problematic for blipped-CAIPI acquisitions. A multi-kernel slice-GRAPPA reconstruction technique is proposed to mitigate this issue.

 
3350.   31 A Nonlinear ARMA Model for GRAPPA Reconstruction
Yuchou Chang1, and Leslie Ying1
1Electrical Engineering, University of Wisconsin - Milwaukee, Milwaukee, Wisconsin, United States

 
IIR GRAPPA incorporates recursive terms to improve conventional GRAPPA, but has the limitation that outliers and noise lead to poor estimation in the recursive coefficients. A novel method using nonlinear ARMA (NLARMA) model is proposed to address the issue in IIR GRAPPA reconstruction. The proposed nonlinear AMRA model improves over the linear MA model used in conventional GRAPPA by incorporating both recursion and nonlinearity. The experimental results demonstrate that the proposed method is able to significantly improve the reconstruction quality of the conventional GRAPPA and IIR GRAPPA in suppressing noise and artifacts.

 
3351.   32 Self-consistent GRAPPA Reconstruction with Close-form Solution
Yu Ding1, Hui Xue2, Ti-chiun Chang3, Christoph Guetter3, and Orlando Simonetti1
1Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States, 2siemens corporate research, 3Siemens Corporate Research

 
Several new algorithms have been proposed to take advantage of k-space correlations, such as SPIRiT and PRUNO. However, these methods have no closed-form solutions, and can only be solved using computationally-intensive iterative methods. We propose a new k-space based pMRI technique, self-consistent GRAPPA by including an extra set of linear equations utilizing the intrinsic correlation between skipped k-space points. SC-GRAPPA combines the linear equations of traditional GRAPPA with these additional equations to solve for the missing k-space data. SC-GRAPPA utilizes a least-square solution of the linear equations, and therefore has a closed-form solution without any free parameters.

 
3352.   33 A Quantitative Study of Sodickson’s Paradox
Yu Ding1, Hui Xue2, Ti-chiun Chang3, Christoph Guetter3, and Orlando Simonetti1
1Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, United States, 2siemens corporate research, 3Siemens Corporate Research

 
GRAPPA reconstructs the missing k-space by applying a convolution kernel which is estimated from ACS lines using linear regression. Intuitively, ACS lines with higher SNR should boost the accuracy of the kernel estimation, and increase the SNR of GRAPPA reconstruction. Paradoxically, Sodickson and his colleagues pointed out that the higher SNR in ACS lines may lead to lower SNR in GRAPPA reconstruction. We study quantitative about how the noise in the ACS lines affects the SNR of the GRAPPA reconstruction, and proposes a simple solution to improve the SNR of TGRAPPA.

 
3353.   34 Minimal Artifact Factor SENSE
Johannes M Peeters1, and Miha Fuderer1
1Philips Healthcare, Best, Netherlands

 
In this work, an extension of the SENSE parallel imaging framework is proposed. In this new framework called Minimal Artifact Factor SENSE (MAF-SENSE), also artifact probability due to incorrect knowledge of the receiver coil sensitivities is taken into account. The latter is realized by adding an uncertainty in this knowledge in order to enable weighting of residual artifact level and SNR in the inversion problem. Results show that MAF-SENSE is well capable of removing residual aliasing artifacts caused by usage of incorrect receiver coil sensitivities.

 
3354.   35 Greater Acceleration through Sparsity-Promoting GRAPPA Kernel Calibration
Daniel S Weller1, Jonathan R Polimeni2,3, Leo Grady4, Lawrence L Wald2,3, Elfar Adalsteinsson1, and Vivek Goyal1
1EECS, Massachusetts Institute of Technology, Cambridge, MA, United States, 2A. A. Martinos Center, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Dept. of Radiology, Harvard Medical School, Boston, MA, United States, 4Dept. of Image Analytics and Informatics, Siemens Corporate Research, Princeton, NJ, United States

 
When applying GRAPPA at high accelerations, it is not always feasible to acquire sufficiently many auto-calibration signal (ACS) lines to properly calibrate the interpolation kernels. The proposed calibration method employs regularization promoting joint sparsity of the coil images that would be reconstructed. This method improves reconstruction quality and increases the total acceleration that is achievable with GRAPPA.

 
3355.   36 The Twisted coil: A New Strip Array Coil Topology for 3D SENSE
Nolwenn Caillet1, Jason Stockmann2, Leo Tam2, Gigi Galiana1, and R. Todd Constable1
1Diagnostic Radiology, Yale University, New Haven, CT, United States, 2Biomedical Engineering, Yale University, New Haven, CT, United States

 
With a traditional cylindrical strip array coil, one cannot accelerate a 3D pulse sequence along z since all the coils present the same sensitivity profile in this direction. To overcome this limitation, we propose to twist the striplines along the substrate, such that the aliased data for a given coil element do not overlap in z in undersampled acquisitions. This permits use of SENSE or GRAPPA in two phase-encoding directions, achieving higher acceleration factors without increasing the number of receiving channels.

 
3356.   37 Free-Breathing Abdominal B1 Mapping at 3T Using the DREAM Approach
Kay Nehrke1, and Peter Börnert1
1Philips Research Laboratories, Hamburg, Germany

 
In the present work a new B1 mapping approach dubbed DREAM (Dual Refocusing Echo Acquisition Mode) is proposed for free-breathing abdominal B1 mapping. The DREAM approach acquires a 2D B1 map in a fraction of a second, making it possible to freeze respiratory motion efficiently. The approach is used to study dynamical changes of B1 in the liver during free breathing at 3T.

 
3357.   38 Flip Angle Mapping in the Presence of B0 Inhomogeneity Using Orthogonal-lower case Greek alpha
Yulin V Chang1,2, and Philip V Bayly2
1Radiology, Washington University, Saint Louis, MO, United States, 2Mechanical Engineering and Materials Science, Washington University, St. Louis, MO, United States

 
Most of the phase-based flip angle (FA) or B1 mapping methods are sensitive to the background field (B0) inhomogeneity. In this work we focus on the recently proposed orthogonal-lower case Greek alpha method and investigate the effect of B0 inhomogeneity on the FA maps. We demonstrate that by acquiring an addition image with only a single RF pulse the FA-map quality can be maintained in the presence of B0 inhomogeneity, provided that the inter-pulse delay is short compared to T2*.

 
3358.   39 Validation of a very fast B1-mapping sequence for parallel transmission on a human brain at 7T
Alexis Amadon1, Martijn Anton Cloos1, Nicolas Boulant1, Marie-France Hang1, Christopher John Wiggins1, and Hans-Peter Fautz2
1I2BM/Neurospin/LRMN, CEA, Gif-sur-Yvette, France, 2Siemens Healthcare, Erlangen, Germany

 
Fast rather than accurate B1-mapping may be seeked for Tx-array calibration. We evaluate a 2D technique which is 6 times faster than a gold standard method. We compare the Flip Angle maps issued from tailored pulses designed with both calibration methods. These pulses target whole human brain excitation homogenization at 7T. Their outcome is very similar, which shows the benefit of using the faster sequence.

 
3359.   40 Accelerated B1+ mapping by model based reconstruction
Alessandro Sbrizzi1, Hans Hoogduin2, Jan J Lagendijk2, Peter R Luijten2, and Cornelis A van den Berg3
1Imaging Division, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2UMC Utrecht, 3UMC Utrecht, Netherlands

 
In this work, a model based reconstruction method for accelerated 3D B1+ mapping is illustrated. Only a limited number of transverse slices is needed as input for the reconstruction problem, reducing the scan time up to a factor 5. Positive results from simulations and in vivo measurements confirm the validity of the method.

 
3360.   41 Simultaneous B1+ magnitude and phase mapping using multi-echo AFI
Narae Choi1, Joonsung Lee1, and Dong-Hyun Kim1
1Electrical and Electronic Engineering, Yonsei University, Sinchon dong, Seoul, Korea

 
The measurement of the transmitted radiofrequency (RF) field is useful for many MR applications. Conventionally, the amplitude of the B1 was measured by B1 mapping methods and the phase of the active magnetic RF field component H+ was estimated by using spin echo (SE) sequence. Using SE sequence has one drawback which is long scan time due to relatively long TR compared to GRE sequence. This study focuses on the estimation of B1 magnitude and phase simultaneously using much faster acquisition, double TR multi-echo gradient echo sequence. This approach is validated in phantom and in-vivo experiments.

 
3361.   42 Intensity Correction at 7T using Bloch-Siegert B1+ Mapping
Mohammad Mehdi Khalighi1, Michael Zeineh2, and Brian K Rutt2
1Global Applied Science Lab, GE Healthcare, Menlo Park, California, United States, 2Radiology Deaprtment, Stanford University, Stanford, California, United States

 
High field MRI image signal is distorted by receive sensitivity variations. With the added complication of highly non-uniform transmit (B1+) at high field, receive sensitivity correction becomes even more challenging. Here we used Bloch-Siegert (B-S) B1+ mapping method to measure B1+ field and thus transmit sensitivity. Then the B-S magnitude images were used to estimate the receive sensitivity map for each individual channel over the whole brain, which was used to correct subsequent structural brain images. These receive sensitivity maps could be also used in parallel imaging reconstruction such as ASSET or SENSE.

 
3362.   43 Saturation Pulse Design with Explicit Sensitivity Maximization for Bloch-Siegert B1+ Mapping
Marcin Jankiewicz1,2, John C. Gore1,2, and William A. Grissom1,3
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, 3Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

 
We propose a novel way of designing saturation pulses for Bloch-Siegert B1+ mapping, which directly maximizes Bloch-Siegert sensitivity subject to a constraint requiring negligible on-resonant excitation.

 
3363.   44 Extending the sensitivity range for transmit array B1 mapping using relative B1 maps
Hans-Peter Fautz1, Rene Gumbrecht1, Patrick Gross1, and Franz Schmitt1
1Siemens Healthcare, Erlangen, Germany

 
The typically large dynamic range of B1 fields generated by local transmit array coils are a limiting factor for fast and robust B1 mapping. This works extends the sensitivity range of quantitative B1 mapping techniques towards low B1 amplitudes incorporating the information gained from relative B1 maps into the B1 map reconstruction.

 
3364.   45 Multi Bloch-Siegert B1+ mapping in a single experiment
Volker Jörg Friedrich Sturm1, Thomas Christian Basse-Lüsebrink1, Thomas Kampf1, and Peter Michael Jakob1
1Experimental Physics 5, University of Würzburg, Würzburg, Germany

 
A new method for phase-based B1+ mapping based on the Bloch-Siegert (BS) shift (ϕBS) was presented in the past. Being a phase-based method, the maximal ϕBS can be restricted since phase wraps cannot easily be removed for all given situations. This can be critical for BS B1 mapping using surface coils. Thus, to also obtain high quality B1 data in insensitive areas phase wraps in more sensitive areas cannot always be prevented. To reduce this problematic, a method is proposed which allows variation of ϕBS in a single echo train. Consequently, by combining the information of the various obtained ϕBS it is possible to remove phase wraps.

 
3365.   46 Rapid and low SAR B1-Mapping using a BURST-based Bloch-Siegert-Shift Sequence
Alexander Gotschy1,2, Uvo C. Hölscher3, Thomas C. Basse-Lüsebrink1,4, André Fischer5, Morwan Choli3, Thomas Kampf1, Volker Sturm1, Daniel Neumann3, Volker Herold1, Herbert Köstler5, Dietbert Hahn5, Guido Stoll4, Wolfgang R. Bauer2, and Peter M. Jakob1,3
1Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany, 2Department of Internal Medicine I, University of Würzburg, Würzburg, Germany, 3Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany, 4Department of Neurology, University of Würzburg, Würzburg, Germany, 5Institute of Radiology, University of Würzburg, Würzburg, Germany

 
An accurate knowledge of the B1+-field distribution becomes increasingly important for many MR applications like B1+ shimming, Spatially Selective Excitation algorithms or guaranteeing patient safety at ultrahigh fields. To meet the requirements of high field applications we used the lately introduced Bloch-Siegert-Shift based B1+-mapping method in a BURST sequence. The new sequence combines robustness against T2* effects with reduced SAR. In the presented study we found that a centric encoded BS-BURST sequence allows highly accelerated B1+-mapping with superior quality. The B1+ map of a whole head could be acquired in 36s which is adequate for applications in clinical routine.

 
3366.   47 Transmit Gain Calibration for Hyperpolarized 13C Patient Studies
Galen D. Reed1, Peder E.Z. Larson1, James Tropp2, Albert P. Chen3, Adam B. Kerr4, Mark van Criekinge1, Douglas A. C. Kelley5, John M. Pauly4, Kayvan R. Keshari1, John Kurhanewicz1, Sarah J. Nelson1, and Daniel B. Vigneron1
1Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, United States, 2GE Healthcare, Fremont, California, United States, 3GE Healthcare, Toronto, Ontario, Canada, 4Electrical Engineering, Stanford University, Stanford, California, United States, 5GE Healthcare, San Francisco, California, United States

 
With hyperpolarized 13C magnetic resonance imaging in the early stages of clinical translation, methods of characterizing transmitter inhomogeneity and calibration of transmit gain become increasingly important. This study presents double angle spectra acquired from a hyperpolarized 13C scan of a human prostate as well as a field mapping using the Bloch Siegert shift with ethylene glycol phantoms for the characterization of transmitter nonuniformity. This nonuniformity was incorporated into the patient study as a 2 dB attenuation adjustment, and the efficacy of this approach was validated in the in vivo patient exam.

 
3367.   48 Fast, indirect assessment of the 19F B1 profile by 1H Bloch-Siegert B1 mapping using double-resonant 1H/19F coils
Thomas Christian Basse-Lüsebrink1, Volker Jörg Friedrich Sturm1, Anna Vilter1, Thomas Kampf1, Volker Christian Behr1, and Peter Michael Jakob1
1Experimental Physics 5, University of Würzburg, Würzburg, Bavaria, Germany

 
Due to 19F properties such as high sensitivity, unambiguous localization of labeled cells and direct quantification, the MR community has regained great interest in 19F MRI. Surface coils, however, are often used due to the normally low SNR in 19F images. Since an inhomogeneous B1 profile is inherent with surface coils quantification of the 19F signal is hampered and thus strategies to map the 19F B1 profile are of great interest. The present study investigates whether or not fast 1H CPMG-based Bloch-Siegert B1 mapping of a double-resonant surface coil can enable assessment of the 19F B1 profile.
 
Electronic Poster Session - Pulse Sequences & Reconstruction A

Endogenous Contrast Applications & B0 Field Correction
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  14:30 - 15:30

  Computer #  
3368.   25 Quantitative Imaging of Selective Relaxation Component in Cartilage
Weitian Chen1, Mai LH Nguyen2, and Garry E Gold2
1Global MR Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 2Radiology, Stanford University, Palo Alto, CA, United States

 
Recently multi-exponential relaxation analysis was reported to have improved specificity of matrix assessment in cartilage. However, quantification of more than one component of T1rho or T2 significantly increases scan time and is impractical in clinical applications. We investigate mono-exponential relaxation methods to quantify relaxation property of a single relaxation component by suppressing signal from other components. Such methods are feasible in terms of clinical scan time, and have potential to achieve improved specificity to matrix component in cartilage compared to conventional mono-exponential relaxation analysis.

 
3369.   26 Optimal Filter Design for Linear Combination Filtering
Marshall Stephen Sussman1, and Walter Kucharczyk2
1Medical Imaging, University Health Network, Toronto, Ontario, Canada, 2Medical Imaging, University of Toronto, Toronto, Ontario, Canada

 
Knowledge of a tissue’s full T2 spectrum may provide additional information on tissue pathology beyond current clinical techniques. Unfortunately, methods used to measure full T2 spectra require impractically long scan times. As a possible alternative, linear combination filtering (LCF) provides information on a specified region of the T2 spectrum in clinically reasonable scan times. However, the effectiveness of LCF depends on the specific filter design. The purpose of this project is to optimize the LCF filter parameters for the myelin component of the white matter T2 spectrum.

 
3370.   27 CEST MRI of Human Knee Cartilage at 3T and 7T
Anup Singh1, Mohammad Haris1, Kejia Cai1, Victor Babu1, Feliks Kogan1, Hari Hariharan1, and Ravinder Reddy1
1Radiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States

 
The sensitivity of gagCEST in human knee cartilage is evaluated at 3T and 7T field strengths. Calculated gagCEST values without accounting for B0 inhomogeneity (~0.6 ppm) were > 20%. After B0 inhomogeneity correction, calculated gagCEST values were negligible at 3T and ~6% at 7T. Results obtained with varying saturation pulse durations and amplitudes as well as the consistency between numerical simulations and our experimental results indicate that the negligible gagCEST observed at 3T is due to direct saturation effects and fast exchange rate. At high fields such as 7T, this method holds promise as a viable clinical technique.

 
3371.   28 Application of chemical exchange saturation transfer (CEST) to the spinal cord at 7 Tesla
Adrienne N Dula1, Pooja Gaur1,2, Catherine E Frame1,3, Jane Anne Trapp Hirtle1, Blake E Dewey1, Richard D Dortch1, and Seth A Smith1
1Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, United States, 2Chemical and Physical Biology, Vanderbilt University Medical Center, Nashville, TN, United States, 3Radiation Oncology, Vanderbilt University Medical Center

 
We apply CEST to healthy cervical spinal cord at 7T and compare the results with our previous studies at 3T. We hypothesize that development of spinal cord CEST could reveal the health of the spinal cord and its relationship to disease earlier than conventional methods. Results include calculation of the amide proton asymmetry effect by integrating the area between a Lorentzian fit and the acquired CEST spectra. APT asymmetry maps at 7T reveal white/gray matter delineation but the mean values of 5 healthy controls were not significant.

 
3372.   29 Comparison of tissues characterized by CEST spectra at 7T
Kimberly L Desmond1, and Greg J Stanisz1,2
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 2Imaging Research, Sunnybrook Research Institute, Toronto, Ontario, Canada

 
The nature of the endogenous CEST Z-spectrum was examined at 7T in six anatomical regions / tissue types in mice: muscle (in vivo and ex vivo), grey matter, white matter, adipose, bladder and tumour. CEST images were acquired for a range of offset frequencies from -2000 to 2000 Hz (6.71ppm) and the shape of the spectrum was observed as a function of amide proton exchange, hydroxyl proton exchange and the presence of mobile lipids.

 
3373.   30 Improving mobile protein level detection using mDIXON-based APT-MRI in bone marrow edema
Guang Jia1, Wenbo Wei1, Xiangyu Yang1, David C Flanigan2, Jochen Keupp3, Jinyuan Zhou4, and Michael V Knopp1
1Department of Radiology, The Ohio State University, Columbus, OH, United States, 2Department of Orthopedics, The Ohio State University, Columbus, OH, United States, 3Innovative Technologies, Research Laboratories, Philips Research Europe, Hamburg, Germany, 4Department of Radiology, Johns Hopkins University, Baltimore, MD, United States

 
Amide-proton-transfer MRI (APT-MRI) has recently emerged as a new protein-based molecular imaging technique. In fat-containing tissue, one of the challenges is that fat gives signal drop at -3.5ppm deteriorating the calculation of asymmetric magnetization transfer ratio (MTR) at 3.5 ppm in APT-MRI, which cannot be resolved using a regular fat-suppression method. This study is to evaluate a multi gradient-echo DIXON (mDIXON)-based APT-MRI in bone marrow edema. The proposed technique has the potential to be applicable to fat-containing tissue tumors, such as osteosarcoma, breast cancer, and fatty liver lesion.

 
3374.   31 A novel application of Magnetisation Transfer MRI for the detection of tumour stromal reaction in spontaneous and transplanted Pancreatic Ductal Adenocarcinoma in mice.
Leanne Katherine Bell1, Davina Honess1, Dominick McIntyre1, David Tuveson2, and John Griffiths1
1Magnetic Resonance Imaging and Spectroscopy, Cambridge Research Institute, Cambridge, Cambridgeshire, United Kingdom, 2Tumour Modelling and Experimental Medicine (Pancreatic Cancer), Cambridge Research Institute, Cambridge, Cambridgeshire, United Kingdom

 
Pancreatic Ductal Adenocarcinoma (PDA) is a lethal disease with minimally effective treatments available. The genetically engineered KPC mouse develops spontaneous PDA in situ, recapitulating the genetic, molecular and pathological aspects of the human disease, including its dense desmoplastic tumour stroma. In contrast, transplanted mouse PDA has minimal stroma. Comparing these tumour types shows that Magnetisation Transfer MRI, specifically Magnetisation Transfer Ratio (MTR), can distinguish between differing stromal contents. We conclude that MTR is an effective in vivo biomarker for assessing macromolecular content and preliminary data suggest it may be valuable in assessing tumour stromal changes in a therapeutic setting.

 
3375.   32 Tumour progression with parametric maps of endogenous CEST at 7T
Kim Desmond1, Firas Moosvi1, and Greg J Stanisz1,2
1Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 2Imaging Research, Sunnybrook Research Institute, Toronto, Ontario, Canada

 
Parametric maps of endogenous CEST Z-spectrum properties (amide, OH-, and mobile lipid peaks) were obtained in five mice with Lewis lung carcinoma xenografts at 7T. Maps were generated by decomposing the spectrum for each voxel into the sum of four Lorentzian functions of variable amplitude and width representing the major endogenous proton pools. The growth of the tumour was followed for five days, and an increase in mean peak amplitude was observed for each pool.

 
3376.   33 Repeatability of chemical exchange saturation transfer measurements in healthy fibroglandular breast tissue at 3T
Adrienne N Dula1,2, Lori R Arlinghaus1,2, Richard D Dortch1,2, Blake E Dewey1, Jennifer G Whisenant1, Dan Ayers3, Thomas E Yankeelov1,2, and Seth A Smith1,2
1Vanderbilt University Institute of Imaging Science, Vanderbilt Medical Center, Nashville, TN, United States, 2Radiology and Radiological Sciences, Vanderbilt Medical Center, Nashville, TN, United States, 3Biostatistics, Vanderbilt Medical Center, Nashville, TN, United States

 
The goal of this study is to determine the repeatability of CEST MRI applied to human fibroglandular (FG) of the breast at 3T. We were able to reliably produce maps of the CEST effect caused by the presence of amide protons in healthy FG tissue. The results from this study indicate that a change in this quantified amide proton transfer effect larger than plus-or-minus sign1.321 for an individual or plus-or-minus sign0.418 for a group of 10 patients would be statistically significant (lower case Greek alpha= 0.05).

 
3377.   
34 Imaging of Regional Distribution of Brain Glutamate with GluCEST MRI
Kejia Cai1, Anup Singh1, Mohammad Haris1, Ravi Prakash Reddy Nanga1, Hari Hariharan1, and Ravinder Reddy1
1CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

 
Glutamate (Glu) is the major excitatory neurotransmitters in the brain, and is likely involved in nearly all signal processing functions of the central nervous system (CNS). Based on Glu amine proton exchange saturation transfer (GluCEST) effect, recently, we demonstrated the feasibility of mapping relative changes in Glu concentration as well as pH in vivo. GluCEST provides markedly increased spatial and temporal resolution than 1H-MRS. In the current study, brain regional variation of GluCEST is investigated and compared to existing MRS and positron emission tomography (PET) studies.

 
3378.   
35 CEST MRI as a Potential Imaging Biomarker of Mitochondrial Metabolic State of Breast Cancer
Kejia Cai1, He N. Xu2, Mohammad Haris1, Anup Singh1, Ravinder Reddy1, and Lin Z. Li2
1CMROI, Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States, 2Dapartment of Radiology, University of Pennsylvania, Philadelphia, PA, United States

 
Predicting breast tumor metastatic potential remains a challenge in cancer research and clinical practice. Previous studies indicate that tumor redox ratio heterogeneity (rim-core difference) serves as a biomarker of tumor metastatic potential. In this study, we demonstrated that CEST MRI showed tumor core-rim heterogeneity correlating with the mitochondrial redox state whereas T1 and T2 weighted MRI did not. CEST MRI of breast tumor metabolites (especially Glu) may be used as a potential non-invasive imaging biomarker of mitochondrial redox state for predicting breast cancer metastatic potential.

 
3379.   
36 Imaging paraCEST Agents Using Frequency Labeled Exchange Transfer (FLEX) MRI
Chien-Yuan Lin1,2, Nirbhay N Yadav2,3, S. James Ratnakar1, A. Dean Sherry1,4, and Peter C. M. van Zijl2,3
1Advanced Imaging Resarch Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 2F.M. Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States, 3Division of MR Research, Russell H. Morgan Dept. of Radiology and Radiological Science, Johns Hopkins University, Baltimore, Maryland, United States, 4University of Texas at Dallas, Dallas, Texas, United States

 
Frequency labeled exchange transfer (FLEX) MRI is a pulse sequence that uses excitation instead of saturation to detect chemical exchange saturation transfer (CEST) agents. It has previously been shown to allow detection of rapidly exchanging water groups on paramagnetic (paraCEST) agents as well as separation of magnetization transfer (MT) effects from exchange effects using time domain analysis. In the present study, we implemented the FLEX method on a preclinical MRI system and show that FLEX imaging of paraCEST agents is possible. This should have potential for imaging the paraCEST agents in vivo where MT effects often obscure such agents due to the need for using high B1 for rapidly exchanging groups.

 
3380.   37 Optimality of Equally-Spaced Phase Increments for Banding Removal in bSSFP
Marcus Björk1, R. Reeve Ingle2, Joëlle K. Barral3, Erik Gudmundson4,5, Dwight G. Nishimura2, and Petre Stoica1
1Department of Information Technology, Uppsala University, Uppsala, Sweden, 2Electrical Engineering, Stanford University, Stanford, California, United States, 3HeartVista, Inc., Los Altos, California, United States, 4Centre for Mathematical Sciences, Lund University, Lund, Sweden, 5Signal Processing Lab, ACCESS Linnaeus Center, KTH – Royal Institute of Technology, Stockholm, Sweden

 
Banding artifacts are a major issue in bSSFP. Several images with equally spaced phase increments are typically acquired to mitigate this issue. However, to the best of our knowledge, no theoretical justification exists for such a distribution of phase increments. We derived the Cramér-Rao bound (CRB) from the bSSFP signal model and optimized the phase increments distribution to minimize the maximum CRB over all possible off-resonances. We show that the worst-case CRB is minimized when using equally spaced phases, and that the resulting performance is relatively close to the optimal, had the off-resonance been known a priori.

 
3381.   38 Time-efficient approximate inhomogeneity correction algorithm for 3D spiral contrast enhanced imaging of the liver
Sarah Eskreis-Winkler1,2, Pascal Spincemaille1, Nanda Deepa Thimmappa1, Martin R. Prince1, and Yi Wang1
1Weill Medical College of Cornell University, New York, NY, United States, 2New York Hospital Queens, Flushing, NY, United States

 
Sliding window 3D spiral contrast enhanced MRI of the liver has been shown to significantly increase the ability to visualize the arterial phase. However, spiral imaging is prone to off-resonance artifacts. In this abstract, a time-efficient approximate algorithm for off-resonance correction was used by acquiring a single off-resonance frequency for each coil and each slice. This did not increase acquisition and reconstruction time and significantly improved image quality (p<0.0001), particularly during the arterial phase.

 
3382.   39 Prescan Phase Correction for Off-isocenter 3D FSE Imaging
Kristin L Granlund1,2, Weitian Chen3, Dawei Gui4, Donglai Huo4, Patrick LeRoux5, and Yuval Zur6
1Radiology, Stanford University, Stanford, California, United States, 2Electrical Engineering, Stanford University, Stanford, CA, United States, 3Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 4MR PSD and Applications, GE Healthcare, Waukesha, WI, United States, 5Applied Science Laboratory, GE Healthcare, Europe, 6GE Healthcare, Israel

 
The use of 3D FSE sequences is limited off-isocenter due to gradient non-idealities, such as gradient-induced eddy currents. By measuring the errors during prescan, we are able to adjust the imaging gradients to improve image quality. We use a phase cycling approach to measure the phase error due to the readout gradients and a z phase encoding approach to measure the phase error due to the slice encoding gradients. The correction removes banding artifacts for off-isocenter 3D FSE acquisitions in short prescan times.

 
3383.   40 EPI Distortion Correction with ORACLE
Wei Lin1, Feng Huang1, Enrico Simonotto1, and Randy Duensing1
1Invivo Corporation, Philips Healthcare, Gainesville, Florida, United States

 
A rapid EPI distortion correction method is proposed by off-resonance artifacts correction with convolution in k-space (ORACLE). A basis kernel is first computed by k-space data fitting between two EPI datasets with slightly different echo times. A B0 map is then computed from the inverse Fourier Transform of this basis kernel, resulting in robust estimations even in low signal intensity regions. Then different convolution kernels are applied to different phase-encoding lines to correct for EPI distortion directly in the k-space. In vivo brain DWI study demonstrates excellent correction results. An additional advantage of ORACLE is the reusability of correction kernels for images acquired with the same sequence but different contrasts.

 
3384.   41 A Deconvolution Approach for Image Deblurring in 3DFSE Acquisition
Weitian Chen1, Lai Peng1, Anja CS Brau1, Mai LH Nguyen2, and Garry E Gold2
1Global MR Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 2Radiology, Stanford University

 
Fast spin echo acquisition (FSE) plays a central role in clinical MRI. A major limitation to this approach is that T2 decay during multiple echoes acquisition can result in image blurring. Methods based on flip angle modulation have been reported to address this problem so that long echo train can be used to achieve high SNR efficiency in 3D imaging without excessive image blurring. In this work, we reported an efficient approach to further reduce the blurring in such advanced 3D FSE imaging methods based on deconvolution of k-space.

 
3385.   42 Impact of frequency drifts during PROPELLER-EPI measurements
Martin Krämer1, and Jürgen R Reichenbach1
1Medical Physics Group, Department of Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Germany

 
Shifts of the resonance frequency will with an EPI readout lead to a shift of the corresponding image in phase encoding direction. With a PROPELLER-EPI sampling scheme the periodically changing phase encoding direction causes the low resolution images to be shifted in different directions, ultimately leading to a strong image blurring. In the present work we characterize the impact of frequency shifts on PROPELLER-EPI measurements while discussing different solutions for measuring and compensating occurring frequency shifts.

 
3386.   43 Predicting field distortions in the human brain using a susceptibility model of the head
Rebecca Sostheim1, Julian Maclaren1, Frederik Testud1, and Maxim Zaitsev1
1University Medical Center Freiburg, Freiburg, Baden Württemberg, Germany

 
Susceptibility-induced field distortions in the human brain lead to image artifacts in MRI data, especially when motion of the head occurs. To predict and correct for these distortions using a susceptibility model it is necessary to accurately distinguish between bone and air, which is difficult in normal MRI images. In this work we compare two methods (a UTE-based method and an atlas-based method) of generating a head model that can be used to calculate the induced magnetic field. We show that it is sufficient to use a model that includes only the head and consists of only two susceptibility components.

 
3387.   44 Point Spread Function (PSF) Map Technique for Distortion Correction of Echo Planar Imaging (EPI) at 7T
Yu Cai1, Mark Woods1, John Grinstaed2, William Rooney1, Xin Li1, Qingwei Liu3, Craig Hamilton4, and Hongyu An5
1Oregon Health&Science University, Portland, OR, United States, 2Siemens Healthcare, U.S.A, 3Barron Neurological Institure, Phonenix, AZ, United States, 4Wake Forest University, 5University of North carolina

 
Point spread function (PSF) mapping method has been proposed to correct for the geometric distortion. We further developed the PSF mapping technique using the regularized inverse solution and dual echo acquisition strategy for EPI distortion correction at 3.0T, in which the first EPI readout serve the PSF mapping and the second EPI readout is the actual EPI acquisition Its advantage is no need of the extra scan time to acquire the PSF map. With the rapidly expanding interest of fMRI study in utilizing ultra high field system, it becomes urgent to develop a robust EPI distortion correction scheme at 7.0T. We attempted to apply PSF mapping technique developed in 3.0T to test its correction efficacy at 7.0T.

 
3388.   45 Retrospective image correction in the presence of temporal magnetic field changes using SENSE navigator echoes
Maarten J. Versluis1,2, Bradley P. Sutton3, Paul W. de Bruin1, Peter Boernert2,4, Andrew G. Webb1,2, and Matthias J.P. van Osch1,2
1Radiology, Leiden University Medical Center, Leiden, Netherlands, 2C.J. Gorter Center for high field MRI, Leiden University Medical Center, Leiden, Netherlands, 3Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, Champaign, IL, United States, 4Research Europe, Philips, Hamburg, Germany

 
Spatio-temporal magnetic field changes in the brain caused by breathing or body movements can lead to image artifacts. This is especially a problem in high magnetic field T2*-weighted sequences. By acquiring a navigator echo using multiple receive channels and their respective coil sensitivity profiles the spatially varying magnetic field was estimated, termed SENSE navigators. A retrospective reconstruction framework was implemented in Matlab using an iterative conjugate gradient solver. Compared to a simple zeroth order navigator the SENSE navigator technique lead to a significant reduction of image artifacts.

 
3389.   46 Magnetic Field Monitoring of Radial Trajectories
Daniel Giese1,2, Christoph Kolbitsch1, Andrew Aitken1, Martin Buehrer2, Tobias Schaeffter1, and Sebastian Kozerke1,2
1Division of Imaging Sciences, King's College London, London, United Kingdom, 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

 
Radial k-space trajectories are widely used in motion correction applications and for undersampled acquisitions given the repeated sampling of the centre of k-space. Radials are, however, prone to eddy currents and gradient delays effects. In this work, we analyze the miscentering of k-space using a 3rd order magnetic field camera, measuring k-space and quantifying gradient delays and eddy currents. Single slice, dual slice and cardiac cine images are acquired in-vivo and corrected using the measured trajectories reducing the level of artifacts. The method uses a single preparation scan to acquire k-space and can be used for any angular spoke distribution and level of undersampling.

 
3390.   47 Evaluation of off-resonance correction with and without an acquired field map in variable-density contrast enhanced spiral perfusion imaging
Christopher Sica1, Matt Restivo2, Chris Kramer3, Craig Meyer2, and Michael Salerno3,4
1Radiology, Pennsylvania State University, Hershey, PA, United States, 2Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, 3Cardiology, University of Virginia, Charlottesville, VA, United States, 4Biomedical Engineering, University of Virginia

 
Off-resonance correction removes spiral-related blurring artifacts. Usually a collected field map is required, lowering the efficiency of data collection. Time sensitive applications would benefit from an automatic deblurring algorithm that does not require an acquired field map. This work compares the performance of a field map based semi-automatic (SA) deblurring technique with full automatic (FA) technique and a standard gridding reconstruction (UC), in the context of spiral stress perfusion imaging. A blinded evaluation of images from 8 subjects yielded mean scores of 3.9 (UC), 4.2 (SA) and 4.3 (FA) (p=0.2), with a trend towards automatic reconstruction (FA/SA) being superior to UC (p=0.14).

 
3391.   48 Volumetric R2* mapping using 3D z-shimmed single scan multi-echo gradient-echo imaging
Dongyeob Han1, Yoonho Nam1, Sung-Min Gho1, and Dong-Hyun Kim1
1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea

 
Accurate R2* value quantification is required for many applications. Multi-echo GRE imaging method is generally used to evaluate R2* value. However, the main drawback of this method is the influence of macroscopic B0 inhomogeneity which occurs as unintended phase dispersion. In this study, we have presented a volumetric R2* map including which corrects for macroscopic B0 inhomogeneity. The methods use a multi-echo 3D GRE approach with increasing field inhomogeneity compensation gradient and does not require additional scan time.
 
Electronic Poster Session - Pulse Sequences & Reconstruction A

Image Analysis & Motion Correction
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  13:30 - 14:30

  Computer #  
3392.   49 Automated Vertebra Numbering and Plane Prescription along the Spine Using a Multi Model Atlas
Hima Patel1, Rajat Vikram Singh2, Vidit Aatrey3, Ramasubramanian Sundararajan1, and Vivek Vaidya1
1Global Research, General Electric, Bangalore, Karnataka, India, 2Information Technology, Indraprastha Institute of Information Technology - Delhi, New Delhi, India, 3Electrical Engineering, Indian Institute of Technology - Delhi, New Delhi, India

 
Manual numbering & plane prescription along spinal MRI image is a tedious and time consuming task. This paper describes a technology for automatic annotation, numbering, and oblique axial plane prescription along the vertebral column. A robust solution was developed for cervical, thoracic, and lumbar regions.

 
3393.   50 Tractography-based method for the estimation of the co-registration error for white matter structures
Christian Ros1, Hellmuth Ricardo Muller-Moran2, Daniel Güllmar1, Martin Stenzel3, Hans-Joachim Mentzel3, and Jürgen Rainer Reichenbach1
1Medical Physics Group, Department for Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Thuringia, Germany, 2McGill University, Montreal, Quebec, Canada, 3Pediatric Radiology, Department for Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Thuringia, Germany

 
With this contribution we present a new tractography-based estimation technique to determine the error of co-registration techniques. Acquired datat sets are used as gold standard (GS). Displacement fields are then utilized to generate prototype data sets (PDS). These PDS are co-registered to the GS and transformed back to the original space. Due to the one-to-one correspondance of the fiber tracts, that were transformed as well, the error can be exactly determined. The technique was used to evaluate the ANTs co-registration framework, in order to determine optimal registration parameter as well as suitable contrasts for the co-registration of white matter regions.

 
3394.   51 Dog’s Whole Brain Probabilistic Diffusion Tensor Imaging Tractography Normalization: A Solution for Brain Image Normalization Difficulty Problems
Witaya Sungkarat1, Jiraporn Laothamatas1, Boonlert Lumlertdacha2, Supaporn Wacharapluesadee3, and Thiravat Hemachudha4
1Advanced Diagnostic Imaging and Image-Guided Minimal Invasive Therapy Center and Radiology Dept., Ramathibodi Hospital Faculty of Medicine, Mahidol University, Rajataewe, Bangkok, Thailand, 2Queen Saovabha Memorial Institute, Thai Red Cross Society, Bangkok, Thailand, 3WHO Collaborating Center for Research and Training on Viral Zoonoses, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand, 4Department of Medicine and WHO Collaborating Center for Research and Training on Viral Zoonoses, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand

 
A new normalization technique using whole brain probabilistic DTI tractography maps is presented. This technique can address immense brain variability, even in dog’s brains. Both FSL and SPM2 were used. The usefulness of the technique was demonstrated in conducting voxel-based group analyses of FA and MD maps of rabid and normal dogs.

 
3395.   52 Improving lesion classification using an empirical knowledge of false classifications in multiple sclerosis
Sushmita Datta1, Xiaojun Sun1, and Ponnada A. Narayana1
1Department of Diagnostic and Interventional Imaging, The University of Texas Health Science Center at Houston, Houston, TX, United States

 
Automated classification of lesions in multiple sclerosis (MS) is often hindered by the presence of false classifications (FCs). These FCs occur due to presence of some regions mimicking lesions. We have developed and implemented a false classification probability (FCP) map for improved lesion classification using the knowledge of false classifications obtained from automated segmented and validated lesion classifications. The application of FCP map significantly improved the lesion classification in 57 MS subjects as assessed by the Dice similarity indices.

 
3396.   53 An Automatic Localization of Anterior Commissure and Posterior Commissure in MR Images Using Hierarchical Attribute Vectors
Ke Gan1, Jianli Wang2, Sica Christopher2, and Daisheng Luo1
1College of Electronics and Information Engineering, Sichuan University, Chengdu, Sichuan, China, 2Department of Radiology, College of Medicine, Pennsylvania State University, Hershey, PA, United States

 
A new method is presented for automatic localization of the anterior and posterior commissure in MR images of human brain. Experimental results demonstrated the accuracy and effectiveness of the method when compared with a neuroradiologist’s manual delineation.

 
3397.   54 A robust Automated Scan Prescription in MRI liver scans
Takao Goto1, and Hiroyuki Kabasawa1
1Global Applied Science Laboratory, GE Healthcare, Hino-shi, Tokyo, Japan

 
We present a new method of the automatic scan prescription for MRI liver scans. This method is robust for the variety of liver shape due to individuals, disease and post-surgery. 3D dataset acquired using fast T1 sequence is preprocessed and converted into 2D coronal projection images as well as previous method. To deal with the shape of deformed live, MAP estimate using local inhomogeneity and liver signal distribution was applied without any shape constraints. 45 volunteers and 12 datasets simulating deformed liver were tested and showed the satisfactory results in the position accuracy and the computation time.

 
3398.   55 Automated Quantitation of CSF Volumes in Central Nervous System by MRI
Ahmet Murat Bagci1, Sudarshan Ranganathan1, Juan S Gomez1, Byron Lam2, and Noam Alperin1
1Radiology, University of Miami, Miami, FL, United States, 2Ophthalmology, University of Miami, Miami, FL, United States

 
The amount of cerebrospinal fluid (CSF) and its distribution with the central nervous system are central to our understanding of CSF related brain and spinal cord disorders. While reliable automated segmentation methods are available for brain, no such method is available for spinal CSF segmentation. Current segmentation of spinal CSF spaces relies on manual delineation which is time consuming and operator dependent. A methodology to delineate the volume of CSF within the whole central nervous system is presented and preliminary results were obtained from scans acquired before and after lumbar puncture.

 
3399.   56 SPatial REgression Analysis of Diffusion tensor imaging (SPREAD) for longitudinal comparison of neurodegenerative disease progression in individual subjects
Tong Zhu1, Rui Hu2, Xing Qiu2, Wei Tian1, Sven Ekholm1, and Jianhui Zhong1
1Imaging Sciences, University of Rochester, Rochester, NY, United States, 2Biostatistics and Computational Biology, University of Rochester, Rochester, NY, United States

 
Diffusion tensor imaging (DTI) technique has been widely applied to study white matter (WM) abnormality longitudinally. For many neurodegenerative diseases, such as multiple sclerosis (MS), the WM abnormality has strong subject- or time-dependent heterogeneous patterns towards which most group-based analyses for DTI, including VBM and TBSS, are less sensitive. In this study, we propose a novel statistical analysis approach for DTI based on a nonparametric spatial regression fitting of DTI data among neighboring voxels. Statistical inference can be made for both group comparison among individuals and longitudinal comparison within the same individual. Effectiveness of this approach on group comparison was compared with the VBM approach while the proof of concept for longitudinal analysis of a single subject was evaluated through a MS patient with progressive lesions. Results show that the new method is comparable to the VBM approach and performs better than VBM when the number of scans per group is small than 5. Moreover, it detected longitudinally decreased FA from only one DTI scan per time point for a MS patient with progressive lesions. Our method provides a potentially better way to assess individual abnormality to determine more directly how the brain has changed as a result of disease/injury.

 
3400.   57 Strain Rate Mapping of the Lower Leg muscles during Plantarfelxion Excursion using MR Velocity Mapping.
Usha Sinha1, Ali Moghaddasi2, and Shantanu Sinha2
1Physics, San Diego State University, San Diego, CA, United States, 2Radiology, University of California at San Diego, San Diego, CA, United States

 
Strain rate describes the rate of regional deformation and does not require 3dal tracking, or a reference state since strain rate is an instantaneous measure of kinematic properties. Our focus was to extract strain rate from spatial gradients of the velocity vector calculated from velocity encoded PC images. A challenge is the noise in the gradient maps which was addressed with a novel application of an anisotropic diffusion filter. Strain rate maps were calculated in 5 normal subjects during ankle plantarflexion excursion. Compressive and expansive strain tensors could be visualized and revealed complex spatial patterns with temporal changes.

 
3401.   58 Tracking Muscle Tissue Displacement during Plantarflexion Excursion using Non-linear Deformation of Magnitude MR Images.
Usha Sinha1, Alec Biccum1, and Shantanu Sinha2
1Physics, San Diego State University, San Diego, CA, United States, 2Radiology, University of California at San Diego, San Diego, CA, United States

 
The study focuses on the application of a non-linear warping algorithm based on optical flow to recover muscle tissue displacements from dynamic magnitude MR images. These were acquired on a 1.5-T GE scanner with a gated VE-PC imaging sequence while the subject exerted periodic ankle plantarflexion excursions. Tissue displacements were extracted from the magnitude images by warping the reference (first) image to images acquired at other phases. The deformation vectors recovered by the algorithm are visualized on a 2D grid; the grid deformation agreed with anticipated tissue displacements. The study shows the potential for deformations to be recovered directly from magnitude images.

 
3402.   59 Automated Navigator Tracker positioning for MRI liver scans
Takao Goto1, and Hiroyuki Kabasawa1
1Global Applied Science Laboratory, GE Healthcare, Hino-shi, Tokyo, Japan

 
We present a new method of automated positioning of Navigator Tracker for MRI liver scans. This method analyzes 2D images acquired by usual scout scan for scan planning and the dome peak of the liver is used for the Navigator Tracker position. Following recognition of body outline and lung location, edge-base detection of the dome peak with organ-dependent constraint enabled a few seconds computation and no additional scan only for this method, resulting in workflow improvement. 51 volunteersf dataset from both SSFSE and FSPGR-base scout scan were tested offline and obtained satisfactory results.

 
3403.   60 Semi-automated Tracking of Tongue Movements in Dynamic MRI of Speech
Bradley P Sutton1, Andrew Naber1, Jason Wang1, Jamie L. Perry2, and David P Kuehn3
1Bioengineering Department, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Department of Communication Sciences and Disorders, East Carolina University, Greenville, NC, United States, 3Department of Speech and Hearing Sciences, University of Illinois at Urbana-Champaign, Champaign, IL, United States

 
As the frame rate of dynamic speech imaging with MRI increases, automated extraction of frame-by-frame soft tissue movements becomes critical for evaluating large studies of pathology or cultural differences in movement. This is a challenging task as dynamic MRI suffers from noisy images and lack of contrast in structures. We present a semi-automated algorithm to extract two tongue positions (tip and dorsum) and compare the tracking results with three trained speech scientists. The semi-automated algorithm performs well in correlating with the manual tracings on data from four study participants.

 
3404.   61 3D PROMO MRI with Automatic Initial Navigator Placement
Dan Rettmann1, Xiaodong Tao2, Jun Xie3, and Ajit Shankaranarayanan4
1Global Applied Science Laboratory, GE Healthcare, Rochester, MN, United States, 2GE Healthcare, Beijing, China, 3MR Engineering, GE Healthcare, Waukesha, WI, United States, 4Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

 
Prospective motion correction techniques have been shown to be beneficial in less compliant patient populations. The image-based PROspective MOtion (PROMO) correction performs best if navigators are optimally placed with respect to the anatomy. This work describes a new technique to automatically position the navigators based on an automatic scan planning algorithm that uses a rapid implicit symmetry axis determination.

 
3405.   62 Navigator Flip Angle Optimization for Navigator-Gated T1-Weighted Gadoxetic Acid-Enhanced Hepatobiliary Liver Imaging
Jens-Peter Kühn1,2, James H Holmes3, Diego Hernando1, and Scott B Reeder1,4
1Department of Diagnostic Radiology, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2Department of Diagnostic Radiology, University Greifswald, Greifswald, MV, Germany, 3Global Applied Science Laboratory, GE Healthcare, Madison, Wisconsin, United States, 4Medical Physics, Biomedical Engineering and Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States

 
This work optimizes the excitation flip angle of a navigator pencil-beam to maximize optimal liver/lung contrast while avoiding saturation artifacts in the liver. We used an investigative navigator-gated T1-weighted 3D GRE sequence under clinical conditions for gadoxetic acid-enhanced liver MRI in the hepatobiliary phase. The presence of saturation artifacts and the optimal navigator flip angle are highly dependent on the imaging flip angle and the presence of gadolinium in the liver. Using an imaging flip angle of 30o, 20-60 minutes after gadoxetic acid, the optimal navigator flip angle is 90o, without any appreciable saturation artifact.

 
3406.   63 Inherent Motion Correction for Multi-Shot Spiral Diffusion Tensor Imaging
Trong-Kha Truong1
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States

 
Multi-shot spiral imaging is a promising alternative to echo-planar imaging for high-resolution diffusion tensor imaging. However, subject motion in the presence of diffusion-weighting gradients causes phase inconsistencies among different shots, resulting in signal loss and aliasing artifacts in the reconstructed images. Such artifacts can be reduced by using a variable-density spiral trajectory or a navigator echo, however at the cost of a longer scan time. Here, we propose a novel iterative phase correction method that can inherently correct for these motion-induced phase errors with no scan time penalty.

 
3407.   64 Evaluation of Coil Selection Algorithms for Body Navigators
Anja Brau1, and Yuji Iwadate2
1Global Applied Science Lab, GE Healthcare, Menlo Park, CA, United States, 2Global Applied Science Lab, GE Healthcare, Hino, Tokyo, Japan

 
Respiratory navigator techniques rely on the processing algorithm to accurately extract motion information from the navigator echo. When using a multi-channel receive coil, the selection of which channel to use can influence the success of the navigator processing algorithm. By selecting a subset of channels, the coil sensitivity modulation of the navigator signal can be exploited to enhance the prominence of features of interest while also improving real-time processing efficiency. In this work, we evaluate the suitability of different coil selection methods for use with navigator processing and propose a method based on a matched filter.

 
3408.   65 Spectrally Selective Crossed-Pair Navigator
Zarko Celicanin1, Oliver Bieri1, Klaus Scheffler2,3, and Francesco Santini1
1Division of Radiological Physics, Department of Radiology and Nuclear Medicine, University of Basel Hospital, Basel, Switzerland, 2MRC Department, MPI for Biological Cybernetics, Tübingen, Germany, 3Dept. Neuroimaging and MR-Physics, University of Tübingen, Tübingen, Germany

 
A spectrally selective pencil-beam navigator method has been recently published for motion compensation of MRgHIFU therapy of abdominal organs. The suggested spectral navigator consisted of a spiral 2D pencil-beam using 1-[-1]-1 binomial pulses and was proposed for the tracking of abdominal organs, such as the liver or kidney, based on the surrounding adipose tissue signal. Here, we present a novel spectrally selective navigator technique based on a spin echo with orthogonal planes for the excitation and refocusing pulses , also called crossed-pair navigator, but using 1-[-1] binomial pulses for excitation and refocusing.

 
3409.   66 Real time Interscan Alignment in the abdomen using a fast spiral Navigator (ISAN): Initial Results
Gabriele Beck1, John Penatzer2, Vincent Denolin3, Kenneth Coenegrachts4, and Gwenael Herigault1
1Philips Healthcare, Best, Netherlands, 2Philips Healthcare, Cleveland, United States, 3Philips Healthcare Benelux, Brussels, Belgium, 4Department of Radiology, AZ St.-Jan Brugge-Oostende AV, Bruges, Belgium

 
In oncology there is a high interest in investigating suspicious lesions over different MR contrasts. In the abdomen breathing motion and breath hold variations are the main issues that restrict the direct comparison of a lesion across different scans which makes the classification of those lesions more difficult. In this work, prospective interscan alignment using a fast spiral Navigator acquisition allowed for real time adaptation of the scan position and registration of the volume of interest. This allows a direct comparison of lesions across breath hold or free breathing scans within an examination. End expiration triggered and breath held scans show a good consistency over the different contrast scans which were tested. While for inspiration breath holds the large feet head difference in the dome level is corrected, variations in the appearance can be larger in some subjects and can be explained by rotation and deformation of part of volume.

 
3410.   67 A Reconstruction Method for Non-rigid Motion Compensation in Brain MRI
Feng Huang1, Wei Lin1, Chiel den Harder2, Gabrielle Beck2, Clemens Bos3, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, FL, United States, 2Advanced Solutions, MRI, Philips Healthcare, Best, Netherlands, 3MR Clinical Science, Philips Healthcare, Best, Netherlands

 
Most existing motion compensation techniques for brain MRI assume that the motion is rigid. In fact, many kinds of non-rigid motion such as eye movement (eye ball rolling), skin movement (frowning), and jaw movement (swallowing, yawning), can also cause serious spatially local artifacts in brain imaging. These inevitable problems have not been carefully addressed. To remove these artifacts, data rejection and reconstruction with remaining unpolluted data can be used. However, the reconstruction with partial data could result in potential artifacts, such as reduced SNR and loss of contrast. In this work, it is proposed to use the image reconstructed with the full k-space, which is locally artifact corrupted but with high SNR, as a regularization in reconstruction to achieve an image with low artifact level and high SNR.

 
3411.   68 Fast Spin Echo T1w and PDw PROPELLER with Motion Correction using Extended Echo Trains
James H Holmes1, Philip J Beatty2,3, Howard A Rowley4, Ann Shimakawa5, and Jean H Brittain1,6
1Global Applied Science Laboratory, GE Healthcare, Madison, WI, United States, 2Global Applied Science Laboratory, GE Healthcare, Toronto, ON, Canada,3Physical Sciences, Sunnybrook Research Institute, Toronto, ON, Canada, 4Radiology, University of Wisconsin-Madison, Madison, WI, United States, 5Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 6Canada

 
In this work, we describe a method for generating motion corrected T1w and PDw (Proton Density) weighted images using the PROPELLER acquisition. Traditionally, PROPELLER relies on wide image blades for motion correction and blade combination methods to maximize the SNR of the overall image. We demonstrate two modifications. First, a centric acquisition is performed. Motion correction parameters are then determined using the full ETL and associated blade width of 35-29 echoes. However, the data used for image generation is taken from only the center 3-5 echoes, representing the shortest TE times. The motion correction parameters from the wide blade acquisition are then used to correct the narrow blade image data.

 
3412.   69 Radial MARs for Correction of Motion Artifacts due to Breathing
Candice A. Bookwalter1, Nicole Seiberlich2, Michael W. Harrell3, Philipp Ehses4,5, Mark A. Griswold1,2, and Vikas Gulani1,2
1Department of Radiology, University Hospitals Case Medical Center\Case Western Reserve University, Cleveland, OH, United States, 2Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, United States, 3School of Medicine, Case Western Reserve University, Cleveland, OH, United States, 4Max Planck Institute for Biological Cybernetics, Tübingen, Germany, 5Department for Neuroimaging, University Hospital Tübingen, Tübingen, Germany

 
While radial k-space trajectories are known to be inherently insensitive to motion due to the oversampling of the center of k-space, patient motion causes image degradation by object distortion and streaking artifacts. An algorithm called Motion Artifact Removal by Retrospective Resolution Reduction (MARs) for rectilinear trajectories has been previously described, which automatically and retrospectively identifies a transition between breath hold to free breathing and subsequently removes the corrupted data for a motion artifact free, yet lower resolution image. This work expands the MARs method to radial sequences demonstrated through volunteer and patient data.

 
3413.   70 Motion Correction for 3D Radial Encoded Spoiled Gradient Echo Imaging of the Head
Andre Jan Willem van der Kouwe1, and Himanshu Bhat2
1A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 2Siemens Healthcare US, Charlestown, MA, United States

 
By ordering the spokes of a 3D radial encoded scan in such a way that images may be reconstructed from smaller windows of the acquisition, rigid body motion detection and correction is possible. A method is presented for uniformly ordering the spokes across a hierarchy of window lengths, along with a hierarchical image reconstruction approach that results in a complete and consistent k-space representation and final reconstruction. The method is demonstrated in an ultrashort TE scan of a volunteer’s brain.

 
3414.   71 Intra-frame motion correction in dynamic radial MRI using the Phase Correlation Method
Ghislain Vaillant1, Claudia Prieto2, Christoph Kolbitsch2, Graeme Penney2, and Tobias Schaeffter2
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom, 2King's College London

 
Motion is a dramatic factor of image quality degradation in MRI. Dynamic MR can be used for limiting the effect of motion during the acquisition. We propose to combine a conventional sliding window reconstruction with a Fourier-based registration technique in order to correct for rigid motion in highly segmented radial acquisitions. The proposed method has been compared to image-based registration and was successfully applied in-vivo on 6 volunteers for 2D brain imaging.

 
3415.   72 Motion Correction for 3D Phase Contrast Flow Imaging with Cranial PCVIPR
Ashley Gould Anderson III1, Julia Velikina1, Oliver Wieben1,2, and Alexey Samsonov2
1Medical Physics, University of Wisconsin, Madison, Wisconsin, United States, 2Radiology, University of Wisconsin, Madison, Wisconsin, United States

 
Robust 3D rigid-body motion correction technique using 3D radial trajectories. The method was adapted for additional challenges of cardiac-gated phase contrast flow imaging.
 
Electronic Poster Session - Pulse Sequences & Reconstruction A

Parametric Mapping - T1, T2, T2*, T1rho/Elastography & Motion Correction
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  14:30 - 15:30

  Computer #  
3416.   49 Synthetic T1rho Mapping with Multispectral Quantitative Magnetic Resonance Imaging: Initial Results with a Non Spin-Lock Technique
Hernan Jara1, Stephan William Anderson1, and Osamu Sakai1
1Radiology, Boston University Medical Center, Boston, Massachusetts, United States

 
Purpose: To develop an algorithm for synthesizing T1rho maps using standard qMRI relaxometry instead of using direct spin-lock imaging acquisition techniques. Methods: A variant of the mixed turbo spin echo pulse sequence which is multispectral in PD, T1, and T2 was used at 3T. Images were processed with qMRI algorithms to generate T1 maps at varying spin-lock phase angles. Results: The resulting T1rho maps vary in appearance as a function of the spin-lock phase angle. Conclusion: A qMRI relaxometry-based technique for mapping the longitudinal relaxation time in the rotating frame T1rho has been developed and tested in the human head.

 
3417.   50 Mapping the T1/T2 Ratio of the Human Head with Multispectral qMRI at 3T
Kotaro Sekiya1,2, Memi Watanabe1, Osamu Sakai1, Rohini N. Nadgir1, Adham A. Mottalib1, Mingxin Zheng3, and Hernan Jara1
1Boston Medical Center, Boston University School of Medicine, Boston, MA, United States, 2Nihon University Graduate School of Dentistry at Matsudo, Chiba, Japan, Japan, 3Graduate Student of Biomedical Engineering Department, Boston University, Boston, MA, United States

 
Purpose: To develop a technique for mapping the qMRI T1/T2 ratio and to study the hierarchical order of T1/T2 ratio values of the normal human head. Methods: A variant of the mixed turbo spin echo pulse sequence which is multispectral in PD, T1, and T2 was used at 3T. Images were processed with qMRI algorithms to generate T1/T2 ratio maps and whole head histogram. Results: The resulting T1/T2 ratio maps exhibit dark CSF and bright muscles. The cerebral tissues appear in the hierarchy of signal intensities of a T2-weighted fluid attenuated with inversion recovery (T2W-FLAIR) image. Conclusion: A technique for mapping the T1/T2 relaxometric ratio has been developed.

 
3418.   51 Robust estimation of T1 and T2 parameters from complex datasets
Umesh Rudrapatna1, Annette van der Toorn1, and Rick Dijkhuizen1
1Biomedical MR Imaging and Spectroscopy Group, Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands

 
Quantitative MRI is an indispensable tool for the research community, the goal of which is to find unbiased and minimum variance estimates of critical MR parameters of interest. Improvements in bias and variance minimization in these estimates can lead to gainful tradeoffs between imaging time, SNR and resolution. Here, we present one such possible improvement in T1 and T2 parameter estimation which holds promise by pushing the limits of confidence in these estimations to low SNR regions, where conventional approaches fail. This technique, based on a separable least-squares approach to fit complex MR data has the ability to overcome the usual difficulties associated with using complex data for T1 and T2 (T2*) mapping.

 
3419.   52 3D Quantitative Imaging of Relaxation Parameters of Whole Brain
Weitian Chen1, Patrick D Koon2, and Ajit Shankaranarayanan1
1Global MR Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 2GE Healthcare, San Francisco, CA, United States

 
Quantification of T2 or T1rho in brain can provide additional diagnostic information to anatomy images. A major challenge to such quantification methods is very long scan time in order to achieve high resolution with 3D coverage of the brain. In this work, we investigated fast 3D quantitative T1rho or T2 imaging of whole brain based on highly SNR efficient 3D fast spin echo acquisition. We reported a simple method to reduce adversary eddy current effect in the developed pulse sequence. The T2-weighted image contrast can be utilized for simultaneous anatomical imaging besides T1rho or T2 quantification.

 
3420.   53 Fast Whole Brain T2 Relaxometry Using Spatial Constraints
Dushyant Kumar1, Thanh Nguyen2, Susan Gauthier3, and Ashish Raj2
1Neuroradiology, University of Hamburg, Hamburg, Hamburg, Germany, 2Radiology, Weill Cornell Medical College, Newyork, NY, United States,3neurology, Weill Cornell Medical College, Newyork, NY, United States

 
Problem: The adoption of conventional T2-relaxometry approach in clinical practice is impeded by long acquisition time and challenging T2-data analysis. Methods: The voxelwise conventional regularization is performed, then the spatial smoothness constraint over local neighborhood is implemented using a Bayesian spatial approach. Results: Our algorithm has better white matter tissue detection ability and better lesions detection compared to other methods. Conclusions: We extract consistent entire brain MWF map by imposing the spatial constraints on noisy T2-prep spiral data acquired within clinically feasible scan time (3T: 10 minutes; 1.5T: 20 minutes).

 
3421.   54 A Novel Fast and Robust T2* Mapping Algorithm Using the Definite Integral of the Signal Decay (DISC) Curve
Mengchao Pei1,2, Thanh D. Nguyen1, Lijia Wang2, Tian Liu1, Mitch Anthony Cooper1, Jianqi Li2, and Yi Wang1,2
1Weill Cornell Medical College, New York, NY, United States, 2Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai, Shanghai, China

 
A novel T2* mapping method based on the definite integral of the T2* signal decay curve (DISC) is proposed. Numerical simulations show that this method is more robust against noise effect than the widely used Levenberg-Marquardt (LM) algorithm, particularly at low SNR. DISC can reduce T2* data fitting time for a brain data set from 20 hours by LM to 5 minutes. This method is easy to implement and does not require an initial guess.

 
3422.   
55 The Feasibility of Endorectal MR Elastography for Prostate Imaging in Human Volunteers
Arvin Arani1,2, Michael Da Rosa3, Elizabeth Ramsay1, Donald Plewes1,2, Masoom Haider1, and Rajiv Chopra1,2
1Sunnybrook Research Institute, Toronto, Ontario, Canada, 2Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 3Institute of Medical Science, Sunnybrook Research Institute, Toronto, Ontario, Canada

 
Problem: The objectives of this study were to investigate the tolerability and technical feasibility of performing endorectal magnetic resonance elastography (eMRE) in human volunteers within the representative age group commonly affected by prostate cancer. Methods: Dynamic endorectal magnetic resonance elastography was conducted on 12 volunteers at oscillation frequencies and displacement amplitudes of 100-300Hz and 1-40µm, respectively. Results: Volunteers were able to tolerate eMRE without experiencing any pain. Wave propagation was observed throughout the entire prostate at frequencies as high as 300Hz. Conclusions: These results suggest eMRE is tolerable and technically feasibility, motivating future evaluation in patients.

 
3423.   56 Rapid 3D periodic motion-encoding using steady-state FFE pulse sequence: applicaton towards multi-frequency rheology
Philippe Garteiser1, Ramin Sahebjavaher2, Ralph Sinkus1, Leon Ter Beek3, Bernard E Van Beers4, Septimian E Salcudean2, and Ralph Sinkus1
1CRB3 U773 Université Paris Diderot, Sorbonne Paris Cite, INSERM, Paris, 75018, France, 2University of British Columbia, Vancouver, Canada, 3Philips Medical Systems, Netherlands, 4Service of Radiology, Hopital Beaujon, Clichy, France

 
A novel magnetic resonance elastography pulse sequence is introduced that strikes the balance between imaging speed, motion-encoding efficiency and high quality phase images. This pulse sequence was experimentally validated as capable of acquiring full 3D motion-encoding in a volume in less than a minute, and as suitable for mono- and multifrequency MR rheology experiments.

 
3424.   57 Fibrous liver stiffness analysis using high frequency Magnetic Resonance Elastography at 7T on an ex vivo rat model. Feasibility and preliminary results
Maxime Ronot1,2, Mathilde Wagner1, Simon Lambert2, Sabrina Doblas2, Ralph Sinkus2, Valerie Vilgrain1,2, and Bernard E Van-Beers1,2
1Radiology, Beaujon Hospital, Clichy, France, 2CRB3 INSERM U773, France

 
The diagnosis, staging and quantification of fibrosis rely on liver biopsy, which is invasive with significant risks. MR Elastography (MRE) is an emerging technique that allows fibrosis assessment by measuring the viscoelastic properties of the liver Our study presents the preliminary results of a high-frequency MRE-assessed fibrous liver analysis in an ex vivo rat model. Fibrosis was induced using CCl4 intoxication. We showed that the mean value of the elasticity shear modulus (Gd) in normal livers was significantly lower than in fibrous ones after 3 weeks of intoxication (p=.01) and correlated to the histological findings. It is expected that Gd will significantly increase in the next 5 weeks.

 
3425.   58 Regularized Harmonic Estimation for Steady-State MR Elastography
Joshua D. Trzasko1, and Armando Manduca1
1Mayo Clinic, Rochester, MN, United States

 
In steady-state magnetic resonance elastography (MRE), the delivery of precise quantitative information about tissue stiffness inherently depends on accurate estimation of the invoked harmonic phase signal. In this work, we propose a novel, statistically-motivated strategy for estimating the first harmonic signal directly from raw, complex, multichannel MRI data, and discuss the incorporation of signal prior models for prospective noise suppression. As a result, the challenge associated with handling the complex and signal-dependent noise distribution of MRE phase images during retrospective denoising is completely mitigated.

 
3426.   59 Phase Correction for Interslice Discontinuities in Multislice EPI MR Elastography
Matthew C Murphy1, John Huston, III1, Kevin J Glaser1, Armando Manduca2, Joel P Felmlee1, and Richard L Ehman1
1Department of Radiology, Mayo Clinic, Rochester, MN, United States, 2Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States

 
MR elastography (MRE) is an MR technique for noninvasively measuring tissue stiffness. Some applications, such as the brain, require a volumetric acquisition and 3D inversion because of through-plane wave propagation. An EPI pulse sequence is useful for such an application because it can acquire a volume of data with short acquisition times. However, slice-to-slice discontinuities in the phase of the EPI images can arise will bias the final inversion results. The purpose of this work is to present a filtering method that removes these slice-to-slice discontinuities, and as a result improves MRE repeatability.

 
3427.   60 Automated Liver Stiffness Measurements with Magnetic Resonance Elastography
Bogdan Dzyubak1, Kevin Glaser2, Meng Yin2, Armando Manduca2, and Richard Ehman2
1Mayo Graduate School, Mayo Clinic, Rochester, Minnesota, United States, 2Radiology, Mayo Clinic, Rochester, Minnesota, United States

 
Measurements of liver stiffness based on MR Elastography images have an inherent variability due to differences in ROI definition between readers. This study was aimed at developing an automatic algorithm for segmenting the liver in MRE images and measuring stiffness in an ROI with reliable wave propagation. The algorithm was shown to perform as well as an experienced MRE reader even in images with high artifact. This technique may streamline the measurement of liver stiffness while reducing time, variability, and cost.

 
3428.   61 High Precision Tracking of Un-Tuned Micro-Coils for Real-Time Motion Correction Applications
Melvyn B. Ooi1, Murat Aksoy1, Ronald D. Watkins1, and Roland Bammer1
1Department of Radiology, Stanford University, Stanford, CA, United States

 
The ability to track the positions of multiple micro RF-coil “active markers” in the MRI scanner has been the foundation of several recent advances in MR-guided intervention, as well as motion correction applications. The current work demonstrates that un-tuned markers, while simplifying coil design and reducing unwanted RF-related effects, provide sufficient signal for accurate/precise position tracking measurements in a temporal resolution suitable for use in real-time applications. A series of position measurements using un-tuned and tuned markers are performed on a well-defined grid-phantom for comparison.

 
3429.   62 Real-Time Correction by Optical Tracking with Integrated Geometric Distortion Correction by PLACE for Reducing Motion Artifacts in fMRI: In-Vivo Experiments
David Rotenberg1,2, Mark Chiew1,2, Fred Tam1,3, Shawn Ranieri1, and Simon Graham2,3
1Rotman Research Institute, Toronto, Ontario, Canada, 2Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada, 3Physical Sciences Sunnybrook Research Institute, Toronto, Ontario, Canada

 
Head motion artifacts are a substantial source of error in Blood Oxygen Level Dependent fMRI that limits its use in neuroscience research and clinical settings. Real-time scan-plane correction by optical tracking has been shown to suppress artifacts due to slice-misalignment and non-linear spin-history effects, however, residual artifacts due to dynamic magnetic field non-uniformity may remain in the data. We demonstrate a novel correction approach that integrates volume by volume, geometric distortion correction by PLACE into a real-time scan-plane update system by optical tracking, applied to an fMRI finger tapping experiment with overt head motion to induce dynamic field non uniformity.

 
3430.   63 Combining Active Markers and Optical Tracking for Prospective Head Motion Correction
Murat Aksoy1, Melvyn Ooi1, Ronald D Watkins2, Daniel Kopeinigg2, Christoph Forman3, and Roland Bammer1
1Center for Quantitative Neuroimaging, Department of Radiology, Stanford University, Stanford, CA, United States, 2Department of Radiology, Stanford University, Stanford, CA, United States, 3Computer Science, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany

 
Active markers and optical tracking systems (i.e. cameras) have been used for prospective correction of motion artifacts in head MRI. Optical tracking systems have the advantage that they require no additional MR data acquisition (i.e. navigators) to detect motion, whereas active markers can detect motion without the need to perform cross-calibration between the scanner and the tracking system. In this study, we combined active marker and optical tracking to benefit from the advantages of both systems. The active marker system was used to perform cross-calibration of the optical tracking system in a very short time with no discomfort to the patient so that the actual tracking can be done with the camera.

 
3431.   64 Analysis of ghosting artifacts for real-time motion correction applications using EPI
Eric K Gibbons1, Samantha J Holdsworth2, Melvyn B Ooi2, Murat Aksoy2, and Roland Bammer2
1Department of Bioengineering, Stanford University, Palo Alto, California, United States, 2Center for Quantitative Neuroimaging Department of Radiology, Stanford University

 
Echo-Planar Imaging (EPI) is a fast acquisition technique that can reduce the effect of patient motion but it is still prone to motion that occurs between volumes. The real-time prospective approach can correct for head rotation by rotating the gradients. However, gradient hardware delays can result in different ghosting parameters for each rotation. Here we test whether the ghost correction parameters estimated from the first EPI scan can be applied to oblique angles that are limited to the expected extent of patient head motion, in order to test whether this extra reference scan is necessary for real-time prospective motion correction applications.We found that even in small rotations of 2.5 degrees ghosting artifacts appeared in the image and required a separate correction parameter to be calculated. Additionally, in the presence of gradient delays, such ghosting correction is equally unfeasible with or without the additional scans.

 
3432.   65 Scan-to-scan unwarping of residual distortions in prospectively motion corrected EPI time series
Benedikt Andreas Poser1, Kazim Gumus1, Brian Robert Keating1, Brian Armstrong2, Todd P Kusik2, Julian Maclaren3, Thomas E Prieto4, Oliver Speck5, Maxim Zaitsev3, V Andrew Stenger1, and Thomas Ernst1
1UH-QMC Neuroscience and MR Research Program, University of Hawaii, Honolulu, Hawaii, United States, 2Department of Electrical Engineering and Computer Science, University of Wisconsin-Milwaukee, United States, 3Magnetic Resonance Development and Application Center, University Hospital Freiburg, Germany, 4Medical College Wisconsin, United States, 5Dept Biomedical Magnetic Resonance, Otto-von-Guericke-University, Magdeburg, Germany

 
fMRI data quality critically depends on subject motion. In EPI, its leads to head pose dependent distortions that cannot be corrected by post-hoc image realignment and hamper the detection of task activation. ‘Prospective’ motion correction approaches have been developed to track head position in real-time and continuously update slice positions during the scan. However, changes in absolute head orientation relative to B0 may alter the field distribution and hence EPI image distortions. To address this concern, we explored a dynamic distortion correction approach. We used IDEA EPI (interleaved dual echo with acceleration EPI) which allows field maps to be extracted from and applied to every fMRI volume, combined with real-time motion correction by means of an retro-grade-reflector (MPT) based tracking system.

 
3433.   66 High-resolution in vivo MR brain imaging at 7T using an embedded optical tracking system for prospective motion-correction
Jessica Schulz1, Thomas Siegert1, Enrico Reimer1, Maxim Zaitsev2, Julian Maclaren2, Michael Herbst2, and Robert Turner1
1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, 2University Medical Center Freiburg, Freiburg, Germany

 
We have designed an embedded optical tracking system that provides real-time motion information for prospective head motion correction for MRI at 7T. This system enables the acquisition of motion-corrected very high resolution in vivo MR images of the human brain (0.4 mm isotropic 3D FLASH, 0.5 mm isotropic 2D TSE). Uncorrected and corrected 3D FLASH images were acquired in four volunteers. Quantitative analysis demonstrated that the image quality was reliably improved by the motion correction.

 
3434.   67 Advantages of Channel by Channel Artifact Detection and Correction
Feng Huang1, Wei Lin1, Chiel den Harder2, Clemens Bos3, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, FL, United States, 2Advanced Solutions, MRI, Philips Healthcare, Best, Netherlands, 3MR Clinical Science, Philips Healthcare, Best, Netherlands

 
Multi-channel coils have been widely used in clinical practice for larger field of view (FOV) and higher signal to noise ratio (SNR). Due to the coil geometry, different coil elements have different sensitivity to some kinds of artifacts, such as flow, pulsation, breathing, hardware imperfections, etc. Conventional artifact reduction algorithms treat all coil elements equally, which could result in lower sensitivity of motion detection, reduced SNR, or residual artifacts. In this work, it is proposed to detect and compensate artifacts for each channel individually. Examples with in-vivo data show that higher SNR and lower residual artifact level can be achieved by using a channel by channel approach than by using a combined channel approach.

 
3435.   68 MRI Using Sharable Information Among Images With Different Contrasts: Motion Compensation
Feng Huang1, Wei Lin1, Chiel den Harder2, Gabrielle Beck2, Clemens Bos3, George Randy Duensing1, and Arne Reykowski1
1Invivo Corporation, Gainesville, FL, United States, 2Advanced Solutions, MRI, Philips Healthcare, Best, Netherlands, 3MR Clinical Science, Philips Healthcare, Best, Netherlands

 
Typical clinical MR examinations are composed of several sets of scans to acquire images with different contrast, such as T1w, T2w and DWI. Currently, the acquisition and reconstruction of these images are kept separate. Since the same subject is scanned in the same system using the same RF coil, there is sharable common information among these images. It is shown that the data correlation among channels from motion insensitive sequence can be shared for a motion compensation. Preliminary results with in-vivo data sets show that rigid motion artifacts can be corrected using sharable information from images with different contrast.

 
3436.   69 3D Fast Spin Echo Double Inversion Recovery with PROspective MOtion Correction (PROMO)
Dan Rettmann1, Jun Xie2, Nathan S White3, Anders Dale4,5, and Ajit Shankaranarayanan6
1Global Applied Science Laboratory, GE Healthcare, Rochester, MN, United States, 2MR Engineering, GE Healthcare, Waukesha, WI, United States,3Dept. of Cognitive Science, University of California, San Diego, La Jolla, CA, United States, 4Dept. of Neuroscience, University of California, San Diego, La Jolla, CA, United States, 5Dept. of Radiology, University of California, San Diego, La Jolla, CA, United States, 6Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

 
The use of double inversion recovery (DIR) sequences for improved lesion detection in multiple sclerosis and diseases involving abnormal grey matter has been increasing in popularity. DIR sequences are inherently long due to necessary T1 recovery and as such are more susceptible to patient motion. In this work we investigate the application of a prospective motion correction (PROMO) technique applied to a 3D FSE DIR sequence.

 
3437.   70 Combining nonrigid motion correction and partial Fourier for 3D high resolution cardiac imaging
Freddy Odille1,2, Anne Menini1,2, Pierre-André Vuissoz1,2, Laurent Bonnemains1,3, Damien Mandry1,2, and Jacques Felblinger1,4
1IADI, INSERM U947 - Nancy Université, Nancy, France, 2Pôle Imagerie, CHU de Nancy, Nancy, France, 3Pôle Cardiologie, CHU de Nancy, Nancy, France, 4CIC-IT 801, CHU de Nancy, Nancy, France

 
The combination of partial Fourier acquisition with motion-compensated reconstruction schemes is investigated. Similar to SENSE, such generalized reconstructions can be modified to include a phase constraint and therefore deal with asymmetric k-space sampling. However partial Fourier is sensitive to the construction of a “good” low resolution phase map from the central part of k-space, which may also be corrupted by motion. Here we propose to build a motion-compensated phase map using the GRICS motion correction framework. The technique was tested on volunteers with a free-breathing high resolution 3D sequence used clinically for myocardial viability assessment.

 
3438.   71 Enhancement of Respiratory Navigated 3D Spoiled Gradient-Recalled Echo Sequence with Variable Flip Angle Scheme
Yuji Iwadate1, Anja C.S. Brau2, and Hiroyuki Kabasawa1
1Global Applied Science Laboratory, GE Healthcare Japan, Hino, Tokyo, Japan, 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

 
Respiratory-gated fat-suppressed 3D spoiled gradient-recalled echo with navigator echo (Navigated LAVA) enables 3D T1-weighted imaging of free breathing patients with considerably reduced motion artifacts. In this work, enhanced navigated LAVA was developed to address the spin saturation effect on navigator signal, utilizing a wait insertion and a variable flip angle scheme. Variable flip angle scheme was realized by combination of ramp-up, ramp-down, and attenuation strategies in order to optimize the point spread function. In volunteer imaging, enhanced navigated LAVA not only increased navigator signal but also improved image quality of LAVA itself.

 
3439.   72 Coil selection with entropy minimization for reduction of motion-induced ghosting artifacts
Suchandrima Banerjee1, and Ajit Shankaranarayanan1
1Global Applied Science Lab, GE Healthcare, Menlo Park, California, United States

 
Motion remains a major source of artifact in day-today MR scans. In recent years there has been several works on utilization of additional information from multiple coils to reduce motion artifacts. Most of these methods use parallel imaging reconstruction algorithms to detect and resynthesize motion-corrupted acquisition segments. In this work we take a different approach and propose to detect individual coil data those are most affected by the motion. Our reconstruction strategy is based on the assumption that coil sensitivities being spatially varying, motion artifacts will appear differently relative to mean signal in the various coil images.
 
Electronic Poster Session - Pulse Sequences & Reconstruction A

Susceptibility & RF Pulses
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  13:30 - 14:30

  Computer #  
3440.   73 High resolution QSM at 7T : Comparison with 3T and 1.5T
Joon-Sup Jeong1, Jong-Ho Lee2, Se-Hong Oh1, Taek-Hyun Ryu1, Dae-Hyuk Kwon1, Young-Bo Kim1, and Zang-Hee Cho1
1Neuroscience Research Institute, Inchon, Korea, 2Department of Radiology, University of Pennsylvania, Pennsylvania, Armenia

 
Quantitative Susceptibility Mapping whose signal intensity is proportional to the underlying tissue magnetic susceptibility. The method provides a novel contrast in MRI and allows us to visualize different magnetic susceptibility components. In this abstract, we applied MEDI method to calculation magnetic susceptibility at 1.5T, 3T and 7T and compared the susceptibility values across the field strengths. In general, high-field-strength provides a better magnitude image than low-field-strength. In MEDI method, this magnitude method affects two aspects of processing QSM. This magnitude method affects two aspects of processing QSM. Therefore, 7T QSM image tends to have more accurate anatomical information than low-field-strength QSM image.

 
3441.   74 B0 inhomogeneity compensated Susceptibility Mapping using Single-scan Multi-echo 3D z-shim method
Sung-Min Gho1, Yoonho Nam1, Dongyeob Han1, Chunlei Liu2, and Dong-Hyun Kim1
1Electrical and Electronic Engineering, Yonsei University, Sinchon-dong, Seoul, Korea, 2Brain Imaging and Analysis Center, Duke University, Durham, NC, United States

 
Image phase has unique information about tissue composition such as gray and white matter structures. Phase imaging is used for various imaging methods such as susceptibility weighted imaging and quantitative susceptibility mapping. To obtain phase image, long echo time is needed to acquire sufficient phase shift. However, there is limitation due to the B0 inhomogeneity artifacts (i.e. signal loss in the frontal and sinus regions). One method to solve this problem in 3D imaging is the 3D z-shimming method. We propose to solve the above problem for obtaining the phase image by using a single-scan 3D multi-echo z-shimming sequence and image reconstruction method.

 
3442.   75 GPU Accelerated Quantitative Susceptibility Mapping
Obaidah Anees Abuhashem1, Berkin Bilgic1, and Elfar Adalsteinsson1,2
1EECS, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States

 
Quantitative Susceptibility Mapping (QSM) is used to quantify tissue magnetic susceptibility, leading to applications such as tissue contrast enhancement, venous blood oxygenation, and iron quantification. Quantification of the susceptibility distribution χ involves removal of background effects on the MRI signal phase and the solution of an ill-posed inverse problem describing the mapping from the phase to the tissue susceptibility. In this work, background removal is achieved by using the effective dipole fitting algorithm and susceptibility inversion is performed via imposing ℓ1 norm regularization on the spatial gradients of χ. As both algorithms are computationally demanding, it is crucial to increase the computational throughput and make regularized QSM a feasible and real-time methodology. Herein, the computational power Graphics Processing Cards (GPUs) is utilized to greatly accelerate the processing times, and both MATLAB and GPU libraries of the regularized QSM method are made available online for reproducibility.

 
3443.   76 A regularized k-space-based method for susceptibility tensor imaging
Wei Li1, Bing Wu1, and Chunlei Liu1,2
1Brain Imaging & Analysis Center, Duke University, Durham, North Carolina, United States, 2Radiology, Duke University, Durham, North Carolina, United States

 
Magnetic susceptibility typically has high contrast and SNR, and is related to the fiber angle with a simple sine-squared relationship, thus provides a promising candidate for extracting the white matter fiber orientation information from gradient echo MRI. The application of susceptibility tensor imaging, however, can be hampered by the imperfect registration due to different image distortion at different head orientations. In this work, we developed a regularized k-space-based method for susceptibility tensor reconstruction, which can effectively reduced the artifacts caused by imperfect registration and enhance the robustness of susceptibility tensor imaging.

 
3444.   77 Feasible 3-orientation acquisition for detecting susceptibility anisotropy in the human brain using prior structural information
Cynthia Wisnieff1,2, Tian Liu1,2, Pascal Spincemaille2, and Yi Wang1,2
1Cornell University, New York City, NY, United States, 2Weill Cornell Medical College, New York City, NY, United States

 
Susceptibility tensor imaging is an ill-posed inverse problem that requires sampling at many impractical orientations. We investigate the ability to detect susceptibility anisotropy in the human brain using structural prior information and reducing the number of orientations to as few as three. The prior information includes 1) the susceptibility tensor shape is cylindrically symmetric (CS); and 2) the susceptibility tensor shares its orthonormal basis with the diffusion tensor. Use of CS was validated in carbon fibers. It is observed here that the susceptibility anisotropy pattern detected in the brain appears to be similar between the 13 and 3 orientation reconstructions.

 
3445.   78 Anatomic prior and cylindrical symmetry constraints for reconstructing susceptibility tensor
Cynthia Wisnieff1,2, Tian Liu1,2, and Yi Wang1,2
1Cornell University, New York City, NY, United States, 2Weill Cornell Medical College, New York City, NY, United States

 
Susceptibility tensor imaging (STI) is an ill posed problem that suffers from noise propagation from non-ideal data. Assuming cylindrical symmetry in the shape of the tensor may improve the condition of this inverse problem. Anatomic prior information may be used to reduce noise through its incorporation into reconstructions of apparent susceptibilities at all orientations, from which the susceptibility tensor can be computed. These ideas were approximately confirmed in our phantom data and initial human data.

 
3446.   79 Initial investigation of the feasibility of Quantitative Susceptibility Mapping in clinical practice: an image quality analysis
Shuai Wang1,2, Weiwei Chen3, Tian Liu4, A. John Tsiouris2, Jianlei Liu5, and Yi Wang2,6
1University of Electronic Science and Technology of China, Cheng Du, Si Chuan, China, 2Radiology, Weill Cornell Medical College, New York, New York, United States, 3Radiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science&Technology, Wuhan, Hubei, China, 4MedImageMetric LLC, New York, New York, United States, 5XiDian University, Xi'an, ShaanXi, China, 6Biomedical Engineering, Cornell University, Ithaca, New York, United States

 
In this study, we retrospectively evaluated 114 consecutive patients imaged with Quantitative Susceptibility Mapping (QSM) by examining image quality under different situations, including presence of diverse pathology, various brain regions, and a wide range of age. The consistent image quality observed in this study suggested the potential of QSM as a tool for clinical diagnosis.

 
3447.   80 Improving accuracy of susceptibility and oxygen saturation quantification of veins using correcting factor method
Jin Tang1, Saifeng Liu1, Jaladhar Neelavalli2, Yu-Chung Norman Cheng2, and E Mark Haacke1,2
1Biomedical Engineering, McMaster University, Hamilton, ON, Canada, 2Academic Radiology, Wayne State University, Detroit, Michigan, United States

 
Mapping susceptibility from field perturbation data often uses a high pass filter to remove the low spatial frequency phase, however, using high pass filter will result in a concomitant loss of important local phase information and lead to decreases of susceptibility values inside vessels, especially for large vessels. To solve this problem and to improve the accuracy of susceptibility quantification of veins, we propose a new method which uses correcting factor (CF) to automatically adjust the underestimated susceptibility value inside the vein. The underestimated susceptibility values will be completely compensated by the CF.

 
3448.   81 A Numerical Comparison of Quantitative Susceptibility Mapping Methods on Simulated Magnetic Field Maps
Meng-Chi Hsieh1,2, San-Chao Hwang3, Hsu Chang3, and Jyh-Horng Chen1,2
1Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, 2Interdisciplinary MRI/MRS Lab, Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, 3Division of Medical Engineering Research, National Health Research Institutes, Zhunan, Taiwan

 
The purpose of this study is to compare four quantitative susceptibility map (QSM) methods, including threshold, Tikhonov, MEDI and Total Variation (TV), by using numerical analysis on simulated magnetic field maps. To quantitatively evaluate the effects, the noise propagation and contrast-to-noise ratio (CNR) were calculated. Theoretical and numerical analysis were used to be fundamental justification for the result of each approach. The threshold method was fast and simple, but those non-linear regularization methods could potentially reduce the noise propagation. In summary, by quantitative comparison, our results suggested that TV regularization method could be a robust method in susceptibility mapping and potentially helpful to further applications.

 
3449.   82 Quantitative Susceptibility Mapping by Using the Morphology Enabled Dipole Inversion (MEDI) Approach with a New Prior Information
Jianlei Liu1,2, Tian Liu2, Shuai Wang3, Keigo Kawaji2,4, and Yi Wang2,4
1XiDian University, Xi'an, Shaanxi, China, 2Radiology, Weill Cornell Medical College, New York, New York, United States, 3University of Electronic Science and Technology of China, 4Biomedical Engineering, Cornell University, Ithaca, New York, United States

 
The morphology enabled dipole inversion with L1_norm (MEDI_L1) method use the structural information of magnitude image as prior information to uniquely determine the susceptibility distribution.The method can get desired results with high resolution of scanning. For low resolution of scanning, the MEDI_L1 is sensitive to the prior information. However, there are inconsistencies between the magnitude gradient and the gradient of the true susceptibility distribution.In this case, we use the structural information which comes from both magnitude image and relative difference field (RDF) image as prior information to improve the performance of MEDI_L1.

 
3450.   83 Correlation of Magnetic Susceptibility and R2* with iron in ferritin
Weili Zheng1, Yu-Chung Norman Cheng1, Saifeng Liu2, Helen Nichol3, and E. Mark Haacke1
1Radiology, Wayne State University, Detroit, MI, United States, 2School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada,3Department of Anatomy and Cell Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

 
Iron is an important endogenous biomarker for many neurological diseases as well as for normal aging. An iron-loaded ferritin phantom was used here to investigate the correlation of iron with susceptibility and the other commonly used iron predictor, R2* (1/T2*). It was found susceptibility mapping predicts iron more reliably than does R2*. Ferritin gelatin phantoms may are a feasible model for human brain iron susceptibility studies. The effect of myelin and chemical exchange may not be negligible when predicting iron using susceptibility mapping and this needs to be further explored in order to accurately predict ferritin iron concentrations in vivo.

 
3451.   84 Temperature-dependent Conductivity Change using MR-based Electric Properties Tomography
Christoph Leussler1, Philipp Karkowski1, and Ulrich Katscher1
1Philips Research Europe, Hamburg, 22457, Germany
 
Thermal energy is used to treat tumors in liver, kidney and other body organs. Radiofrequency (RF) ablation, microwave ablation, and hyperthermia therapy use the penetration and absorption of electromagnetic waves, which depend on tissue conductivity. The conductivity of tissue depends on frequency and temperature. Relative changes of conductivity of the lesion during treatment with RF energy depend on biochemical changes and on tissue temperature. In this study, we report on the temperature-related change of conductivity, which will need to be distinguished and separated during treatment from biochemical conductivity changes during treatment.

 
3452.   
85 Spatially selective RF quadratic fields excitation
Yi-Cheng Hsu1, I-Liang Chern1, and Fa-Hsuan Lin2,3
1National Taiwan University, Taipei, Taiwan, 2National Taiwan University, Taiwan, 3Massachusetts General Hospital, United States

 
Using one single transmitter and quadratic magnetic fields, we propose the spatially selective RF quadratic field excitation (QEF) to 1) efficiently excite small FOV and 2) to generate a distribution of Mxy to compensate the B1 inhomogeneity in high field MRI. Specifically, compared to using linear gradients and 25 spokes, QFE is more than 2 times faster to complete the 1/3 FOV excitation with the improved accuracy of the excitation profile by 2.2-fold. In addition, QFE is 2.5 times faster than fast-Kz to excite a slice with in-plane circular symmetric flip angle distribution complementary to high field B1 inhomogeneity.

 
3453.   
86 STABLE-2: A shorter, more B0-insensitive option for adiabatic slice-selective excitation
Priti Balchandani1, Daniel M. Spielman1, and John M. Pauly2
1Radiology, Stanford University, Stanford, California, United States, 2Electrical Engineering, Stanford Universiy, Stanford, California, United States

 
An improved Slice-selective Tunable-flip AdiaBatic Low peak-power Excitation (STABLE) pulse with shorter duration and increased off-resonance immunity was designed. The new pulse, STABLE-2, utilizes a more uniform spectral pulse envelope generated using the adiabatic SLR method for pulse design. The improved pulse properties for STABLE-2 make it suitable for use in more pulse sequences and at higher field strengths. The pulse performance was validated in a phantom and in vivo.

 
3454.   87 Novel 2DRF optimization framework for spatially selective rf pulses incorporating B1, B0 and variable-density trajectory design
Rainer Schneider1,2, Dieter Ritter1, Jens Haueisen2, and Josef Pfeuffer1
1Siemens Healthcare, Erlangen, Germany, 2Institute of Biomedical Engineering and Informatics, TU Ilmenau, Ilmenau, Germany

 
Echo-planar imaging with a reduced FOV has been often used to increase imaging speed or acquire high-resolution images. However, to date nearly all of the studies use analytically designed pulses neglecting off-resonance effects and B1 inhomogeneity. In this work a 2DRF pulse optimization framework is proposed, which takes individual B0 and B1 maps into account. In addition, a novel trajectory design incorporating off-resonance information is introduced to further tackle geometric distortions. The proposed methods are evaluated with simulated and experimental data. It is shown that optimized 2DRF pulses outperform analytically designed pulses in regard to the overall excitation.

 
3455.   88 2D Composite Pulses: A novel method for spatially selective excitation
Rene Gumbrecht1,2, and Hans-Peter Fautz1
1Siemens Healthcare, Erlangen, Germany, 2Department of Physics, University of Erlangen, Erlangen, Germany

 
The power of 2D selective RF pulses is to excite any spatial pattern within the field of view. However, the length of these pulses causes artifacts that especially affect background suppression. It can be observed that conventional 1D slice selective RF pulses have a superior sharpness and background suppression compared to 2D selective pulses. The goal of this study is to transfer these qualities of a 1D slice selective RF pulse to a 2D selective excitation

 
3456.   89 The Tip-Angle-Doubling method and its applications to large tip angle pulse design
Alessandro Sbrizzi1, Cornelis A van den Berg2, Peter R Luijten3, Jan J Lagendijk3, and Hans Hoogduin3
1Imaging Division, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2UMC Utrecht, Netherlands, 3UMC Utrecht

 
In this work, we introduce the Tip Angle Doubling (TAD) principle, which makes possible to use small tip angle design methods to achieve large tip angles at no extra computation costs. Bloch equation simulations show how the method works in practice. The methods allows fast large tip angle pulse design and is applicable to multi transmit systems with B1+ inhomogeneities correction and (local) SAR optimization.

 
3457.   90 Optimized transmit pulses for excellent whole-brain excitation homogeneity in high field MRI
Tingting Shao1, Ling Xia1, Feng Liu2, and Stuart Crozier2
1Biomedical Engineering, Zhejiang University, Hangzhou, Zhejiang, China, 2School of Information Technology & Electrical Engineering, University of Queensland, Brisbane, Australia

 
This work presents a novel approach for designing RF pulses to achieve excellent whole-brain excitation homogeneity in high field MRI. Based on the parallel transmission technology, an optimized 3D tailored RF (TRF) pulse has been proposed to account for the severe RF(B1) inhomogeneity at 11.7T. The pulse is designed with an adaptive stack-spiral trajectory tailored according to the trajectory container, whose interior is mostly responsible for the desired excitation pattern. An iterative RF pulse design method is employed to ensure the excitation accuracy. Test simulations show that the proposed scheme provides homogeneous excitation over the entire brain volume in spite of the inhomogeneous field and insufficient longitudinal coverage.

 
3458.   91 Improving Slab Excitation by Parallel Transmission
Ulrich Katscher1, Hanno Homann1, and Peter Börnert1
1Philips Research Europe-Hamburg, Hamburg, Germany

 
Transmit SENSE is usually applied to improve 2D or 3D RF pulses. This study applies Transmit SENSE to 1D pulses, possible in case of large B1 variations across the slice or slab to be excited. Typically, such large B1 variations are found across the slabs excited for 3D imaging or for REST. 1D Transmit SENSE can improve excitation profile and particularly RF power / SAR behavior. The resulting pulses have the same duration as standard pulses, and can easily be incorporated in standard sequences maintaining sequence timing. The approach was tested using synthetic and realistic coil sensitivity profiles.

 
3459.   92 Evaluation of 2DRF echo-planar pulse designs for parallel transmission
Rainer Schneider1,2, Dieter Ritter1, Jens Haueisen2, and Josef Pfeuffer1
1Siemens Healthcare, Erlangen, Germany, 2Institute of Biomedical Engineering and Informatics, TU Ilmenau, Ilmenau, Germany

 
Parallel transmission (pTx) has been shown to enable B1 and B0 inhomogeneity mitigating spatially selective pulses. The majority of studies uses multichannel spatially selective pulses based on a spiral trajectory design and analyze the potential of pulse acceleration due to the additional rf transmit channels. Here, spatially-selective pulses based on a rectilinear EPI trajectory design (2DRF) are successfully implemented on a parallel transmission system. Further, the differences in excitation performance compared to one channel pulses are analyzed and demonstrated in simulations and phantom experiments. In conclusion, a second rf transmit channel significantly increases the excitation accuracy of optimized 2DRF pulses.

 
3460.   93 Fast non-linear pTx pulse design with integrated peak local RF energy minimization
Rene Gumbrecht1,2, and Hans-Peter Fautz1
1Siemens Healthcare, Erlangen, Germany, 2Department of Physics, University of Erlangen, Erlangen, Germany

 
For ultra-high field strengths of 7T and above and especially for parallel transmission, tissue heating due to RF field exposure is a dominant limiting factor for high performance human imaging. However, most current pulse design methods use a constraint on forward RF energy to find a trade-off between excitation quality and RF energy deposition. The goal of this study is to optimize the flip-angle distribution of non-linear high flip-angle RF pulses, such as composite pulses for parallel transmission, and to minimize the peak local RF energy at the same time in one run of a non-linear solver.

 
3461.   94 VERSE Optimized Multi-Channel Transmission
Davut I. Mahcicek1, Haldun Ozgur Bayindir2, Taner Demir1, and Ergin Atalar3
1National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey, 2Department of Mathematics, Middle East Technical University, Ankara, Turkey, 3National Magnetic Resonance Research Center (UMRAM), Bilkent University, Department of Electrical and Electronics Engineering, Ankara, Turkey

 
Specific Absorption Rate (SAR) and B1 inhomoeneity are two main problems of high field Magnetic Resonance Imaging. Multi-channel transmit systems may be used to fight againts inhomogeneity problems. Variable Rate Selective Excitation (VERSE) is an useful method to deal with SAR problems. Application of VERSE method to multi-channel transmit system gives chance to design SAR efficient RF pulses with minimum B1 inhomogeneity. To obtain maximum SAR reduction with VERSE method RF pulse design should be optimized.

 
3462.   95 Parallel Transmit SAR Estimation using FDTD Modeling in the Human Head at 7T
Mohammad Mehdi Khalighi1, Priscilla Chan2, and Brian K Rutt3
1Global Applied Science Lab, GE Healthcare, Menlo Park, California, United States, 2Electrical Engineering Department, Stanford University, Stanford, California, United States, 3Radiology Deaprtment, Stanford University, Stanford, California, United States

 
Present methods of measuring SAR are insufficient to verify safety in MR scans at high field especially with the use of parallel transmit. An FDTD-modeling software package with realistic body models was used to model SAR using either quadrature (qTx) or 2-channel parallel (pTx) transmit with a birdcage head coil. These numerical simulations were validated by comparison to experimentally-measured in-vivo B1+ fields. SAR and B1+ uniformity were compared between qTx and different pTx pulses; results show that pTx pulses with greater number of spokes create better uniformity and lower average SAR with similar SAR hot spot distribution compared to qTx.

 
3463.   96 Optimal Control Joint Design of Large-Tip-Angle RF Pulses and Gradient Waveforms for Parallel Transmission
Weiran Deng1, Benedikt Poser1, and V Andrew Stenger1
1Department of Medicine, University of Hawaii JABSOM, Honolulu, HI, United States

 
Optimal Control Joint Design of Large-Tip-Angle RF Pulses and Gradient Waveforms for Parallel Transmission
 
Electronic Poster Session - Pulse Sequences & Reconstruction A

Electromagnetic Property Imaging & Parallel Transmit
Click on to view the abstract pdf and click on to view the video presentation. (Not all presentations are available.)
Tuesday 8 May 2012
Exhibition Hall  14:30 - 15:30

  Computer #  
3464.   73 Simultaneous Electromagnetic Property Imaging using multiecho gradient echo
Dong-Hyun Kim1, Sung-Min Gho1, Narae Choi1, and Chunlei Liu2
1Electrical and Electronic Engineering, Yonsei University, Sinchon dong, Seoul, Korea, 2Brain Imaging and Analysis Center, Duke University, Durham, NC, United States

 
MRI has shown to be able to quantify both magnetic and electrical property. Current studies normally perform one of the above methods individually. Being able to simultaneously quantify both susceptibility (lower case Greek chi) and conductivity (lower case Greek sigma) mapping can be useful since misregistration can be alleviated due to separate measurements. Here, we introduce a simultaneous susceptibility and conductivity quantification method. Using a multiecho GRE sequence, the phase of the spins at TE=0 can be retrieved providing conductivity information while the subsequent phase evolution can be used for susceptibility mapping.

 
3465.   74 Potential of functional MREIT to Detect Neural Activity Related Conductivity Changes: Numerical Simulation Studies
Hyung Joong Kim1, Zijun Meng1, Saurav ZK Sajib1, Woo Chul Jeong1, Young Tae Kim1, Rosalind J Sadleir2, and Eung Je Woo1
1Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea, 2University of Florida, Gainesville, Florida, United States

 
Imaging of cell membrane conductivity change may provide a truly direct method of locating neural activity compared to fMRI. The advantage of MREIT as a basis for direct neural activity imaging is that the imaged quantity, membrane conductivity, is a scalar and therefore is not subject to cancellation errors such as those inherent in neural current imaging techniques. In this work, we use a realistic head model to compute signal levels produced as a consequence of a predicted 5% conductivity change occurring within gray matter. We reconstructed conductivity images, showing that these small conductivity differences can be detected and imaged.

 
3466.   75 Wave-number imaging at 7T: increasing accuracy of EPT at high field strengths
Astrid L.H.M.W. van Lier1, Ulrich Katscher2, Alexander Raaijmakers1, and Cornelis A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Philips Research Europe, Hamburg, Germany

 
Recently, it was shown that dielectric properties can be mapped using MRI. Electrical properties mapping relies on measurements of the B1+ amplitude and phase. This phase, however, cannot be measured directly; therefore, the assumption that the transceive phase is twice the B1+ phase is used in a transceiver setup. This assumption is acceptable at low field strengths, however, leads to significant reconstruction errors at 7T. Here we show, that the wave-number (|k|) is less susceptible to these errors, and can be mapped more reliably than the permittivity and conductivity at 7T.

 
3467.   76 Measuring electrical conductivity at low frequency using the eddy currents induced by the imaging gradients.
Astrid L.H.M.W. van Lier1, Cornelis A.T. van den Berg1, and Ulrich Katscher2
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Philips Research Europe, Hamburg, Germany

 
The complex permittivity (lower case Greek epsilon*) of biological tissues depends on their biochemical composition and the applied frequency. In this study we investigate a method that measures the tissue conductivity in the biologically interesting low frequency (LF,=Hz-kHz) range. A first implementation of this method – LF-EPT– is based on similar reconstruction principles as MR-CDI, but it employs the imaging gradient instead of electrodes to induce (eddy) currents. First experiments show that this method is feasible in phantoms.

 
3468.   77 Feasibility of EPT in the Human Pelvis at 3T
E. Balidemaj1, A. L. van Lier2, A.J. Nederveen3, J. Crezee1, and C.A.T. van den Berg2
1Radiotherapy, Academic Medical Center, Amsterdam, Netherlands, 2Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 3Radiology, Academic Medical Center, Amsterdam, Netherlands

 
Feasibility of EPT in the human pelvic at 3T for use in Hyperthermia Treatment Planning, SAR determination or tumour detection and characterization.

 
3469.   78 Calculation of Electrical Properties from B1+ Maps - A Comparison of Methods
Selaka Bandara Bulumulla1, Seung-Kyun Lee1, and Teck Beng Desmond Yeo1
1GE Global Research, Niskayuna, New York, United States

 
Extracting electrical properties (relative permittivity and conductivity) from B1+ maps is a promising method that has applications in local SAR estimation, RF hyperthermia treatment planning and diagnosis of tissue malignancy. In this work, we compare the two primary calculation methods, Laplacian and Integral based, under the constraint that both methods use a constant number of B1+ samples to calculate permittivity and conductivity. Our results indicate that under the constraint, (a) both methods predict accurate values, (b) Laplacian based method is advantageous for rapid estimates and (c) Integral based method is more robust with noisy B1+ maps.

 
3470.   79 Decreasing SAR of a multi-dimensional central brightening inhomogeneity correction pulse using nonlinear gradient fields and VERSE
Emre Kopanoglu1,2, Yildiray Gokhalk2, Ugur Yilmaz1,2, Volkan Acikel1,2, and Ergin Atalar1,2
1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2UMRAM, Bilkent University, Ankara, Turkey

 
To correct for B1 inhomogeneity artifacts, multi-dimensional pulses are widely used. However, such pulses increase SAR significantly. In this study, we compare, and combine two SAR reduction methods, the variable rate selective excitation and excitation using nonlinear gradient fields in order to observe their effect on SAR. 5-spoke pulses are designed for both methods to correct for a central brightening inhomogeneity, which is widely seen at the UHF regime. When two methods are used separately, SAR reductions around 75% were obtained whereas when combined, the methods yielded an SAR reduction of 91%.

 
3471.   80 Localizing the excitation to reduce scan time using nonlinear gradient fields
Emre Kopanoglu1,2, Ugur Yilmaz1,2, Burak Akin2, Volkan Acikel1,2, and Ergin Atalar1,2
1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey, 2UMRAM, Bilkent University, Ankara, Turkey

 
For numerous applications, the region of interest is merely a portion of the imaged volume. Conventional one-dimensional RF pulses have relatively low SAR, but they cannot excite local regions and therefore causes long scan times. Although small volumes can be excited using multi-dimensional excitation pulses, such pulses are long and/or have relatively high SAR. It is shown that, using gradient fields with nonlinear variation in space, excitation regions can be confined in three dimensions without increasing pulse duration and SAR. In this abstract we show that a 60% decrease in required phase-encoding steps is obtained while imaging the occipital lobe of the brain. Initial in-vivo results are presented.

 
3472.   81 Neither Flat Profile Nor Black Spots: A Simple Method to Achieve Acceptable CP-like Mode Transmit B1 Pattern for Whole Brain Imaging with Transmit Arrays at 7 Tesla
Sebastian Schmitter1, Gregor Adriany1, Edward J Auerbach1, Kamil Ugurbil1, and Pierre-Francois Van de Moortele1
1Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

 
At 7T the short transmit B1 (B1+) RF wavelength leads to spatial variations of |B1+| including possible B1+ nodes of fully destructive interference. RF phase shimming using multi-channel TX coils can mitigate this problem. However, a 'good starting-phase set' without B1+ nodes and with reasonably high B1+ efficiency is not necessarily known before starting a scanning session. Yet, such “CP-like” mode is indispensable for whole brain anatomical imaging, B0 mapping and RF power calibration. In this work we present a simple but efficient method to determine a good starting set of “CP-like” RF phases for multi-channel head coils at 7T.

 
3473.   82 Design of Robust Thin Slice Spectral Spatial RF Pulses
Yuval Zur1
1GE Healthcare, Tirat Carmel, Israel

 
Spectral spatial (spsp) RF pulses are used for simultaneous fat suppression and slice selective excitation. Reduction of the minimum slice width to less than 2 mm at high field strength (3T) requires very powerful gradients. The purpose of this work is to design spsp RF pulses with lower gradients, such that thin slices ¡Ü 1.5 mm become feasible. The drawback is that spsp pulses are very sensitive to RF gradient delay and eddy currents. We present a calibration method and design a new spsp RF pulse that is less sensitive to system imperfections. The combination of the two results in robust 1.3 mm spsp RF pulse.

 
3474.   83 Selective excitation of metabolite signals for 1H MRS
Mirjam Holbach1, Joerg Lambert2, and Dieter Suter3
1Physics, Technical University Dortmund, Dortmund, Germany, 2Leibniz-Institute for Analytical Sciences – ISAS, Dortmund, Germany, 3Technical University Dortmund, Dortmund, Germany

 
Selective excitation of metabolite signals in in vivo MRS is important for the correct and robust quantification of the content of some key metabolites, which is of particular relevance in low field strength MRS, where signal overlap and low intensities impede quantification of MRS signals. In this study a Krotov-based optimal control theory approach is used to develop optimized pulse shapes for the selective excitation of individual metabolites. The resulting pulses were investigated by simulation of the corresponding spectra, which were then verified using experimental data. Further simulations of the performance of such pulses show an enhanced robustness to experimental imperfections compared to standard pulses.

 
3475.   84 Let's do the Time Warp again - Slice Profile Evolution of Adiabatic Pulses at 7 Tesla
Mathies Breithaupt1, Moritz Cornelius Berger1, Ann-Kathrin Homagk1, Wolfhard Semmler1, and Michael Bock1,2
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, 2Radiology - Medical Physics, University Hospital Freiburg, Freiburg, Germany

 
Adiabatic pulses are commonly used to overcome B1 inhomogeneity which is particularly important at ultra-high magnetic fields due to standing wave effects. In slice-selective adiabatic pulses, the frequency sweep causes Beff,z-dependent off-resonances leading to an asymmetric evolution of the slice profile. Here, we present a detailed temporal analysis of the magnetization manipulation during slice-selective adiabatic pulses by comparing measured and simulated data.

 
3476.   85 Selective Excitation of Arbitrary Three-Dimensional Targets in Vivo using Parallel Transmit
Martin Haas1, Jeff Snyder1, Stefanie Buchenau1, Denis Kokorin1,2, Johannes T. Schneider1,3, Peter Ullmann3, Jürgen Hennig1, and Maxim Zaitsev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2International Tomography Center, Novosibirsk, Russian Federation, 3Bruker BioSpin MRI GmbH, Ettlingen, Germany

 
Spatially selective excitation of an arbitrary three-dimensional target pattern is demonstrated in vivo in the head of a volunteer at 3T for the first time. A parallel transmit system with eight independent RF channels is used in combination with a slew-optimized single-shot 3D shells trajectory. The good excitation fidelity allows for the reduction of the field of view below the extent of the head and consequently for a shorter acquisition with higher spatial resolution.

 
3477.   86 Nonlinear RF Pulse Optimization for Segmented Multi-Dimensionally Selective Excitation with Parallel Transmit
Martin Haas1, Jeff Snyder1, Jürgen Hennig1, and Maxim Zaitsev1
1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

 
The duration of multi-dimensionally spatial selective excitation (SSE) RF pulses usually implies high excitation fidelity of a given target pattern only for a narrow range of frequencies. Segmentation of an SSE pulse across several repetitions results in short RF pulses and broadband excitation of the target pattern in the summed signal. In this work, a generalized nonlinear large tip angle RF optimization algorithm is presented which jointly optimizes the RF segments and thus extends previous approaches using small tip angles or segment-wise large tip angle optimization.

 
3478.   87 Comparison of active and passive parallel transmit in 3T breast
Laura Sacolick1, Mika W. Vogel1, William A. Grissom2, Guido Kudielka1, Theodor Vetter1, and Ileana Hancu3
1GE Global Research, Garching b. Munchen, Bayern, Germany, 2Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, 3GE Global Research, Niskayuna, NY, United States

 
B1 homogeneity and relative SAR is compared in the 3T breast for several configurations of parallel transmit system. Active RF shimming with 1, 2, and 8 transmit channels is compared to passive shimming- where one off-tuned coil element is placed around the right breast, weakly coupling to the main transmit field. B1 homogeneity improves with increasing channel count, with the passive transmit coil giving B1 homogeneity similar to a two-channel system, and significantly lower SAR than any active parallel transmit configuration.

 
3479.   88 Maximum Efficiency RF Shimming
Cem Murat Deniz1,2, Ryan Brown1, Riccardo Lattanzi1,2, Leeor Alon1,2, Daniel K. Sodickson1,2, and Yudong Zhu1,2
1Department of Radiology, Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States

 
Radiofrequency shimming with multiple channel excitation has been proposed to increase the transverse magnetic field uniformity and reduce specific absorption rate at high magnetic field strengths (≥ 7 Tesla), where wavelength effects can make traditional single channel volume coils unsuitable for transmission. In the case of deep anatomic regions and power-demanding pulse sequences, optimization of transmit efficiency may be a more critical requirement than homogeneity. This work introduces a new method to maximize transmit efficiency using multiple channel excitation and radiofrequency shimming. Shimming weights are calculated in order to obtain the highest possible transverse magnetic field using the lowest possible net radiofrequency power deposition into the subject.

 
3480.   89 Parallel Transmission Three-Dimensional Tailored RF (PTX 3DTRF) Pulse Design for Simultaneously Recovering Multi-slice Signal Loss at 7T
Hai Zheng1, Tiejun Zhao2, Yongxian Qian3, Claudiu Schirda3, Tamer Ibrahim1,3, and Fernando Boada1,3
1Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Siemens Medical Solutions USA, Pittsburgh, Pennsylvania, United States, 3Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

 
T2* weighted fMRI in ultra high field is hampered by susceptibility-induced signal loss near air/tissue interfaces of the brain. We demonstrate a robust RF pulse design, based on parallel transmission (PTX) and 3D tailored RF (3DTRF), that is capable of simultaneously and precisely recovering signal loss at multiple locations. An additional scheme for PTX 3DTRF based on time-interpolation approach, is also presented. All schemes were observed to significantly and reproducibly improve signal recovery across multiple slices in human subjects. Time-interpolation method proved to be more robust at regions with large frequency offsets, albeit at the expense of increased computational demand.

 
3481.   90 pTX Array Optimized Composite Pulse for B1+ inhomogeneity compensation at 3T
Christopher Sica1, Sukhoon Oh1, and Christopher Collins1
1Radiology, Pennsylvania State University, Hershey, PA, United States

 
An implementation of an array optimized composite pulse (ACP) for parallel transmit applications is presented. The pulse design utilizes two RF pulses, with independently adjustable magnitude and phase per channel and per pulse. A non-selective version of the ACP pulse is compared with RF shimming and a quadrature drive configuration in a water phantom, and with quadrature drive in the human brain at 3T. The ACP pulse offers improved excitation uniformity relative to RF shimming in phantoms, and significant improvement over a quadrature drive configuration in-vivo. Future potential for a slice-selective version of the ACP pulse is also demonstrated.

 
3482.   91 Estimation of breast tumor conductivity using parabolic phase fitting
Ulrich Katscher1, Karim Djamshidi1, Tobias Voigt2, Marko Ivancevic3, Hiroyuki Abe4, Gillian Newstead4, and Jochen Keupp1
1Philips Research Europe-Hamburg, Hamburg, Germany, 2Philips Research Europe-Aachen, Aachen, Germany, 3Philips Healthcare, Cleveland, United States, 4University of Chicago, Chicago, United States

 
Ex vivo studies exhibited significantly altered electric conductivity of breast tumors, opening the chance to increase the specificity of breast tumor characterization. Conductivity can be measured in vivo using “Electric Properties Tomography” (EPT), which has shown its potential in phantom, volunteer, and initial clinical studies. However, the complex frayed structure of fat and ductile tissue in the breast hampers the straight-forward application of EPT, based on the second derivative of the RF TX phase. In this study, a new EPT reconstruction via fitting local parabolic functions on the TX phase is developed and applied to an example breast tumor.

 
3483.   
92 Conductivity Imaging of an Ischemic Pig Heart Model using Electric Properties Tomography
Tobias Voigt1, Andreas Schuster2, Masaki Ishida2, Christian Stehning3, Ulrich Katscher3, Amedeo Chiribiri2, Eike Nagel2, and Tobias Schaeffter2
1Philips Research, London, United Kingdom, 2King’s College London, London, United Kingdom, 3Philips Research, Hamburg, Germany

 
In this work we present the application of EPT conductivity mapping in two isolated perfused pig hearts. Conductivity values of normally perfused heart tissue were compared to values in ischemic regions after a blockade of the left anterior descending artery (LAD). It could be shown that ischemic ventricular tissue is less conductive than healthy myocardium.

 
3484.   93 Electrical conductivity in ischemic stroke at 7.0 Tesla: A Case Study
Astrid L.H.M.W. van Lier1, Anja G. van der Kolk2, Manon Brundel3, Jeroen Hendrikse2, Peter R. Luijten2, Jan J.W. Lagendijk1, and Cornelis A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Netherlands, 3Neurology, UMC Utrecht, Netherlands

 
In ischemic stroke, [Na+] increases due to ischemia and subsequent disturbance of ion homeostasis. Recently, electrical properties tomography (EPT) was introduced as a new contrast in MRI. This contrast enables us to visualize the local electrical properties of tissue, being the conductivity and permittivity; the electrical conductivity is related to [Na+]. In this study, it was shown that electrical conductivity was locally elevated in the tissue affected by the infarction.

 
3485.   94 Feasibility of Breast MREIT Conductivity Imaging for Cancer Detection: Experimental and Numerical Simulation Studies
Hyung Joong Kim1, Saurav ZK Sajib1, Woo Chul Jeong1, Young Tae Kim1, Tong In Oh1, and Eung Je Woo1
1Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea

 
Conductivity values of cancerous tissues in the breast are significantly higher than those of surrounding normal tissues, breast MREIT may provide a new noninvasive way of detecting early stage of breast cancer. As a step toward clinical application, we present results of experimental and numerical simulation studies of breast MREIT. From phantom experiments, we evaluated practical amounts of noise in measured Bz and built a realistic three-dimensional model. Simulation results are promising to show that we can detect a cancerous anomaly in the breast while restricting the maximal current density inside the heart below the level of nerve excitation.

 
3486.   95 Imaging Electrical Properties of Human Head with Tumor Using Multi-channel Transceiver Coil at UHF: A Simulation Study
Jiaen Liu1, Xiaotong Zhang1, and Bin He1
1Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States

 
In the present study, we investigate the feasibility of a complex B1 mapping technology using a multi-channel transceiver coil at ultrahigh field for the purpose of imaging electrical properties of realistic human head by computer simulation. Complex B1 mapping and electrical properties reconstruction were carried out on both normal symmetric head and pathological asymmetric head with a tumor at 7 T and 9.4 T. The simulation results show that on realistic asymmetric geometry, the method performs equally well as on symmetric geometry and suggest its practical value for diagnostic purpose and SAR calculation at UHF.

 
3487.   96 RF shimming improves Phase-Based Conductivity Imaging
Ulrich Katscher1, Astrid L.H.M.W. van Lier2, Cornelis A.T. van den Berg2, and Jochen Keupp1
1Philips Research Europe-Hamburg, Hamburg, Germany, 2University Medical Center Utrecht, Utrecht, Netherlands

 
In the framework of “Electric Properties Tomography” (EPT), approximate conductivity imaging is possible by analyzing the B1 phase, assuming constant B1 amplitude. The more this assumption is violated, the less accurate the reconstructed conductivity. This study analyzes the influence of modifying the B1 amplitude by parallel RF transmission on the precision of phase-based EPT. It turns out that phase-based EPT benefits significantly from optimizing B1 amplitude homogeneity via with RF shimming.