Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Pulse Sequences - RF

Tuesday May 10th
Exhibition Hall  13:30 - 15:30 Computer 118

13:30 4408.   Simultaneous B1 and B0 mapping using dual echo actual flip angle imaging (DE-AFI) 
Claudia Lenz1, Oliver Bieri1, Klaus Scheffler1, and Francesco Santini1
1Radiological Physics, University of Basel Hospital, Basel, Switzerland

Only recently, actual flip angle imaging (AFI) has been introduced as a fast and robust 3D method for mapping the B1 transmit field by measuring the spatial variations of the effective flip angle. The AFI pulse sequence consists of a dual TR conventional spoiled gradient echo pulse sequence, where TR2 > TR1. In this work, a second echo has been added to the standard AFI timing diagram, which enables additional B0 mapping by reconstructing phase difference maps based on the phase images of the two acquired echoes. In vivo results of fast simultaneous B1 and B0 mapping using dual echo AFI are presented.

14:00 4409.   T1-nonlinearity corrections for fast Transmit-Array B1+-mapping of the human brain in the small-tip-angle regime 
Martijn Anton Cloos1,2, Nicolas Boulant1, Guillaume Ferrand2, Michel Luong2, Christopher J Wiggins1, Denis Le Bihan1, and Alexis Amadon1
1LRMN, CEA, DSV, I2BM, NeuroSpin, Gif-Sur-Yvette, ile-de-France, France, 2CEA, DSM, IRFU, Gif-Sur-Yvette, ile-de-France, France

Currently, B1+-mapping is particularly difficult due to the combination of time and conservative specific absorption rate (SAR) constraints applicable to parallel transmission studies involving human subjects. Measuring relative B1+-maps in the low-tip-angle regime provides a low SAR solution. Inherently, this method requires a relatively long TR (0.2-1.0s) to remain in the domain where the signal intensity is linearly dependent for a large range of flip-angles. Considering 3D tailored excitation pulses, such TR values require too much time for transmit-array B1+-mapping and pulse validation. To tackle the aforementioned problems, an optimized version of this method for the quantification of non-selective excitation pulses is presented.

14:30 4410.   An experimental comparison of B1-mapping Techniques at two field strengths 
Rolf Pohmann1
1Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany

B1 mapping was shown

15:00 4411.   Fast B1 Mapping using a STEAM-based Bloch-Siegert Preparation Pulse 
Kay Nehrke1, and Peter Börnert1
1Philips Research Laboratories, Hamburg, Germany

Fast B1-mapping is an essential prerequisite for multi-element transmit applications like e.g. RF-shimming or multi-dimensional RF pulse design. However, the acquisition speed of B1-mapping sequences is typically limited by SAR constraints, relaxation times, or characteristic sequence properties. In this work, a novel STEAM-based preparation sequence is presented, which employs the recently introduced Bloch-Siegert B1-mapping approach. The preparation sequence stores the Bloch-Siegert phase shift along the longitudinal magnetization, which allows the fast readout of the stimulated echo by a subsequent train of small angle pulses. The flexibility and versatility of this concept is demonstrated in experiments on phantoms and in vivo.

Wednesday May 11th
  13:30 - 15:30 Computer 118

13:30 4412.   Gradient and frequency modulated excitation for a tailored spatial trajectory with two-dimensional time encoding for Fourier-free imaging 
Angela Lynn Styczynski Snyder1, Curt Corum2, Steen Moeller2, Nathan Powell3, and Michael Garwood2
1Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, United States, 2Department of Radiology, University of Minnesota, 3Department of Neuroscience, University of Minnesota

A frequency-swept RF pulse and modulated gradients can be used to move a resonance region through space to generate sequential excitation and subsequent echo formation with time-dependence, which allows image formation without use of the Fourier transform. This two-dimensional time encoding (2DTE) has the unique and important property that each region in space can be treated independently, which is potentially of great benefit for solving problems that are inherently spatial in nature, such as compensating for B0 and B1 inhomogeneities, which is of increasing interest for higher field strengths.

14:00 4413.   Simultaneous Bloch Siegert B1+ and T2 mapping in one experiment using a multi spin echo sequence 
Volker Sturm1, Thomas Christian Basse-Lüsebrink1,2, Thomas Kampf1, Guido Stoll2, and Peter Michael Jakob1
1Experimental Physics 5, University of Würzburg, Würzburg, Germany, 2Neurology, University of Würzburg, Würzburg, Germany

A novel method for B1+ mapping based on the Bloch-Siegert (BLS) shift was recently introduced. BLS-based B1+ mapping employs off-resonant pulses before signal acquisition to encode B1 information into the signal phase. In the present study, BLS B1+ mapping was extended to CPMG-based Multi-Spin-Echo (MSE). Through only one experiment, this method simultaneously provides the data needed for B1+ mapping with the data necessary for T2-quantification. Ex vivo phantom and in vivo experiments were performed to investigate the proposed method.

14:30 4414.   A novel B1-insensitive outer volume suppression pulse 
Travis Benjamin Smith1, and Krishna S Nayak1
1Electrical Engineering, University of Southern California, Los Angeles, CA, United States

Reduced field-of-view imaging enables accelerated acquisitions or finer resolutions than standard prescriptions. Outer volume suppression reduces signals outside a region of interest and attenuates aliasing energy when a reduced field-of-view is prescribed. We present a new design for B1-insensitive outer volume suppression and demonstrate its performance at 3 Tesla in a phantom and in vivo with cardiac-gated scans.

15:00 4415.   Time Interleaved Acquisition of Modes (TIAMO): an Analysis of SAR and Image Contrast Implications 
Stephan Orzada1,2, Stefan Maderwald1,3, Benedikt A. Poser1,4, Sören Johst1,2, Mark E. Ladd1,2, Stephan Kannengiesser5, and Andreas K. Bitz1,2
1Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, NRW, Germany, 2Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, NRW, Germany, 3University of Duisburg-Essen, Essen, NRW, Germany, 4Donders Institute for Brain, Cognition and Behaviour, Centre for Cognitive Neuroimaging, Radboud University Nijmegen, Nijmegen, Netherlands, 5Siemens Healthcare Sector, Erlangen, Germany

High static field strengths of 7 Tesla and above are challenging due to the severe B1 inhomogeneities caused by the short wavelength. Several methods have been proposed to tackle this problem including RF Shimming and Transmit SENSE. Recently, a technique called Time-Interleaved Acquisition of Modes (TIAMO) has been proposed to reduce the impact of B1 inhomogeneity. In this work the influence of TIAMO on the image contrast as well as on the time-averaged SAR at 7 Tesla is addressed in detail, showing that TIAMO is superior to RF shimming in terms of image homogeneity and SAR.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
B1 & Mapping

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 119

14:00 4416.   Saturated Double Angle Method with radial sampling 
Liyong Chen1,2, and Edward V.R. DiBella1,2
1Utah Center for Advanced Imaging Research, Department of Radiology, University of Utah, Salt Lake City, Utah, United States, 2Department of Bioengineering, University of Utah, Salt Lake City, Utah, United States

Saturated double angle method with radial sampling was proposed to get B1+ map.

14:30 4417.   A new phase-based method for rapid 3D B1 mapping using double RF pulses 
Yulin V Chang1
1Mechanical Engineering, Washington University, St. Louis, MO, United States

A fast, easy-to-implement, phase-based 3D B1 mapping method is presented. This method uses a pair of orthogonal RF pulses to generate a flip-angle-dependent phase deviation of the magnetization vector from lower case Greek pi/4. It is robust to T1 and T2 relaxations and the B0 field inhomogeneity.

15:00 4418.   Comparison of four phase based methods for the B1+ mapping at 7T 
Flavio Carinci1,2, Federico von Samson-Himmelstjerna1,3, Davide Santoro1, Tomasz Lindel1,4, Matthias Dieringer1,5, Frank Seifert1,4, Jan Sobesky3,6, and Thoralf Niendorf1,5
1Berlin Ultra-High Field Facility (BUFF), Max Delbrück Center for Molecular Medicine (MDC), Berlin, Germany, 2Department of Physics, Insubria University, Como, Italy,3Center for Stroke Research Berlin (CSB), Charitè Universitaetsmedizin Berlin, Berlin, Germany, 4Physikalisch-Technische Bundesanstalt (PTB), 5Experimental and Clinical Research Center (ECRC)), Charitè Campus Berlin, Berlin, Germany, 6Department of Neurology, Charitè Universitaetsmedizin Berlin, Berlin, Germany

In ultra-high field MRI the increase of signal to noise ratio comes together with longer T1 and shorter T2* relaxation times, higher specific absorption rates and higher B1 field inhomogeneities. Phase-based methods for B1 mapping have been shown to be more accurate than magnitude-based methods as the phase of the signal is insensitive to T1 relaxation effects and coil sensitivity profiles. In this work we compare four phase-based methods taken from literature and adapted to 7T MRI: the Mugler method, the Morrell method, the Santoro method and the Sacolick method. The methods are compared in terms of the sensitivity to the B1 and B0 inhomogeneities, SAR levels and repetition times, using simulations together with phantom and in vivo experiments.

15:30 4419.   Reduction of Required Gradient Spoiler Size For AFI B1 Mapping 
Kim Shultz1, Greig Scott1, and John Pauly1
1Electrical Engineering, Stanford University, Stanford, CA, United States

AFI is a powerful, fast technique for B1 mapping, useful for quantitative imaging and parallel transmit pulse design. It is made more difficult by the requirement of very large gradients to spoil the transverse magnetization at the end of each TR. We present a technique to correct for the error that occurs with small spoiler gradients based on the expected reconstruction error seen in simulations for various tissues. This allows accurate AFI results with more reasonable gradient sizes. Additionally, the error seen in lipids is smaller than that seen with very large spoiler gradients.

Tuesday May 10th
  13:30 - 15:30 Computer 119

13:30 4420.   On the Effectiveness of RF Spoiling at 7T 
Douglas A C Kelley1,2, and Janine M Lupo2
1Global Applied Science Laboratory, GE Healthcare, San Francisco, CA, United States, 2Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States

RF spoiling is a common technique for suppression of transverse coherence, but T2 reduction, T1 elongation and RF inhomogeneity in human tissue at 7T alter the effectiveness of the technique in quantitative imaging methods like Actual Flip Imaging.

14:00 4421.   Asymmetric field distribution in B1+ and B1- maps are caused by phase differences in field components in the laboratory frame 
Hidehiro Watanabe1, Nobuhiro Takaya1, and Fumiyuki Mitsumori1
1Environmental Chemistry Division, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan

Magnitude of B1+ has an asymmetric profile in human brain at high field. We investigated the source of this asymmetry through simple change of the formula on the relationship of RF fields in the rotating and laboratory frames. |B1+| can be expressed as the magnitude and the phase difference of the RF field components in the laboratory frame. While the former component has symmetric profile, the latter has asymmetry in human brains at 4.7 T. From these results, we concluded that the asymmetries in |B1+| and |B1-*| maps are derived from the phase difference in the laboratory frame.

14:30 4422.   3D Slab Selective AFI utilizing a thin slab approach 
Christopher Thomas Sica1, and Christopher M Collins1
1Radiology, The Pennsylvania State University, Hershey, Pennsylvania, United States

AFI is an established B1+ mapping technique that can suffer from slice profile effects, and is thus typically implemented with 3D non-selective RF pulses, necessitating 3D encoding of a large volume and long scan duration. This work presents a 3D slab-selective AFI technique with a significant reduction in scan time. A thin slab is excited and a small number of slices are encoded along the slab select axis. Slices within the central portion of the slab are kept and outlying slices are discarded. This approach was investigated using simulation and experiment in a phantom. Agreement between non-selective and slab-selective AFI is very good.

15:00 4423.   Sa2RAGE sequence improvements and in-vivo brain RF-shimming at 7 Tesla 
Florent Eggenschwiler1, Arthur William Magill1,2, Tobias Kober1, Rolf Gruetter1,3, and José Pedro Marques1,2
1EPFL, Laboratory for Functional and Metabolic Imaging, Lausanne, Vaud, Switzerland, 2University of Lausanne, Department of Radiology, Lausanne, Vaud, Switzerland,3Universities of Geneva and Lausanne, Department of Radiology, Switzerland

The accuracy of the recently proposed B1+-mapping sequence: Saturation prepared with 2 RApid Gradient Echoes (Sa2RAGE) was improved in terms of T1-insensitivity by considering partial Fourier encoding as well as a parallel imaging technique (GRAPPA). This sequence was then used to map the B1+ field distribution obtained when performing in-vivo brain RF-shimming at 7 Tesla. Shimming was performed by solving the Magnitude Least Squares (MLS) problem and the B1+ homogeneity improvement throughout the brain was demonstrated by showing that the distribution of the B1+ values after shimming is more centered on the mean B1+, illustrating the validity of the Sa2RAGE sequence as well.

Wednesday May 11th
  13:30 - 15:30 Computer 119

13:30 4424.   Statistical Analysis of B1 Mapping Techniques 
Daniel Joseph Park1, Ahsan Javed1, Neal Kepler Bangerter1,2, Mohammad Mehdi Khalighi3, and Glen R Morrell2
1Electrical and Computer Engineering, Brigham Young University, Provo, UT, United States, 2Department of Radiology, University of Utah, Salt Lake City, UT, United States, 3Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States

A statistical analysis of the Bloch-Siegert (BS), phase-sensitive (PS), dual-angle (DA), and actual flip angle (AFI) B1 mapping techniques is presented. The analysis employed a Monte Carlo simulation of the statistical performance of each technique based on the Bloch equations. The phase-sensitive B1 method is shown to yield consistently lower mean-bias estimates of the flip angle with a smaller standard deviation than each of the other techniques, even in low-SNR situations.

14:00 4425.   Theoretical and Experimental Efficiency and Optimization of Flip Angle Mapping Techniques 
Trevor Wade1,2, Charles McKenzie2,3, and Brian Rutt4
1Robarts Research Institute, London, Ontario, Canada, 2Biomedical Engineering, The University of Western Ontario, London, Ontario, Canada, 3Medical Biophysics, The University of Western Ontario, London, Ontario, Canada, 4Department of Radiology, Stanford University, Stanford, California, United States

A theoretical propagation of noise analysis was conducted on 3 flip angle (lower case Greek alpha) imaging techniques (the saturated double angle method, actual flip angle imaging, and the non-inverted double angle Look-Locker method). This analysis was used to predict the optimal imaging parameters, and the imaging efficiency (lower case Greek alpha to lower case Greek alpha noise ratio (ANR) normalized by scan time). The predicted ANR was then compared to the experimentally measured value for a range of flip angles and T1 values.

14:30 4426.   A short TR, MFA approach to simultaneous B1+ and T1 mapping 
Christopher Thomas Sica1, and Christopher M Collins1
1Radiology, The Pennsylvania State University, Hershey, Pennsylvania, United States

A novel, simultaneous B1+ and T1 mapping method is presented here. The proposed method relies upon a series of spoiled GRE scans acquired with a fixed TR and increment of the flip angle between scans. A non-linear fit is applied to the signal expression M0(1-E1)sin[λθ] / (1 – E1cos[λθ]) to obtain both B1+ and T1. The proposed method is compared to the Actual Flip Angle Imaging (AFI) B1+ mapping method. The B1+ mapping results show excellent agreement with AFI, with error between the two methods typically on the order of several percent.

15:00 4427.   B1-Mapping with the Transient Phase of SSFP 
Carl Ganter1, Marcus Settles1, Klaus Scheffler2, and Oliver Bieri2
1Department of Radiology, Technische Universität München, Munich, Germany, 2Division of Radiological Physics, University of Basel Hospital, Basel, Switzerland

In rapid SSFP sequences, the approach toward dynamical equilibrium (transient phase) typically consists of a smooth decay and a superimposed damped oscillation. Recent theoretical studies for the FID signal of unbalanced SSFP showed that the frequency of the latter is closely connected to the actual flip angle lower case Greek alpha and depends only weakly on tissue parameters. In this work, we show that fast and accurate B1-mapping, based on a frequency analysis of the transient phase of SSFP, can be implemented in a conceptually simple and flexible manner.

Thursday May 12th
  13:30 - 15:30 Computer 119

13:30 4428.   Fast 3D B1 mapping with single-shot EPI 
Jay Moore1,2, Marcin Jankiewicz1,3, Adam W Anderson1,4, and John C Gore1,4
1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, United States, 3Department of Radiology and Radiological Sciences, Vanderbilt University, 4Department of Biomedical Engineering, Vanderbilt University

A workflow is demonstrated for B1 mapping using a multi flip-angle fitting technique in conjunction with a single-shot EPI read-out. Resulting field maps are shown to differ minimally when compared to the same measurements made with a low EPI factor. With the protocol presented here, all necessary measurements for whole-brain mapping are acquired in less than 2 minutes.

14:00 4429.   In-vivo RF Receiver Sensitivity Measurement Using Phase-Based B1+ Mapping on a Reverse-Oriented Subject 
Seung-Kyun Lee1, and William Thomas Dixon1
1GE Global Research, Niskayuna, NY, United States

A method is described to measure the receiver sensitivity of a circularly polarized transmit and receive RF coil by mapping the transmit RF field strength on a reverse-oriented subject. A phase-based RF field mapping method allows robust RF mapping unaffected by tissue T1 or image contrast. The method is verified on a multi-slice abdominal scan of a volunteer at 3 T.

14:30 4430.   Multi-Slice B1+ Shimming for 7T MRI 
Andrew T Curtis1, Kyle M Gilbert1, Martyn L Klassen1, Joseph S Gati1, and Ravi S Menon1
1Centre for Functional and Metabolic Mapping, University of Western Ontario, London, Ontario, Canada

Leveraging multi-channel transmit arrays to produce efficient and uniform RF fields becomes a difficult task as field strength increases, thanks to the well known wave effects, and greater coupling between the coils and the sample, especially in tight-fitting arrays. In this situation, the traditional geometric driving phase configuration fails to produce the expected maximum excitation efficiency. It is demonstrated that utilizing the extra degrees of freedom present in multi-slice imaging protocols allows calculation of B1+ shim solutions that can markedly reduce transmitted power (and consequently global SAR) by shimming to recover efficient excitation modes.

15:00 4431.   RF Pulse Optimization for Bloch-Siegert B1+ Mapping 
Mohammad Mehdi Khalighi1, Brian K. Rutt2, Manojkumar Saranathan2, and Adam B. Kerr3
1Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, 2Department of Radiology, Stanford University, Stanford, CA, United States,3Department of Electrical Engineering, Stanford University, Stanford, CA, United States

B1+ mapping by the Bloch-Siegert (BS) method has been shown to be fast and accurate; however, at high field it suffers from high SAR and long TE, which results in lengthened scan times and signal loss due to B0 inhomogeneity. We have designed a new BS RF pulse that can be applied closer to the water resonance yet still limits excitation within the on-resonant band of interest. Comparison of BS B1+ mapping using the new pulse versus the conventional Fermi pulse in both phantoms and human brain shows improved B1+ map quality with substantial reductions in both TE and SAR.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Tailoring Excitation with Parallel Transmission & Advanced Pulse Design

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 120

14:00 4432.   Relaxation-Enhanced Multiple Inner-Volume Imaging Using Parallel 3D Spatially Selective Excitation 
Johannes Thomas Schneider1,2, Martin Haas2, Wolfgang Ruhm1, Juergen Hennig2, and Peter Ullmann1
1Bruker BioSpin MRI GmbH, Ettlingen, Germany, 2Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Recently, first examples of 3D Parallel Spatially Selective Excitation (PEX) have been presented. This technique allows the restriction of the generated transverse magnetization to specified 3D target volumes, while outside these volumes the magnetization is fully restored into the longitudinal direction by the end of the pulse. Exploiting this feature, Multiple Inner-Volume Imaging (MIVI) allows interleaved excitation and data acquisition of multiple different inner-volumes within one repetition time. Compared to successive imaging of multiple inner-volumes in individual experiments, MIVI results in reduced scan times and/or enhanced SNR due to prolonged T1-relaxation periods.

14:30 4433.   Selective Excitation of Arbitrary Three-Dimensional Targets on a Human MR System using Parallel Transmit 
Martin Haas1, Jeff Snyder1, Johannes T Schneider1,2, Peter Ullmann2, Denis Kokorin1,3, Hans-Peter Fautz4, Jürgen Hennig1, and Maxim Zaitsev1
1Department of Radiology Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Bruker BioSpin MRI GmbH, Ettlingen, Germany, 3International Tomography Center, Novosibirsk, Russian Federation, 4Siemens Healthcare, Erlangen, Germany

Spatially selective excitation of an arbitrarily shaped three-dimensional target volume is demonstrated on a human MR scanner at 3T, accelerated by means of 8-channel parallel transmission. The good excitation fidelity and effective restoration of magnetization outside the volume of interest to the longitudinal direction allows for a reduction of the readout field of view in all three dimensions, resulting in an increase of resolution by a factor of two in all three directions while maintaining the measurement time.

15:00 4434.   Sparse Parallel Transmit Excitation Trajectory Design for Rapid Inner-Volume Excitation 
Cem Murat Deniz1,2, Dong Chen3, Leeor Alon1,2, Ryan Brown1, Hans-Peter Fautz4, Daniel K Sodickson1, and Yudong Zhu1
1Center for Biomedical Imaging, Department of Radiology, NYU School of Medicine, New York, NY, United States, 2Sackler Institute of Graduate Biomedical Sciences, NYU School of Medicine, New York, NY, United States, 3Center for Mathematical Science, Technical University of Munich, Munich, Germany, 4Siemens Medical Solutions, Erlangen, Germany

Tailored inner-volume excitation on whole-body scanners is currently limited by long 3D RF pulses. Effective pulse length reduction with parallel transmission requires careful selection of the excitation k-space trajectory. In this work, two methods of determining sparse excitation trajectories were compared for parallel transmit pulse design in the small-tip angle and large-tip-angle regimes: a) an Orthogonal Matching Pursuit (OMP) algorithm, and b) a one-step basic thresholding approach. Good inner-volume excitation with a pulse length of less than 9ms was achieved using an eight-channel transmitter on a whole-body human 7T scanner.

15:30 4435.   Volume Localization using Adiabatic Inversion Pulses in FAIR Imaging 
Ziqi Sun1, Sergey Petryakov1, George Caia1, Alex Samouilov1, and Jay L Zweier1
1Davis Heart & Lung Research Institute, The Ohio State University, Columbus, Ohio, United States

Adiabatic inversion pulses have been widely used in slice- and whole-volume spin inversion in perfusion-weighted MRI. To date, no reports are available for using selective adiabatic inversion pulses for localized volume inversion in perfusion measurements. In this study, we proposed a 3D volume localization using adiabatic inversion pulses for FAIR imaging on a flow phantom. In comparison to the conventional slice-inversion FAIR technique, the perfusion rate measured using the localized volume-inversion FAIR method is in the acceptable accuracy and generates enhanced T1-weighting contrast.

Tuesday May 10th
  13:30 - 15:30 Computer 120

13:30 4436.   Large Tip Angle Segmented RF Design for Multi-Dimensionally Selective Imaging and Spectroscopy with Parallel Transmit 
Martin Haas1, Jeff Snyder1, Peter Ullmann2, Jürgen Hennig1, and Maxim Zaitsev1
1Department of Radiology Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2Bruker BioSpin MRI GmbH, Ettlingen, Germany

Multi-dimensionally selective RF excitation suffers from artifacts related to the typically long pulse duration. In particular, applications in MR spectroscopy would significantly benefit from shorter pulses due to increased bandwidth. Previous approaches to mitigate this problem using segmented selective excitation across several repetitions have been limited to small tip angles. In this work, a segmented RF design algorithm for large tip angle pulses, with additional parallel transmit acceleration, is described for multi-dimensionally selective excitation and demonstrated in simulations and a phantom. The method is based on a segment-wise optimal control optimization and not limited to 2D or a particular segmentation.

14:00 4437.   Flexibly shaped saturation band excitation using 7T parallel transmit system 
Borjan Gagoski1, Khaldoun Makhoul2,3, Dieter Ritter4, Kawin Setsompop2,3, Josef Pfeuffer4, Himanshu Bhat5, Philipp Hoecht5, Michael Hamm5, Ulrich Fontius4, Lohith Kini1, Joonsung Lee1, Lawrence L Wald2,6, and Elfar Adalsteinsson1,6
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2A.A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, 3Harvard Medical School, Boston, MA, United States, 4Siemens Healthcare, Erlangen, Germany, 5Siemens Healthcare, Charlestown, MA, United States, 6Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

Parallel RF transmission (pTx) offers significant flexibility over single-channel excitations for creating arbitrarily shaped spatial excitation patterns, which can be designed for undersampled spiral-based excitation k-space trajectories played during the pTx RF waveform. In this work we validate the feasibility of using 7T 8-channel pTx for flexibly shaped saturation bands that suppresses a user-defined spatial shape, in combination with a B1+ mitigated pTx slice-selective "spokes" excitation.

14:30 4438.   In vivo Zoom Imaging using Transmit SENSE 
Ingmar Graesslin1, Sebastian Boetzl1, Ulrich Katscher1, Kay Nehrke1, Bjoern Annighoefer2, Giel Mens3, and Peter Börnert1
1Philips Research Laboratories, Hamburg, Germany, 2TU Hamburg-Harburg, Hamburg, Germany, 3Philips Healthcare, Best, Netherlands

Zoom imaging allows an increase of the spatial resolution in the targeted region of interest (ROI) without increasing the scan time. Alternatively, maintaining spatial resolution, zoom imaging allows a reduction of the scanning time by reducing the field of view (FOV) to the ROI. For both techniques, potential backfolding artefacts from body regions outside the reduced FOV can be suppressed via local excitation. This local excitation can be performed by multi-dimensional RF pulses, which can be accelerated using spatial transmit sensitivity encoding instead of full gradient encoding. This paper presents (first) zoom imaging volunteer experiments carried out on an 8-transmit channel 3T MRI system, with a fully integrated real-time SAR validation prior to the scan allowing the safe use of spatially selective Transmit SENSE RF pulses and their fast calculation for optimal workflow.

15:00 4439.   Practical Considerations for the Design of Parallel Transmission Pulses at ultra high field 
Tiejun Zhao1, Hai Zheng2, Yik-Kiong Hue3, Tamer Ibrahim2,3, Yongxian Qian3, and Fernando Boada2,3
1Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, 2Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Parallel transmission was recently proposed as one of the methods to accelerate multidimensional selective excitation using multiple coils driven with independent waveforms. The parallel excitation could be a potential solution for mitigating or solving the RF and SAR problems at the ultra-high field (e.g, 7T). One of the popular methods was proposed by Grissom et al. In this work, we propose two novel methods that the artifacts due to finite gradient raster step can be successfully compensated to avoid tilted and excitation errors. Significant improvement can be obviously seen from both simulations and experiments on 7T scanner.

Wednesday May 11th
  13:30 - 15:30 Computer 120

13:30 4440.   Characterization and correction of eddy currents for ultra high field parallel transmission with RF pulse design 
Hai Zheng1, Tiejun Zhao2, Yongxian Qian3, Tamer Ibrahim1,3, and Fernando Boada1,3
1Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2Siemens Medical Solutions, Pittsburgh, Pennsylvania, United States, 3Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Hardware and experimental imperfections can severely impact the excitation patterns in ultra high field parallel transmission. In this work, we propose a new eddy current correction method combining existing eddy current characterization method for parallel transmission RF pulse design to compensate the overall distortion induced by gradient and RF coils as well as the system delay to reduce the distortions in parallel transmission. Our proposed compensation method is a straightforward and easy to implement, but yields an evident improvement in the performance.

14:00 4441.   Parallel Transmission in Human Brain at 9.4T Counteracting Eddy Current Induced Excitation Errors in RF Pulse Design 
Xiaoping Wu1, Gregor Adriany1, Kamil Ugurbil1, and P-F. Van de Moortele1
1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States

14:30 4442.   An Interleaved Spatial-Spectral Pulse for Imaging Large Chemical-shift Components 
Jing Chen1, Jing An2, and Yan Zhuo1
1State Key Laboratory of Brain and Cognitive Science, Inst. of Biophysics, Chinese Academy of Sciences, Beijing, China, People's Republic of, 2Siemens Healthcare, MR Collaboration NE Asia, Siemens Mindit Magnetic Resonance, China, People's Republic of

This work describes an interleaved spatial-spectral RF pulse for use with large excitation/suppression difference frequency, for example, exciting water while suppressing fat on a 7T system. The excitation is divided into three repetitions to fill the excitation k-space in an interleaving pattern. Interleaving allows driving the gradient at a lower slew rate. Therefore, this method has the advantages of less eddy current distortion, relative ease of implementation, and thinner slice thickness.

15:00 4443.   RF energy reduction by parallel transmission using large-tip-angle composite pulses 
Rene Gumbrecht1,2, Elfar Adalsteinsson3,4, Paul Müller2, and Hans-Peter Fautz1
1Siemens Healthcare, Erlangen, Germany, 2Department of Physics, Friedrich-Alexander University, Erlangen, Germany, 3Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, United States

For ultra high field strengths of 7T and above, peak RF power and SAR are limiting factors for high performance imaging. One way to keep these quantities low is to prolong the RF pulses. However, long RF pulses are prone to B0 homogeneities because the bandwidth of such pulses is reduced. In this work, we investigate the potential of prolonging large-tip-angle composite RF pulses for power and SAR reduction by using pTx pulse design methods which account for local B0 field variations.

Thursday May 12th
  13:30 - 15:30 Computer 120

13:30 4444.   B1 inhomogeneity mitigation in the human brain at 7T with selective pulses by using Average Hamiltonian Theory 
Nicolas Boulant1, Martijn Cloos1, and Alexis Amadon1
1NeuroSpin, CEA Saclay, Saclay, France

The design of the strongly modulating pulses, developed by the same authors and initially non-selective, has been adjusted to create selective pulses by using average Hamiltonian theory. Such a theory formulates an approximate analytical expression of the dynamics which allows navigating quickly in some pulse parameter space. Once a pulse is found to perform sufficiently well using that approximation, it can be modified with a few iterations by calculating more accurately the spin evolution. Using that technique, in-vivo results are reported which show good mitigation of the B1 inhomogeneity problem over an axial slice in the human brain at 7T.

14:00 4445.   Non-Slice Selective Uniform Tipping RF Pulse Design for 3D MRI at High Field 
Hui Liu1,2, and Gerald B. Matson1,3
1Center for Imaging of Neurodegenerative Diseases (CIND), Veterans Affairs Medical Center, San Francisco, CA, United States, 2Northern California Institute for Research and Education, San Francisco, CA, United States, 3University of California, San Francisco,CA, United States

Although high-field MRI offers increased signal-to-noise (SNR), the non-uniform tipping produced by conventional RF pulses leads to spatially varying contrast such as a bright center, and sub-optimal S/N, thus complicating the interpretation of the MR images. The aim of this research was to develop non-slice-selective (NSS) RF pulses with immunity to B1 inhomogeneity and resonance offset for a full range of tip angles. To accomplish this, we developed an optimization routine to design RF pulses with a desired range of immunity to B1 inhomogeneity and to resonance offset. Simulations were validated by phantom tests and an in vivo human study. The resulting pulses were more efficient (in terms of length) than previous pulses in the literature. These pulses have promise for 3D MRI experiments at high field.

14:30 4446.   T2-Weighting Enhancement using Pseudo-Echoes Generated by Selective Adiabatic Refocusing Pulses in a CPMG Pulse Sequence 
Ziqi Sun1
1Davis Heart & Lung Research Institute, The Ohio State University, Columbus, Ohio, United States

Selective adiabatic excitation pulses have been utilized to generate pseudo-echoes to improve image contrast and quality. In this study, pseudo-echo images were obtained using a customized CPMG pulse sequence incorporated with selective adiabatic refocusing pulses that alternate frequency sweep directions between each of the echoes. Apparent T2 time constants were measured from the pseudo-echo images using the customized CPMG sequence. T2-weighting was significantly increased using the sequence in comparison to the CPMG sequence using amplitude modulated selective refocusing pulses.

15:00 4447.   Fast Spin Echo Imaging with Quadratic Phase-Modulated non-CPMG Echo Train in Parallel Transmit – a Simulation Study 
Seung-Kyun Lee1, Mika W Vogel2, William A Grissom2, Graeme C McKinnon3, and Patrick H Le Roux4
1GE Global Research, Niskayuna, NY, United States, 2Advanced Medical Applications Laboratory, GE Global Research, Munich, Bavaria, Germany, 3Applied Science Lab, GE Healthcare, Waukesha, WI, United States, 4Applied Science Lab, GE Healthcare, Palaiseau, France

In parallel transmit, phase-relaxed RF pulse design significantly improves image quality in gradient echo and spin echo images. Here we present a simulation study showing that phase-relaxed 90-180 RF pulses can also be used in fast spin echo imaging with Le Roux’s quadratic phase modulation implemented on all transmit channels.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Quantitative MRI

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 121

14:00 4448.   Experimental Evaluation of RF Non-uniformity Correction in the Mapping of the Proton Density 
Vincent Gras1, Zaheer Abbas1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany, 2Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

Mapping of the proton density (PD) is a common MRI application, with interesting perspective in medical research. At 3 Tesla, PD imaging supposes an accurate correction of the sample-dependent RF non-uniformity, which is measured using a dedicated protocol termed B1 mapping. Such measurement is possible if one assumes 1) the linear relationship between flip angle and B1 and 2) the NMR reciprocity principle. From these 2 assumptions, it follows a unique correction scheme. In this work, the accuracy of the correction is evaluated to 2%, setting an upper limit to the precision of the PD measurement achievable with this general approach.

14:30 4449.   Quantitative Water Content Mapping at 1.5 and 3 Tesla Field Strength 
Vincent Gras1, Zaheer Abbas1, Anna-Maria Oros-Peusquens1, Klaus Hans Manfred Möllenhoff1, Fabian Keil1, Miriam Rabea Kubach1, and Nadim Jon Shah1,2
1Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Forschungszentrum Jülich GmbH, Jülich, Germany, 2Faculty of Medicine, Department of Neurology, RWTH Aachen University, Aachen, Germany

A 1.5T and 3T quantitative water content imaging protocol is proposed, extending a previously developed method, suited to 1.5T only. The benefit of working at 3T is a noticeable gain in SNR compared to 1.5T, although refinements are needed for the accuracy to be preserved. The gradient echo approach, envisaged in this work, allows for the detection of myelin water, exhibiting short relaxation times. Furthermore, the required short scanning time, 15 minutes, is particularly suited to the clinical practice. The accuracy of the method is evaluated to 2%, making this method eligible for the detection of cerebral oedema of various origins. This method is presented and in vivo results at 1.5T and 3T are shown.

15:00 4450.   Quantitative Magnetic Resonance Imaging in Light-Chain (AL) Amyloidosis: Preliminary Experience 
Stephan William Anderson1, Jennifer Ellis-Ward2, Erskine Hawkins3, James A Hamilton4, Carl J O'Hara5, Lawreen H Connors6, Jorge A Soto1, David C Seldin2, and Hernan Jara1
1Radiology, Boston University Medical Center, Boston, MA, United States, 2Hematology and Medical Oncology, Boston University Medical Center, 3Boston University School of Medicine, 4Physiology and Biophysics, Boston University Medical Center, 5Pathology and Laboratory Medicine, Boston University Medical Center, 6Biochemistry, Boston University School of Medicine

Purpose: To evaluate the effects of amyloid deposition on T2 and apparent diffusion coefficient (ADC) measurements in human autopsy specimens of myocardium, liver, spleen, and kidney of patients with AL amyloidosis using 11.7T MRI. Methods: T2 and ADC values of tissues with amyloid deposition were compared to control specimens. Results Significant differences in T2 and ADC values were seen when comparing control and involved specimens of myocardium, spleen and kidney (all p<0.002). Conclusion: Deposition of amyloid protein in human autopsy specimens substantially affects ADC values in myocardium, liver, spleen, and kidney and T2 values in myocardium, spleen and kidney.

15:30 4451.   Characterization of Modified Look Locker (MOLLI) using Bloch simulations and corroboration with scan measurements 
Neville D Gai1, Christian Stehning2, Marcelo Nacif1, and David A Bluemke1,3
1Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, United States, 2Philips Research Europe, Hamburg, Germany, 3NIBIB, Bethesda, MD, United States

The MOLLI technique for T1 mapping has found favor in cardiac imaging due to its relative robustness to motion. A subsequent work explored optimization of parameters based purely on performing phantom scans while varying scan parameters. Such an approach could fail to be comprehensive in the covered parameter space or parameters affecting accuracy. Here, we develop Bloch simulation based characterization of MOLLI and evaluate T1 accuracy for several scan parameters. We corroborate T1 values obtained from simulation with values obtained from scanning phantoms. Based on simulations and scanning, it is shown that the simulation is a valuable tool in understanding the accuracy of T1 values given different scan conditions.

Tuesday May 10th
  13:30 - 15:30 Computer 121

13:30 4452.   Comparison of Different EPI-based Approaches to Measure T2’ in Human Brain for the Purpose of Oxygenation Measurements 
Thomas Christen1, Heiko Schmiedeskamp1, Matus Straka1, Roland Bammer1, and Greg Zaharchuk1
1Department of radiology, Stanford University, Stanford, California, United States

We compared in this study three different EPI-based approaches for measuring T2’ : (1) a subtraction of T2 from T2* relaxation rates that are derived from separate multiecho sequences; (2) an asymmetric spin echo (ASE) sequence; (3) a combined multiple gradient echo and spin echo (SAGE) sequence. The results obtained in the brain of 4 subjects suggest that the different approaches give similar T2’ values. They however showed spatial differences. The highest-quality maps were obtained with the ASE method. The SAGE approach, while containing spatial artifacts, could be used in a dynamic approach with high time resolution.

14:00 4453.   On the T1 of fat calculated from a segmented Look Locker scout scan and its implications in cardiac imaging 
Neville D Gai1, Christian Stehning2, Saman Nazarian3, Evrim Turkbey1, and David A Bluemke1,4
1Radiology & Imaging Sciences, National Institutes of Health, Bethesda, MD, United States, 2Philips Research Europe, Hamburg, Germany, 3Division of Cardiology, Johns Hopkins University, Baltimore, United States, 4NIBIB, Bethesda, MD, United States

T1 mapping can differentiate between diffuse fibrosis and normal myocardium. Several longitudinal cardiac studies do not have a dedicated T1 mapping scan as part of the protocol. However, segmented Look-Locker (LL) with b-SSFP is typically used as a scout scan. T1 values may then be derived from such a scan. Certain diseases exhibit fatty infiltration as part of their etiology. Based on simulations and scanning, we show that fat T1 quantification so obtained can be highly erroneous based on the scan parameters used. Therefore, conclusions based on observed cardiac T1 values in cases where fatty infiltration is substantial might be fraught with complications.

14:30 4454.   Accurate T1 Measurement with IR-prepared Segmented Gradient Echo and A New Regression Algorithm 
Haosen Zhang1, Kevin Hitchens1, Qing Ye1, EriK B. Schelbert2, and Chien Ho1
1Pittsburgh NMR Center for Biomedical Research, Department of Biological Science, Carnegie Mellon University, Pittsburgh, PA, United States, 2Department of Medicine, University of Pittsburgh, Pittsburgh, PA, United States

In this study, an inversion recovery (IR)-prepared segmented gradient echo sequence was developed to sample the T1 recovery curve in Look-Locker scheme at 7 T. Via a multi-variable regression algorithm corrected for the saturation effect induced by the á-train, we have obtained more accurate T1 values than with the conventional three-parameter fit (average error of -0.53% vs. -5.4% separately, compared to T1s measured with IR-SE) in agarose phantoms simulating human myocardium and blood.

15:00 4455.   Non-Exponential T2* Decay in White Matter 
Peter van Gelderen1, Jacco A de Zwart1, Jongho Lee1, Pascal Sati2, Daniel S Reich2, and Jeff H Duyn1
1Advanced MRI section, LFMI, NINDS, National Institutes of Health, Bethesda, MD, United States, 2Translational Neuroradiology Unit, Neuroimmunology Branch, NINDS, National Institutes of Health, Bethesda, MD, United States

A number of methods have been proposed to determine the myelin distribution in human brain, which may report on pathology. One potentially promising method is measurement of the T2* relaxation curve ,which may be affected by restricted mobility of myelin associated water. Here we investigated this possibility using multi-gradient echo MRI at 3T and 7T in normal brain. In myelin-rich regions, we observed relaxation characteristics more consistent with effects from susceptibility variations rather than from mobility restrictions. This may complicate the interpretation, as susceptibility effects are affected by additional factors independent of myelin content.

Wednesday May 11th
  13:30 - 15:30 Computer 121

13:30 4456.   Fast Radio-frequency Enforced Steady State (FRESS) Spin Echo MRI for Quantitative T2 Mapping 
Jerry S. Cheung1, Enfeng Wang1,2, XiaoAn Zhang2, Emiri Mandeville3, Eng H. Lo3, A. Gregory Sorensen1, and Phillip Zhe Sun1
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, MGH and Harvard Medical School, Charlestown, MA 02129, United States, 2Department of Radiology, 3rd Affiliated Hospital, Zhengzhou University, China, People's Republic of, 3Neuroprotection Research Laboratory, Department of Radiology and Neurology, MGH and Harvard Medical School, Charlestown, MA 02129, United States
Transverse relaxation time (T2) is a basic but very informative MRI parameter, widely used in imaging to examine a host of diseases including multiple sclerosis, stroke, and tumor. When the repetition time (TR) is very long, T2 can be derived by fitting T2-weighted images as a function of echo time (TE). However, short TR is often used to minimize scan time, which may introduce non-negligible errors in T2 measurement. Our study proposed a fast RF-enforced steady state (FRESS) spin echo MRI sequence, which saturates the magnetization after the spin echo and ensures a TE-independent steady state for accurate T2 mapping.

14:00 4457.   Quantitative T1 estimation using Tissue Specific Imaging 
Arezou Koohi1, and Vasiliki N Ikonomidou1
1Electrical and Computer Engineering, George Mason University, Fairfax, VA, United States

This study presents the application of Tissue Specific Imaging (TSI), a double inversion recovery variant that produces three single tissue type images, to the quantitative mapping of tissue T1 values. The methodology presented, which can add value to the application of TSI, is stable over a wide range of T1 values, up to 4500 ms for usually encountered signal-to-noise ratio values.

14:30 4458.   Single-slice mapping of submillisecond T2 using spin echo prepared ultra-short echo time imaging 
Stefan Kirsch1, and Lothar R Schad1
1Computer Assisted Clinical Medicine, Heidelberg University, Mannheim, Germany

Measurement of the transversal relaxation time T2 is one of the most established techniques to characterize material samples or biological tissue by means of NMR. If molecular motion is restricted, direct spin-spin interactions become relevant and extremely short T2 values are expected. Here we present a slice-selective MRI method for mapping of submillisecond T2. The method utilizes a spin echo preparation followed by slice-selective ultra-short echo time imaging. Mapping of submillisecond T2 could be useful in studies on material samples, short T2 biological tissue like bone, tendon or cartilage and on quadrupolar nuclei like 23Na, 35Cl, and 17O.

15:00 4459.   Effect of the Slice Profile on the T1 Measurement with Steady-State Magnetization 
Jung-Jiin Hsu1
1Radiology, University of Miami School of Medicine, Miami, Florida, United States

The accuracy of the T1 measurement depends on the accuracy of the flip angle (FA). The FA is non-uniform in a slice across the slice-thickness direction, which can result in serious T1 measurement error. Although it has been recognized that measuring the FA regional inhomogeneity in a volume is important, the effect of the slice profile is still less known. In this work, the slice-profile effect is studied systematically for various common experimental conditions. The results provide essential guidelines for experiment design and scan parameter selection for the T1 measurement with steady-state magnetization (e.g., DESPOT).

Thursday May 12th
  13:30 - 15:30 Computer 121

13:30 4460.   T2* myelin water imaging with bmGESEPI for macroscopic field inhomogeneity compensation 
Yoonho Nam1, Eung-Yeop Kim2, Dosik Hwang1, and Dong-Hyun Kim1
1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, 2Radiology, Yonsei University, Seoul, Korea, Republic of

Myelin water imaging is a useful tool for studying white matter diseases. So far, a multi-exponential T2 analysis using multi-echo spin echo sequence has been mostly used for myelin water imaging. But, using a multi-echo spin echo sequence has some limitations such as high SAR, small coverages. Therefore, several studies have been conducted using multi-echo gradient echo sequences recently. However, T2* decay curve measured by gradient echo sequence can be easily distorted by macroscopic field inhomogeneity. In this study, the bmGESEPI method was applied for myelin water imaging to remove the effects of macroscopic field inhomogeneity.

14:00 4461.   Simulation of the Filtering Effect of the FLASH Readout on Saturation Recovery T1 Evaluation 
Moritz Cornelius Berger1, Wolfhard Semmler1, and Michael Bock1
1Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Fast saturation recovery turboFLASH imaging introduces a saturation-time dependent filter on the magnetization-prepared k-space. To mitigate these filtering effects for reliable T1 measurements, multiple k-space segmentation schemes were simulated to characterize the tradeoff between the accuracy of T1 determination and total measurement time.

14:30 4462.   Rapid T2 Mapping of Mouse Heart Using CPMG Sequence and Model-based Compressed Sensing Reconstruction 
Yong Chen1,2, Wen Li1,2, and Xin Yu1,2
1Department of Biomedical Engineering, Case Western Reserve Univ, Cleveland, OH, United States, 2Case Center for Imaging Research, Case Western Reserve Univ, Cleveland, OH, United States

In this study, we developed a novel method for rapid T2 mapping of mouse heart in vivo. Our results demonstrate that a high temporal resolution of ~15 seconds can be achieved by combining a fast multi-echo spin-echo sequence with a model-based compressed sensing reconstruction.

15:00 4463.   Multi-slice Look-Locker T1 mapping for the mouse heart 
Adrienne E Campbell1,2, Anthony N Price3, Bernard M Siow1, Jack A Wells1, Mark F Lythgoe1, and Roger J Ordidge2
1Centre for Advanced Biomedical Imaging, Division of Medicine and Institute of Child Health, University College London, London, United Kingdom, 2Department of Medical Physics and Bioengineering, University College London, London, United Kingdom, 3Robert Steiner MRI Unit, Imaging Science Department, Hammersmith Hostpital, Imperial College London, London, United Kingdom

A time-efficient multi-slice ECG gated Look-Locker sequence is developed for multi-slice T1 mapping in the mouse heart. With this sequence, multi-slice T1 maps can be generated for the mouse heart in less than 10 minutes. Multi-slice T1 mapping was tested in phantoms and in a CD-1 mouse, and it was found that T1 measurements agreed with single-slice T1 measurements within 4% for the phantom and within 10% in vivo. This sequence will have great applicability for multi-slice arterial spin labelling perfusion measurements to study cardiac disease models.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Electromagnetic Tissue Property Mapping

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 122

14:00 4464.   Electrical conductivity imaging of brain tumours. 
Astrid L.H.M.W. van Lier1, Johannes M. Hoogduin2, Daniel L. Polders2, Vincent O. Boer2, Jeroen Hendrikse2, Pierre A. Robe3, Peter A. Woerdeman3, Jan J.W. Lagendijk1, Peter R. Luijten2, and Cornelis A.T. van den Berg1
1Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 2Radiology, UMC Utrecht, Utrecht, Netherlands, 3Neurosurgery, UMC Utrecht, Utrecht, Netherlands

Electrical conductivity mapping is a new technique to generate MRI contrast. Over the last years, the theory and practical implementation of the method has been shown, and measurements of phantoms and healthy volunteers were presented. Here we present for the first time conductivity mapping in brain tumour patients. Distinct differences between the conductivity of some tumours compared to surrounding tissue were observed. The potential of this conductivity mapping for tumour detection, characterization and staging will be further investigated.

14:30 4465.   Electrical impedance tomography using magnetic resonance as the voltage source 
Michiro Negishi1, Tangji Tong1, Peter Brown1, Terrence Nixon1, and R Todd Constable1,2
1Diagnostic Radiology, Yale University, New Haven, CT, United States, 2Neurosurgery, Yale University, New Haven, CT, United States

We present a novel impedance imaging method called Magnetic Resonance Driven Electrical Impedance Tomography (MRDEIT), where magnetic resonance is used to apply voltages and the signals from surface electrodes or surface RF detectors are analyzed to obtain the complex permittivity distribution in the target volume. In the current study, we test whether the RF voltages measured by surface electrodes changes when the conductance of the phantom is altered as the theory predicts. The experiment results showed that a higher conductivity results in a higher average electrode voltage and that the spatial voltage profile from the Finite Element Method based simulations.

15:00 4466.   In vivo conductivity mapping using double spin echo for flow effect removal 
Narae Choi1, Minoh Ghim1, Seungwook Yang1, Sang-Young Zho1, and Dong-Hyun Kim1,2
1Electrical and Electronic Engineering, Yonsei University, Sinchon dong, Seoul, Korea, Republic of, 2Radiology, Yonsei University, Sinchon dong, Seoul, Korea, Republic of

The electric properties tomography (EPT) is used to evaluate tissue conductivity in vivo by analyzing B1 map. The B1 map, however, is hampered by attenuation of signal amplitude from the flow within a voxel. This study focuses on the reconstruction of in vivo conductivity map using double spin echo signal for flow compensation.

15:30 4467.   Rapid estimation of conductivity and permittivity using Bloch-Siegert B1 mapping at 3.0T 
Selaka Bandara Bulumulla1, Seung-Kyun Lee1, Teck Beng Desmond Yeo1, W Thomas Dixon1, and Thomas K Foo1
1GE Global Research, Niskayuna, New York, United States

Tissue conductivity and permittivity are critical to estimating local RF power deposition in the human body during MR imaging. These electrical properties may also have diagnostic value as malignant tissue types have shown higher permittivity and conductivity than surrounding healthy tissue. In this work, we explore rapid estimation of conductivity and permittivity using Bloch-Siegert B1 mapping at 3.0T. In a 24cm axial plane FOV, 128x128 resolution, permittivity was obtained in approximately 1 ½ min. Obtaining conductivity required an additional 1min.

Tuesday May 10th
  13:30 - 15:30 Computer 122

13:30 4468.   MREIT and EPT: a comparison of two conductivity imaging modalities 
Dong-Hyun Kim1, Min-oh Ghim1, Ohin Kwon2, Hyung Joong Kim3, Jin Keun Seo4, and Eung Je Woo3
1Electrical and Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, 2Mathematics, Konkuk University, Korea, Republic of, 3Biomedical Engineering, Kyung Hee University, Korea, Republic of, 4Mathematics, Yonsei University, Seoul, Korea, Republic of

Magnetic resonance electrical impedance tomography (MREIT) and MR electrical properties tomography (MREPT) are medical imaging modalities capable of visualizing the electrical permittivity and conductivity distribution of conducting objects at different operating frequencies. MREIT provides conductivity information at low frequency while MREPT is related to the conductivity at the Larmor frequency. Here both experiments are carried out to show the contrast differences in the two imaging methods.

14:00 4469.   Mechanism of Conductivity Image Contrast in MREIT: Numerical Simulation and Phantom Experiment 
Young Tae Kim1, Tong In Oh1, Atul Singh Minhas1, Hyung Joong Kim1, Jin Keun Seo2, Oh In Kwon3, and Eung Je Woo1
1Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi, Korea, Republic of, 2Computational Science and Engineering, Yonsei University, Seoul, Korea, Republic of,3Mathematics, Konkuk University, Seoul, Korea, Republic of

MREIT utilizes MR phase images affected by externally injected currents to reconstruct conductivity images. Understanding its contrast mechanism could be difficult due to complexities in associated mathematical expressions of bioelectromagnetism. We constructed stable conductivity phantoms not affected by the ion diffusion process placing thin insulating hollow cylinders with holes of different diameters inside a saline tank. When we extracted induced magnetic flux density images from MR phase images, their slopes changed with conductivity contrasts. Analyzing measured and computed magnetic flux density images of the phantoms, we could quantitatively validate the contrast mechanism in MREIT.

14:30 4470.   Quantitative Susceptibility Imaging using L1 regularized reConstruction with Sparsity Promoting Transformation: SILC 
Deqiang Qiu1, Greg Zaharchuk1, Shangping Feng1, Thomas Christen1, Kyunghyun Sung1, and Michael E. Moseley1
1Lucas Imaging Center, Stanford University, Stanford, CA, United States

We describe a novel method (SILC) for reconstructing susceptibility distribution from phase maps using L1 regularized iterative method with a sparsity promoting transformation. Both simulations and application to in vivo human brain imaging are presented. The SILC method was also compared to a kernel modification method.

15:00 4471.   In vivo whole brain susceptibility mapping using compressed sensing 
bing Wu1, Wei Li1, and Chunlei Liu1
1Brain imaging and analysis center, Duke University, Durham, NC, United States

A novel suscepibility mapping method based on compressed sensing is proposed, in which the ill-conditioned k-space regions are estimated using compressed sensing. No prior knowledge of the underlying susceptibility map is required. Much lower lelvel of streaking artifacts are received comparing to the direct threshold method using in vivo brain data set.

Wednesday May 11th
  13:30 - 15:30 Computer 122

13:30 4472.   Regularized Quantitative Susceptibility Mapping for Phase-based Regional Oxygen Metabolism (PROM) at 7T 
Audrey Peiwen Fan1, Berkin Bilgic1, Thomas Benner2, Bruce R Rosen2,3, and Elfar Adalsteinsson1,3
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 2Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 3Health Sciences and Technology, Harvard-MIT, Cambridge, MA, United States

Venous oxygen saturation (Yv) is an important indicator for brain function and absolute quantification of Yv is critical to estimation of the cerebral metabolic rate of oxygen (CMRO2). Here we implement an l1-regularized quantitative susceptibility mapping technique to measure Yv in cerebral veins at 7T without assumptions about vessel orientation and geometry. QSM measurements in parallel vessel segments resulted in mean Yv = 61.2% and were comparable to mean Yv = 62.1% estimated with MR susceptometry. QSM measurements in curved, in-plane vessel segments resulted in mean Yv = 66.7%, which lies in expected physiological range.

14:00 4473.   A theoretical analysis of the Morphology Enabled Dipole Inversion (MEDI) method: using anatomical information to improve the calculation of susceptibility 
Tian Liu1,2, Weiyu Xu3, Amir Salman Avestimehr3, and Yi Wang1,2
1Biomedical Engineering, Cornell University, Ithaca, NY, United States, 2Radiology, Weill Cornell Medical College, New York, NY, United States, 3School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, United States

The inverse problem from magnetic field to susceptibility source is ill-posed. Even in a noise-free senario, there are infinite number of solutions fulfilling the observation, and a little error in the input data will result in severe noise propagation in the final outcome. In this abstract, we provide a detailed analytical and numerical analysis to demonstrate that the Morphology Enabled Dipole Inversion (MEDI) approah provides a unique and accurate solution under ideal conditions, and the error of the reconstruction is tightly bounded by the error in the gradient echo image in the presence of Gaussian noise.

14:30 4474.   Fast in vivo susceptibility imaging using compressed sensing and parallel imaging 
bing Wu1, Wei Li1, and Chunlei Liu1
1Brain imaging and analysis center, Duke University, Durham, NC, United States

Susceptibility map may be derived from the image phase information, however obtaining the image phase using a 3D SPGR sequence is usually a time consuming process. A novel image reconstruction method is proposed to accelerate the susceptibility imaging by exploiting the complementary properties of compressed sensing and parallel imaging. We show that qualitatively and quantitatively accurate whole brain susceptibility map at 1mm isotropic resolution with a TE of 40ms may be obtained within 8 minutes.

15:00 4475.   Susceptibility mapping: computation of the field map using water-fat separation at 7T 
Ildar Khalidov1, Tian Liu1, Martin R. Prince1, and Yi Wang1
1Radiology, Weill Cornell Medical College, NYC, NY, United States

Susceptibility mapping in animals is a promising technique for contrast agent quantification. To get a susceptibility map, the inverse problem solver requires high-quality field map as input. To estimate the field, the water-fat separation problem in the conditions of strong field inhomogeneity at 7T is solved in this abstract. We use the combination of the VARPRO method with a Markov chain to enforce spatial consistency between field map values. We expect the method to be useful for contrast quantification in high-field animal MRI.

Thursday May 12th
  13:30 - 15:30 Computer 122

13:30 4476.   Improving Susceptibility Mapping of Veins Using a K-space Iterative Approach 
Jin Tang1, Saifeng Liu1, Jaladhar Neelavalli2, and E Mark Haacke2,3
1School of Biomedical Engineering, McMaster University, Hamilton, Ontario, Canada, 2The MRI Institute for Biomedical Research, Detroit, Michigan, United States,3Academic Radiology, Wayne State University, Detroit, Michigan, United States

Mapping susceptibility from field perturbation data is a difficult inverse problem. Here we present a unique k-space iteration/image processing approach which dramatically reduced reconstruction streak artefacts caused by an ill-posed problem of inverse filter and simultaneously improved the accuracy of susceptibility quantification. This method could potentially be used for quantitative in vivo venous oxygen saturation measurement using SWI data.

14:00 4477.   Susceptibility Mapping in Rat Deep Brain Structures using UHF MRI 
David A Rudko1, L M Klassen1, Sonali N de Chickera2, Greg A Dekaban2, and Ravi S Menon1
1Centre for Functional and Metabolic Mapping, Robarts Research Institute, London, Ontario, Canada, 2Biotherapeutics Research Group, Robarts Research Institute, London, Ontario, Canada

In this study, microscopic field (µB0) maps were used to asses the Generalized Lorentzian model (GLmodel) of field shifts in healthy rat brain at 9.4 T. Experimentally measured µB0 at multiple sampling orientations was within measured error tolerance compared to the GLmodel shifts in subcortical GM and cerebral veins. The enhanced complexity of white matter field shifts was addressed by examining: (i) the elliptical cylinder and (ii) the circular cylinder approximations for axonal bundle fields. The circular cylinder approximation produced negative field shifts comparable to µB[0 estimates and the fields around phospholipid-like susceptibility inclusions. lower case Greek chi and R2* maps were reconstructed independently to estimate iron concentration around susceptibility inclusions.

14:30 4478.   Susceptibility Mapping of Human Brain Reflects Spatial Variation in Tissue Composition 
Wei Li1, Bing Wu1, and Chunlei Liu1,2
1Brain Imaging & Analysis Center, Duke University, Durham, NC, United States, 2Radiology, Duke University, Durham, NC, United States

A novel susceptibility mapping method is developed, which is based on two complementary equations, i.e., the Fourier relationship between phase and susceptibility, and its k-space first-order derivatives. This method allows high quality susceptibility mapping of human brain in vivo. The resultant susceptibility maps allow excellent visualization of deep nuclei and white matter fiber bundles, which reflects spatial variation in tissue composition, especially iron and myelin distribution. This method is robust and efficient, thus providing a convenient tool for routine susceptibility mapping for the study of brain physiology and neurological diseases.

15:00 4479.   Susceptibility quantification in MRI using phase gradient mapping 
Luning Wang1, and Qun Zhao1
1Department of Physics and Astronomy, University of Georgia, Athens, GA, United States

Susceptibility quantification in MRI is a novel technique that can be involved in many applications, such as tracking stem cells labeled with super-paramagnetic iron oxide (SPIO) nanoparticles. Because of the tight relationship between susceptibility and magnetic field inhomogeneity, most of the published techniques employ the MR phase images to estimate susceptibility distributions. However, the wrapping effect in MR phase maps is a headachy problem and has to be solved before any further data processing. In this work, we present a new technique that implements the phase gradient mapping (PGM) method to directly calculate the susceptibility distribution.

Electronic Posters : Pulse Sequences, Reconstruction & Analysis
Click on to view the abstract pdf and click on to view the video presentation.
Pulse Sequences - Contrast Mechanisms

Monday May 9th
Exhibition Hall  14:00 - 16:00 Computer 123

14:00 4480.   Feasibility of myelin water fraction quantification using multi-component gradient echo sampling of spin echoes 
Yann Gagnon1,2, Neil Gelman1,2, and Jean Théberge1,2
1Medical Biophysics, University of Western Ontario, London, Ontario, Canada, 2Lawson Health Research Institute, London, Ontario, Canada

A new acquisition scheme is proposed consisting of symmetrically sampling, using gradient echoes, the rephrasing and subsequent dephasing parts of multiple spin echoes, termed multi-component gradient echo sampling of spin echoes (mcGESSE). The theoretical ability of this method to calculate the MWF is demonstrated in a two-component model using simulated data and realistic temporal signal to noise profiles. Implementation of this sequence would allow for whole-brain MWF data in a clinically relevant scan time of approximately 10 to 20 minutes.

14:30 4481.   2D Multi-slice Quantitative Myelin Water Imaging at 3T 
Junyu Guo1, Qing Ji1, and Wilburn E. Reddick1
1Radiological Sciences, St Jude Children's Research Hospital, Memphis, TN, United States

Myelin water fraction (MWF) provides a direct indicator of myelin structure and component change due to white matter diseases. Conventionally, the data acquisition time for generating a MWF map of a single slice takes about 25 minutes. In this study, we proposed a 2D multi-slice acquisition scheme with much higher efficiency and capturing the small contribution of the myelin-water signal. This acquisition scheme could cover most of the brain volume in less than 12 minutes. We also provided a weighted regularized nonnegative least squares (wrNNLS) algorithm to generate reliable parametric maps.

15:00 4482.   Simulation of Double Pulsed Field Gradient Experiments 
Gregory T. Baxter1, Evren Ozarslan2,3, Peter J. Basser2, and Lawrence R. Frank1,4
1Radiology, UCSD, La Jolla, CA, United States, 2STBB / PPITS / NICHD, National Institutes of Health, Bethesda, MD, United States, 3Center for Neuroscience and Regenerative Medicine, USUHS, Bethesda, MD, United States, 4VASDHS, La Jolla, CA, United States

Double pulsed field gradient (DPFG) MR experiments are growing in popularity owing to their ability to reveal new structural features of tissue. Here, we simulate DPFG experiments in restricted environments and compare these results against theory. We then simulate diffusion in arrays of microcapillaries both filled and surrounded by water. We find significant changes in the MR signal as a function of cylinder spacing.

15:30 4483.   Intermolecular double-quantum coherence imaging without coherence selection gradients 
Yanqin Lin1, Guiping Sheng1, Congbo Cai1, Shuhui Cai1, Jianhui Zhong2, and Zhong Chen1
1Department of Physics, Xiamen University, Xiamen, Fujian, China, People's Republic of, 2Department of Imaging Sciences, University of Rochester, Rochester, NY, United States

Intermolecular double-quantum coherences (iDQCs) have some unique properties and have been applied for novel contrast of MRI. In the conventional iDQC imaging experiments, the distant dipolar field (DDF) is generated by coherence selection gradients (CSGs). However, it is found that DDF can arise from certain sample geometry in the absence of CSGs. Here, we demonstrate that sample geometry plays an important role in generating DDF in the absence of CSGs, and this DDF can yield stronger iDQC signal than that from the CSGs if an appropriate phase cycling scheme is adopted. This will facilitate iDQC practical applications.