ISMRM 21st Annual Meeting & Exhibition ○ 20-26 April 2013 ○ Salt Lake City, Utah, USA
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B
4170 -4193 | Contrast Mechanisms: Electromagnetic Property Mapping
4194 -4206 | Contrast Mechanism: Relaxometry - T2* & Iron Quantification
4207 -4217 | Contrast Mechanisms: Relaxometry - Novel Sequences & Quantification Methods
4218 -4241 | All Flavors of Saturation Transfer Floors
4242 -4265 | RF Pulse Design 2
4266 -4271 | B1 Mapping, Water/Fat & Contrasts: B1 Mapping
4272 -4281 | B1 Mapping, Water/Fat & Contrasts: Water/Fat
4282 -4289 | B1 Mapping, Water/Fat & Contrasts: Contrast
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (16:00-17:00) Exhibition Hall
Contrast Mechanisms: Electromagnetic Property Mapping
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4170. | 1 | MREIT Conductivity Imaging of Pneumonic Canine Lung: Preliminary Feasibility Study Woo Chul Jeong1, Munish Chauhan1, Hyung Joong Kim1, Hee Myung Park2, Oh In Kwon2, and Eung Je Woo1 1Kyung Hee University, Yongin, Gyeonggi, Korea, 2Konkuk University, Seoul, Korea MREIT is one of the unique imaging modalities capable of visualizing a high-resolution conductivity distribution of the human body in a non-invasive manner. Unlike conventional MRI, we expect MREIT to be effective in chest imaging. To investigate any change of electrical conductivity due to pneumonia, canine chests having a regional pneumonic model were scanned along with separate scans of chest having no disease model. Reconstructed conductivity images of normal lungs exhibit a peculiar pattern of salt and pepper noise. Conductivity images of pneumonic lungs show significantly enhanced conductivity contrast in the lung parenchyma due to the accumulation of pleural fluid.
4171. | 2 | Comparison of Data Approximation Methods Used in MR-Based Tissue Electrical Property Mapping – a Simulation Study Selaka Bandara Bulumulla1, Seung-kyun Lee1, and Ileana Hancu1 1GE Global Research, Niskayuna, NY, United States Calculation of electrical properties from B1+ maps is a potentially powerful method for non-invasive imaging of conductivity and permittivity. The method accurately calculates conductivity and permittivity when complex B1+ maps are available in the region of interest. Since B1+ phase is not directly available in an MRI scan, various approximation schemes have been proposed. We compare four such methods using analytical and numerical simulation models. The results indicate that sqrt(|B1+B1–|), which may be obtained from a low flip angle gradient echo image and transceiver phase, may provide accurate conductivity and permittivity of rotationally symmetric as well rotationally asymmetric objects.
4172. | 3 | Experimental Evaluation of Frequency-Dependent Conductivity Using a Simultaneous Imaging of MREIT and MREPT Munish Chauhan1, Min Oh Kim2, Woo Chul Jeong1, Hyung Joong Kim1, Oh In Kwon3, Eung Je Woo1, and Dong Hyun Kim2 1Kyung Hee University, Yongin, Gyeonggi, Korea, 2Yonsei University, Seoul, Korea, 3Konkuk University, Seoul, Korea Biological tissues show frequency-dependent conductivity spectra and its values at different frequencies may provide valuable diagnostic information. MREIT provides conductivity images at frequencies below a few kHz, while MREPT produces conductivity images at 128 MHz at 3T. Those two techniques are supplementary to each other and can provide new information when combined together. In this study, we perform two different phantom imaging experiments for the understanding of frequency-dependency using simultaneous dual-frequency conductivity imaging from the one MR scan. We present experimental results of both MREIT and MREPT and highlighted their distinct features in probing and visualizing an object.
4173. | 4 | Phase Unbanding in BSSFP for Liver Conductivity Imaging at 3.0T Min-Oh Kim1, Narae Choi1, Jaewook Shin1, Joonsung Lee1, and Dong-Hyun Kim1 1Electrical and Electronic Engineering, Yonsei University, Seoul, Korea Phase-based conductivity imaging using bSSFP suffers from off-resonance effect (banding artifact) in abdomen imaging. Here, we present a phase unbanding technique for conductivity reconstruction focused especially on liver imaging.
4174. | 5 | How Well Can Magnetic Susceptibility Anisotropy Be Estimated? an Error Analysis of Cylindrically Symmetric Susceptibility Tensor Reconstructions from Few Orientations Cynthia Wisnieff1, Pascal Spincemaille2, Tian Liu3, and Yi Wang1 1Cornell Univerisity, New York, New York, United States, 2Weill Cornell Medical College, New York, New York, United States, 3Medimagemetric, New York, New York, United States Susceptibility tensor imaging, STI, has shown evidence of being intrinsically linked to the organization and composition of the myelin sheath of white matter. However, estimating the magnetic susceptibility anisotropy within human subjects is limited by both the acquisition time necessary and the difficulty in reorienting the subject in the scanner. In this work we present an error analysis of constrained system used for cylindrically symmetric susceptibility tensor imaging reconstructions and examine the feasibility of estimating the anisotropy with these constrained reconstructions with few subject orientations in simulations and in vivo.
4175. | 6 | Generalized Local Maxwell Tomography for Mapping of Electrical Property Gradients and Tensors Daniel K. Sodickson1,2, Leeor Alon1,2, Cem Murat Deniz2,3, Noam Ben-Eliezer1, Martijn A. Cloos1, Lester A. Sodickson4, Christopher Michael Collins1,2, Graham C. Wiggins1, and Dmitry S. Novikov1 1Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, 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, 3Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University, New York, NY, United States, 4Cambridge Research Associates, Newton, MA, United States At last year’s ISMRM meeting, we introduced the Local Maxwell Tomography (LMT) method for noninvasive mapping of the electrical properties of tissue or materials. Here, we generalize the theory of LMT to encompass the electrodynamic effects of a) non-vanishing spatial gradients of electrical properties, e.g. at tissue boundaries, and b) structural anisotropies resulting in nontrivial electrical property tensors. We demonstrate that the generalized LMT framework eliminates edge artifacts observed in simpler implementations. We also outline strategies by which tensor structure may be determined if a sufficient number of measurements and coil elements are deployed, potentially enabling electrical property tractography.
4176. | 7 | Characterization of Prostate Tissues Using MREIT Conductivity Imaging: In Vivo Canine Study Hyung Joong Kim1, Woo Chul Jeong1, Munish Chauhan1, Hee Myung Park2, Oh In Kwon2, and Eung Je Woo1 1Kyung Hee University, Yongin, Gyeonggi, Korea, 2Konkuk University, Seoul, Korea Prostate is an imaging area of growing concern related with aging. Prostate cancer and benign prostatic hyperplasia are the most common diseases and significant cause of death for elderly men. The conductivity imaging of the male pelvis is a challenging task with a clinical significance. In this study, we performed in vivo MREIT imaging experiments of the canine male pelvis using a 3T MRI scanner. The reconstructed conductivity images of the prostate show a clear contrast between the central and peripheral zones which are closely related with prostate diseases including cancer and benign prostatic hyperplasia.
4177. | 8 | Localized Electrical Property Retrieval – Theories and Numerical Examples Shao Ying Huang1, Elfar Adalsteinsson2, Berkin Bilgic2, Shaohui Foong1, and Lawrence L. Wald3 1Singapore University of Technology and Design, Singapore, Singapore, Singapore, 2Massachusetts Institute of Technology, Cambridge, Massachusetts, United States,3Massachusetts General Hospital, Charlestown, Massachusetts, United States In our work, we propose a new method to retrieve electrical properties of tissues when the half phase assumption holds, termed Localized Electrical Property Retrieval (LEPR). For this method, only surface integration is needed rather than a volume one. Furthermore, the surface integrals can be chosen so that only B1+ or B1- is needed, meaning it does not require the z-component of the magnetic field, which is similar to electric properties tomography (EPT). In this abstract, the theory of LEPR is presented in detail. Under the tested simulation data where ground-truth is known, the LEPR maps out-perform EPT.
4178. | 9 | Determining the Patient-Specific Conductivity of Pelvic Tumours for Use in Hyperthermia Treatment Planning E. Balidemaj1, A.L van Lier2, J. Crezee1, R.F. Remis3, Aart J. Nederveen4, L.J.A. Stalpers1, and C.A.T. van den Berg2 1Radiotherapy, Academic Medical Center, Amsterdam, Netherlands, 2Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 3Faculty of Electrical Engineering, TU Delft, Delft, Netherlands, 4Radiology, Academic Medical Center, Amsterdam, Netherlands Determining the conductivity of pelvic tumours for use in Hyperthermia Treatment Planning.
4179. | 10 | Optimal Combination of a Multi-Receive Coil for Conductivity Mapping Using Phase Based MREPT Joonsung Lee1, Narae Choi1, Jaewook Shin1, and Dong-Hyun Kim1 1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea A novel method of locally optimized combination of multi-receive coil was proposed for phase based MREPT. The proposed approach locally homogenizes the magnitude of the receive profile and thus can reduce the possible errors in phase based MREPT. The proposed coil combination method results in much more homogeneous conductivity estimates than a conventional coil combination method. The performance of the proposed method was verified in a 12 channel multi-receive head coil. Many clinical systems are operated using multi-receive coils, therefore our method can be useful in clinical imagers.
4180. | 11 | Coil Combine for Conductivity Mapping of Breast Cancer Jaewook Shin1, Min Jung Kim2, Joonsung Lee1, Minoh Kim1, Narae Choi1, Yoonho Nam1, and Dong-Hyun Kim1 1Electrical and Electronic Engineering, Yonsei University, Seoul, Seodaemun-gu, Korea, 2Research Institute of Radiological Science, Yonsei University College of Medicine, Seoul, Seodaemun-gu, Korea According to ex-vivo study, breast tumor has higher conductivity value than normal breast tissue. As based on the research, breast conductivity imaging was attempted using phase-based electrical property tomography (EPT). However, to use phase-based EPT, the spatial variation of the magnitude of receive field (B1-) have to be negligible. In this study, using the transceive phase with zero-order phase combine, the error in conductivity map was minimized and the method was also applied to patient's breast data.
4181. | 12 | Evaluation of Effective Regions in Deep Brain Stimulation Using MR-Based Current Density Imaging (MRCDI): In Vivo Canine Brain Study Munish Chauhan1, Saurav ZK Sajib1, Woo Chul Jeong1, Hyung Joong Kim1, Oh In Kwon2, and Eung Je Woo1 1Kyung Hee University, Yongin, Gyeonggi, Korea, 2Konkuk University, Seoul, Korea Deep brain stimulation (DBS) is widely used technique for the treatment of various movement disorders such as dystonia, tremor, and Parkinson disease. Due to the inherent limitations of the imaging modalities, physicians cannot diagnosis the exact response of the brain tissues during the stimulation. Recent MR-based current density imaging (MRCDI) technique enables us to estimate the current density distribution using one component of the measured magnetic flux density data. Applying MRCDI technique to DBS, we can predict the current pathway and volume tissue activation which could be useful information for adjusting the electrode parameters and neuronal surgical planning.
4182. | 13 | Detection of Neural Activity Using Magnetic Resonance Electrical Impedance Tomography Rosalind J. Sadleir1,2, Corey A. Falgas3,4, Samuel C. Grant3,4, and Eung Je Woo2 1J. Crayton Pruitt Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States, 2Biomedical Engineering, Kyung Hee University, Yongin, Gyeonggi-do, Korea, 3Dept. of Chemical & Biomedical Engineering, The Florida State University, Tallahassee, Florida, United States, 4The National High Magnetic Field Laboratory, Tallahassee, Florida, United States We hypothesized, and have found, MR phase contrasts arising from spike rate changes in a neural tissue phantom. The method used is a variation on Magnetic Resonance Electrical Impedance Tomography, and the contrast was related to changes in membrane conductance. The signal magnitude was compared with models and an independent gold standard and found to be consistent with these results. We believe that this contrast could provide a robust and direct method of imaging brain function.
4183. | 14 | Reduction of Boundary Artifact in Electrical Property Mapping Using MREPT Joonsung Lee1, Narae Choi1, Jin Keun Seo2, and Dong-Hyun Kim1 1Electrical & Electronic Engineering, Yonsei University, Seoul, Korea, 2Computational Science & Engineering, Yonsei University, Seoul, Korea Magnetic Resonance Electrical Property Tomography (MREPT) is an imaging modality to map the distribution of electric conductivity and permittivity of the subject at Larmor frequency using measured B1 maps from MRI. At the tissue boundaries, the assumption of locally homogeneous electric properties is violated, and thus the conductivity estimates deviate from the actual values, so called "Boundary Artifact". The proposed approach reconstructs the conductivity, permittivity, and two components of the electric fields, Ez and Ex+iEy. A novel reconstruction approach was developed to reduce the boundary artifact using the B1+ map acquired at a single transmit channel MR system.
4184. | 15 | Evaluation of Liver Radiofrequency Ablation Lesions Using MREIT Conductivity Imaging Hyung Joong Kim1, Munish Chauhan1, Woo Chul Jeong1, Oh In Kwon2, and Eung Je Woo1 1Kyung Hee University, Yongin, Gyeonggi, Korea, 2Konkuk University, Seoul, Korea Radiofrequency (RF) ablation causes thermal injury due to the resistive heating and leads to coagulation necrosis. Thermal injury may cause changes in cellular structure, concentration and mobility of ions in intra- and extra-cellular fluids, and other factors. These features could be advantageous to the MREIT technique which provides a high-resolution conductivity distribution of the human body in a non-invasive manner. Conductivity images shown in this study indicated the potential of MREIT technique following RF ablation in terms of the capability to detect ablated lesion and differentiate tissue conditions according to the different ablation exposure times and RF power levels.
4185. | 16 | CSI-EPT: A Novel Contrast Source Inversion Approach to EPT and Patient-Specific SAR Based on B1+ Maps E. Balidemaj1, R.F. Remis2, A.L van Lier3, J. Crezee1, Aart J. Nederveen4, Alessandro Sbrizzi3, L.J.A. Stalpers1, and C.A.T. van den Berg3 1Radiotherapy, Academic Medical Center, Amsterdam, Netherlands, 2Faculty of Electrical Engineering, TU Delft, Delft, Netherlands, 3Radiotherapy, UMC Utrecht, Utrecht, Netherlands, 4Radiology, Academic Medical Center, Amsterdam, Netherlands CSI-EPT: A novel Contrast Source Inversion approach to EPT and patient-specific SAR based on B1+ maps
4186. | 17 | Investigating the Effect of Image Resolution on Susceptibility Values Inside the Vessels for Venous Oxygen Saturation Quantification Jin Tang1, Thomas Stewart Denney2, Nouha Salibi3, Sagar Buch4, Yongquan Ye5, and Ewart Mark Haacke1,5 1Magnetic Resonance Innovations, Detroit, MI, United States, 2MRI Research Center, Department of Electrical and Computer Engineering, Auburn University, Auburn, AL, United States, 3Siemens Healthcare USA, Malvern, PA, United States, 4School of Biomedical Engineering, McMaster University, Hamilton, ON, Canada, 5Academic Radiology, Wayne State University, Detroit, MI, United States Knowledge of oxygen saturation is important to characterize the physiological or pathological state of tissue function in the brain. Quantitative susceptibility mapping (QSM) can be potentially used to detect venous oxygen saturation levels. When using QSM, image resolution is very important to measuring oxygen saturation since partial voluming will dramatically decrease the estimated susceptibility inside the veins especially for small vessels. In this work, effect of image resolution on susceptibility inside different sized vessels has been investigated using 3D brain model simulations and a 7T dataset. Additionally, sources of error in oxygen saturation quantification derived by QSM are also investigated.
4187. | 18 | Magnetic Resonance Electrical Properties Tomography (MREPT) Based on the Solution of the Convection-Reaction Equation Fatih Suleyman Hafalir1, Omer Faruk Oran1, Necip Gurler1, and Yusuf Ziya Ider1 1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey Currently available practical MREPT methods reconstruct electrical properties within local homogeneous regions where conductivity (σ) and permittivity (ε) values are almost constant. In this study, we propose a novel algorithm named convection-reaction equation based MREPT (cr-MREPT) which reconstructs σ and ε also in transition regions where σ and ε vary. In regions where convective field of the convection-reaction equation is small, some reconstruction artifacts appear. Solution for this artifact is also proposed and demonstrated. The overall algorithm is tested using both simulated and experimental data from phantoms and successful reconstructions are obtained.
4188. | 19 | Convection-Reaction Equation Based Low-Frequency Conductivity Imaging Using Readout Gradient Induced Eddy Currents Omer Faruk Oran1, Fatih Suleyman Hafalir1, Necip Gurler1, and Yusuf Ziya Ider1 1Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey Imaging electrical conductivity provides both anatomical and pathological information about the tissues. Eddy-currents, which are induced in the object due to the ramp of readout gradient field, generate a secondary magnetic flux density which may be measured using MRI. In this study, we derive the key equation which relates conductivity and induced current to this measured magnetic flux density and which is in the form of the convection-reaction equation. We propose and demonstrate a low-frequency conductivity imaging algorithm which is based on the solution of this equation. We also propose and demonstrate a method for reconstructing the induced current density.
4189. | 20 | Single Acquisition Electrical Property Mapping José P. Marques1, Daniel K. Sodickson2, Christopher Michael Collins2, and Rolf Gruetter3,4 1CIBM, University of Lausanne, Lausanne, Vaud, Switzerland, 2Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, 3LIFMET - Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland,4Department of Radiology, Universities of Geneva and Lausanne, Lausanne, VD, Switzerland All methods presented to date to calculate electrical property maps rely on the acquisition of multiple images including quantitative B1+ maps. In this work we present a formalism to compute conductivity and permittivity maps based on one single MR acquisition performed with an array of 4 or more elements. The method is based on the measurement of relative receive coil sensitivity maps and uses as only assumption that the B1- associated with any receive coil obeys the Helmholtz equation.
4190. | 21 | Conductivity Mapping Using Ultrashort Echo Time (UTE) Imaging Ferdinand Schweser1,2, Li Huang1,3, Karl-Heinz Herrmann1, Martin Krämer1, Andreas Deistung1, and Jürgen R. Reichenbach1 1Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, Jena University Hospital - Friedrich Schiller University Jena, Jena, Germany, 2School of Medicine, Friedrich Schiller University Jena, Jena, Germany, 3Abbe School of Photonics, Faculty for Physics and Astronomy, Friedrich Schiller University Jena, Jena, Germany MR-based Electric Properties Tomography (EPT) provides a non-invasive means to assess electric tissue properties based on B1 field maps. It was recently shown that B1 phase is reflected in the phase of ultrashort echo time (UTE) signal. In this contribution we investigated the possibility of using UTE phase for in vivo conductivity mapping of the brain.
4191. | 22 | Determining Electrical Properties Based on Complex B1-Fields Measured in an MR Scanner Using a Multiple Transmit/Receive Coil: A General Approach Jiaen Liu1, Xiaotong Zhang1, Pierre-Francois Van de Moortele2, Sebastian Schmitter2, and Bin He1,3 1Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, United States, 3Institute for Engineering in Medicine, University of Minnesota, Minneapolis, Minnesota, United States Electrical Property Tomography (EPT) aims for noninvasive imaging of electrical conductivity and permittivity of biological tissues at radio frequencies used in MR scanners. For current development of EPT, assumptions about the structure of imaged sample and RF coil, phase distribution and main magnetic field have been adopted to compensate the absence of direct measurement of the absolute B1 phase. Thus, application of EPT has been limited within specific scenarios. In this study, using a multi-channel transmit/receive coil, we introduced and validated experimentally the framework of a new general approach for EPT, which does not depend on previously mentioned assumptions.
4192. | 23 | Minimum Squared Error Estimate of Electrical Properties from B1 Maps Selaka Bandara Bulumulla1, Seung-Kyun Lee1, and Ileana Hancu1 1GE Global Research, Niskayuna, NY, United States In pixel by pixel calculation of conductivity and permittivity from B1 maps, the additive noise in B1 can impair the quality of reconstructed electrical properties images. In previous work, discarding of non-physical values (e.g. negative conductivity) or filtering of B1 maps have been considered. Discarding values lead to missing pixels in the electrical properties images and filtering may remove spatial variation containing information on electrical properties. In this work, we consider minimum squared error estimate of conductivity and permittivity for a region of constant electrical properties and show promising results for a phantom with conductivity contrast.
4193. | 24 | Nonlinear Estimation of Cylindrically Symmetric Magnetic Susceptibility Anisotropy in Image Space Without a Rigid DTI Prior Cynthia Wisnieff1, Pascal Spincemaille2, and Yi Wang1 1Cornell Univerisity, New York, New York, United States, 2Weill Cornell Medical College, New York, New York, United States In this work we explore methods of estimating magnetic susceptibility anisotropy, MSA, of the human brain in vivo in image space using only a shape constraint on the susceptibility tensor without imposing prior information on the fiber orientation. Estimation of cylindrically symmetric tensor anisotropy is explored in a carbon fiber phantom and human in vivo data. It was found that anisotropy estimation was similar with some sensitivity to noise in the nonlinear method compared to previously explored k-space MSA estimation methods.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (17:00-18:00) Exhibition Hall
Contrast Mechanism: Relaxometry - T2* & Iron Quantification
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4194. | 1 | Calibration of Confounder-Corrected R2* for Liver Iron Quantification at 1.5T and 3T: Preliminary Results Diego Hernando1, Naila Qazi1, and Scott B. Reeder1,2 1Radiology, University of Wisconsin-Madison, Madison, WI, United States, 2Medical Physics, University of Wisconsin-Madison, Madison, WI, United States Measurement of liver iron concentration (LIC) is needed for detection and treatment monitoring of iron overload. R2-based techniques (eg: Ferriscan) are accurate at 1.5T, however they require long acquisition times. R2*-based techniques are fast, but suffer from several confounding factors: liver fat, background B0 variations and noise floor effects. In this work, we calibrated confounder-corrected R2*-based LIC quantification at 1.5T and 3T using multiple different protocols, with Ferriscan-LIC (1.5T) as reference standard. Nearly identical calibrations were obtained with different protocols at each field strength, suggesting that R2* may provide accurate and robust LIC quantification if relevant confounding factors are addressed.
4195. | 2 | Can We Use Simple Linear Model for the Relaxometry to Represent the Concentration of Metal Ions? Chih-Ching Lai1 and Fu-Nien Wang1 1Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan Iron (Fe) and copper (Cu) are essential elements important for metabolism and biochemical functions in brain. In this study, we design a phantom experiment to investigate whether the relaxation rates of Fe and Cu solutions could be modeled as a linear combining relationship. We observed that the relaxation rates of Fe2+ and Cu2+ mixed solutions could be predicted successfully by measuring R1 and R2 of Fe2+ and Cu2+ solutions respectively. However, the nonlinear R1 and R2 of Fe3+ were improper for linear model. Care should be taken as using relaxometry to represent the concentration of metal ions.
4196. | 3 | The Use of Appropriate Calibration Curves Can Correct the Systematic Differences Between Softwares in Hepatic R2* Estimation Antonella Meloni1, Hugh Young Rienhoff2, Amber Jones2, Aessia Pepe1, Massimo Lombardi1, and John C. Wood3 1CMR Unit, Fondazione G. Monasterio CNR-Regione Toscana and Institute of Clinical Physiology, Pisa, Italy, 2FerroKin BioSciences, Inc, San Carlo, California, United States, 3Division of Cardiology, Children’s Hospital Los Angeles, Los Angeles, California, United States R2* values vary with post-processing method but yield statistically identical LIC values when technique-appropriate calibration curves are used. In the literature, R2* values should be converted into LIC values to facilitate comparisons across studies.
4197. | 4 | Systematic Investigation of Various Strategies for T2* Mapping for Liver Iron Quantification in the Presence of Noise Takeshi Yokoo1,2, Qing Yuan1, and Ivan E. Dimitrov2,3 1Radiology, UT Southwestern Medical Center, Dallas, TX, United States, 2Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, 3Philips Medical Systems, Highland Heights, OH, United States Various strategies for T2* mapping for liver iron quantification in the presence of noise is investigated in this study, including log-linear and nonlinear curve fitting, either using magnitude or complex signal data.
4198. | 5 | Evaluation of Correction Methods for Errors in T2* Quantification Caused by Background Gradients Ruitian Song1, Travis Bevington1, Brian Allen Taylor1, Axel J. Krafft1, Ralf B. Loeffler1, and Claudia M. Hillenbrand1 1Radiological Sciences, St Jude Children's Research Hospital, Memphis, Tennessee, United States T2* measurement accuracy can be impacted by macroscopic field inhomogeneities (i.e., background gradients) that are introduced by susceptibility changes. Two major methods have been proposed to correct for the errors in T2*-quantification that arise from these background gradients: sinc-weighted fitting of the signal decay (FIT) and direct measurement of the magnetic field (DMF). These two methods are compared and evaluated via phantom and volunteer tests. We conclude that FIT is preferred unless the z component of the magnetic field dominates among the three spatial components.
4199. | 6 | Enhanced Contrast of Superparamagnetic Iron Oxide Contrast Agents by Spin-Lock MR Rik P.M. Moonen1, Pieternel van der Tol1, Stefanie J.C.G. Hectors1, Klaas Nicolay1, and Gustav J. Strijkers1 1Biomedical Engineering/ Biomedical NMR, Eindhoven University of Technology, Eindhoven, Netherlands In this in vitro study we show that T1ρ provides enhanced sensitivity for the detection of SPIO and USPIO contrast agents in comparison to T2. ΔR1ρ values at 1.41 T of agar gels containing different concentrations of Sinerem and Resovist were respectively up to 4.8-fold and 6.6-fold higher as compared to ΔR2.
4200. | 7 | Value of High Field Dependent Transverse Relaxation Increase for Increasing Iron Specificity in Human Brain Md Nasir Uddin1, R. Marc Lebel1, and Alan H. Wilman1 1Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada Transverse relaxometry at multiple field strengths may provide increased iron specificity using field dependent relaxation increase (FDRI). We compared high field (4.7 T) transverse relaxometry to single and multislice FDRI using 1. 5 T and 4.7 T. Results for iron-rich subcortical grey matter demonstrate the value of high field measurement, with only slight improvement using FDRI.
4201. | 8 | An Automatic Parenchyma Extraction Method for MRI R2* Relaxoemtry of Iron Loaded Liver Meiyan Feng1, Huashuai Gao1, Xinyuan Zhang1, Yanqiu Feng1, Wufan Chen1, Xuegang Xin1, and Taigang He2,3 1School of Biomedical Engineering, Southern Medical University, Guangzhou, China, 2Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, United Kingdom,3National Heart and Lung Institute, Imperial College, London, United Kingdom The whole liver ROI method for R2* measurement has been shown better reproducibility than the routinely used mROI method, but still suffers from noise, partial volume effect and subjective segmentation of liver parenchyma and vessels. We proposed an automatic parenchyma extraction (APE) method of R2* measurement, the measurement accuracy of which was evaluated in both simulation and patient studies. The mean R2* evaluation error percentage and the coefficient of variation (CoV) of inter-observer reproducibility for the APE method severally were 0.34% and 1.39%. The proposed APE method may be important for increasing the diagnostic confidence of R2* measurement.
4202. | 9 | Effect of Nanoparticle-Protein Interaction on Relaxivity and MRI Contrast Efficiency of Superparamagnetic Iron Oxide Nanoparticles Houshang Amiri1,2, Morteza Mahmoudi3,4, Jolanda de Vries2, Arend Heerschap1, and Alessandro Lascialfari5 1Radiology Department, Radboud University Nijmegen Medical Centre, Nijmegen, Gelderland, Netherlands, 2Tumor Immunology Department, Nijmegen Centre for Molecular Life Sciences, Nijmegen, Gelderland, Netherlands, 3Nanotechnology Research Centre, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Tehran, Iran, 4Pasteur Institute of Iran, Tehran, Tehran, Iran, 5Physics Department, Milan University, Milan, Lombardia, Italy To investigate the effects of a protein corona (PC) on MRI contrast efficiency of superparamagnetic iron oxide NPs (SPIONs), we synthesized two series of SPIONs with various thickness and functional groups of the dextran surface coating. 1H longitudinal and transverse relaxivities of the SPIONs as a function of the Larmor frequency were obtained. Transverse relaxivity was dependent on the functional group of the SPIONs. The presence of the PC did slightly increased the relaxivity of the negatively charged SPIONs and dramatically decreased it for positively charged ones. in vitro MRI experiments at were in full agreement with the relaxometry findings.
4203. | 10 | On the Influence of Particle Size in MR Iron Quantification Jan Sedlacik1, Jürgen R. Reichenbach2, and Ferdinand Schweser2 1Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, 2Medical Physics Group, Institute of Diagnostic and Interventional Radiology I, University Hospital-Friedrich Schiller University Jena, Jena, Germany Due to diffusion effects, the transverse relaxivity caused by small iron particles depends on the particles’ size. Consequently, the same amount of iron can cause very different relaxation rates for particles of different size compromising relaxation-based iron quantification measurements. However, the bulk frequency shift is supposed to be determined by the average magnetic susceptibility of the solution and, therefore, independent of particle size, aggregation or distribution. The purpose of this work was to investigate this theoretical behavior in a phantom experiment and to discuss implications for future in vivo studies.
4204. | 11 | Robustness of R2* Mapping for Liver Iron Assessment at 1.5T and 3T Naila Qazi1, Scott B. Reeder1,2, and Diego Hernando1 1Radiology, University of Wisconsin-Madison, Madison, WI, United States, 2Medical Physics, University of Wisconsin-Madison, Madison, WI, United States R2*-MRI has the potential to provide rapid and accurate iron quantification. However, the robustness of liver R2* mapping to variations in imaging parameters is unknown. Indeed, lack of robustness is the main criticism of R2* mapping, currently precluding it from becoming widely accepted for iron quantification. In this work, we demonstrate that liver R2* mapping in patients with liver iron overload can be performed with excellent robustness to variations in spatial resolution, slice orientation and echo time combination at both 1.5T and 3T.
4205. | 12 | Iron and Myelin Induced Contrast Variations in the Corpus Callosum Christian Langkammer1, Nikolaus Krebs2, Walter Goessler3, Eva Scheurer2, Franz Fazekas1, and Stefan Ropele1 1Department of Neurology, Medical University of Graz, Graz, Austria, 2Ludwig Boltzmann Institute for Clinical-Forensic Imaging, Graz, Austria, 3Institute of Analytical Chemistry, University of Graz, Graz, Austria This study provides regional reference values for iron concentrations in the corpus callosum and demonstrates a heterogeneous distribution along the corpus callosum. These variations substantially impact R2* and, thus, will consequently impact also phase and bulk susceptibility.
4206. | 13 | B1+ Inhomogeneity Effects on Clinical Liver Iron Quanitification at 1.5T and 3T Eamon Doyle1, Nilesh R. Ghugre2, Krishna S. Nayak3, and John Wood4 1University of Southern California, Los Angeles, CA, United States, 2Imaging Research, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, 3Electrical Engineering, University of Southern California, Los Angeles, CA, United States, 4Cardiology, Children's Hospital of Los Angeles, Los Angeles, CA, United States Monte Carlo simulation of iron-loaded liver tissue indicates that B1+ inhomogeneity may lead to inaccurate iron quantification due to increased R2 value estimates.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (17:00-18:00) Exhibition Hall
Contrast Mechanisms: Relaxometry - Novel Sequences & Quantification Methods
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4207. | 14 | Multi-Slice Myelin Water Imaging for Practical Clinical Applications at 3.0 T Junyu Guo1, Qing Ji1, and Wilburn E. Reddick1 1Division of Translational Imaging Research, St Jude Children Research Hospital, Memphis, TN, United States Myelin water imaging is a promising technique for evaluating white matter diseases. Poor image quality and a long acquisition time are major obstacles to practical clinical applications. In this study, a novel postprocessing method with an efficient multi-slice acquisition scheme, called T2 spectrum analysis using a weighted regularized non-negative least squares algorithm and non-local mean filter (T2SPARC), is presented to overcome these obstacles. In vivo results from healthy volunteers and a patient with leukoencephalopathy showed that the T2SPARC method can generate robust and high-quality myelin water fraction (MWF) maps of 10 slices within 11 minutes.
4208. | 15 | T1 Based Myelin Water Detection at 3 Tesla Using Phased-Array Adaptive Reconstruction and Long Range TI Sampling Christian Labadie1, Monique Aubert-Frécon1, Stefan Hetzer2, and Harald E. Möller3 1Laboratoire de Spectrométrie Ionique et Moléculaire, Université Claude Bernard, Lyon, France, 2Bernstein Center for Computational Neuroscience, Berlin, Germany, 3Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany We propose a method to coherently combine phase-array using coil sensivitivities estimated in place from a phased Look-Locker inversion recovery. Additionally we investigate the effect of the range of the geometrically sampled inversion times (TI) on the estimation of the T1 based MWF at 3T.
4209. | 16 | Simulation of Myelin Water Imaging Junyu Guo1 and Wilburn E. Reddick1 1Division of Translational Imaging Research, St Jude Children Research Hospital, Memphis, TN, United States Myelin water imaging is a promising, noninvasive technique for evaluating white matter diseases. Myelin water fraction (MWF) can serve as a direct indicator of myelin component change due to white matter diseases. To calculate MWF, the weighted regularized non-negative least squares (wrNNLS) algorithm with a large regularization coefficient was used to balance the sensitivity and reliability to measure MWF values. In this study, simulations were performed to compare the regularization of wrNNLS with the regularized non-negative least squares (rNNLS) algorithm and validate the large empirical selected regularization coefficient for wrNNLS due to imperfect refocusing pulses.
4210. | 17 | A Constrained Estimator of Myelin Water Fraction from Steady-State Data John M. Ollinger1, Samuel A. Hurley2, Andrew L. Alexander3, and Gerard Riedy4 1NICoE, Walter Reed National Military Medical Center, Bethesda, Maryland, United States, 2Medical Physics, University of Wisconsin-Madison, Madison, WI, United States, 3Medical Physics, University of Wisconsin, Madison, WI, United States, 4NICoE, Walter Reed National Military Medical Center, Bethesda, MD, United States The parameters of the two-compartment mcDESPOT model for myelin water fraction are estimated with a non-linear least-squares algorithm constrained by a uniform prior. Combined with improved flip angle calibration, flip angle selection, and phase-cycling angles, the method yields estimates of myelin water fraction of visually high quality. However, estimates of myelin T1 and myelin residence time were strongly dependent on the choice of constraint and starting values. Quantitative values of myelin water fraction depended on these values as well as the parameterization of the model. This suggests that myelin water fraction images may represent a combination of physiological parameters.
4211. | 18 | Fast 3D T2 Measurement with a Magnetization Prepared TrueFISP Sequence Philipp Krämer1 and Lothar R. Schad1 1Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany 3D spin-echo and turbo-spin-echo T2 weighted imaging suffers from high acquisition duration because of the necessary long repetition times. For 2D cardiac T2 measurement a sequence was proposed which applies two 90° rectangular pulses and a Malcolm-Levitt composite pulse train of four 180° refocusing pulses for T2 weightening prior to imaging. In this work, the same T2 preparation method is combined with a fast 3D TrueFISP imaging sequence enabling fast 3D T2 measurement.
4212. | 19 | TOWERS: T-One with Enhanced Robustness and Speed Cihat Eldeniz1, Weili Lin1,2, and Hongyu An2 1Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, 2Radiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States Fast and accurate T1 mapping can be useful in many ways. T-One With Enhanced Robustness and Speed [TOWERS] is a new EPI-based sequence that can acquire enough data for the T1 mapping of the whole brain in less than 2 minutes and a half. It has two segments which are independent of each other in terms of spin history, making it robust to motion in any of the two segments.
4213. | 20 | MR Parameter Quantification (T1, T2, PD) with Integrated Fat Water Separation Using a Multi-Echo - Phase Cycled BSSFP-Sequence Thomas Benkert1, Martin Ott1, Riad Ababneh2, Martin Blaimer1, Peter M. Jakob1,3, and Felix A. Breuer1 1Research Center Magnetic Resonance Bavaria, Würzburg, Bavaria, Germany, 2Yarmouk University, Irbid, Jordan, 3Experimental Physics 5, University Würzburg, Würzburg, Bavaria, Germany A phase cycled bSSFP sequence with a multi-echo readout is proposed to achieve T1,T2 and PD maps as well as robust fat-water separation without any banding artifacts due to offresonances with just one single sequence.
4214. | 21 | 3D T2 Mapping of Human Brain with High Accuracy by 3D Turbo-Flash Imaging Prepared by Multiecho Adiabatic Spin Echo Hidehiro Watanabe1, Nobuhiro Takaya1, and Fumiyuki Mitsumori1 1Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan 3D MASE method for whole brain T2 mapping with high accuracy was developed at 4.7T. This has a feature of accurate 3D T2 mapping by a precise slice selection with a pair of adiabatic pulses for the refocusing slice selection. After magnetization decayed purely by T2 is generated by a multi-pulse adiabatic spin echo sequence, it is flipped back to the longitudinal magnetization by a flipback adiabatic pulse. Then, signal is accumulated by the 3D Turbo-Flash imaging. In human brain measurements, T2 values were in good agreement with those by the conventional 2D MASE method.
4215. | 22 | Acceleration of Spin-Locked 3D GRE Acquisitions for Rapid T1rho Mapping of the Brain Casey P. Johnson1, Daniel R. Thedens1, and Vincent A. Magnotta1,2 1Radiology, University of Iowa, Iowa City, IA, United States, 2Psychiatry, University of Iowa, Iowa City, IA, United States Acceleration methods are assessed for 3D T1rho mapping of the brain. It is demonstrated that substantial reductions in acquisition time (R>5) can be realized while largely retaining T1rho contrast detectability. The use of only two vs. four spin-lock times is also shown to be highly effective, particularly when combined with high degrees of undersampling, yielding net sampling reductions of R>10. The methods demonstrated in this work may greatly improve the utility of 3D T1rho mapping of brain diseases such as Alzheimer’s and Parkinson’s while also enabling state-based dynamic imaging studies such as investigations of stimulus-induced T1rho-sensitive pH fluctuations.
4216. | 23 | Simultaneous Relaxometry and Susceptibility Imaging in the Brain Cheng-Chieh Cheng1,2, Tzu-Cheng Chao3, Hsiao-Wen Chung1, Lawrence P. Panych2, and Bruno Madore2 1Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan, 2Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, United States, 3Department of Computer Science and Information Engineering, National Cheng-Kung University, Tainan, Taiwan Brain iron accumulation may be related to various neurological diseases such as Parkinson’s disease, Alzheimer’s disease, and multiple sclerosis. Quantitative MR techniques, such as MR relaxometry and susceptibility mapping can be helpful toward quantifying brain iron content. A novel approach is proposed that can simultaneously measure T2, T2* and susceptibility-induced internal field perturbations from the same rapid scan. It is hoped that the present method may prove a useful tool toward investigating conditions linked with elevated brain iron content.
4217. | 24 | Rapid Field-Cycling Relaxometric Imaging Using Fast Spin-Echo Peter J. Ross1, Lionel M. Broche1, Kerrin J. Pine1, and David J. Lurie1 1Aberdeen Biomedical Imaging Centre, University of Aberdeen, Aberdeen, Scotland, United Kingdom Fast Field-Cycling (FFC) adds a new dimension to MRI by rapidly switching B0 between levels during a pulse sequence. In this way it is possible to observe the variation of tissue T1 with field strength. Relaxometric FFC imaging collects data for T1 images at a range of field strengths, but is inherently time-consuming. We have greatly increased the speed of acquisition by collecting only one inversion-recovery image per field and by implementing an FFC Fast Spin-Echo sequence. Typical acquisition time is 30 min for a set of T1images at 22 field strengths, making volunteer or clinical studies feasible.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (16:00-17:00) Exhibition Hall
All Flavors of Saturation Transfer Floors
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4218. | 25 | Multivalent Imaging with a Cocktail of PARACEST Agents: Utility of BIRDS for CEST Imaging Yuegao Huang1,2, Daniel Coman1,2, Garry E. Kiefer3, Sara Samuel4, and Fahmeed Hyder1,4 1Diagnostic Radiology, Yale University, New Haven, CT, United States, 2Magnetic Resonance Research Center, Yale University, New Haven, CT, United States, 3Macrocyclics, Dallas, TX, United States, 4Biomedical Engineering, Yale University, New Haven, CT, United States A cocktail of PARACEST agents, each sensitive to an independent parameter, is believed to allow multi-parametric detection. But the multiple-pool proton exchange situation is not a linear combination of two-pool exchange models. To enable multivalent imaging for a cocktail of PARACEST agents, we posited that because PARACEST agents also contain nonexchangeable protons that provide molecular readout with ultrafast chemical shift imaging, as detected by Biosensor Imaging Redundant Deviation in Shifts (BIRDS), the BIRDS properties in a cocktail of PARACEST agents will not be affected, but also enhance precision by adding redundancy for quantifying the CEST contrast.
4219. | 26 | ParaCEST: Imaging pH with High µeff Ln(III) Complexes on a 1T Permanent Magnet. Giaime Rancan1, Daniela Delli Castelli2, and Silvio Aime3,4 1Technische Universität München, München, Bayern, Germany, 2University of Torino, Torino, Piemonte, Italy, 3Universitá di Torino, Torino, Piemonte, Italy, 4Institute for Advanced Study, Technische Universität München, Garching, Bayern, Germany Lanthanide-HPDO3A chelates are stable and safe compounds, some of which apt for contrast agent mediated ParaCEST imaging. In this work we observe some promising candidates for functional CEST ratiometrical analyses and determine their suitability for studies at 1T field strength. An in vivo proof of concept study was performed to further investigate this methodology. The use of entry level MRI instrumentation will expand the scope of ParaCEST techniques.
4220. | 27 | Iopamidol CEST for PH Measurements on a Clinical 3T Scanner: Phantom and First Human in vivo Study Anja Müller-Lutz1, Nadia Khalil1, Rotem S. Lanzman1, Georg Oeltzschner1, Gael Pentang1, Vladimir Jellus2, Benjamin Schmitt2, Gerald Antoch1, and Hans-Jörg Wittsack1 1University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, NRW, Germany, 2Siemens, Healthcare Sector, Imaging & Therapy Division, Erlangen, BY, Germany Chemical exchange saturation transfer (CEST) imaging with the contrast agent Iopamidol enables pH determination in vitro and in vivo. However, in vivo pH determination with Iopamidol as CEST contrast agent was only performed in animals. Nevertheless, in vivo pH measurements in human with Iopamidol at clinical used MRI systems are desirable. The aim of this study was to assess the feasibility of pH measurements with Iopamidol CEST on clinical MRI systems (3T) by using a CEST presaturation module consisting of a pulse train of presaturation pulses in vitro and to perform a first in vivo measurement in a human subject.
4221. | 28 | In Vivo Detection of ParaCEST Contrast Agents at 9.4T Nevin McVicar1, Alex Li2, Mojmir Suchy2,3, Robert H.E Hudson3, and Robert Bartha1,2 1Medical Biophysics, University of Western Ontario, London, ON, Canada, 2Imaging Research Group, Robarts Research Insitute, London, ON, Canada, 3Chemistry, University of Western Ontario, London, ON, Canada In vitro properties are characterized for four paraCEST contrast agents. Each paraCEST agent was then individually injected directly into a mouse leg prior to immediate acquisition of CEST spectra. All four agents were detected in vivo. Using the properties measured in vitro along with the paraCEST contrast measured in vivo, it is concluded that in vivo performance can be predicted based on in vitro characterization of the MR properties of each agent.
4222. | 29 | Intervertebral Disc CEST Imaging with Improved Reliability Using Reduced-FOV TSE Qi Liu1,2, Ning Jin3, Zhaoyang Fan1, Yutaka Natsuaki4, Wafa Tawackoli1, Dan Gazit1, Gadi Pelled1, and Debiao Li1,5 1Biomedical Imaging Research Institute, Cedars-Sinai Medical Center, Los Angeles, CA, United States, 2Biomedical Engineering, Northwestern University, Chicago, IL, United States, 3Siemens Medical Solutions, Columbus, OH, United States, 4Siemens Healthcare, Los Angeles, CA, United States, 5University of California, Los Angeles, los angeles, California, United States A reduced-field-of-view (rFOV) TSE method is used to reliably measure IVD gagCEST signal in vivo by reducing bowel movement artifacts on a 3.0T clinical scanner. The proposed method is verified by a phantom study, and is compared with the conventional full-FOV CEST technique on nine volunteers.
4223. | 30 | Toward Rapid Macromolecular Pool Size Mapping Via Selective Inversion Recovery Richard D. Dortch1,2, Ke Li1,2, Daniel F. Gochberg1,2, John C. Gore1,2, and Seth A. Smith1,2 1Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States, 2Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States The purpose of this study was to optimize the selective inversion recovery (SIR) quantitative magnetization transfer sequence for mapping of the macromolecular-to-free proton pool size ratio (PSR). Previous work has demonstrated that PSR is related to myelin content. Despite this promise, the time required for SIR imaging can be prohibitively long. Here, we reduce to total number of samples required for SIR imaging by fixing the rate of MT exchange and choosing a sampling strategy that minimizes the bias in PSR. Results indicate that unbiased, high SNR estimates of PSR can be obtained using this optimized approach.
4224. | 31 | 3D Acquisition of the Inhomogeneous Magnetization Transfer Effect for Greater White Matter Contrast Gopal Varma1, Gottfried Schlaug2, and David C. Alsop1 1Radiology, Division of MR Research, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States, 2Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States The contrast from inhomogeneous MT (IHMT) appears more specific to white matter (WM) than regular MT imaging, and requires fewer acquisitions than T2 mapping. However prior work with IHMT is limited to single slice acquisition. IHMT is developed towards a 3D acquisition based on traditional MT sequences: 3D IHMT data were obtained in vivo using spoiled gradient-echo acquisitions in ~5 minutes. The nature of the IHMT acquisition also provides MT images for direct comparison. IHMT and MT ratios from WM, and basal ganglia grey matter (BG GM) are compared and a greater difference is observed between WM and BG GM from the IHMT technique.
4225. | 32 | Quantitative Magnetization Transfer Imaging with Non-Exchanging Compartment Modeling: from CSF Partial Volume Correction to More Accurate Characterization of White Matter? Pouria Mossahebi1, Andrew L. Alexander2,3, Aaron S. Field1,4, and Alexey A. Samsonov4 1Biomedical Engineering, University of Wisconsin, Madison, WI, United States, 2Medical Physics, University of Wisconsin, Madison, WI, United States, 3Waisman Lab for Brain Imaging and Behavior, University of Wisconsin, Madison, WI, United States, 4Radiology, University of Wisconsin, Madison, WI, United States This study was performed to investigate the effect of non-exchanging component in quantitative magnetization transfer (qMT) parameters estimation. We have introduced third (non-exchanging or very slowly exchanging) pool to the common two-pool model used in majority of qMT imaging. The presence of such non-exchanging or very slowly exchanging compartments may result in significant underestimation of key parameters of qMT, especially in gray matter (GM) where significant partial volume effect (PVE) from cerebrospinal fluid (CSF). Our results show that this model can remove partial volume effect (PVE) from non-exchanging pool on qMT parameters maps.
4226. | 33 | Amine/Amide Concentration Independent Detection (AACID) of Intracellular pH by CEST MRI at 9.4T Nevin McVicar1, Alex Li2, Robert Bartha2, Daniela F. Goncalves3,4, Susan Meakin2, and Marco A. Prado2 1Medical Biophysics, University of Western Ontario (UWO), London, ON, Canada, 2Robarts Research Institute, London, ON, Canada, 3Physiology and Pharmacology, UWO, London, ON, Canada, 4Graduate Program in Physiology and Biophysics, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil A novel ratiometric CEST approach is developed for amine/amide concentration independent detection (AACID) of intracellular pH. In vitro results demonstrate a linear relation between pH and the amine/amide CEST ratio. In vivo pH-calibration allowed quantitative pH mapping in both stroke and brain tumor mouse models.
4227. | 34 | Biochemical MRI with GagCEST (Glycosaminoglycan Chemical Exchange Saturation Transfer Imaging) of Finger Joint Cartilage in Rheumatoid Arthritis Anja Müller-Lutz1, Benedikt Ostendorf1, Christoph Schleich1, Nadia Khalil1, Benjamin Schmitt2, Vladimir Jellus2, Philipp Sewerin1, Axel Scherer1, Georg Oeltzschner1, Gael Pentang1, Matthias Schneider1, Gerald Antoch1, Hans-Jörg Wittsack1, and Falk Miese1 1University Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Dusseldorf, NRW, Germany, 2Siemens, Healthcare Sector, Imaging & Therapy Division, Erlangen, BY, Germany MRI plays an increasing role in the diagnosis and treatment monitoring of arthritis. Next to synovitis, erosions and osteoedema, cartilage composition is of increasing importance in the research of arthritis. gagCEST has recently been demonstrated to be sensitive to alterations in the biochemical composition of cartilage in the knee in patients following cartilage repair surgery as well as in vertebral disks. Our work shows the feasibility of gagCEST imaging in finger joint cartilage in healthy volunteers and patients with rheumatoid arthritis.
4228. | 35 | Uniform-MT CEST to Isolate GagCEST Contrast from Asymmetric MT Effects: First in vivo Study on Human Knees at 7 T Jae-Seung Lee1,2, Prodromos Parasoglou1, Ding Xia1, Alexej Jerschow2, and Ravinder R. Regatte1 1Radiology, New York University, New York, NY, United States, 2Chemistry, New York University, New York, NY, United States The in-vivo quantification of glycosaminoglycan (GAG) concentration is important for the early diagnosis of osteoarthritis. One promising method to measure GAG content in articular cartilage is chemical exchange saturation transfer (CEST). However, the CEST measurement may be interfered with the magnetization transfer (MT) effects resulting from the background extracelluar matrix. Recently, we have proposed a new strategy to disentangle CEST effects from asymmetric MT effects by using a simultaneous two-frequency RF irradiation technique to make the MT effects uniform. For the first time, this uniform-MT CEST method is applied in an in vivo human knee MRI study.
4229. | 36 | Creatine Imaging Using Chemical Exchange Filter Imaging Zhongliang Zu1, Junzhong Xu1, Vaibhav Janve1, Christopher C. Quarles1, Mark D. Does1, John C. Gore1, and Daniel F. Gochberg1 1Institue of Imaging Science, Vanderbilt University, Nashville, TN, United States Creatine imaging may provide useful biological information. MRS is able to image creatine. However, it suffers from relatively low resolution and long acquisition times. Here, we provide a chemical exchange filter imaging technique based on the recently developed chemical exchange rotation transfer (CERT) approach, that can select specific metabolites based on their exchange rates with water. Known phantom experiments show that CERT signal from creatine dominates signals from other metabolites. In vivo experiments on a rat brain with 9L tumor show that creatine imaging using CERT may serve as a new imaging biomarker to detect cancer.
4230. | 37 | Chemical Exchange Saturation Transfer Angiography - CESTA Shaokuan Zheng1, Imramsjah M.J. van der Bom1, Zhongliang Zu2, Guoxing Lin3, Matthew J. Gounis1, and Yansong Zhao4 1Radiology, UMASS Medical School, Worcester, MA, United States, 2Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 3Gustav H. Carlson School of Chemistry, Clark University, Worcester, MA, United States, 4Philips Healthcare, Cleveland, OH, United States Due to flow sensitivity of non-enhanced MRA, neurovascular diseases that present with slow or complex flow may not be fully appreciated. The feasibility of using Chemical Exchange Transfer Saturation (CEST) as angiography method is investigated. CEST imaging was performed on blood samples and the femoral artery of healthy human volunteers. The blood sample experiments showed that CEST contrast of 16% was achieved. In vivo CEST signal of blood was an order of magnitude greater than surrounding muscular tissue. Preliminary results show that blood is a suitable CEST agent that generates sufficient contrast to allow for angiographic imaging.
4231. | 38 | A Free Breathing, Retrospectively Gated, Saturation Transfer Encoded Steady State Cardiac Cine Method for Preclinical Chemical Exchange Saturation Transfer Imaging in the Heart Moriel Vandsburger1, Avigdor Leftin1, Senzeni Mpofu1, and Michal Neeman1 1Weizmann Institute of Science, Rehovot, None, Israel Chemical exchange saturation transfer (CEST) imaging is emerging as a powerful MRI technique for selective visualization of a variety of targeted contrast agents and synthetic reporter genes. CEST imaging has been applied primarily to stationary organs or tumors, and never to the heart because of cardiac and respiratory motion. We developed a free breathing, retrospectively gated, CEST-encoded steady state gradient echo cardiac cine imaging sequence for the purpose of pre-clinical cardiac CEST imaging.
4232. | 39 | Towards the Contrast Mechanism of Chemical Exchange Saturation Transfer (CEST) in Tumors at 9.4T Junzhong Xu1, Zhongliang Zu1, Jingping Xie1, Daniel F. Gochberg1, and John C. Gore1 1Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States To investigate whether the APT contrast in vivo reflects real differences in protein concentrations between tumors and normal tissues, we correlated APT contrast with multiple other MR parameters and protein concentration in 9L gliomas and normal tissues. R1 and PSR confirm that the total macromolecular content relevant for affecting water relaxation is lower in tumors, whereas APT and R2 detect other variations in composition that cause an increased contribution from exchanging protons. In additional, nuclear Overhauser effects (NOE) were also investigated which may provide a new imaging parameter to detect cancer, and the underlying biophysical mechanism is under investigation.
4233. | 40 | Comparison of 3D Acquisition Techniques for Amide Proton Transfer in Brain Tumor Applications Mariya Doneva1, Jochen Keupp1, Silke Hey2, Osamu Togao3, and Takashi Yoshiura3 1Philips Research Europe, Hamburg, Germany, 2Philips Healthcare, Best, Netherlands, 3Department of Clinical Radiology, Kyushu University, Fukuoka, Japan Amide proton transfer (APT) is a novel contrast mechanism enabling molecular MR imaging of proteins as well as the assessment of local pH. Clinical applications of APT imaging are often limited to a single slice acquisition due to the long scan time caused by multiple acquisitions at different saturation offset frequencies as well as SAR limitations. Previous studies were mainly focused on low resolution scans with large number of saturation offset frequencies and short saturation times Tsat < 1s. Parallel transmission based APT enables long saturation pulses at 100% duty cycle at clinical scanners and it was recently shown that an optimal CNR efficiency can be achieved at Tsat ≈ 2s. The purpose of this work was to investigate the application of 3D APT sequences with optimized saturation length and whole brain coverage. 3D GRASE and fast spin echo (TSE) sequences for APT were compared in phantom and in vivo studies.
4234. | 41 | Does It Affect the Quantification If Amide Proton Transfer Imaging Is Performed Pre- Or Post-Gadolinium Contrast Agent Administration? Yee Kai Tee1, Manus J. Donahue2, Stephen J. Payne1, and Michael A. Chappell1 1Department of Engineering Science, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, United States Gadolinium contrast agents (Gd-CA) are widely used in clinical perfusion MRI. Amide proton transfer (APT) imaging is an emerging chemical exchange saturation transfer MRI technique for pH mapping that may provide complementary information to perfusion MRI in various clinical applications such as cancer and stroke. In this study, we compared the APT quantification pre- and post-Gd-CA infusion, and found that in some cases the APT effect showed significant difference after contrast administration even when using an asymmetry measure.
4235. | 42 | Two-Frequency Irradiation of the pH-Dependent Amide Proton Transfer Effect in a Clinical Scanner:simulation and Experiment Chao Xu1, Christian Labadie1, André Pampel1, Samer Salamekh1, and Harald E. Möller1 1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Two-frequency radiofrequency (RF) irradiation was claimed to allow the isolation of the chemical exchange saturation (CEST) from magnetization transfer (MT) asymmetry. We implemented this technique for detecting pH-dependent APT effect in a clinical 3T MRI scanner and compared the experimental data acquired from egg white solutions with the simulation result using a three-pool model. According to our study, the double-frequency irradiation enables the partial correction of the MT asymmetry. A linear dependence between pH and measured MTRasym by the double-frequency pulse was observed in the cross-linked egg white solutions.
4236. | 43 | Characterization of Tissue Acidosis Response in Transient Acute Ischemic Stroke with pH-Sensitive APT MRI Phillip Zhe Sun1, Jerry S. Cheung1, Enfeng Wang1, and Xiaoan Zhang2 1Radiology, Martinos Center for Biomedical Imaging, Charlestown, MA, United States, 2Radiology, 3rd Affiliated Hospital, Zhengzhou, Henan, China pH-sensitive APT MRI is a metabolic index that remains promising to define ischemic tissue injury. We evaluated ischemic tissue response to reperfusion with multi-parametric MRI, and our results showed that quantitative pH imaging delineated salvageable DWI lesion from the irreversibly injured ischemic core. Therefore, it is important to develop multi-parametric tissue outcome prediction model that combines perfusion, pH and diffusion MRI, which may more accurately identify salvageable ischemic tissue for late thrombolytic therapy and ultimately help guide the development of neuroprotection agents that target tissue acidosis.
4237. | 44 | 3D Fast Spin Echo Acquisition for Combined Amide Proton Transfer and Elecric Properties Tomography Mariya Doneva1, Ulrich Katscher1, Christian Stehning1, Osamu Togao2, and Jochen Keupp1 1Philips Research Europe, Hamburg, Germany, 2Department of Clinical Radiology, Kyushu University, Fukuoka, Japan Amide proton transfer (APT) and electric properties tomography (EPT) are two novel MR methods for molecular and quantitative imaging of tissue properties. The APT signal is defined by the asymmetry of the magnetization transfer (MT) at +3.5ppm relative to water and reflects the concentration of endogenous cytosolic proteins or peptides as well as local pH. EPT is based on the curvature of the transceive phase (B1 field) of a fast spin echo (FSE) or balanced steady state free precession (bSSFP) image and reflects the electric conductivity of the tissue. Both elevated protein levels and tissue conductivity are related to pathological changes in tumors. Acquisition of the two contrasts in the same imaging sequence could potentially deliver complementary information for tumor tissue characterization and reduce the scan time compared to acquiring APT and EPT in separate scans. In this work, we propose an FSE acquisition, which allows the reconstruction of APT and EPT data from the same imaging sequence and demonstrate its feasibility in phantom and in vivo experiments.
4238. | 45 | Detection of Protein Accumulation by Amide Proton Transfer (APT) in the Spinal Cord of SOD1 Mice Using Exchange-Modulated PRESS Marilena Rega1, Francisco Torrealdea1, Phillip Smethurst1, James Dick1, Anna Gray1, Linda Greensmith1, Katie Sidle1, Simon Walker-Samuel2, David L. Thomas1, and Xavier Golay3 1Institute of Neurology, UCL, London, Greater London, United Kingdom, 2Centre for Advance Biomedical Imaging, UCL, London, Greater London, United Kingdom, 3Institute of Neurology, University College London, London, Greater London, United Kingdom Amide proton transfer (APT) is able to produce contrast originating from endogenous cellular proteins and peptides. In this study we explore the possibility of using APT as a biomarker of Amyotrophic lateral sclerosis (ALS) through a SOD1 mutate mouse model that closely resembles the disease. Comparisons of the APT signal between healthy and SOD1 animals at the same age, as well as validation of the results with protein assays (ex-vivo) show a significant difference between the two groups at a pre-symptomatic stage of the disease. These results suggest that APT could potentially become an early biomarker for ALS.
4239. | 46 | Estimation of Parameters from Sparsely Sampled in-vivo Magnetization Transfer Data Using Artificial Neural Networks Henrik Marschner1, Dirk K. Müller1, André Pampel1, Jane Neumann1, and Harald E. Möller1 1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany We examine whether Artificial Neural Networks (ANN) can be trained to estimate MT parameter sets from sparsely sampled in-vivo MT data. ANNs were trained using densely sampled MT data from healthy volunteers and the MT parameters obtained using conventional fitting as input. ANNs were used to extract MT parameters from sparsely sampled data. The obtained parameters were compared with those that come out using the conventional method. It is shown that parameters obtained with both methods are highly correlated (R>0.97). Once ANNs are trained subsequent measurements of other individuals and parameter estimation can be notably accelerated.
4240. | 47 | T2 Relaxation Dispersion Technique to Detect Intermediate and Fast Exchanging Protons in Metabolites and Proteins Jiadi Xu1,2, Nirbhay N. Yadav1,2, Kannie W.Y. Chan1,2, Amnon Bar-Shir2, Qin Qin1,2, Guanshu Liu1,2, Michael T. McMahon1,2, and Peter C.M. van Zijl1,2 1F. M. Kirby Center, Kennedy Krieger Institute, Baltimore, MD, United States, 2Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States A T2 relaxation dispersion technique is proposed to detect low concentration metabolites with protons that exchange in the intermediate to fast regime on the MR time scale. It employs a Carr-Purcell-Meiboom-Gill (CPMG) pulse train module with a fixed total length. The R2 (1/T2) values measured are dispersed by changing the number of 180 pulses in this module, which varies the pulse spacing. The dispersion curves reflect the concentration, exchange rate, and chemical shift difference of the exchangeable protons with water. The technique easily detects glutamate, myo-inositol and creatine and can quantify their exchange properties.
4241. | 48 | Imaging of Amide Proton Transfer (APT) and Nuclear Overhauser Effect (NOE) Using Chemical Exchange Rotation Transfer (CERT) Zhongliang Zu1, Junzhong Xu1, Hua Li1, Christopher C. Quarles1, Mark D. Does1, John C. Gore1, and Daniel F. Gochberg1 1Institue of Imaging Science, Vanderbilt University, Nashville, TN, United States CEST Z-spectra show dips from exchangeable sites (-NH2, -NH, and OH) at down field frequencies and from Nuclear Overhauser Enhancement (NOE) at up field frequencies. Quantitative mapping of such effects is difficult as conventional asymmetric analyses include contributions from both exchangeable sites and NOE. Here, we use a modified CEST method, chemical exchange ration transfer (CERT), to quantify amide proton transfer (APT) and NOE through subtraction of CEST signals at two irradiation flip angles instead of two frequency offsets. In vivo experiments on a rat brain with 9L tumor show interesting contrasts from APT and NOE.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (17:00-18:00) Exhibition Hall
RF Pulse Design 2
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4242. | 25 | Multidimensional Shinnar-Le Roux RF Pulse Design Chao Ma1,2 and Zhi-Pei Liang1,2 1Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, United States, 2Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, United States The SLR method is the “method-of-choice” in 1D RF pulse design. It is desirable to generalize the SLR method to design multidimensional RF pulses, which is accomplished in this work. We convert the problem to a series of 1D RF pulse design problems, each of which is equivalent to a 1D polynomial design problem that can be efficiently solved using convex optimization. The proposed method preserves almost all the desirable features of the SLR method in terms of handling the nonlinearity of the Bloch equation and tradeoffs among design parameters and computational efficiency.
4243. | 26 | Direct Design of 2D Pulses Using Matrix Inversion Rolf F. Schulte1 and Florian Wiesinger1 1GE Global Research, Munich, Germany Multi-dimensional RF pulses are used in special applications like targeted excitation or spectrally-spatially selective excitation. Commonly, spectral-spatial pulses are designed in a separable design, by first choosing a suitable gradient trajectory, designing a 1D spectral and a 1D spatial filter function and finally combining this into the actual 2D pulse. In this work, we introduce a simple 2D pulse design by direct matrix inversion, which helps to reduce sideband artefacts. Exemplary spectral-spatial pulses as well as 2D pulses with a quadratic phase are designed which can be used for efficient CSI encoding using SPEN.
4244. | 27 | Spatially Selective Excitation Applied to Aortic Vessel Wall Imaging Ronald Mooiweer1, Alessandro Sbrizzi1, Hamza el Aidi1, Cornelis A.T. van den Berg1, Fredy Visser1,2, Tim Leiner1, Peter R. Luijten1, and Hans Hoogduin1 1UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Philips Healthcare, Best, Noord-Brabant, Netherlands Spatially Selective Excitation in combination with reduced field of view imaging was used to efficiently image the aortic vessel wall over a large trajectory.
4245. | 28 | 2D Compensating RF Pulse with Uniform Image Contrast in Combination with an Internal Transceiver at 7T. Irene M.L. van Kalleveen1, Hugo Kroeze1, Alessandro Sbrizzi1, Vincent Oltman Boer2, Reerink Onne1, Marielle E.P. Philippens1, Cornelis A.T. van den Berg1, Peter R. Luijten1, and Dennis W.J. Klomp1 1Radiology, UMC Utrecht, Utrecht, Utrecht, Netherlands, 2Radiology, University Medical Center Utrecht, Utrecht, Utrecht, Netherlands In high field clinical MRI the B1 field is limited and inhomogeneous, while RF power deposition is high. The use of local antennas at 7T can be beneficial to image for example the rectal wall. However the B1 inhomogeneity becomes even more challenging when using internal transceivers. To compensate for their radial B1 inhomogeneity, we designed a 2D compensating RF pulse. In combination with two harmonic gradients the RF pulse provides a uniform flip angle in two dimensions as demonstrated by 3D FFE in the human rectum.
4246. | 29 | Fast Monotonic Convergent Optimal Control Algorithm for 2D RF Pulses Mitigating B0 and B1 Inhomogeneities Mads Sloth Vinding1, Ivan I. Maximov2, Zdenek Tosner3, and Niels Christian Nielsen1 1iNANO, inSPIN, Aarhus University, Aarhus, Jutland, Denmark, 2Institute of Neuroscience and Medicine 4, Juelich, Germany, 3Charles University, Prague, Czech Republic We present numerical simulations of B0 and B1 inhomogeneity compensation for 2D RF pulses derived using a monotonical convergent optimal control algorithm. The algorithm has proven rather fast compared to other gradient-based methods which is paramount for in vivo applications and it is quite robust with respect to the initial guess. Following up on our recent published experimental validation we here show that the algorithm in this study is capable of alleviating B0 inhomogeneity in a fictive B0 map of a 250 Hz linewidth, as well as B1 inhomogeneity of at least 9% inside the ROI.
4247. | 30 | Mitigate B1+ Inhomogeneity by Slice-Selective Composite Excitation Pulses Yi-Cheng Hsu1, Ying-Hua Chu2, Thomas Witzel3, I-Liang Chern4, and Fa-Hsuan Lin2 1Department of Mathematics, Nnational Taiwan University, Taipei, Taiwan, 2Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, 3A. A. Martinos Center, Massachusetts General Hospital, Charlestown, MA, United States, 4Department of Mathematics, National Taiwan University, Taipei, Taiwan To mitigate the B1+ inhomogeneity and to achieve more homogeneous large flip angle in high field MRI, we propose a method of composite excitation pulses, which does not require the refocusing slice selection gradient between two pulses. At 3T MRI, we demonstrate and compare this method to the standard single pulse excitation and a previously reported two-pulse method. We also used the Bloch equation to simulate the magnetization after our two-pulse excitation over a slice FOV to prove that our proposed composite pulses method can also work with slice-selective pulses.
4248. | 31 | Local Shape Adaptation for Curved Slice Selection Hans Weber1, Martin Haas1, Denis Kokorin1,2, Jürgen Hennig1, and Maxim Zaitsev1 1Department of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany, 2International Tomography Center, Novosibirsk, Russian Federation ExLoc allows excitation and geometrically matched spatial encoding of customized curved slices, based on a combination of linear and nonlinear gradients. The combination of ExLoc with multidimensional RF-pulses allows compensating for varying slice thickness originating from the nonlinearity of the applied slice-selection field. In this study, we exploit this technique for additional local adaptation of the slice shape. Compared to conventional multi-dimensional excitation with linear encoding fields to excite a curved slice, using this approach allows considerably shorter RF-pulses to be used.
4249. | 32 | Spin Echo Formation with a Phase Pre-Winding Pulse Jakob Assländer1 and Jürgen Hennig1 1Dept. of Radiology - Medical Physics, University Medical Center Freiburg, Freiburg, Germany A type of global pulses is proposed that pre-wind the phase of the spin ensemble within a finite frequency range. The resulting phase distribution in the particular frequency range is similar to the one after the combination of excitation and refocusing pulse in a standard spin echo experiment. The result is a spin echo formation after a single excitation pulse. Choosing a small tip angle, most of the longitudinal magnetization is maintained, potentially allowing T2-weighted imaging at low repetition times, e.g. for 3D encoding.
4250. | 33 | Inner Volume Imaging of the Kidney in vivo Using Parallel Transmit Martin Haas1, Denis Kokorin1, Stefanie Buchenau1, Ara K. Yeramian1, Hans-Peter Fautz2, Tobias Wichmann3, Jürgen Hennig1, Michael Bock1, and Maxim Zaitsev1 1Medical Physics, Department of Radiology, University Medical Center Freiburg, Freiburg, Germany, 2Siemens Healthcare, Erlangen, Germany, 3RAPID Biomedical GmbH, Rimpar, Germany Inner volume imaging with multi-dimensionally selective RF pulses has become feasible with introduction of parallel transmit acceleration techniques. Small organs like the kidney can profit from IVI, where the significant reduction of phase encoding steps decreases the acquisition time, which is limited by the patient’s ability to hold their breath. In this work, selective excitation of the right kidney of a volunteer is demonstrated, using eight-channel accelerated parallel transmit selective excitation. The kidney is imaged using segmented EPI in one breathhold and T2* maps are acquired with the aim to assess oxygenation changes in cortex and medulla under water loading.
4251. | 34 | Is a 2D-Spiral Excitation Trajectory Sufficient for 3D Inner Volume Imaging ? Alexis Amadon1, Alexandre Vignaud1, Aurélien Massire1, Michel Bottlaender1, and Nicolas Boulant1 1CEA, DSV, I2BM, Neurospin, LRMN, Gif-sur-Yvette, France, France Parallel transmission allows shortening fancy spatially-selective RF pulses. For a parallelepiped volume of interest, we investigate the possibility to use a mere 2D-spiral in excitation k-space to insure 3D selectivity for Inner Volume Imaging or CSI, by making the third dimension be the readout axis of a 3D sequence. We thereby observe to what extent the excitation profile is preserved along the readout direction. Moreover we demonstrate a zooming application on an ex-vivo baboon brain at 7T.
4252. | 35 | Spatial Selective Excitation Performance of Parallel Transmission Using a 3x8 Z-Stacked RF Coil Array at 3T Rainer Schneider1,2, Bastien Guérin3, Michael Hamm1, Jens Haueisen2, Elfar Adalsteinsson4,5, Lawrence L. Wald5,6, and Josef Pfeuffer1 1Siemens Healthcare, MR Application Development, Erlangen, Germany, 2Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Ilmenau, Germany, 3Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, 4Dept of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 5Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, United States, 6Martinos Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General Hospital, Charlestown, MA, United States The increased number of TX channels and Z-stacked pTX array geometry has been shown beneficial for better B1-shimming performance. No studies are known so far analyzing the different coil configurations for spatially-selective RF pulses. We simulate transverse and sagittal SSP pulses for two single-row arrays and a Z-stacked 3T body multi-channel TX array. Simulation results are analyzed with respect to TX acceleration factors and RF hardware efficiency. The Z-stacked coil setup shows significant gains in hardware efficiency and excitation performance along the sagittal direction, but also benefits along transverse direction. The beneficial effects are more prominent at higher acceleration factors.
4253. | 36 | Peak RF Power Constrained Pulse Design for Multi-Band Parallel Excitation Xiaoping Wu1, Kamil Ugurbil1, and Pierre-Francois Van de Moortele1 1CMRR, Radiology, University of Minnesota, Minneapolis, MN, United States The use of multi-band (MB) RF excitation along with subsequent unaliasing via parallel imaging principles leads to significant acceleration in volume coverage along the slice direction; this approach is becoming increasingly common and has recently been demonstrated with significant success in functional and diffusion-weighted imaging studies of the brain. Conventionally, the total RF energy and peak RF power required in slice accelerated MB imaging increase linearly and approximately quadratically, respectively, with the MB factor that defines the number of simultaneously excited slices. This increase can easily limit the maximum MB factor, especially when spin echo acquisitions are required and/or high magnetic fields are employed. Here we introduce a novel formulation for optimum peak power constraint using MB pTx pulse design based on spoke RF pulses with simultaneously targeting improved B1+ inhomogeneity. The formulation incorporates the interaction of the base pulses of individual bands by taking into account the final summed pulses. The new formulation is validated using B1+ maps simulated in a human whole body model and is shown to result in larger reduction of peak RF power than the conventional formulation for pTx pulses used for optimizing single-slice or sequential multi-slice excitation.
4254. | 37 | Optimization of 1D RF Pulses with Parallel Transmission Ulrich Katscher1, Kay Nehrke1, and Peter Boernert1 1Philips Research Europe, Hamburg, Germany Usually, Transmit SENSE is applied to improve spatially selective RF pulses in two or three dimensions. This study investigates the application of Transmit SENSE to one-dimensional RF pulses. For these RF pulses, Transmit SENSE is applicable in case of large B1 variations across the slice or slab to be excited as found for 3D volume imaging or REST. 1D Transmit SENSE can improve the excitation profile and reduce the required RF power. The approach was tested in vivo in the framework of a commercial 3T system with two transmit channels using the recently developed, ultrafast B1-mapping technique DREAM.
4255. | 38 | An Algorithm for Fast Parallel Excitation Pulse Design Shuo Feng1 and Jim X. Ji1 1Electrical and Computer Engineering, Texas A&M University, College Station, Texas, United States Spatially selective excitations with transmit array have been regarded as a key in solving several problems in high field MRI such as the transmit field inhomogeneity and the high power deposition. However, pulse design can be time consuming which may hinder its use from real-time applications. In this work, we propose a fast pulse design method by exploring the sparsity of the target spatial excitation pattern. The size of the system equation can be significantly reduced after a sparse transform and therefore the design speed is increased. Computer simulations in several common scenarios show that the proposed design method can achieve up to an order-of-magnitude speedup than the conventional design methods while still maintaining similar excitation accuracy.
4256. | 39 | First Implementation of Quantum Process Tomography in MRI Nicolas Boulant1, Aurelien Massire1, and Alexis Amadon1 1Neurospin, CEA, Saclay, Ile de France, France In their investigations, radiofrequency pulse designers often use flip angle measurements to validate their new developments. However when the objective is to implement true target matrix rotations, as for instance in the spin-echo sequence, those measurements inform about the performance of the RF pulse only for a particular input state. For the first time in MRI, we report the implementation of a Quantum Process Tomography experiment at 7 Tesla in order to characterize a transmit-SENSE 180° refocusing RF pulse, thereby providing information about the performance of the operation regardless of the input state.
4257. | 40 | Design of Non-Selective Refocusing Pulses with Phase-Free Rotation Axis by Gradient Ascent Algorithm in Parallel Transmission at 7 T Aurélien Massire1, Martijn A. Cloos2, Alexandre Vignaud1, Denis Le Bihan1, Alexis Amadon1, and Nicolas Boulant1 1CEA DSV I2BM NEUROSPIN LRMN, Gif-sur-Yvette, France, 2Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY, United States We use gradient ascent pulse engineering combined with the kT-point method to design non-selective refocusing pulses that mitigate severe B1 and ΔB0 inhomogeneities. The novelty of the method lays in the optimization of the relevant rotation matrices themselves rather than magnetization states. Experimental validation was performed on a phantom and using a 7 T scanner equipped with an 8-channel transmit array. The rotation matrix on every voxel was measured using Quantum Process Tomography. In addition, a modified non-selective Spin-Echo sequence was run to evaluate the ability to refocus dephased magnetization. Both experiments confirmed high fidelity of the here-introduced technique.
4258. | 41 | Asymmetric Spokes: A Demonstration of Free-Breathing PTX in the Human Torso at 7T Martijn A. Cloos1, Wonje Lee2, Graham C. Wiggins2, and Daniel Sodickson2,3 1Radiology, New York University School of Medicine, New York, NY, United States, 2Radiology, New York University Langone Medical Center, New York, NY, United States, 3The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY, United States In the recent past several publications have demonstrated parallel transmission for flip-angle homogenization at ultra-high field in the human brain. In this work we introduce, the asymmetric spokes design for slab-selective imaging with reduced echo times. To facilitate a completely free-breathing protocol, an optimized B1-mapping approach is detailed. Subsequently, the comprehensive method is demonstrated by homogenizing the flip-angle on a 6cm axial slab through the human torso at 7T using the 3DVIBE sequence.
4259. | 42 | Improved Off-Resonance Correction for segmented Spatially Selective Excitation Pulses to Achieve Large Excitation Bandwidth Patrick Waxmann1, Tomasz Dawid Lindel1, Frank Seifert1, Bernd Ittermann1, and Ralf Mekle1 1Physikalisch-Technische Bundesanstalt, Berlin, Germany, Germany Single voxel MR spectroscopy desires to acquire spectra from an anatomically defined region of interest. Spatially selective excitation (SSE) has been studied to adapt the voxel shape to the anatomy. Segmentation of SSE pulses can enhance the excitation bandwidth. Here, we introduce an off-resonance correction for segmented SSE-pulses designed with a small-tip-angle algorithm. The pulses can be designed as a whole and segmented only afterwards. This correction enhances target pattern fidelity even for large off-resonances and thus provides for uniform voxel localization over a wide frequency range.
4260. | 43 | Ultra-Fast Selective RF Pulse Design for Parallel Transmission Using Pre-Calculated Base Pulses Ingmar Graesslin1, Annighoefer Bjoern1, Ulrich Katscher1, and Peter Börnert2 1Philips Research, Hamburg, Germany, 2Philips Research Laboratory, Hamburg, Germany Parallel transmission in high-field MRI can improve the B1 homogeneity, as well as speed up multidimensional RF pulses (Transmit SENSE). However, the calculation of such pulses often takes too long for the use in a clinical setting, in particular if RF safety constraints are considered. This work presents a novel simple and efficient approach to calculate selective RF pulses for arbitrary target patterns based on pre-calculated base pulses. The base pulses can be precalculated by using arbitrary RF pulse design algorithms. They can be optimized for SAR or power and are valid for certain k-space trajectories and transmit coil arrangements.
4261. | 44 | Target-Pattern-Informed Variable-Density Trajectory Design for Low-SAR Pulse Design in Parallel Transmission Rainer Schneider1,2, Matthias Gebhardt1, Jens Haueisen2, and Josef Pfeuffer1 1Siemens Healthcare, MR Application Development, Erlangen, Germany, 2Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Ilmenau, Germany A lot of work has been done towards SAR-constrained optimization in pTX. However, in clinical use these methods can be too computationally intensive for highly parameterized spatially selective pulses. We propose a target-pattern-driven variable-density k-space trajectory (TD) metric, which inherently offers significant RF hardware efficiency and a beneficial impact on local and global SAR performance. To evaluate potential benefits of the TD approach, an elaborate simulation study for an 8ch 3T whole-body multi-channel TX array was conducted. The TD method was applied to a 3D-selective stack-of-spirals trajectory and compared to equal and fixed variable-density designs for varying TX acceleration factors.
4262. | 45 | Multi-Channel Implementation of Semi-Adiabatic Excitation Pulses Marcin Jankiewicz1 and Jay Moore2 1MRC/UCT Medical Imaging Research Unit, Department of Human Biology, University of Cape Town, Observatory, Western Cape, South Africa, 2Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, TN, United States We show a construction that enables the design and implementation of semi-adiabatic waveforms with performance optimized on a set of grids of predefined (B1+)i and Δf0 values associated with a multi-channel transmission system.
4263. | 46 | Steady-State SR-EPG Optimization of Pseudo-Steady-State Sequences Shaihan J. Malik1 and Joseph V. Hajnal1 1Division of Imaging Sciences and Biomedical Engineering, Kings College London, London, London, United Kingdom Dynamic RF shimming using a Spatially-Resolved Extended Phase Graph signal model was recently proposed for optimising pseudo-steady-state pulse sequences. The SR-EPG framework is more powerful than simple RF shimming because it considers the effect on the signal from multiple RF pulses. The original method modelled the transient state arising from a single shot, neglecting the effect of incomplete (and spatially variable) recovery that really occurs during multi-shot sequences. This leads to suboptimal results when such sequences are used in practice. In this work the steady-state that arises after multiple shots is modelled and optimized directly, improving the resulting solutions.
4264. | 47 | Designing a Hyperbolic Secant Excitation Pulse to Reduce Signal Dropout in GE-EPI Stephen James Wastling1 and Gareth John Barker1 1Department of Neuroimaging, King's College London, London, United Kingdom GE-EPI images suffer from signal dropout caused by susceptibility gradients. This can be reduced using Hyperbolic Secant (HS) RF excitation pulses with quadratic phase profiles. We determine by Bloch simulation the HS pulse parameters to give the most uniform signal response across the range of susceptibility gradients observed in the human head and show that the previous theoretical model for this is inaccurate. We also derive an expression for the bandwidth of a HS pulse used for excitation that is flip angle dependent. Finally using our optimised pulse we demonstrate recovery of signal in regions of dropout in six subjects.
4265. | 48 | Large Tip Angle KT-Points Based on a Linearization of the Bloch Equations Florent Eggenschwiler1, Rolf Gruetter2, and José P. Marques3 1EPFL, Laboratory for Functional and Metabolic Imaging, Lausanne, Vaud, Switzerland, 2Universities of Geneva and Lausanne, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland, 3University of Lausanne, Department of Radiology, Lausanne, Vaud, Switzerland This work presents a new approach for designing high tip angle kT-point pulses based on a linearization of the Bloch equations and usage of symbolic notation to accelerate the computation when the optimization has to be performed for large number of pixels. Based on the differentiation of the analytic form of the Bloch equations, the kT-point weights and positions were iteratively optimized in order to converge towards a targeted distribution of the magnetization across the brain. The validity of the method was demonstrated by designing high tip angle kT-points excitation and refocusing pulses.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (16:00-17:00) Exhibition Hall
B1 Mapping, Water/Fat & Contrasts: B1 Mapping
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4266. | 49 | Fast B1 Mapping Using Transient Phase Signals of /3 Prepared BSSFP Min-Oh Kim1, Jaewook Shin1, Narae Choi1, Joonsung Lee1, and Dong-Hyun Kim1 1Electrical and Electronic Engineering, Yonsei University, Seoul, Korea An extremely fast B1 mapping method is proposed based on the oscillatory signal behaviors in transient phase of /3balanced SSFP (bSSFP) sequences.
4267. | 50 | Optimum RF Pulse Width for Adiabatic Bloch-Siegert B1+ Mapping Mohammad Mehdi Khalighi1, Adam B. Kerr2, and Brian K. Rutt3 1Applied Science Lab, GE Healthcare, Menlo Park, California, United States, 2Department of Electrical Engineering, Stanford University, Stanford, California, United States,3Department of Radiology, Stanford University, Stanford, California, United States The adiabatic Bloch-Siegert (B-S) method has been introduced to design short highly sensitive frequency-swept B-S pulses to address the long TE and high SAR problems of B-S B1+ mapping method; however, it is not clear which ABS pulse width gives the best results. Here we have compared ABS pulses with different pulse widths and showed that the best ABS pulse width, which generates the highest angle-to-noise ratio (ANR) is ¾ T2*. We used 2, 4 and 6ms ABS pulses in brain at 7T and showed that 6ms ABS pulse generates highest ANR maps.
4268. | 51 | Three Dimensional Fast Spin Echo Bloch-Siegert B1 Mapping with Navigator Based Phase Correction at 11.7T Xiaoying Cai1, Wu Dan2, and Jiangyang Zhang3 1Biomedical Engineering, Tsinghua University, Beijing, Beijing, China, 2Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, United States,3Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States We propose the use of a twin-navigator phase correction scheme to monitor and correct phase errors in fast spin echo Bloch-Siegert B1 mapping sequences. The proposed sequence was implemented and tested on an 11.7T MR system. With phase correction, both individual phase images and calculated B1 maps contained fewer artifacts. The technique can be used to acquire 3D B1 map on high field magnet and tolerate certain degree of subject motion and instrument instability.
4269. | 52 | Fourier Domain Approximation for Bloch Siegert Shift Esra Abaci Turk1,2, Yusuf Ziya Ider1, Arif Sanli Ergun3, and Ergin Atalar1,2 1Electrical and Electronics Engineering Department, Bilkent University, Ankara, Turkey, 2National Magnetic Resonance Research Center (UMRAM), Ankara, Turkey, 3Electrical and Electronics Engineering Department, TOBB-University of Economics and Technology, Ankara, Turkey In this study, a new simple Fourier domain based analytical expression is proposed for the Bloch-Siegert phase shift based B1 mapping method. With this new expression off- and on-resonance effects can be understood more easily due to the Fourier domain relation. It is shown that |B1+| can be obtained more accurately by the aid of this expression for short pulse durations and offset frequencies.
4270. | 53 | Fast Isotropic Volumetric B1+ Calibration Improves RF Shimming in Abdominal MRI at 3T Alois M. Sprinkart1,2, Georg Schmitz2, Frank Träber1, Wolfgang Block1, Jürgen Gieseke3, Winfried A. Willinek1, Hans H. Schild1, Peter Börnert4, and Kay Nehrke4 1Dept. of Radiology, University of Bonn, Bonn, Germany, 2Institute of Medical Engineering, Ruhr-University Bochum, Bochum, Germany, 3Philips Healthcare, Hamburg, Germany,4Philips Research Laboratory, Hamburg, Germany The recently published ultra-fast B1+ mapping approach DREAM was used to acquire an volumetric B1+ calibration dataset of the whole upper abdomen with an isotropic voxel size of 4.7mm within a single breath-hold acquisition in 12 patients and 2 volunteers at 3T. Based on this data RF settings were optimized separately for each of 60 transversal and 40 coronal reformatted slices, adaptive to position and angulations to evaluate potential improvements in flip angle accuracy and B1+ homogeneity by multi-slice adapative RF shimming. Results were compared to conventional transversal single-slice optimization approach.
4271. | 54 | Fast B1+ Mapping for Cardiac MR Using a Black Blood DREAM Sequence Kay Nehrke1, Alois M. Sprinkart2,3, Hans H. Schild2, and Peter Börnert1 1Philips Research Laboratory, Hamburg, Germany, 2Department of Radiology, University of Bonn, Bonn, Germany, 3Institute of Medical Engineering, Ruhr-University Bochum, Bochum, Germany The recently introduced DREAM B1+ mapping approach has been combined with a black-blood prepulse to allow a 2D B1+ map of the heart to be acquired in the diastolic phase of a single heart beat. The approach has been studied in vivo for RF shimming of the heart using a dual-transmit 3T MRI system. Application of the black blood prepulse facilitated automatic threshold-based masking of the B1+ maps, thus improving the reliability of the maps. RF shimming resulted in significant improvement of RF homogeneity.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (16:00-17:00) Exhibition Hall
B1 Mapping, Water/Fat & Contrasts: Water/Fat
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4272. | 55 | Chemical Shift Correction in Fat-Water Separation Using Two-Point Dixon SSFP Yi Wang1,2, Glen Morrell2, and Dennis L. Parker2 1Neurology, University of California, Los Angeles, Los Angeles, California, United States, 2Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, Utah, United States SSFP sequences offer superior signal intensity in a relative short time. The potential of a dual-echo SSFP sequence has been investigated for breast imaging applications, where fat signal is separated from the water signal using the two-point Dixon technique [3]. Dual echo SSFP provides robust water-only and fat-only images in the presence of B0 and B1 inhomogeneity. Due to the sensitivity of SSFP to off resonance, short TR is needed to minimize the banding artifact. The two echoes required for the two-point Dixon fat-water separation can be acquired using a bipolar gradient. Compared to mono-polar readout, a bipolar gradient can reduce echo spacing and therefore result in more efficient readout. However, due to the opposite chemical shift, mis-registration between images from the two echoes using bipolar readouts exists. In this work, we improved the dual-echo 3D SSFP sequence by correcting the bi-directional chemical shift error in two-point Dixon fat/water separation.
4273. | 56 | Single Acquisition Fat Water Separation Using a Golden Ratio Radial BSSFP Sequence with Dynamic Echotime Shifting Thomas Benkert1, Riad Ababneh2, Martin Blaimer1, Peter M. Jakob1,3, and Felix A. Breuer1 1Research Center Magnetic Resonance Bavaria, Würzburg, Bavaria, Germany, 2Yarmouk University, Irbid, Jordan, 3Experimental Physics 5, University Würzburg, Würzburg, Bavaria, Germany To achieve fat water separation out of just one single acquisition, we propose a golden ratio radial bSSFP sequence. The echotime of each radial projection is shifted dynamically, allowing to extract images with different echotimes by using a k-space weighted image contrast (KWIC) filter.
4274. | 57 | Water-Fat Separation Using Time Series Correlation Markus Florian Untenberger1, Martin Uecker2, Dirk Voit1, and Jens Frahm3 1Biomedizinische NMR Forschungs GmbH, Max-Planck Insitut fuer biophysikalische Chemie, Goettingen, Niedersachsen, Germany, 2Dept. of Electrical Engineering and Computer Sciences, University of California, Berkeley, California, United States, 3Biomedizinische NMR Forschungs GmbH, Max Planck Institute, Goettingen, Niedersachsen, Germany A novel chemical species separation method is presented. We repetitively switch a saturation pulse and acquire multiple images afterwards to get a global behavior, a paradigm, of the data. The correlation and significance of each pixel with the paradigm is calculated and used for visualization of the saturated species. The results are compared with conventional iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL), giving good agreement.
4275. | 58 | Real-Time Water-Fat Separation Markus Florian Untenberger1, Martin Uecker2, Sebastian Schaetz1, Dirk Voit1, and Jens Frahm3 1Biomedizinische NMR Forschungs GmbH, Max-Planck Insitut fuer biophysikalische Chemie, Goettingen, Niedersachsen, Germany, 2Dept. of Electrical Engineering and Computer Sciences, University of California, Berkeley, California, United States, 3Biomedizinische NMR Forschungs GmbH, Max Planck Institute, Goettingen, Niedersachsen, Germany In this abstract the extension of water-fat separation from static images to dynamic, real-time imaging is presented. We used a regularized nonlinear inverse image reconstruction on top of which an adapted iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) was performed. Results from different anatomical views at different temporal and spatial resolutions are shown. Expected improvements from a model-based reconstruction and the extension to fat quantification are also discussed. The results show the feasibility of water-fat separation in real time.
4276. | 59 | Robust High Resolution Fat-Water Separation in the Abdomen During Free-Breathing by Self-Gated 2D Radial TrueFISP Imaging Riad Ababneh1, Thomas Benkert2, Martin Blaimer2, and Felix A. Breuer2 1Physics, Yarmouk University, Irbid, Jordan, 2Research Center Magnetic Resonance Bavaria, Würzburg, Bavaria, Germany We present a robust approach to separate fat and water signals in the abdomen during free breathing. The approach combined with a self-gated reconstruction of different respiratory phases in free-breathing. In this study a radial TrueFISP sequence was modified, wherein TE was made to vary between subsequent readouts. Good separation without streaking artifacts or blurring due to respiratory motion was obtained in all studied cases.
4277. | 60 | 3D Mapping of T2* and B0 Inhomogeneities for Water/Fat Separation Abraam S. Soliman1,2, Jing Yuan2, Terry M. Peters1,2, and Charles A. McKenzie1,3 1Biomedical Engineering, University of Western Ontario, London, Ontario, Canada, 2Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada, 3Medical Biophysics, University of Western Ontario, London, Ontario, Canada Several confounding factors can compromise the ability of MRI to accurately quantify fat, particularly B0 inhomogeneities and T2* decay. Recently, a labeling approach has been proposed to estimate B0 field variations in fat/water separation and was shown to outperform the widely-used region growing method. In this work, we extend this technique to 3D as well as integrate pixel-by-pixel calculation of T2* decay, necessary for accurate fat quantification. We demonstrate our approach on data for healthy volunteers and NAFLD patients.
4278. | 61 | Towards Clinical Robustness in 3D Abdominal Water/Fat Imaging Nadine Gdaniec1, Tim Nielsen2, Peter Börnert3, Holger Eggers2, Mariya Doneva4, and Alfred Mertins1 1University of Lübeck, Lübeck, Germany, 2Philips Research Laboratories, Hamburg, Germany, 3Philips Research Laboratory, Hamburg, Germany, 4Philips Research Europe, Hamburg, Germany Breath-holding is an efficient strategy to minimize respiration induced artifacts in the abdomen if the patient’s capability is sufficient. The sampling pattern used deals with premature breathing onset by flexible scan termination. A temporally continuous compromise is made between SNR, undersampling aritifacts and resolution. This work aims at finding the optimal compromise by simulations on phantom experiments. To meet real clinical needs, dual-echo imaging was added for water-fat separation. The scan was complemented with a fast motion detection navigator that does not disturb the steady state and triggers automatic scan termination. Coil compression was applied for reduced reconstruction time.
4279. | 62 | Breast Implant MRI with an Extended 4-Point Ideal Method Jedrzej Burakiewicz1, Annette Jones2, Sarah McWilliams2, Jyoti Parikh2, Hema Verma2, Tobias Schaeffter1, and Geoffrey David Charles-Edwards1,2 1Biomedical Engineering, King's College London, London, United Kingdom, 2Guy's and St. Thomas' NHS Trust, London, United Kingdom Separating silicone signal is an important issue in breast imaging, particularly when ruptures of the implant are suspected. Methods used up to date include either STIR or spectral suppression, or a combination of both. These however are susceptible to B0 inhomogeneities and can reduce signal strength. We present a combination of a 4-point IDEAL method with an optimised initial echo time,and with a region growing algorithm to provide a good initial estimate for the B0 map to efficiently separate water, fat and silicone signals; we also show first clinical results from a breast implant patient.
4280. | 63 | Multiecho Water-Fat Separation with Navigated Free-Breathing 3D Spoiled Gradient-Recalled Echo Sequence Yuji Iwadate1, Anja C.S. Brau2, Yoshihiro Tomoda3, Kenji Asano3, and Hiroyuki Kabasawa1 1Global Applied Science Laboratory, GE Healthcare Japan, Hino, Tokyo, Japan, 2Global Applied Science Laboratory, GE Healthcare, Munich, DE, Germany, 3MR Engineering, GE Healthcare Japan, Hino, Tokyo, Japan Multiecho water-fat separation with multifrequency fat spectrum modeling (IDEAL IQ) provides accurate estimates of fat fraction. Liver imaging is suitable for this technique, since fat is the hallmark feature of nonalcoholic fatty liver disease. However, respiratory motion often causes artifacts in liver imaging. We developed respiratory gated IDEAL IQ with navigator echo for free-breathing image acquisition. A navigator is inserted after imaging sequence and used for data acceptance/rejection. Navigator did not corrupt fat fraction calculation, and enabled free-breathing data acquisition with minimum motion related artifacts. This technique may be useful for patients who cannot hold their breath.
4281. | 64 | Hiding Your Fat: Comparison of Fat Saturation Techniques for Single-Shot Fast Spin Echo Sequences for 7T Body Imaging Sören Johst1,2, Stephan Orzada1,2, Anja Fischer1,2, Lale Umutlu1,2, Mark E. Ladd1,2, and Stefan Maderwald1 1Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany, 2Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany Several different fat saturation (FS) techniques for single-shot fast spin echo (SSFSE) were compared at 7 Tesla, whereby the recently proposed Time Interleaved Acquisition of Modes (TIAMO) was used for the imaging portion of the sequence: A novel method using TIAMO (multiple fat-selective 90° RF pulses applied with alternating transmit RF modes), slice-selective gradient reversal (SSGR), and slice-selective smaller bandwidth refocusing pulses (SSB). SSGR performed best regarding FS, homogeneity of FS, and preservation of tissue signal intensity.
ELECTRONIC POSTER SESSION • PULSE SEQUENCES & RECONSTRUCTION B Wednesday, 24 April 2013 (16:00-17:00) Exhibition Hall
B1 Mapping, Water/Fat & Contrasts: Contrast
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4282. | 65 | What Is Really Causing the Contrast in Spin-Echo Imaging at 7T? Robert Trampel1 and Robert Turner1 1Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany Spin-echo and turbo-spin echo images of brain tissue displaying a strong contrast between grey and white matter are usually referred to as “T2-weighted”. However, since earlier studies show very little difference in T2 relaxation times between grey and white matter, the actual underlying contrast mechanism remains unclear. We therefore investigated the contrast obtained using a common spin-echo sequence at 7T with a range of sequence parameters. The results clearly show that T2 relaxation contributes hardly at all to the contrast obtained in brain tissue. Depending on the sequence parameters, variations in proton density, T1 relaxation, and magnetization transfer are the main sources of image contrast in common spin-echo imaging.
4283. | 66 | Application of a Non-CPMG Single-Shot Turbo Spin Echo Sequence to Multi-Contrast Imaging of the Human Lung at 1.5T Flavio Carinci1,2, Morwan Choli2,3, Felix A. Breuer3, and Peter M. Jakob2,3 1MRB Research Center, Wuerzburg, Germany, 2Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany, 3Research Center Magnetic Resonance Bavaria e. V. (MRB), Wuerzburg, Germany Magnetic resonance imaging of the lung is challenging due to low proton density, short T2*, respiratory and cardiac motion. Single-shot turbo spin-echo (ssTSE) sequences can be used to obtain good signal-to-noise ratio in the lungs and to suppress motion artifacts. However preparation schemes such as diffusion and T2* preparation can result in the violation of the CPMG conditions and generate severe artifacts. In this work we present the application of a non-CPMG ssTSE sequence to diffusion-weighted and T2*-weighted imaging of the human lung. We show that this approach allows for apparent diffusion coefficient (ADC) and T2* mapping of the human lung in a single 10s breath-hold.
4284. | 67 | Comparison of SSFP and GRE Sequences for QMT Acquisition Nicholas G. Dowell1, Hannah van den Boomen2, and Mara Cercignani3 1CISC, Brighton and Sussex Medical School, Brighton, East Sussex, United Kingdom, 2Life Sciences, University of Sussex, Brighton, East Sussex, United Kingdom, 3CISC, Brighton & Sussex Medical School, Brighton, East Sussex, United Kingdom Quantitative MT data is often not considered in imaging protocols due to the lengthy acquisition times that are required (up to 25 minutes). This is because the normal acquisition demand the collection of up to 12 gradient echo volumes. In response, a new approach, based on SSFP acquistion can dramatically cut acquisition times to less than 10 minutes. In this work, we rigorously compare the qMT data that is produced by both methods and assess whether the new SSFP method is a drop-in replacement for the established GRE approach.
4285. | 68 | Respiratory Self-Gating for Free-Breathing Magnetization Transfer MRI of the Abdomen Weiguo Li1, Ning Jin2, Tianjing Zhang1, and Andrew C. Larson1 1Radiology, Northwestern University, Chicago, Illinois, United States, 2Siemens Healthcare, Columbus, Ohio, United States Respiratory self-gated magnetization transfer (RSG-MT) sequence was developed and applied to abdominal organs to generate magnetization transfer ratio (MTR) maps during free breathing (FB) of patients. Results showed that respiratory motion artifacts were significantly reduced and high quality MTR maps were generated. Future studies will evaluate the application of these RSG FB MT techniques for the assessment of liver fibrosis and tumor desmoplasia in clinical settings.
4286. | 69 | Side Effects of the Spoiler Gradient in Gradient Echo Sequences: Diffusion Attenuation of the Signal from Nuclei in Thermal Equilibrium and in Hyperpolarised State Sebastien Bär1, Matthias Weigel1, Valerij G. Kiselev1, and Jochen Leupold1 1Medical Physics Department of Radiology, University Hospital Freiburg, Freiburg, Germany Simulations and experiments exploring the steady state signal amplitude dependency on the spoiler gradient in unbalanced gradient echo sequences and RF-spoiled gradient echo sequences are shown. Additionally, for these sequences and also under consideration of diffusion, signal evolution over the sequence repetition cycles is simulated for hyperpolarized nuclei in gas and liquid phase.
4287. | 70 | Localization of US Focal Spot in in vivo Tissue Using 3D Acoustic Radiation Force Impulse Imaging Joshua de Bever1,2, Nick Todd2, Mahamadou Diakite2,3, and Dennis Parker2 1School of Computing, University of Utah, Salt Lake City, Utah, United States, 2Utah Center for Advanced Imaging Research, Salt Lake City, Utah, United States, 3Physics Department, University of Utah, Salt Lake City, Utah, United States This work evaluates the effectiveness of a 3D MRI pulse sequence for performing Acoustic Radiation Force Impulse imaging (ARFI) when applied in vivo. Building on 2D MR-ARFI techniques, this sequence provides enhanced volumetric coverage and would be especially beneficial for easily and safely localizing the ultrasound focal spot in all three dimensions before an MR guided high intensity focused ultrasound treatment.
4288. | 71 | Ultrafast High-Resolution NMR Spectroscopy Through Indirect Zero-Quantum Coherence Detection in Inhomogeneous Fields Hanping Ke1, Hao Chen1, Zhiyong Zhang1, Yanqin Lin1, Zhong Chen1, and Shuhui Cai1 1Department of Electronic Science, Xiamen University, Xiamen, Fujian, China In some cases, high-resolution NMR spectra are virtually impossible to obtain by conventional NMR methods because of intrinsic or extrinsic field inhomogeneity. In this study, spatial encoding intramolecular zero-quantum coherence (ZQC) technique was proposed to ultrafast achieve high-resolution NMR spectra under inhomogeneous fields. Theoretical analyses and experimental observations demonstrate that high-resolution NMR spectral information can be revived with two scans even when the field inhomogeneities are severe enough to erase most spectral information. This work may provide a new way to extremely enhance the acquisition efficiency of ZQC high-resolution spectroscopy for in vivo study of metabolites in organisms.
4289. | 72 | Ex Vivo 1H Magnetic Resonance Spectroscopy of Intact Salmon Muscle Via Hadamard-Encoded Intermolecular Multiple-Quantum Coherence Technique Honghao Cai1, Xiaohong Cui1, Shuhui Cai1, and Zhong Chen1 1Department of Electronic Science, Xiamen University, Xiamen, Fujian, China The flavour and nutrition of a fish are greatly influenced by its fat content and its composition. However, it is difficult to obtain high-resolution (HR) NMR spectrum of intact fish tissues by traditional methods owing to the magnetic susceptibility gradients among the tissues. In this study, a Hadamard-encoded intermolecular multiple-quantum coherence (iMQC) method was implemented to obtain HR NMR spectrum of intact salmon muscle. The experimental results indicate that iMQC technique is a feasible way for HR NMR spectrum of fish tissues. Compared to magic angle spinning, it is non-invasive and suitable for in vivo and in situ applications.