ISMRM 21st Annual Meeting & Exhibition 20-26 April 2013 Salt Lake City, Utah, USA

MRS: Methods, Physiologic & MR Parameters
Wednesday 24 April 2013
Room 155 EF  16:00 - 18:00 Moderators: Priti Balchandani, Andrew A. Maudsley

16:00 0529.   
Higher-Order Feedback Field Control Improves Linewidths in MR Spectroscopy at 7T -permission withheld
Bertram J. Wilm1, Yolanda Duerst1, Benjamin E. Dietrich2, Michael Wyss1, David Otto Brunner2, Christoph Barmet2,3, Thomas Schmid1, Signe Johanna Vannesjo1, and Klaas P. Pruessmann1
1Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, ZH, Switzerland, 2Institute for Biomedical Engineering, University and ETH Zurich, Zurich, ZH, Switzerland,3Skope Magnetic Resonance Technologies, 8004, ZH, Switzerland

Dynamic field changes caused by hardware imperfections or physiological induced field perturbations can cause signal loss due to increased T2* decay, inaccurate data averaging and off-resonant application of RF pulses. To prevent artifacts in MR spectroscopy, we present a higher-order real-time feedback field control system based on NMR probes which is tested for field stabilization in single-voxel brain MRS at 7T.

16:12 0530.   
Spectroscopy with Linear Algebraic Modeling (SLAM): Speed and Quantification in Brain Tumor Studies
Yi Zhang1,2, Refaat E. Gabr1, Jinyuan Zhou1,3, Robert G. Weiss1,4, and Paul A. Bottomley1,2
1Division o MR Research, Department of Radiolgoy, Johns Hopkins University, Baltimore, Maryland, United States, 2Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 3F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, United States, 4Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland, United States

The inclusion of potentially useful MRS acquisitions in clinical MRI exams is often precluded by long study times for chemical shift imaging (CSI). Global- or lesion-averaged MRS-measurements can usually suffice for assessing metabolic status. A recently proposed method—spectroscopy with linear algebraic modeling (SLAM)—could provide such assessments, in addition to a many-fold speed-up in scan-time. Here, SLAM applied retroactively to patients with brain tumors, is shown to yield quantitatively indistinguishable results from conventional 2D 1H CSI with an acceleration factor of six. Proactive studies demonstrate comparable results to CSI with a speedup factor of 14.

16:24 0531.   Indirectly-Detected Heteronuclear MR Spectroscopy & Imaging by Amplified Solvent Proton Signals -permission withheld
Zhao Li1, Jamie D. Walls1, Susie Y. Huang1, and Yung-Ya Lin1
1Chemistry and Biochemistry, UCLA, Los Angeles, CA, United States

A general spin amplification scheme is developed to enhance the sensitivity of heteronuclear MR spectroscopy and imaging based on dynamic instability of the solvent proton magnetization under collective feedback fields of radiation damping and the distant dipolar field. The heteronuclear solute spins are first detected by the solvent proton spins through various magnetization transfer mechanisms and serve as small “input” signals to perturb the solvent proton magnetization, which is prepared in an unstable state. The weakly detected signal is then amplified through subsequent nonlinear evolution of the solvent proton magnetization to achieve 10x SNR improvement for 13C NMR and MRI.

16:36 0532.   Combining Parallel Detection of Proton Spectroscopic Imaging (PEPSI) Measurements with a Data-Consistency Constraint Improves SNR
Shang-Yueh Tsai1, Ying-Hua Chu2, Yi-Cheng Hsu3, Wen-Jui Kuo4, and Fa-Hsuan Lin2
1Graduate Institute of Applied Physics, National Cheng-Chi University, Taipei, Taiwan, 2Institute of Biomedical Engineering, National Taiwan University, Taipei, Taiwan, 3Department of Mathematics, Nnational Taiwan University, Taipei, Taiwan, 4Institute of Neuroscience, National Yang-Ming University, Taipei, Taiwan

Fast MR spectroscopic imaging (MRSI) is challenged by its relative low signal-to-noise ratio (SNR), which can be improved by using a surface coil array. Instead of using a coil array to accelerate image encoding at the cost of the reduced SNR, here we propose to exploit this sensitivity information to enforce the k-space data-consistency (DC) in order to suppress noise and consequently to improve MRSI SNR. With in vivo experimental data at 3T using a 32-channel coil array, we found that the DC constraint can improve the SNR of PEPSI by approximately 40%.

16:48 0533.   
An Accurate Calibration of MRS Thermometry at 3T
Ben Babourina-Brooks1, Rob Simpson2, Theodoros N. Arvanitis3,4, Andrew C. Peet1,4, and Nigel Paul Davies1,5
1School of Cancer Sciences, University of Birmingham, Birmingham, West Midlands, United Kingdom, 2National Physical Laboratory, Middlesex, Greater London, United Kingdom, 3School of Electronic, Electrical & Computer Engineering, University of Birmingham, Birmingham, West Midlands, United Kingdom, 4Birmingham Children's Hospital NHS Foundation Trust, Birmingham, West Midlands, United Kingdom, 5Imaging & Medical Physics, University Hospitals Birmingham NHS Foundation Trust, Birmingham, West Midlands, United Kingdom

MRS can be used as a non-invasive temperature probe by measuring the chemical shift difference between water and a reference metabolite. The water chemical shift is linearly dependent on temperature, however protein and ionic concentrations may effect this dependence. Water chemical shift calibrations using accurate temperature methods were used in this study to assess the effect of ionic strength and protein strength at 3T. A recent investigation of the effects of ionic strength and a protein concentration has been performed on a 1.5T clinical scanner, vescovo et al. Temperature calibration curves were sensitive to ionic and protein concentrations. Agreement of results with Vescovo et al for similar solutions were also observed.

17:00 0534.   
Uniform Spinning Sampling Gradient Electron Paramagnetic Resonance Imaging
David H. Johnson1, Zhiyu Chen1, Rizwan Ahmad1, Alexandre Samouilov1, and Jay L. Zweier1
1Davis Heart and Lung Research Institute, Ohio State University, Columbus, OH, United States

17:12 0535.   
Intracellular Water Preexchange Lifetime in Cultured Mixed Neurons and Astrocytes -permission withheld
Donghan Yang1, James E. Huettner2, Jeffrey J. Neil3,4, and Joseph J.H. Ackerman1,5
1Department of Chemistry, Washington University in St. Louis, St. Louis, MO, United States, 2Department of Cell Biology & Physiology, Washington University in St. Louis, St. Louis, MO, United States, 3Department of Neurology, Washington University in St. Louis, St. Louis, MO, United States, 4Department of Pediatrics, Washington University in St. Louis, St. Louis, MO, United States,5Department of Radiology, Washington University in St. Louis, St. Louis, MO, United States

Knowledge of intracellular water preexchange lifetime in neurons and astrocytes is essential for understanding intracellular water diffusion in brain. Employing a previously described cultured cell system, the longitudinal 1H MR relaxation of intracellular water in mixed cultured neurons and astrocytes was distinguished from that of the extracellular media where the apparent relaxation rate was greatly enhanced via either rapid flow or relaxation agent. Under such conditions, where the true intracellular T1 is 50 fold greater than the apparent T1 of the extracellular media (MR slow exchange regime) the intracellular water preexchange lifetime is readily derived, 0.26 plus-or-minus sign 0.3 s.

17:24 0536.   
Metabolite T1 Relaxation Enhancement by Spectrally-Selective Excitation
Noam Shemesh1, Jean-Nicolas Dumez1, and Lucio Frydman1
1Department of Chemical Physics, Faculty of Chemistry, Weizmann Institute of Science, Rehovot, Israel

Modification of proton T1 relaxation upon band-selective excitation is well known in protein solution NMR; however, such effects have never been observed in CNS metabolites. Here, we show statistically significant T1 relaxation enhancement in non-water-suppressed band-selective excitation for several metabolites in excised mouse brains. A 30-50% decrease in T1 was observed compared to conventional water suppressed schemes, suggesting some form of cross-relaxation as a mechanism. Our methodology affords a straightforward way to enhance MRS’s sensitivity per unit time, and opens new routes to investigate the nature of metabolic interactions among them and with water in tissues, at a molecular level.

17:36 0537.   
Simultaneous Measurement Carbon-13 MR Spin-Relaxation, Diffusion, and Kinetic Parameters
Christine Leon1, Cornelius Von Morze1, Bertram Koelsch1, Adam B. Kerr2, Robert A. Bok3, John M. Pauly2, John Kurhanewicz1, Daniel B. Vigneron1, and Peder E.Z. Larson1
1Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, United States, 2Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, CA, United States, 3Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, United States

Magnetic resonance spectroscopy of hyperpolarized substrates provides a powerful tool to investigate metabolism. Recently, we showed that the T1,Eff of lactate was significantly shorter in tumors suggesting a different cellular environment, in addition to increased KPyr→Lac using MAD-STEAM. However, the measurement of the T1,Eff is a combination of diffusion and spin-relaxation. We modified the MAD-STEAM pulse sequence to include varying gradient strengths to separate diffusion weighting from T1 relaxation effects. This new method allows for measurements of ADCs and T1s values in addition to multiple rates of conversion, simultaneously, providing further biological information about the cellular environment of the metabolites.

17:48 0538.   
Quantification of T1 Relaxation Times and Nuclear Overhauser Effect of 31P Metabolites in the Human Prostate at 7T
Miriam W. Lagemaat1, Marnix C. Maas1, Eline K. Vos1, Thiele Kobus1, Andreas K. Bitz2,3, Mark J. van Uden1, Stephan Orzada2,3, Arend Heerschap1, and Tom W.J. Scheenen1,2
1Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands, 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany, 3Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany

We assessed T1 relaxation times of 31P metabolites in the human prostate and evaluated the nuclear Overhauser effect (NOE) as signal enhancement strategy for 31P MRSI of the prostate at 7T. T1 relaxation times were found to be relatively long compared to other human tissues at 7T. To obtain a 3D 31P MRSI dataset within a clinically acceptable measurement time (TR ≤ 1.5s) with optimal SNR per unit time, a strongly reduced flip angle (≤ 45°) is required. Signal enhancement by irradiating the water resonance to obtain NOE was successful, yielding up to 42% more signal for PE.