MRS Acquisition & Quantification Methods
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Friday 11 May 2012
Room 109-110  10:30 - 12:30 Moderators: Peter Boesiger, Kim M. Cecil

10:30 0706.   
In Vivo MR Spectroscopy of Arbitrarily Shaped Voxels Using 2D-Selective RF Excitations Based on a PROPELLER Trajectory with Eliminated Side Excitations and Adapted Sampling Density Correction
Martin G Busch1,2, and Jürgen Finsterbusch1,2
1Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany, 2Neuroimage Nord, University Medical Centers Hamburg-Kiel-Lübeck, Hamburg-Kiel-Lübeck, Germany

The recently presented 2D-selective RF excitations based on the PROPELLER trajectory suffer from residual side excitations caused by trajectory imperfections and limitations of the Voronoi diagram used to estimate the sampling density. Here, one of the refocusing RF pulses of a PRESS-based pulse sequence is used to eliminate the unwanted side excitations of each segment which completely avoids signal contributions from outside of the desired region-of-interest. With an appropriately adapted sampling density correction, arbitrarily shaped profiles can be excited at high spatial resolutions that are used to acquire MR spectroscopy of anatomically defined voxels in the living human brain.

10:42 0707.   
Three dimensional arbitrary voxel shapes in spectroscopy with sub-millisecond echo times
Jeff Snyder1, Martin Haas1, Iulius Dragonu1, Juergen Hennig1, and Maxim Zaitsev1
1Dept. of Radiology, Medical Physics, University Medical Center Freiburg, Freiburg, Germany

Excitation of arbitrarily-shaped three dimensional voxels in spectroscopy is investigated in vivo in the healthy brain to alleviate voxel geometry restrictions and consequently improve localization of specific regions and decrease partial-volume effects. The technique uses a 3D spatial/spectral excitation scheme in a pulse-acquire type sequence to achieve a broad bandwidth and allow acquisition of the signal in less than 1 ms following the pulse onset. 3D spatial localization is demonstrated with a gradient-echo sequence implementing the specialized pulses, and LCModel analysis is used for spectral evaluation of brain metabolites.

10:54 0708.   Accelerated Spiral Chemical Shift Imaging with Compressed Sensing
Borjan Gagoski1, Berkin Bilgic1, Trina Kok1, and Elfar Adalsteinsson1,2
1Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 24Harvard-MIT Division of Health Sciences and Technology, MIT, Cambridge, MA, United States

The goal of this work is to reduce the acquisition times of the spiral CSI readouts by combining its concepts with compress sensing (CS). We perform random undersampling along the kf axis, by playing spiral k-space trajectories of different durations repeatedly during the long acquisition window. It is shown that for a given voxel size and spectral BW, the combined spiral-CS CSI provided equivalent spectral quality, and a decrease in acquisition times by a factor of 3 when compared to the original spiral CSI encoding. The feasibility of the methods was tested in vivo on a 3T Siemens scanner.

11:06 0709.   
Dramatic speedup in 1D-, 2D- and 3D-MRS scan times with linear algebraic modeling (SLAM)
Yi Zhang1,2, Refaat E. Gabr1, Michael Schär1,3, He Zhu1,4, Peter Barker1,4, Robert G. Weiss1,5, and Paul A. Bottomley1,2
1Division of MR Research, Department of Radiology, Johns Hopkins Univesity, Baltimore, MD, United States, 2Department of Electrical and Computer Engineering, Johns Hopkins Univesity, Baltimore, MD, United States, 3Philips Healthcare, Cleveland, OH, United States, 4F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, 5Division of Cardiology, Department of Medicine, Johns Hopkins Univesity, Baltimore, MD, United States

Scan-time is a central concern for chemical shift imaging (CSI). While model-based MRS reconstruction methods could reduce scan times significantly, their in vivo application is limited and focused on suppressing inter-compartmental leakage. Here, spectroscopy localization with linear algebraic modeling (SLAM) is introduced to dramatically speed-up scan-time. SLAM uses a minimal number of phase-encoding steps that are selected from central k-space, to reconstruct average spectra from pre-selected sample compartments. We demonstrate that SLAM yields essentially the same spectra as compartmentally averaged 1D, 2D and 3D CSI spectra, but 4-, 16- and 100-fold faster, respectively. The signal-to-noise ratio cost was ≤50%.

11:18 0710.   
Lipid Artifact Suppression for Detection of Cortical Metabolites in High-Resolution CTPRESS
Trina Kok1, Berkin Bilgic1, Borjan Gagoski1, and Elfar Adalsteinsson1,2
1Massachusetts Institute of Technology, Cambridge, MA, United States, 2Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States

Changes in cortical metabolites e.g. Glu and Gln are complicated by the spatial proximity of the cortex to the subcutaneous lipid layer. Methods such as outer-volume suppression (OVS) and inversion-recovery effectively suppresses lipid signals but trade off outer cortical brain metabolite signals. Our work combines a recent lipid suppression technique that exploits the approximate orthogonality between lipid and metabolite spectra, with a high-spatial-resolution CTPRESS acquisition in a spiral encoding. Here we demonstrate the successful recovery of cortical metabolites in a high resolution 0.51cc in vivo CTPRESS experiment with total scan-time of 20:32min (Navg = 3).

11:30 0711.   1H MRS in the human spinal cord at 7T using a combined RF shimming and travelling wave transmit approach
Anke Henning1,2, Wouter Koning2, Alexander Fuchs1, Alexander Raaijmakers2, Johanna J. Bluemink2, Erin L. MacMillan1,3, Cornelius A.T. van den Berg2, Peter Luijten2, Peter Boesiger1, and Dennis W.J. Klomp2
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland, 2University Medical Center Utrecht, Utrecht, Netherlands, 3Department for Clinical Research, University of Bern, Bern, Switzerland

Due to its non-invasive nature 1H MRS is of specific benefit to study alterations of biochemical processes in human spinal cord (SC) pathologies where performing biopsies is perilous. However, the finite size and deep location of the human SC limit the obtainable SNR at field strengths < 3T. Hence 1H MRS of the human SC at 7T is introduced to tackle the intrinsic SNR and spectral resolution problems and increase the number of quantifiable metabolites. A dual-channel RF shimming and travelling wave transmit approach is combined with adiabatic inner -volume saturated localization and a 30-channel receive array to obtain optimal SNR.

11:42 0712.   
In vivo GABA T2 determination with J-refocused echo time extension at 7T
Anna Andreychenko1, Dennis W.J. Klomp1, Robin A. de Graaf2, Peter R. Luijten1, and Vincent O. Boer1
1Imaging Division, UMC Utrecht, Utrecht, Netherlands, 2Departments of Diagnostic Radiology and Biomedical Engineering, Yale University, Yale, United States

A method to measure T2 relaxation times when using spectral editing techniques is proposed. A spectrally selective refocusing pulse was incorporated into MEGA-sLASER editing technique to refocus J-modulation of the edited signal at different echo times. In this way the echo time can be arbitrary extended while preserving the shape of the edited signal. The efficiency of the method was demonstrated for in vivo creatine and GABA T2 measurements at 7T.

11:54 0713.   
Optimized diffusion-weighted LASER sequence for single-shot measurement of metabolite diffusion by the trace of the tensor
Charlotte Marchadour1,2, Vincent Lebon1,2, and Julien Valette1,2
1CEA-MIRCen, Fontenay-aux-Roses, France, 2CEA-CNRS URA 2210, Fontenay-aux-Roses, France

One way to characterize intracellular microenvironment regardless of anisotropic organization is the measurement of the trace of the diffusion tensor (Dav) for intracellular metabolites by diffusion-weighted spectroscopy. Here we propose a sequence to measure Dav in a single scan. This sequence consists in two improvements of a previously proposed sequence. First, diffusion gradients are inserted to fill the whole dead time of the sequence. Second, effective gradient amplitude is increased by combining gradients to generate a new set of three orthogonal directions. These two modifications yield a significant multiplication sign2.75 increase of the b-value while keeping echo time unchanged.

12:06 0714.   Sodium MRI on Human Brain at 7T with 15-channel Array Coil
Yongxian Qian1, Tiejun Zhao2, Graham C. Wiggins3, Lawrence L. Wald4, Hai Zheng5, Jonathan Weimer5, and Fernando E. Boada1,5
1Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2R&D, Siemens Medical Solutions USA, Pittsburgh, Pennsylvania, United States, 3Radiology, New York University, New York, New York, United States, 4Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, Massachusetts, United States, 5Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States

Phased array coils have been shown significantly improving SNR in proton imaging over volume coils. This study investigates SNR advantage of a 15-channel array head coil (birdcage volume coil for transmit/receive and 15-channel array insert for receive-only) in sodium imaging at 7T.

12:18 0715.   
Nadia Benkhedah1, Peter Bachert1, Wolfhard Semmler1, and Armin M Nagel1
1Dept. of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

Triple-quantum filtered (TQF) sodium images were proposed to image intracellular sodium ions. However, TQF images suffer from signal to noise ratios (SNR) an order of magnitude lower than normal sodium images. TQF image contrast can be generated by the difference of a tissue sodium concentration weighted image and a single-quantum filtered image acquired in one measurement. The developed method is evaluated on both, phantom and in vivo data. Images generated with this new difference image method show significantly higher SNR and seem to be less sensitive to main magnetic field inhomogeneities.