MRS Methodology
Monday 20 April 2009
Room 315 16:30-18:30

Moderators:

 Gabriele R. Ende and Malgorzate Marjanska
 
16:30  130. BISEP-Based, Ultra-Short TE 1H–[13C] NMR Spectroscopy of the Rat Brain at 14.1 T
   

Lijing Xin1, Bernard Lanz1, Hanne Frenkel1, Rolf Gruetter1,2
1Laboratory of functional and metabolic imaging, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland; 2Department of Radiology, University of Lausanne , Lausanne, Switzerland
    Indirect detection of 13C label through proton offers higher sensitivity but suffers from lower spectral resolution, such as the GluC3 and GlnC3 region. A novel 1H-[13C] sequence combining SPECIAL localization and BISEP pulse was proposed and applied in vivo during infusion of the glia-specific substrate - [2-13C] acetate at 14.1T. The results showed the separate measurement of GluC4, GlnC4, GlnC3 and GluC3 time courses with high temporal resolution at 14.1T, which greatly enhanced the ability to study neuron-glial metabolism using 1H-[13C] NMR spectroscopy.
     
16:42 131. High Acceleration 3D Compressed Sensing Hyperpolarized 13C MRSI of a Transgenic Mouse Model of Liver Cancer
    Simon Hu1,2, Asha Balakrishnan3, Michael Lustig4, Peder E Z Larson1, Robert Bok1, John Kurhanewicz1,2, Sarah J. Nelson1,2, John M. Pauly4, Andrei Goga3, Daniel B. Vigneron1,2
1Dept. of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA; 2UCSF & UCB Joint Graduate Group in Bioengineering, San Francisco, CA, USA; 3Dept. of Medicine, Division of Hematology/Oncology, University of California, San Francisco, CA, USA; 4Dept. of Electrical Engineering, Stanford University, Stanford, CA, USA
    Hyperpolarized technology has enabled rapid in vivo 13C spectroscopic imaging at high SNR. Acquisition time limitations due to rapid hyperpolarized signal loss make accelerated imaging methods, such as compressed sensing, extremely valuable. In this project, we developed a 3.4-fold accelerated compressed sensing 3D-MRSI sequence and acquired hyperpolarized spectra in a transgenic mouse model of liver cancer, observing elevated lactate and alanine in tumors at a 0.034 cm3 spatial resolution. We also developed a 7.5-fold accelerated sequence, which we validated in simulations and phantom experiments and applied to prostate cancer mice to achieve 4-fold resolution enhancement in approximately half the acquisition time.
     
16:54 132. Cost Function Guided 3rdorder B0 Shimming for MR Spectroscopic Imaging at 7T
    Jeroen Cornelis Willem Siero1,2, Vincent Oltman Boer2, Johannus Marinus Hoogduin1,2, Peter R. Luijten2, Dennis W. Klomp2
1Brain Division, University Medical Center Utrecht, Utrecht, Netherlands; 2Radiology, University Medical Center Utrecht, Utrecht, Netherlands
    A novel shimming method was developed for finding optimal shim fields that minimize B0 inhomogeneities on a user-defined region of interest while confining the B0 inhomogeneities outside this ROI. Experiments show that employing this shimming approach, chemical shift imaging (CSI) can be obtained without baseline distortions while maintaining a narrow spectral line width.
     
17:06 133. Higher Order B0 Shimming of the Human Brain at 7T
    Hoby Patrick Hetherington1, Andrey M. Kuznetsov1, Nikolai I. Avdievich1, Jullie W. Pan1
1Neurosurgery, Yale University, New Haven, CT, USA
    Ultrahigh field systems (7T), offer significant advantages for spectroscopic imaging studies of the human brain. Although excellent B0 homogeneity is a requisite for SI, the hardware requirements in terms of shim strength and shim order necessary for 7T is controversial, with the majority of systems delivered having only 2nd order shims. The goal of this work was to: 1) determine the role of 3rd order shims for SI studies at 7T in two representative regions (the frontal and temporal lobes); 2) characterize the remaining inhomogeneity and 3) demonstrate high resolution spectroscopic imaging in the frontal and temporal lobes.
     
17:18  134. A Comparison of Two Phase Correction Strategies in Multi-Channel MRSI Reconstruction
    Wei Bian1, Jason C. Crane1, Wonjoon Sohn2, Ilwoo Park1,3, Esin Ozturk-Isik1, Sarah J. Nelson1,3
1Radiology, University of California San Francisco, San Francisco, CA, USA; 2Computer Science, University of California Berkeley, Berkeley, CA, USA; 3Program in Bioengineering, University of California San Francisco, San Francisco, CA, USA
    Two phase correction strategies for the reconstruction of multi-channel MRSI were compared in this study. The first is to find the optimal phase for voxels from each channel prior to coil combination. The second is to determine the optimal phase from the sum of the spectra from the central 8 voxels from each channel, and then applying this phase to all voxels in that channel prior to coil combination. Results from phantom and glioma patient experiments showed that the first strategy yielded a slightly improved phase correction for high SNR data but the second was more robust and accurate for the clinical relevant flyback echo-planar encoding data.
     
17:30 135. High Resolution 31P Magnetic Resonance Spectroscopic Imaging with Polarization Transfer of Phosphomono and -Diesters in the Human Brain at 3T
    Jannie Petra Wijnen1, Tom W.J. Scheenen1, Arend Heerschap1
1Radiology, Radboud University Nijmegen Medical Centre, Nijmegen, Gelderland, Netherlands
    (Glycero)phosphocholine and (glycero)phosphoetanolamine are important substances in membrane metabolism, and can be detected in the brain by 31P MRS. We have developed a spectroscopic imaging sequence with efficient 1H to 31P polarisation transfer, optimized for the signals of PE, PC, GPE and GPC by using chemical shift selective refocusing pulses. Here we present the first results of the ratios of these compounds in the cerebellum, white matter and gray matter of the normal human brain at different ages.
     
17:42 136. 31P Exchange Sensitive Imaging in Human Brain at 7T
    Jullie W. Pan1,2, Nikolai Avdievich1, Dennis Spencer1, Hoby P. Hetherington1,3
1Neurosurgery, Yale University School of Medicine, New Haven, CT, USA; 2BME, Yale University School of Medicine, New Haven, CT, USA; 3Radiology, Yale University School of Medicine, New Haven, CT, USA
    As a functional measure of bioenergetic state in human brain, 31P MRS is sensitive to effects of relaxation, concentration and chemical exchange. While the sensitivity to creatine kinase has been well used in muscle spectroscopy with saturation transfer experiments it has been less developed for brain. Given that creatine kinase rates have demonstrated sensitivity to physiologic condition it may be informative for pathologic state. We implemented exchange sensitive weighting to the 31P spectroscopic imaging acquisition, parameters based on 3site exchange simulations to ascertain sensitivity to varying levels of exchange. We demonstrate this approach in controls and epilepsy patients at 7T.
     
17:54 137. Improved 31P Saturation Transfer Approach for Imaging Cerebral ATP Metabolic Rates In Vivo
    Xiao-Hong Zhu1, Qiang Xiong1,2, Yi Zhang1, Wei Chen1,2
1CMRR, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, USA; 2Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA
    The cerebral ATP metabolism plays a central role in neuroenergetics for supporting brain energy and function. The approach of combining in vivo 31P MRS with magnetization saturation transfer (ST) is useful for noninvasively determining the cerebral metabolic rates of ATP involving ATPase reaction (CMRATP) and CK reaction (CMRCK). However, the conventional ST measurement requires a fully relaxed condition before the frequency-selected γ-ATP saturation for precise quantification of flux, resulting in a long repetition time (TR) and low efficiency. This poses a major hurdle for 3D CSI application in which many scans are needed. In this study, we implemented a newly developed ST strategy, which can achieve the same saturation transfer effect with a much short TR, with 3D 31P CSI for imaging CMRATP and CMRCK in animal at 9.4T with high efficacy.
     
18:06 138. Dual Band Water and Lipid Suppression for Multi-Slice MRSI of Human Brain at 3T
    He Zhu1,2, Ronald Ouwerkerk1, Richard A.E. Edden1,2, Michael Schär1,3, Peter B. Barker1,2
1Russell H Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Maryland, MD, USA; 2F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Maryland, MD, USA; 3Philips Healthcare, Cleveland, OH, USA
   

A dual band water and lipid suppression sequence was developed for in vivo multi-slice MRSI of the brain. This pre-pulse sequence consists of five frequency modulated pulses with variable delay times and flip angles. Both timing and flip angle parameters were optimized via simulations to suppress water and lipid signals simultaneously. Outer volume suppression pulses were integrated into the sequence to improve lipid suppression, particularly for lipid resonances outside of the dual-band suppression bandwidth. Experimental results at 3T show comparable water suppression performance to the longer VAPOR sequence, and excellent lipid suppression factors.
   

 
18:18 139.

In Vivo Cross-Relaxation in ATP in Skeletal Muscle Measured by 31P Saturation Transfer MRS
    Christine Nabuurs1, Bertolt Huijbregts1, Andor Veltien1, Be Wieringa2, Cees Hilbers3, Arend Heerschap1
1Radiology, Radboud University Nijmegen Medical Center, Nijmegen, Netherlands; 2Cellbiology, Radboud University Nijmegen Medical Center, Nijmegen, Netherlands; 3Physical Chemistry, Radboud University, Nijmegen, Netherlands
   

ATP involvement in multiple enzymatic exchange reactions has been extensively studied by 31P saturation transfer (ST) MR spectroscopy. So far, however, little attention has been paid to in vivo 31P-31P cross-relaxation processes possibly interfering in the analysis of the exchange rates. Here we performed 31P ST experiments on hind-limb muscle of mice with deficiencies in adenylate and creatine kinase. In these conditions the enzyme contributions to exchange effects can be excluded and cross relaxation contributions to ST effects observed. However, in experiments on ATP, free in solution, cross relaxation effects did not become manifest. This was corroborated by theoretical calculations. These results indicate that in vivo ATP is involved in the formation of short lived complexes where cross relaxation is effective and saturation effects can be can be transferred to the free ATP.