""""""""Whole-body"""""""" magnetic resonance (MR) scanners operating with main fields that are 2-3 times stronger than those of most existing human instruments (1.5-2.0T) have recently become available for clinical investigations; this laboratory has completed installation of a 4.23 T clinical spectrometer/imager, current the highest field whole-body MR in the U.S. Due to the novelty of these high-field human instruments, a great deal of technological development is still required to fully harness and realize their potential. Therefore, the applicants proposed: (a) To develop and optimize volume selection pulse sequences suitable for high-field 1H spectroscopic imaging (SI) studies of the human brain, with emphasis on overcoming spatial localization errors due to increased spectral dispersion, and (b) to develop efficient methods for automatically processing, analyzing and converting recorded SI spectral amplitudes to absolute metabolite concentrations on a voxel-by-voxel basis. All pulse sequences will employ spatially tailored outer volume suppression (OVS) pulses to achieve 2-D conformal localization of the brain that will eliminate the thin rim of pericranial lipids and tissues, without affecting spins in the region of interest. Full volume localization and spin excitation will then be achieved with a single echo sequence utilizing an orthogonal slice-selective 90 degree and spectrally-selective 180 degree refocusing pulse. Multi-echo and multi-slice version of this sequence will be developed to maximize the efficiency of SI data acquisition. Metabolite relaxation times will be measured and entered into databases, which will subsequently be utilized to efficiently convert SI spectral amplitudes to absolute concentrations, voxel-by-voxel, using cerebral tissue water as an internal concentration standard. Computer software will be developed to automate this conversion of peak amplitudes to molar concentrations. Through the development and optimization of pulse sequences, the applicants proposed to preserve the inherent signal-to-noise advantage of a high field magnet, which can then be exchanges (a) for smaller voxel sizes to allow the study of smaller lesions, tumors or infarcts, or (b) for shorter scan times to minimize cost and patient discomfort. Absolute quantitation of SI data will yield metabolite maps or images in which pixel intensities will represent actual metabolite concentrations. This will standardize results, facilitating comparisons with biochemical data or with results obtained at different sites using different localization sequences or instruments. Finally, automation of metabolite quantitation will make quantitative SI practical for routine clinical use.
