CORE PROJECT I: SPECTROSCOPIC METHODS

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1H MRSI allows one to obtain metabolic maps of different brain compounds such as N-acetyl aspartate, creatine, choline compounds, lactate, and glutamine. By the implementation of improved acquisition techniques it has been possible to further improve the spatial resolution of these metabolite maps. By using a broad-band water/fat suppressing refocusing pulse in the measuring sequence the SNR (signal-to-noise ratio) has been improved. The use of a shorter recycle delay TR allows one to collect larger data sets, for a improved spatial resolution. With this approach it has been possible to obtain 1H MRSI data sets with a spatial resolution of 0.175 cc. This improved spatial resolution is especially important for the examination of stroke patients, and of temporal lobe epilepsy. Further improvements of the 1H MRSI technique are underway, in particular multislice capabilities to cover a larger part of the brain.  The high-contrast T1 weighted 1H MR images obtained at 4.1T allows one to segment the images in gray and white matter. This information has been used to determine the gray/white matter contribution to individual voxels of 1H MRSI measurements, and this information has been used to obtain separate measurements of metabolite ratios and concentrations of gray and white matter, This image segmentation approach has been applied to 31P data sets, to obtain measurements of PCr/ATP, and PCr/Pi for gray and white matter as well The TCA cycle activity can be measured in the human brain, by monitoring the appearance to the 13C label in the brain glutamate pool, following infusion with [1-13C]-glucose. These measurements have been extended, as to obtain separate measurements of the TCA cycling rate of gray and of white matter. Homonuclear editing techniques have been further improved, to uncover hidden resonances in the 1H MRS spectrum of the human brain, in particular to observe GABA, and glutamate. Contributions from macro molecules to the GABA resonance has been reduced, by the use of an improved editing pulse. These techniques are being used to follow GABA levels in epilepsy patients, who are on anti-seizure medication.