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Zusammenfassung:
In vivo 1H MR spectroscopy allows the quantification of various metabolites and neurotransmitters in the brain. We used high magnetic field (7 T) and a combination coil setup to improve signal strength and spectral dispersion. An anaesthetized monkey preparation guaranteed stable physiological conditions over hours without any movement artifacts. Detailed controls and adjustments of the MR setup enabled us to acquire MR spectra from a brain region as thin as the primary visual cortex (V1) of a macaque monkey (cortical thickness: 1.6-1.8 mm). The shimming problem of the curved cortex in direct vicinity of the cranial bone was accessed by quantitative field mapping and solved by a dedicated shimming strategy (Juchem, 2004, ISMRM Proc). Linewidths of 11.5-12.5 Hz for water and 10-11 Hz for the creatine+phosphocreatine (Cr+PCr) resonance at 3 ppm were reproducibly achieved in a 5x1.6x5 mm3 (40 µL) spectroscopy voxel placed into pure V1 gray matter tissue.
The data quality from 1280 acquisitions (64 min) was high enough to quantify more than 10 metabolites: N-acetylaspartate (NAA), Cr, PCr, glutamate (Glu), myo-inositol (Ins), glutathione, aspartate, γ-aminobutyric acid (GABA), glutamine (Gln), and choline-containing compounds (Cho). Notably, Glu and Gln could be separated, as well as Cr from PCr and GABA was above the detection limit.
It is now possible to resolve the neurochemical content of discrete cortical areas with minimized partial volume from other brain regions using 1H MR spectroscopy. The application of this method will lead to a better understanding of neurochemical changes as a function of sensory stimulation and cortical reorganization.
