Sung-Tak Hong

In vivo Proton Spectroscopy in the Rat Brain at 16.4 T

At ultra-high field, spectroscopy benefits not only from the increased SNR, but also from the increased spectral dispersion which reduces overlapping between different spectral lines and makes quantification easier and more accurate. At 16.4 T, MR-spectroscopy in the rat brain was implemented and optimized.

Goals
A technique for acquisition and analysis of in vivo proton spectroscopy in the rat brain is developed and optimized. In extensive studies, the accuracy, precision and practicability of this method is assessed.

Methods
Using an optimized STEAM sequence with ultra-short echo time and improved water suppression, in vivo spectra from voxels in the rat brain are acquired. Quantification is performed using an improved technique for taking macromolecular signals into account. To assess the quality of the information gained, additional studies investigated the inter- and intra-animal variability, the dependence of quantification precision on the number of averages and differences between different rat strains and brain regions.

Results
The developed technique made it possible to accurately quantify up to 20 metabolites in the rat brain, including acetate and glycine. Comparisons to published data from different field strengths showed a considerably improved accuracy and precision, even at relatively small numbers of averages. High-quality spectra could be obtained from all positions in the rat brain, including difficult regions like the cerebellum and the medulla oblongata, and differences between these structures were detected with high accuracy. Only small metabolic differences were found between rats of different strains.

In vivo proton spectra from different brain regions (hippocampus, thalamus, cerebellum and medulla oblongata). The concentration of up to 20 metabolites was possible in all compartments.

Conclusion
Spectroscopy benefits greatly from the increased SNR and spectral dispersion at ultra-high field. Quantifying up to 20 metabolites with a variability of less than 10%, this technique is capable of measuring a detailed metabolic profile within relatively short times and to detect even small variations in metabolite concentrations, making it a valuable method in preclinical and neuroscientific research, making it possible to detect changes caused by disease or by brain activation with high accuracy.




References
1.     S.-T. Hong, D. Balla, G. Shajan, C. Choi, K. U?urbil, R. Pohmann (2011): Enhanced Neurochemical Profile of the Rat Brain using in vivo 1H NMR Spectroscopy at 16.4 T. .
2.     S.-T. Hong, D. Balla, R. Pohmann (2011): Determination of regional variations and reproducibility in in vivo 1H NMR spectroscopy of the rat brain.
3.     S.-T. Hong, D. Balla, C. Choi, R. Pohmann (2011): Rat-strain dependent variations in brain metabolites detected by in vivo 1H NMR spectroscopy at 16.4 T.