T1 and T2 Metabolite Relaxation Times in Normal Brain at 3T and 7T

Abstract

This study was designed to measure T1 and T2 relaxation times of the singlets in normal brain at 7T. Our results demonstrated that the T1 relaxation values of total creatine (tCr)-CH3 and N-acetyl aspartate (NAA) in the parietal white matter significantly increased at 7T compared to 3T, while the T1 of Choline-containing compounds (Cho) was similar between field strengths. T2 values of all metabolites investigated were significantly shorter at 7T. To compare signal-to-noise ratio (SNR) values between different field strengths, data were corrected for the effects of T1 and T2 relaxation. The average SNR ratio between 7T and 3T was 1.6. The increase in peak height SNR was less than linear with respect to B0, primarily due to the differences in linewidth. The average linewidth of tCr-CH3 in TE-averaged spectra was 18.62 Hz while it was 8.38 Hz in the single echo time using spectral-spatial RF pulses at 7T. The Cramer-Rao lower bounds (CRLBs) of metabolites were much lower at 7T compared to 3T. These data are important for the optimization of acquisition parameters for future spectroscopy studies in clinical applications at 7T.