A comparison of in vivo 13C MR brain glycogen quantification at 9.4 and 14.1 T

The high molecular weight and low concentration of brain glycogen render its noninvasive quantification challenging. Therefore, the precision increase of the quantification by localized 13C MR at 9.4 to 14.1 T was investigated. Signal-to-noise ratio increased by 66%, slightly offset by a T1 increase of 332 +/- 15 to 521 +/- 34 ms. Isotopic enrichment after long-term 13C administration was comparable (similar to 40%) as was the nominal linewidth of glycogen C1 (similar to 50 Hz). Among the factors that contributed to the 66% observed increase in signal-to-noise ratio, the T1 relaxation time impacted the effective signal-to-noise ratio by only 10% at a repetition time = 1 s. The signal-to-noise ratio increase together with the larger spectral dispersion at 14.1 T resulted in a better defined baseline, which allowed for more accurate fitting. Quantified glycogen concentrations were 5.8 +/- 0.9 mM at 9.4 T and 6.0 +/- 0.4 mM at 14.1 T; the decreased standard deviation demonstrates the compounded effect of increased magnetization and improved baseline on the precision of glycogen quantification. Magn Reson Med, 2011. (c) 2011 Wiley Periodicals, Inc.