|| Checking for direct PDF access through Ovid
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 aT1 increase of 332 ± 15 to 521 ± 34 ms. Isotopic enrichment after long-term 13C administration was comparable (˜40%) as was the nominal linewidth of glycogen C1 (˜50 Hz). Among the factors that contributed to the 66% observed increase in signal-to-noise ratio, theT1 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.