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

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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.

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