This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Recently we proposed a method for imaging glycogen by MRI through the interaction of the OH protons of glycogen with the water protons which can be measured using magnetization transfer. Briefly, the exchangeable protons (OH) in the glycogen molecule can be selectively irradiated with the correct proton NMR frequency. Because of the fast chemical exchange with water protons, this spin label can be detected through the water line, and hence through the conventional MRI experiment. Like other magnetization transfer experiments, the key is to compare the bulk water signal in the presence of irradiation of the OH protons of glycogen with the bulk water signal at the opposite frequency with respect to the water resonance. The exchange of the OH protons in glycogen can be detected as a significant difference between the normalized water signal intensities obtained by irradiating at these two frequencies. More sophisticated approaches are also feasible. For example, instead of using the minimum of two frequencies, a full Z-spectrum can be obtained. The asymmetry in the z spectrum can be attributed to exchangeable OH groups. Noninvasive measurement of glycogen is an integral part of profiling the metabolic state in vivo. While many studies have reported detection of glycogen, there are limited reports that have focused on its quantification. Furthermore, the expanded use of 7T whole body scanners requires optimization of the glycogen acquisition protocols for this particular field. We will investigate three different approaches for glycogen detection and quantification at 7T: direct 13C MRS, glycocest and direct proton MRS. A half-cylinder transmit-receive surface coil with radius of 13-cm was used for all studies. The coil runs in quadrature for both 1H and 13C.
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