Accurate Quantification in Physiologic Phosphorus MR Spectroscopy

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We find that alternations in data acquired at alternating flip angles from the perfused rat heart are eliminated by the O-DAM correction. Corresponding simulations demonstrate that accurate saturation correction can be performed when metabolite changes are modest. Using typical parameters, we find that, as expected, greater degrees of accuracy can be achieved for smaller fractional changes in PCr. A decrease in PCr of less than 12% permits accuracy in PCr/Pi measurement to within 20%. For TR = 2 s, PCr can decrease by over 50% with accuracy of the corrected ratio remaining within 20%. Simulation of an ischemia-reperfusion experiment indicates the high degree of accuracy obtainable except at times of rapid concentration changes. Thus, the O-DAM procedure may permit accurate monitoring of metabolite concentrations even in the setting of chemical exchange and T1 changes. In addition, due to the ability to more accurately quantify PCr recovery after the cessation of stress, the O-DAM method permits a more accurate measurement of the time constant for metabolic recovery, a widely-used marker for mitochondrial synthetic capability. We are also performing extensive dynamic 31P exercise studies in the BLSA population too develop bioenergetic correlates of aging, walking speed, and other outcome measures from the BLSA.