Clinical magnetic resonance spectroscopy: Technical development and application to the study of ischemia

The dependence of levels of phosphocreatine (PCr) on work and the rate of recovery of PCr concentrations after work can be used to determine the Michaelis Menten constants of the mitochondria. Information from steady state and recovery measurements can be combined to obtain an efficiency parameter describing the work done as a function of the ATP utilized. The precision with which time constants for PCr recovery after exercise can be extracted from experimental recovery data depend on the noise of the data, the extent of depletion of the PCr before the onset of recovery, and the length of time the recovery data is collected. The precision of the time constant as a function of these parameters was determined by propagation of error analysis. Localization of the spectroscopic signal is possible with the steady state approach. Implementation of the Hadamard method of spectroscopic localization on a Signa scanner is described. A double tuned birdcage coil for improved localization has been developed which acquires H-1 images and P-31 spectra with homogeneity and signal to noise comparable to that of single tuned volume coils. The optimization criteria for designing the double tuned birdcage are described. Recovery rates of PCr after exercise have been determined for claudicants with peripheral vascular disease. The time constants were evaluated in a double blind crossover study before and after treatment with oral L-carnitine over a one month period. The relative uncertainty of time constant determination due to the effects of noise on P-31 spectra was determined to be 11% as opposed to the relative uncertainty due to drug independent variation of time constant values which was determined to be 35%. No statistically significant effect of L-carnitine on recovery rates was observed when ten patients were studied