Measurement of enzymatic rates in humans

This thesis describes the development of an analysis method for data acquired using magnetic resonance (MR) techniques for the measurement of enzymatic rates in humans. We will evaluate aspects and compare the practicality of magnetization transfer experiments available to us for the study of enzyme kinetics. As an example we measure the creatine kinase reaction in human skeletal muscle. We discuss problems which are inherent in the MR techniques as well as in the system we chose to study. While theoretical analyses of magnetization transfer (MT) techniques have been determined to be valid (Forsen & Hoffman 1964, and our own unpublished results), only the saturation transfer technique has been validated in an in vivo system (Friedrich et al. 1993). We demonstrate that MT methods do not always yield accurate kinetic measurements. This failure, in the case of the saturation transfer method, is due to the introduction of unavoidable incomplete saturation. Here we derive, from theory, a modified approach for the analysis of this saturation transfer data. We demonstrate how this new method works on non-ideal saturation transfer data from human skeletal muscle with incomplete saturation of the $\gamma$P-ATP resonance. The problem of incomplete saturation is further complicated by inhomogeneous B$\sb1$ fields. A saturation pulse used with a surface coil to observe a large sample volume yields a saturation which is not constant throughout the sample volume. While we can correct for errors arising from an incomplete saturation produced within homogeneous B$\sb1$ fields, it is not trivial nor may it be possible to provide a full correction for errors arising from apparent incomplete saturation produced because of an inhomogeneous B$\sb1$ field. While the correction for incomplete saturation derived in chapter 2 is valid for homogeneous B$\sb1$ fields, it can be used as an approximate correction for saturation transfer data acquired with inhomogeneous B$\sb1$ fields