Magnetic resonance spectroscopy and imaging of muscle--a physiological approach

Magnetic resonance spectroscopy (MRS) and imaging (MRI) are now well established techniques for the study of cellular metabolism and gross structure of muscle. Using non-ferrous materials, we have constructed a system for the measurement of isometric force of quadriceps in response to percutaneous electrical stimulation and voluntary effort within the bore of a 48 cm diameter 1.5 T General Electric SIGNA whole body MR system. Using this system we have been able to study the relationship between electromechanical coupling and chemistry of muscle, with 31P MRS for the measurement of high-energy phosphates and pH, during electrically stimulated activity. Image analysis using the Context Vision system enables a distinction to be made, in 1H MRI by T1/T2 mapping, of muscle, fat and connective tissue to give force per unit cross sectional area of muscle. The combination of MR and functional measurements provide a valuable tool for further detailed analysis of human muscle weakness and fatigue.