Clinical utility of muscle MR spectroscopy.

31Phosphorus (31P) magnetic resonance spectroscopy (MRS) is well suited for gathering data on skeletal muscle energetics in vivo. The technique has evolved to the point where it has become an important tool in the study of the pathophysiology both of rare primary disorders of muscle such as the mitochondrial myopathies and of more common systemic diseases such as renal failure, which also influence muscle metabolism. 31P-MRS is used for providing information about the biochemical composition of tissue without invasive sampling, and it has the unique ability to measure intracellular pH. In some conditions it can be used as an aid to diagnosis. Because MRS is well tolerated and examinations are easily repeated, the technique can also be employed in longitudinal studies of disease progression or the effects of treatment. Magnetic resonance spectroscopy is being increasingly used in conjunction with other noninvasive technologies to investigate effects of gene function on metabolism.