IMAGING OF PHOSPHOENERGETIC STATE AND INTRACELLULAR PH IN HUMAN CALF MUSCLES AFTER EXERCISE BY P-31 NMR-SPECTROSCOPY

Phosphoenergetic and pH images in human calf muscles before and after ischemic exercise were generated by P-31 NMR chemical shift imaging (C SI) with a 1.5 T standard clinical MR machine using a home-built volum e coil. Acquisition of data was repeated four times with 8 x 8 phase-e ncoding steps and Is repetition time. The total acquisition time was 4 min 16 s. After 3-dimensional (3D) Fourier transformation with zero-f illing, 2-dimensional (2D) images with 32 x 32 matrices of phosphocrea tine (PCr), inorganic phosphate (Pi), PCr/(PCr + Pi) and pH were const ructed. These metabolic images were overlaid with concurrently observe d H-1 MRI to locate the areas showing metabolic response. After 3 min exercise consisting of repeated plantarflexion of the foot under ische mic conditions, decreases in phosphoenergetic levels and acidosis were the most severe in the peroneus muscles, moderate in the tibialis ant erior muscle, and slight in the triceps muscle of the calf. Under main tained ischemic conditions, phosphoenergetic level further decreased, but the acidosis in each muscle did not progress further. Heterogeneou s metabolic and pH changes throughout the entire calf muscle were clea rly demonstrated in detail by these images.