Mapping of electrical muscle stimulation using MRI.

The purpose of this study was to map the pattern of muscle contractile activity elicited by electromyostimulation (EMS). A secondary interest was to determine whether EMS evoked a different pattern of contractile activity than voluntary (VOL) efforts. These objectives were addressed by examining the pattern and extent of contrast shift in magnetic resonance (MR) images after isometric actions of the left m. quadriceps of seven subjects had been elicited by EMS (1-s train of 500-microseconds sine wave pulses at 50 Hz) or by VOL means. For both conditions, five sets of 10 muscle actions were executed at each of the three force levels equal to 25, 50, and 75% of maximal VOL isometric torque. There were 1-s, 1.5-min, and 30-min rests between muscle actions, sets, and torque levels, respectively. Transaxial proton MR images (TR/TE = 2,000/30, 60) of m. quadriceps femoris were obtained with a 1.5-T imager at rest and after completion of the five sets of isometric actions at each force level. MR image contrast shift, as indicated by T2 values > 1 SD above the mean resting muscle T2, was calculated per pixel. Torque declined approximately 18% (P < 0.05) during each EMS set independent of the preset relative force level but recovered between sets. EMS increased T2 values above rest (29 +/- 0.2 to 36 +/- 0.5, P < 0.05) in regions of muscle dispersed throughout a given cross section. The pattern of muscle stimulation, as reflected by increased T2 values, varied markedly among subjects.(ABSTRACT TRUNCATED AT 250 WORDS)