RELATIONSHIP BETWEEN MRI RELAXATION-TIME AND MUSCLE-FIBER COMPOSITION

The relationship between nuclear magnetic resonance relaxation time ob tained with magnetic resonance imaging (MRI) and muscle fiber composit ion of the lateral gastrocnemius was examined in 13 men. There was a p ositive correlation (r = 0.80, P less than or equal to 0.001) between longitudinal relaxation time and the relative percentage of slow-twitc h muscle fibers (type I). There was no relationship between transverse relaxation time and type I percentage (r = 0.17, P = 0.57). These res ults suggest that MRI longitudinal relaxation time can be used for the noninvasive estimation of muscle fiber composition in humans.