AbstractT1ρdispersion, or the frequency dependence of T1relaxation in the rotating frame, was used forin vivomuscle tissue characterization in 13 patients with primary skeletal muscle disease and in eight normal subjects for comparison. T1ρdispersion measurements represent a new approach to magnetic resonance tissue characterization, possibly reflecting the macromolecular constituents of tissue. A definite, statistically significant, difference was found between the relative T1ρdispersion values of normal and diseased muscle tissue. T1ρdispersion measurements and images may increase the accuracy of identification of diseased muscles. Early identification of affected muscles is important for accurate diagnosis by muscle biopsy.