Fat-corrected T2 measurement as a marker of active muscle disease in inflammatory myopathy.

OBJECTIVE: We sought to improve the utility of T2 measurement as a marker of active muscle disease in patients with idiopathic inflammatory myopathy by correcting for T2 prolongations caused by fatty replacement of muscle that accompnaies chronic muscle damage. SUBJECTS AND METHODS: Twenty-one patients with idiopathic inflammatory myopathy underwent a standardized MRI evaluation of the thighs. Fat fraction maps were calculated from dual-echo gradient-echo images. Fat-corrected T2 maps were generated from multiecho spin-echo images on the basis of a biexponential model that incorporated voxelwise fat fraction estimates. Semiautomated summaries of conventional and fat-corrected muscle T2 values were compared with one another and with standardized visual scores of muscle disease based on T1-weighted spin-echo and STIR images.
RESULTS: Fat-corrected muscle T2 maps showed lower mean values and greater histogram entropy than conventional T2 maps, as analyzed over a standardized portion of the thigh muscles. Conventional and fat-corrected T2 values correlated with visual scores of active muscle disease on STIR images and with the varying intensity of disease depicted with STIR in focal muscle regions.
CONCLUSION: MRI T2 maps of muscle can be corrected for varying fat content by combining the information from chemical shift-sensitive gradient-echo and multiecho spin-echo images. Use of this strategy may prove useful in the study of idiopathic inflammatory myopathy and other diseases characterized by both muscle inflammation and atrophy.