The National Institute of Arthritis and Musculoskeletal Skin Diseases has an ongoing protocol to study polymyositis. As part of this protocol, subjects are imaged with magnetic resonance imaging using a special pulse sequence to suppress signal from fat but enhance signal from diseased tissue. In the past, the images were usually evaluated visually to determine the extent and progress of disease. A more quantitative method for analysis has been developed and is being tested. This method produces a three-dimensional histogram of signal intensity values. In normal subjects, this histogram is nearly Gaussian in shape, while in abnormal subjects this histogram is skewed to higher intensity values. A method was developed that could give quantitative indices of both degree of disease and volume of diseased tissue. This method is based on the assumption that the low signal intensity values within the tissue being studied represent normal tissue. The left half of the histogram is then reflected about its peak to approximate how the subject's normal histogram might have looked. Comparing the reflected histogram with the actual histogram allows the degree and volume of disease to be estimated. Study of this method is now complete and was presented orally at the Society of Magnetic Resonance Imaging. A manuscript describing the method is in preparation. The collaborating institute is now testing the method on human subjects as part of its own protocol.
