Magnetic resonance imaging of the normal and pathologic muscular system

Evaluation of the muscular system with magnetic resonance (MR) was conducted: (1) to assess the capability of MR to depict muscular abnormalities; (2) to evaluate the ability of MR to discriminate between various types of muscular pathologies based on relaxation parameters; and (3) to determine the optimal spin echo (SE) sequence that produced optimal contrast. Retrospective analysis was performed on 59 consecutive patients with a variety of muscular abnormalities. MR muscle analysis included visual inspection of contour and size; muscle intensity changes in relation to various TR/TE combinations; measurement of T1 and T2 relaxation and spin density; and calculation of percent contrast variation with different SE imaging combinations. Contour and size abnormalities were not reliable for detection of muscular pathology. For each individual subject intensity and relaxation times of all muscles involved by pathology differed from normal muscle. Although all pathologies caused increase in signal intensity of muscle, the alterations in relaxation times were variable. Fatty atrophy caused a decrease in T1 and increase in T2; while post-surgical changes, infection, acute intramuscular hemorrhage, and tumor invasion caused an increase in both T1 and T2. Percent contrast indicated that the optimum sequence for evaluation of fatty atrophy was a short (0.5 sec) repetition time (TR) and echo delay time (TE) of 56 msec, while for demonstration of the remaining muscular abnormalities, including post-surgical changes, infection, acute intramuscular hemorrhage, and tumor invasion, a long TR (TR = 2.0 sec) and TE (56 msec) was optimal. Differentiation between various benign and malignant muscular abnormalities (excluding fatty atrophy) was not possible using either quantitative intensity values or relaxation times.