Muscle Fat-Fraction and Mapping in Duchenne Muscular Dystrophy: Evaluation of Disease Distribution and Correlation with Clinical Assessments. A Preliminary Experience

PURPOSE To examine the usefulness of dual-echo dual-flip angle spoiled gradient recalled (SPGR) MRI technique in quantifying muscle fat infiltration of pelvic and thighs muscles as a marker of disease progression in boys with Duchenne muscular dystrophy (DMD). We also tried to identify characteristic patterns of disease distribution. METHOD AND MATERIALS Following ethics approval, written informed consent of all patients was obtained. Twenty consecutive boys with DMD were recruited at Neuromuscular Disorders Center of our University for evaluation. Spin density- and T1-weighted fast-SPGR in- phase/opposed-phase (IP/OP) dual-echo sequences were obtained respectively with 20° and 80° flip-angle values. All patients were evaluated with dual-echo dual-flip angle SPGR MRI technique, calculating muscle fat fraction (MFF) of 8 muscles in pelvic girdle and thigh, and clinically (patient age, clinical function score, timed Gower score, time-to-run 10 meters). Color-coded parametric maps of MFF were also obtained. The relationships between mean MFF and clinical assessments was investigated using Spearman’s rho coefficient. Positive and negative correlations were evaluated and considered significant if the P value was < .05. RESULTS The highest mean MFF was found in the gluteus maximus (mean, 46.3 % ± 24.5 [standard deviation, SD]), whereas the lowest in the gracilis muscle (mean, 2.7 % ± 4.7 SD). Mean MFF of the gluteus maximus was significantly higher than that of the other muscles (P < 0.01), except for the adductor magnus and biceps muscles. A significant positive correlation was found between the mean MFF of all muscles and the patients age (20 patients) (P < 0.005), clinical function score (19 patients) (P < 0.001), timed Gower score (17 patients) (P < 0.03), and time-to-run 10 meters (20 patients) (P < 0.001). A positive correlation was also found between mean MFF of gluteus maximus muscle and timed Gower score. Color-coded maps provided an efficient visual assessment of muscle fat content and its heterogeneous distribution. CONCLUSION MFF calculation and mapping obtained with dual-echo dual-flip angle SPGR MRI technique is useful to evaluate the degree and pattern of distribution of muscle fatty infiltration in patients with DMD.