Abstract
OBJECTIVE: To evaluate healthy skeletal muscle pre- and post-exercise via 7 T (23)Na MRI and muscle proton T(2) mapping, and to evaluate diabetic muscle pre- and post-exercise via 7 T (23)Na MRI. METHODS: The calves of seven healthy subjects underwent imaging pre- and post-exercise via 7 T (23)Na MRI (3D fast low angle shot, TR/TE = 80 ms/0.160 ms, 4 mm x 4 mm x 4 mm) and 1 week later by (1)H MRI (multiple spin-echo sequence, TR/TE = 3,000 ms/15-90 ms). Four type 2 diabetics also participated in the (23)Na MRI protocol. Pre- and post-exercise sodium signal intensity (SI) and proton T(2) relaxation values were measured/calculated for soleus (S), gastrocnemius (G), and a control, tibialis anterior (TA). Two-tailed t tests were performed. RESULTS: In S/G in healthy subjects post-exercise, sodium SI increased 8-13% (p < 0.03), then decreased (t(1/2) = 22 min), and (1)H T(2) values increased 12-17% (p < 0.03), then decreased (t(1/2 )= 12-15 min). In TA, no significant changes in sodium SI or (1)H T(2) values were seen (-2.4 to 1%, p > 0.17). In S/G in diabetics, sodium SI increased 10-11% (p < 0.04), then decreased (t(1/2) = 27-37 min) without significant change in the TA SI (-3.6%, p = 0.066). CONCLUSION: It is feasible to evaluate skeletal muscle via 3D (23)Na MRI at 7 T. Post-exercise muscle (1)H T(2) values return to baseline more rapidly than sodium SI. Diabetics may demonstrate delayed muscle sodium SI recovery compared with healthy subjects.