Detection of muscle activity with forearm pronation exercise using T₂-map MRI

[Purpose] We aimed to detect muscle activity during a forearm pronation exercise using a 0.2 T MRI system. [Participants and Methods] We recruited healthy adult volunteers (7 males, 4 females). Transverse relaxation time (T₂) values for 10 forearm muscles were obtained from transverse multiple-spin-echo MR images of one-third of the ulna, lengthwise from the olecranon, in the resting state and after isotonic forearm pronation exercise at three strength levels (5, 15, and 25% of the maximum voluntary contraction). Z values were calculated as (T_2e - T_2r)/SD_r, where T_2e, T_2r and SD_r were T₂ after exercise, 34 ms, and 3 ms, respectively. A Z value of 2.56 was used as the threshold for defining muscle activation. [Results] T₂ values increased significantly in the pronator teres muscle (agonist), while those in the supinator muscle (antagonist) showed no change. The sensitivity and specificity values obtained were high and low, respectively, for all of the three exercise strength levels employed. In some of the participants, activity was detected in the flexor carpi radialis, extensor carpi ulnaris, and extensor digitorum. [Conclusion] Using T₂-map MRI, we detected activity in primary and secondary mover muscles. We also found individual variations in the use of forearm muscles during pronation.