We constructed an arm holder for muscle exercise from a forearm-shaped plastic shell and magnetic resonance (MR) imaging position markers and determined the echo time (39 ms) for T 2 -weighted spin-echo MR imaging from T 2 values of the exercised (50 ms) and resting (32 ms) muscle at 0.2 tesla. The smallest detectable muscle was the extensor digiti minimi muscle (cross-sectional area 25 mm 2 ). This combination could be useful to monitor finger exercise in patients undergoing physical therapy.

Purpose: In order to detect exercised muscles by the increase in T 2 , we have defined a Gaussian T 2 distribution and reference values (T 2 r and SD r ) in resting state muscles, and a threshold for detecting exercised muscles. Methods: The subjects were healthy adult volunteers (14 males and 12 females). Multiple-spin-echo (MSE) MR images were obtained with 10 TE values from 10 to 100 ms using a 0.2T MRI system. T 2 values for 10 forearm muscles were obtained in the resting state and after isometric wrist flexion exercise with 5%, 15%, and 25% of the maximum voluntary contraction (MVC). Z values were obtained by (T 2 e − T 2 r )/SD r , where T 2 e was T 2 after exercise. Based on sample size calculations, three thresholds ( Z T = 1.00, 2.56, and 3.07) were applied to agonist and antagonist muscles. Results: A normal distribution of T 2 was detected in resting muscles at 34 ± 3 ms (mean ± standard deviation [SD]) in 26 subjects using the Kolmogorov–Smirnov test, the Shapiro–Wilk test, and the Jarque–Bera test ( P > 0.05). No gender differences were shown between the T 2 or SD, and a similar result was obtained in 12 measurements on a single subject ( P < 0.01). The T 2 r and SD r were used for reference values. The threshold Z T = 1.00 showed the highest sensitivity (0.86) even with 5% MVC, but it showed a lower specificity (0.85) than the other thresholds. Z T = 3.07 showed the highest specificity (1.0), but it showed a lower sensitivity (0.36) with the 5% MVC, compared with Z T = 2.56 (0.50). The receiver operating characteristics analysis also supported these results. Conclusion: We found that the T 2 distribution in muscles was Gaussian, suggesting that a one-sample t -test can be applied, and that Z T = 2.56 could cover low-intensity exercise with high specificity and a low false-positive rate.

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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 (T 2 ) 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 T 2 after exercise, 34 ms, and 3 ms, respectively. A Z value of 2.56 was used as the threshold for defining muscle activation. [Results] T 2 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 T 2 -map MRI, we detected activity in primary and secondary mover muscles. We also found individual variations in the use of forearm muscles during pronation.

[Purpose] In order to detect muscle activity with manual muscle testing, T2-weighted magnetic resonance (T2w-MR) images were detected by a 0.2 T compact MRI system. [Subjects and Methods] The subjects were 3 adult males. Transverse T2-weighted multi-slice spin-echo images of the left forearm were measured by a 39 ms echo-time with a 2,000 ms repetition time, a 9.5 mm slice thickness, 1 accumulation and a total image acquisition time of 4 min 16 s. First, T2w-MR images in the resting condition were measured. Then, manipulative isometric contraction exercise (5 sec duration) to the supinator muscle, the pronator teres muscle or the extensor indicis muscle was performed using Borg’s rating of perceived exertion (RPE) scale of 15–17. The T2w-MR images were measured immediately after the exercise. [Results] T2w-MR image intensities increased significantly in the supinator muscle, the pronator teres muscle and the extensor indicis muscle after the exercise. However, the image intensities in the rest of the muscle did not change. [Conclusion] Using T2w-MR images, we could detect muscle activity in a deep muscle, the supinator muscle, and a small muscle, the extensor indicis muscle. These results also support the reliability of the manual muscle testing method.