Changes to Muscle T₂ after Single-finger Exercise Measured with 0.2T MR Imaging

Abstract

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.

Changes in T₂-weighted MRI of supinator muscle, pronator teres muscle, and extensor indicis muscle with manual muscle testing

“…It can be considered that the strength of the manual resistance of the MMT is important. In a previous report12 ) , the MMT for the extensor digiti minimi muscle was applied until the subjects were unable to continue the extension of the digitus minimus. As a result, we detected other muscle activity in the extensor carpi ulnaris muscle that acts to extend and adduct at the carpus, in addition to the extension of the digitus minimus.…”

“…MR images of each forearm were obtained with a 0.2 T compact MRI system (MRTechnology, Tsukuba, Japan) equipped with an oval 1 H solenoidal radiofrequency probe12 ) . The transverse T 2w -MR images were measured using multi-slice spin-echo MR image sequences with a 200 × 200 mm field-of-view, a 128 × 128 data matrix, a 39 ms echo-time with a 2,000 ms repetition time, 11 slices with an interval 10 mm, a 9.5 mm slice thickness, 1 accumulation and a total image acquisition time of 4 min 16 s. Each left forearm was fixed by a shell-type holder of the forearm12 ) , and a T 2w -MR image in the resting condition was measured at first.…”

“…The transverse T 2w -MR images were measured using multi-slice spin-echo MR image sequences with a 200 × 200 mm field-of-view, a 128 × 128 data matrix, a 39 ms echo-time with a 2,000 ms repetition time, 11 slices with an interval 10 mm, a 9.5 mm slice thickness, 1 accumulation and a total image acquisition time of 4 min 16 s. Each left forearm was fixed by a shell-type holder of the forearm12 ) , and a T 2w -MR image in the resting condition was measured at first. Then, manipulative isometric contraction exercise (5 sec duration) was applied to the supinator muscle, the pronator teres muscle or the extensor indicis muscle using Borg’s rating of perceived exertion (RPE) scale of 15–1716 ) .…”

“…), where I R was the SNR for resting muscle. This criterion is almost the same as used in our previous report12 ) .…”

“…Recently, magnetic resonance imaging (MRI) has been used to monitor muscle activities by using the T 1 , T 2 , and water content values of skeletal muscles that increased after muscle exercise7,8,9 ) . Intensive studies have been conducted on the determination of agonist muscles using the increase in T 2 values10, 11 ) , and Takamori detected increases in the T 2 weighted MR (T 2w -MR) image intensity of the extensor digiti minimi muscle after extension exercise of the MP joint of the digitus imnimus12 ) .…”