T₂ Distribution in the Forearm Muscles and the T₂ Threshold for Defining Activated Muscle

Abstract

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.

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

“…Ten muscles were assigned using a T 2w -MR image in comparison with an MRI atlas of the human forearm (Fig. 1A) 4,7) : including the pronator teres muscle (PT) (agonist muscle), the supinator muscle (SM) (antagonist muscle), the flexor carpi radialis muscle (FCR), the flexor carpi ulnaris muscle (FCU), the palmaris longus muscle (PL), the flexor digitorum superficialis muscle (FDS), the flexor digitorum profundus muscle (FDP), the extensor carpi radialis longus/brevis muscle (ECU), the extensor carpi ulnaris muscle (ECR) and the extensor digitorum muscle (ED). In each of the T 2 -map images, the ROIs with 16 pixels (9.8 mm 2 ) were set near the center of the muscle, but we excluded visible fat tissue and vessels.…”

“…The means and SDs of the T 2 values were obtained using iPlus software and Image J software (v1.44p, NIH, Bethesda, MD, USA). Z values were calculated by (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, and activated muscles were detected by the one-sample t-test with a threshold (Z T =2.56) 4) .…”

“…From the literature available on manual muscle tests (MMT), the prime movers of a movement can be identified, and while secondary or accessory movers may be equally important, definitive studies remain incomplete 3) . Compared with EMG and US, MRI can provide images with all of the muscles in a single field of view (FOV) in the arm, and we observed 10 forearm muscles in 1 slice simultaneously 4) . Transverse relaxation time weighted MRI (T 2w -MRI) is useful to detect activities of the forearm muscles including the extensor digiti minimi muscle using a 0.2 T MRI system 5,6) .…”

“…However, image intensity of T 2w -MRI is hard to treat quantitatively. Therefore, in a previous study, we defined Gaussian T 2 distribution and reference values (T 2r and SD r ) in the resting state for forearm muscles, and a threshold (Z T =2.56) for detecting exercised muscles using a one-sample t-test 4) . Based on receiver operating characteristic (ROC) analysis, we detected muscle activity that was not expected: 70% of participants used the supinator muscle as one of the synergist muscles for palmar flexion of the wrist joint 4) .…”

Quantitative MR-Bildgebung zur Charakterisierung der Skelettmuskulatur

“…Daneben steht eine Standardisierung der Methoden, zu der wichtige Ergebnisse bereits 2010 im Rahmen des TREAT-NMD Workshops zu "Skeletal Muscle NMR Imaging: Advanced Quantitative Imaging, Image Registration and Segmentation, Texture Analysis, Pattern Recognition, Imaging Registries" erarbeitet wurden [42], die aber an die neueren MR-Scanner-Generationen angepasst werden müssen. Weiterhin ist das Thema von Populationsreferenzwerten bisher in der Literatur bis auf wenige Ausnahmen nicht diskutiert worden [103].…”