The Effect of Repetition Time during The Measurement of Muscle T2 for Investigating Muscle Activity at 1.5 Tesla MRI

Abstract

The evaluation of muscle function by T2 mapping is important in sports medicine and rehabilitation. Repetition time (TR) is one of the most important parameters for calculating T2 and affects the accurate T2 measurements. The previous study used SE or MSE to calculate T2 and there were few reports about the extensive comparative evaluation of the imaging parameters using SE-EPI. Thus, the goals of this study were 1) to evaluate the effect of TR in decreasing scan time for muscle T2 measurement in the pulse sequences at 1.5 Tesla MRI and 2) to investigate the feasibility of shortening scan time of T2 measurement to detect the muscle activity that induced by exercise. A PVA-gel phantom and right lower legs of eight healthy male subjects were scanned using a 1.5 tesla MR scanner. MSE and SE-EPI were performed with TR 1,000, 2,000, ..., 4,000 ms, TE 15, 30, ..., 390 ms. To evaluate the feasibility of SE-EPI to detect muscle activity. Subject performed ankle plantar flexion of the right leg 200 times and MR images were acquired at rest and after exercise. T2 was calculated by mono-exponential linear least-squares of TE 30, 45, 60, 75 ms. Phantom and in vivo: comparison studies showed the result in the same way. For MSE, the relaxation curve of TR 2,000 ms or more is likely to be the same MR signal. For SE-EPI, all relaxation curve showed approximately the same MR signal and all SE-EPI’s MR signal were lower than the signals of MSE. However, all of T2 have no significant difference between TR and sequences. Regarding in vivo: exercise study, T2 of gastrocnemius muscle at after exercise was significantly higher than T2 at rest. In conclusion, MR images with a short TR (TR 1,000 ms) under suitable condition are possible to calculate muscle T2 to reduce the scan time dramatically. Calculating T2 using SE-EPI, can be applied to detect the muscle activity that induced by exercise with the shortening acquisition time of approximately 1/17 of the previous methods.