Magnetic resonance T2-weighted IDEAL water imaging for assessing changes in masseter muscles caused by low-level static contraction.

The aim of this study was to clarify the changes, using magnetic resonance (MR) images, in the masseter muscles caused by low-level static contraction.Ten healthy male volunteers were enrolled in the study. The MR scans were performed before, immediately after, and 10 minutes after low-level static contraction. Two imaging sequences were acquired: a diffusion-weighted image and an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) image. The apparent diffusion coefficient (ADC), the signal-to-noise ratio (SNR), and the thicknesses of the right and left masseter muscles were examined.The ADC and SNR immediately after exercise were significantly higher than those before exercise and 10 minutes after exercise. The muscles were significantly thicker immediately after exercise than before exercise and 10 minutes after exercise.We confirmed the presence of edema in the masseter muscles caused by low-level static contraction using MR images.