Assessment of the sequential change of the masseter muscle by clenching: a quantitative analysis of T1, T2, and the signal intensity of the balanced steady-state free precession

Background: The persistent muscle contractions during clenching are thought to cause some temporomandibular disorders. However, no report has so far evaluated the effect of clenching on the masticatory muscles by magnetic resonance imaging (MRI).Purpose: To investigate the effect of clenching with maximum voluntary contraction on the T1, T2, and signal intensity (SI) of the balanced fast field-echo (b FFE) of the masseter muscle.Material and Methods: A total of 11 volunteers participated. Multi-echo spin-echo echo-planar imaging was used for T2 measurements, and multi-shot Look-Locker sequence for T1 measurements. The Look-Locker sequence has been used for fast T1 mapping and this method has been applied for the imaging of various tissues. In addition, the b FFE was used due to the high temporal resolution. These three sequences lasted for 10 min and the participants were instructed to clench from 60 s to 80 s after the start of the data acquisition. T2, T1, and SI were normalized compared to pre-clenchin...