Temporal course of perfusion in human masseter muscle during isometric contraction assessed by arterial spin labeling at 3T

Object Examination of blood perfusion in the masseter muscle in the course of repetitive isometric contraction by arterial spin-labeling (ASL) MR imaging and additional T2 relaxation time measurements during and after masseter muscle activation. Materials and methods Anatomical and ASL imaging was performed (3 T) in the masseter muscle of seven healthy volunteers before and after sustained clenching (30 s) at maximum voluntary contraction (MVC). Several cycles of clenching were repeated in an overall period of 11 min. ASL imaging was performed by an adapted FAIR-TrueFISP technique. Time to peak and time to baseline were systematically analyzed in recorded perfusion curves. T2 relaxation times were estimated using a multi-echo spin-echo sequence. The influence of MVC on T2 was statistically analyzed. Results In all cases, perfusion imaging and assessment of T2 relaxation time was feasible. Mean perfusion values at rest calculated from all volunteers were 97.9 +/- 17.1 ml/min/100 g (right masseter) and 83.0 +/- 18.1 ml/min/100 g (left masseter). The percentage mean perfusion increase in all volunteers immediately after clenching ranged between 114 and 154%. Mean time to peak was 13.7 s (range: 8.0-26.7 s; SD 5.6 s), and mean time to baseline was 25.6 s (range: 18.7-37.0 s; SD 5.4 s). No significant influence of MVC on T2 relaxation time was found, although a tendency to T2 increase after each clenching stress was observed. Conclusion Clear contraction-related perfusion changes of the masseter muscle could be assessed in high spatial and temporal resolution by means of ASL. In contrast, no significant T2 changes were measured. ASL imaging could serve as supplementing tool for studying masticatory function and dysfunction.