ANATOMIC MRI STUDY OF A SMALL MUSCLE - TH E MASSETER

Magnetic resonance imaging (MRI) provides functional information in an anatomic presentation allowing to distinguish soft tissues with high sensitivity. The goal of this study was to investigate the normal anat omy of the major masticatory muscle, the masseter, both al rest or dur ing contraction by using three dimensional (3D) MRI. Eighteen subjects aged from 19 to 28 years, all in good health, were studied. Several e xperiments were first realized on phantoms to test the SD-MRI techniqu e. After reconstruction and segmentation processing, 3D acquisition, e nabled obtaining data on the masseter anatomy. The normal anatomical p osition of the masseter was reported to the skin plan as the mean inte rnal distance (7.9 +/- 0.42 mm) and external distance (15.2 +/- 0.41 m m). While there was no difference between internal distance, for sex o r side, the external distance was significantly (p = 0.02) shorter in male (7.7 +/- 0.5 mm) than in female (8.8 +/- 0.4 mm) for both sides. The mean volume for all subjects and both sides (20.3 +/- 1.1 cm(3)) d id not change significantly between rest and excercise. The masseter v olume was significantly (p < 0.00001) greater in male (24.2 +/- 2.0 cm (3)) than in female (16.4 +/- 3.6 cm(3)) groups. These physiological r eferences may be useful for further MRI investigations of masticatory system pathologies.