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Quantitative analysis of human masticatory muscles using magnetic resonance imaging.

OBJECTIVES
The objective of this study was to quantitatively evaluate the correlation between left and right masticatory muscle volumes in normal subjects.


METHODS
Contiguous 1 mm MR scans were obtained of 12 normal adult subjects aged 20-25 years using a Siemens 1.5 T MR scanner. The volumes of the human masticatory muscles (masseter, lateral and medial pterygoid) were measured from the scans using our previously proposed method. To test for inter- and intraobserver reproducibility, measurements were performed by two users on two separate occasions, with a span of 2 weeks between them and with the previous results blinded. Good inter- and intraobserver reproducibility was achieved in our study.


RESULTS
The mean volumes for left and right masseters, and lateral and medial pterygoids were 29.54 cm3, 29.65 cm3, 9.47 cm3, 10.23 cm3, 8.69 cm3 and 8.92 cm3, respectively. The Pearson correlation coefficients between the volumes of the left and right masseters, lateral and medial pterygoids are 0.969, 0.906 and 0.924, respectively.


CONCLUSIONS
The computed volumes of the masticatory muscles show a strong correlation between the volumes of the left and right masseters, and lateral and medial pterygoids for normal adult subjects. The total masticatory muscle volume on the left and right sides of normal subjects is similar.