Visualization and quantification of digitally dissected muscle fascicles in the masticatory muscles of Callithrix jacchus using non-destructive DiceCT.

Abstract

The organization and length of a muscle s fascicles contributes its contractile properties. Longer fascicles permit increased muscle excursion, while changes in fascicle orientation relate to the overall vector of contractile force. Collecting data on fascicle architecture has traditionally involved destructive and irreversible gross dissection. In recent years, however, new imaging modalities have permitted muscles and their fascicles to be visualized non-destructively. Here we present data from a primate (Callithrix jacchus) in which, for the first time, individual muscle fascicles are digitally dissected (segmented and reconstructed) using non-destructive, high-resolution diffusible iodine-based contrast-enhanced computed tomography (DiceCT) techniques. We also present quantitative data on the length and orientation of these fascicles within ten muscle divisions of the jaw adductor and abductor musculature (superficial, deep, and zygomatic portions of temporalis and masseter; medial and lateral pterygoid; anterior and posterior digastric) and compare these digitally measured lengths to fascicular lengths measured using traditional gross and chemical dissection. Digitally-derived fascicle lengths correspond well to their dissection-derived counterparts. Moreover, our analyses of changes in fascicle orientation across the adductor complex enable us to visualize previously uncharacterized levels of detail, and highlight significant variation between adjacent muscle layers within muscle groups (e.g., between superficial, deep and zygomatic portions of masseter and temporalis). We conclude that this technique offers great potential to future research, particularly for questions centered around the visualization and quantification of obscured and often-overlooked muscles such as the pterygoid and digastric muscles, and for deriving more accurate models of the masticatory system as a whole. This article is protected by copyright. All rights reserved.