Robert A Clark1, Joseph L Demer. 1. Departments of Ophthalmology, David Geffen Medical School, University of California, Los Angeles, California 90095-7002, USA.
Abstract
PURPOSE: We explored multiple quantitative measures of horizontal rectus extraocular muscle (EOM) morphology to determine the magnetic resonance imaging (MRI) measure best correlating with duction and thus contractility. METHODS: Surface coil coronal MRI was obtained in target-controlled central gaze and multiple positions of adduction and abduction in 26 orbits of 15 normal volunteers. Duction angles were determined by position changes of the globe-optic nerve junction. Cross-sectional areas, partial volumes, and location of peak cross-sections of the horizontal rectus EOMs were computed in contiguous image planes 2-mm thick spanning the EOM origins to the globe equator. RESULTS: All measures correlated significantly with duction angle (P < 0.0001). The best measures obtainable in single image planes were the maximum change in the cross-sectional area between equivalent image planes, with coefficients of determination R(2) = 0.92 for medial rectus (MR) and 0.91 for lateral rectus (LR), and percentage change in maximum cross-section with R(2) = 0.79 for MR and 0.78 for LR. The best partial volume measure of contractility was the change in partial volumes in four contiguous posterior planes (R(2) = 0.86 MR and for 0.89 LR), particularly when combined with the corresponding change in partial volume for the antagonist EOM (R(2) = 0.95 for MR and LR). CONCLUSIONS: EOM morphologic changes are highly correlated with degrees of duction and thus contractility. Both changes in single-plane maximum cross-sectional areas and posterior partial volumes provide accurate, quantitative measures of EOM contractility.
PURPOSE: We explored multiple quantitative measures of horizontal rectus extraocular muscle (EOM) morphology to determine the magnetic resonance imaging (MRI) measure best correlating with duction and thus contractility. METHODS: Surface coil coronal MRI was obtained in target-controlled central gaze and multiple positions of adduction and abduction in 26 orbits of 15 normal volunteers. Duction angles were determined by position changes of the globe-optic nerve junction. Cross-sectional areas, partial volumes, and location of peak cross-sections of the horizontal rectus EOMs were computed in contiguous image planes 2-mm thick spanning the EOM origins to the globe equator. RESULTS: All measures correlated significantly with duction angle (P < 0.0001). The best measures obtainable in single image planes were the maximum change in the cross-sectional area between equivalent image planes, with coefficients of determination R(2) = 0.92 for medial rectus (MR) and 0.91 for lateral rectus (LR), and percentage change in maximum cross-section with R(2) = 0.79 for MR and 0.78 for LR. The best partial volume measure of contractility was the change in partial volumes in four contiguous posterior planes (R(2) = 0.86 MR and for 0.89 LR), particularly when combined with the corresponding change in partial volume for the antagonist EOM (R(2) = 0.95 for MR and LR). CONCLUSIONS: EOM morphologic changes are highly correlated with degrees of duction and thus contractility. Both changes in single-plane maximum cross-sectional areas and posterior partial volumes provide accurate, quantitative measures of EOM contractility.
Authors: T Ohnishi; S Noguchi; N Murakami; J Tajiri; M Harao; H Kawamoto; H Hoshi; S Jinnouchi; S Futami; S Nagamachi Journal: Radiology Date: 1994-03 Impact factor: 11.105