Direct and reconstructed multiplanar computed tomography of the orbits of healthy dogs

Abstract

Objective - To describe anatomy of the orbits as revealed by computed tomography (CT) in different scan planes, determine the most useful scan plane for imaging the eye, optic nerve, and extraocular muscles, and compare image quality of direct CT images with reconstructed images obtained from 2-mm-thick and 5-mm-thick transverse images. Animals - 9 dogs with no ocular abnormalities. Procedure - In 3 dogs, CT was combined with cisternography to facilitate imaging of the optic nerve and determine the scan plane that allowed optimum imaging of the optic nerve in a single image. In 6 dogs, CT images were made in transverse, dorsal oblique, and sagittal oblique scan directions. Dorsal and sagittal reconstructions were made from transverse images. Results - In all dogs, scanning in different planes enabled identification of ocular structures, optic nerves, and orbital adnexa, as well as identification of the confines of the orbit. Imaging of optic nerve and extraocular muscles was optimal on dorsal oblique scans at an angle of 43 to 45° to the skull base and on sagittal oblique images at an angle of 59 to 61° to the midline of the skull. Conclusions and Clinical Relevance - All scan directions provided detailed images of orbital structures. Transverse images were convenient for survey examination, and dorsal oblique and sagittal oblique images were superior for imaging optic nerves and extraocular muscles. Image quality of reconstructed images obtained from the 2-mm-thick transverse images was superior to that obtained from the 5-mm-thick images. Optimum quality was achieved with direct multiplanar imaging. (Am J Vet Res 1999;60:1500-1507).