A comparison of computed tomographic techniques in the diagnosis of Graves' ophthalmopathy

We performed CT scans on 24 patients with clinically typical Graves' ophthalmopathy to compare the advantages of various scanning techniques. Scans were performed before and after intravenous contrast material infusion, and the contrast-enhancement of abnormal muscles was compared with that of known orbital tumors. Images were also obtained using 5-mm and 8-mm collimators, and the diagnostic value of these collimators was compared. Sagittal and coronal scans were performed in some of the cases, using a new direct technique for the sagittal plane. In general, the 5-mm collimators provided sharper definition of the ocular muscles and optic nerves. Contrast-enhancement alone was not helpful in differentiating enlarged muscles from orbital tumors because of the great overlap of attenuation coefficients. Sagittal and coronal images were helpful in confirming muscle enlargement suspected from axial scans, and were most useful in showing enlarged superior and/or inferior recti in cases with normal medial and lateral recti. The advantages of our method of obtaining sagittal scans through the long axis of the orbit and the potential application of this technique to orbital CT scanning are discussed.