Optic neuritis and orbital lesions: lipid-suppressed chemical shift MR imaging

A derivative of the Dixon method, chopper fat suppression, was used in the magnetic resonance imaging evaluation of 40 patients: 37 with suspected optic nerve lesions, predominantly optic neuritis, and three with orbital lesions. In patients with optic neuritis, the technique was sensitive, allowing detection of 29 of 34 visual-evoked-response-confirmed lesions on T2-weighted lipid-suppressed images. There were no false-positive studies. Sensitivity for detection of optic neuritis was 89%; specificity, 100%; and accuracy, 86%. The technique was also useful for depicting inflammatory changes in the orbital apex due to fungal abscess and confirming the fatty nature of an extraconal dermoid tumor. A slight increase in noise and mild accentuation of susceptibility effects at interfaces of air, bone, and brain did not degrade images significantly. The chopper-based technique requires only standard imaging time and has usual spin-echo sensitivity. The results are comparable to short-inversion-time inversion-recovery imaging, without the constraints of sequence limitations or artifacts at fat and water interfaces.