Vascular perfusion of choroidal melanoma by 3.0 Tesla magnetic resonance imaging

Purpose: Because signal-to-noise performance improves with increased magnetic field strength, the quality of magnetic resonance images is greater at 3.0 tesla (T) than at 1.5 T. Because of the longer T1 values at higher field strength, intravenously administered magnetic resonance contrast agents provide improved T1 enhancement at 3.0 T. We have used these factors to obtain high-quality contrast-enhanced imaging of small intraocular lesions using a standard head radiofrequency volume coil. Specifically, we have examined lesion size and magnitude of maximum contrast enhancement in a series of intraocular melanomas before and during therapy. Methods: Eighteen patients with intraocular masses were examined by 3.0 T magnetic resonance imaging (MRI) including intravenous contrast enhancement. Precontrast images were acquired through the orbits followed by sequential postcontrast images at 1-minute intervals for 5 minutes. The magnitude of contrast enhancement of the lesion, extraocular muscles, and brain parenchyma was measured as a percentage increase in magnetic resonance signal over the preenhancement signal intensity. Results: Lesions demonstrated different levels of enhancement ranging up to 130%. Three patterns of enhancement - 0% to 20%, 20% to 50%, and >50% - were identified. Brain parenchyma, benign lesions, and responsive tumors following brachytherapy with ¹²⁵I demonstrated enhancement of less than 20%. Four choroidal melanomas showed intermediate (20% to 50%) levels of enhancement. Four malignant lesions (three melanomas, one metastatic tumor), as well as the extraocular muscles, showed strong, rapid enhancement (>50%). Four patients who had MRI studies before and following plaque brachytherapy ultimately demonstrated a decline in the contrast enhancement following treatment. Conclusions: Contrast enhancement of intraocular lesions measured by 3.0 T MRI demonstrates different patterns of enhancement that may be useful for indicating the degree of malignancy and in monitoring response to therapy.