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MRI of the Human Eye Using Magnetization Transfer Contrast Enhancement

¹ From the Laboratory of Ocular Therapeutics, ² Ophthalmic Genetics and Clinical Services Branch, National Eye Institute; and ³ Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute; National Institutes of Health, Bethesda, Maryland.

PURPOSE. To determine the feasibility of using magnetization transfer contrast–enhanced magnetic resonance imaging (MRI) to track cataractous lens changes.

METHODS. A fast spin–echo sequence was modified to include a magnetization transfer contrast (MTC) preparation pulse train. This consisted of twenty 8.5-msec sinc pulses, 1200 Hz upfield from the water resonance and 1.2-Hz power. The MTC preparation pulse was followed by acquisition through fast spin–echo imaging. The imaging parameters were number of excitations (NEX) = 1, echo time (TE) = 14 msec, recovery time (TR) = 2 sec, echo train length of eight echos, and a matrix size of 256 x 160. To reduce motion artifacts, the volunteers were asked to fixate on a blinking LED. Normal and MTC-enhanced images were acquired from normal volunteers and volunteers with nuclear or cortical cataracts.

RESULTS. The eye was adequately imaged, with few motion artifacts appearing. The lens was well resolved, despite the short T₂. The cornea and ciliary body were also clearly visible. In the lens, resolution of the epithelium and cortex were enhanced with MTC. In addition, contrast-to-noise ratios were measured for each image. Examination of the contrast-to-noise ratio confirmed that MTC increased the contrast between the nucleus and cortex. Unenhanced MRIs showed significant differences between the cortex of normal volunteers and volunteers with cataracts. MTC-enhanced images improved the sensitivity to changes in the nucleus.

CONCLUSIONS. In this preliminary study, we were able to use MTC-enhanced MRI to obtain high-contrast images of the human lens. Regular and enhanced MRIs detected statistically significant differences between normal and cataractous lenses.

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