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J. B. Christoforidis, P. A. Wassenaar, G. A. Christoforidis, M. V. Knopp, P. Schmalbrock; Imaging of Retro-Orbital Structures and Vasculature With Ultra High Field 7T Magnetic Resonance Imaging Using Dedicated Eye Coil. Invest. Ophthalmol. Vis. Sci. 2009;50(13):333.
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Noninvasive imaging of retro-orbital vascular structures such as the ophthalmic artery and its branches is challenging because of the fine resolution that is required. Recent improvements in imaging with ultra high field MRI is allowing for improved visualization of fine ocular structures. In this study we utilized a dedicated single-loop eye coil at 7 Tesla for imaging of posterior ocular structural and vascular anatomy.
Imaging was performed with 7T (Philips, Achieva) using a transmit head coil for excitation (Nova Medical) and a dedicated 5 cm eye surface coil for receive (Rapid MR International LLC). Previously, safety testing on phantoms as well as canine and porcine models had shown no temperature elevation or other untoward side effects (Wassenaar, Schmalbrock et al). Optimization at 7T for 3D spoiled gradient echo (3D-SPGR) and 3D inversion prepared turbo-field echo (IR-TFE) sequences were performed. 5 subjects were imaged under IRB approved protocol.
Images of the posterior segment were obtained with good visualization of the ophthalmic artery and first order branches. Ocular imaging at 7T is sensitive to motion, as well as susceptibility artifacts particularly from air-tissue interfaces at the lids. Although this can affect imaging of the cornea, anterior chamber and lens, retro-orbital structures remain well-visualized. Furthermore, these artifacts may be reduced using thin-section 3D imaging, minimum TE and the use of very short scan times. There were no untoward side effects in any of the subjects tested.
7T MRI with a dedicated eye coil provides improvements in noninvasive image quality of retro-orbital structural anatomy. Imaging with gadolinium may further delineate retro-orbital vascular anatomy. The resolution provided may be particularly applicable in evaluating abnormalities of retrobulbar vascular structures such as the ophthalmic artery, posterior ciliary branches and central retinal artery that may occur in vascular disorder such as ocular ischemic syndrome and central retinal artery occlusion.
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