John B. Christoforidis, P.A. Wassenaar, G.A. Christoforidis, M.V. Knopp, P. Schmalbrock  (Columbus, USA)

Advantages:  

Noninvasive imaging of retrobulbar vascular structures such as the ophthalmic artery and its branches is challenging because of the fine resolution required. Recent improvements in imaging with ultra high field MRI allows 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.

Methods:  

Imaging was performed at 7T (Philips, Achieva) using a transmit head coil for excitation (Nova Medical) and a dedicated 4 cm eye surface coil for reception (Rapid MR International LLC). Previously, safety testing on phantoms as well as canine and porcine models had shown no untoward side effects. Optimization at 7T for 3D spoiled gradient echo (3D-SPGR) and 3D inversion prepared turbo-field echo (IR-TFE) sequences were performed. Six subjects were imaged with and without gadolinium under IRB approved protocol.

Effectiveness / Safety:

Images of the posterior segment were obtained with good visualization of the ophthalmic artery and first order branches with and without gadolinium. 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.

Take home message:  

7T MRI with a dedicated eye coil provides improvements in noninvasive image quality of retro-orbital structural anatomy. Further improvements are expected with multi-channel eye coil and post-processing noise reduction. The resolution provided may be particularly applicable in evaluating and guiding future treatments in retinal vascular disorders particularly in central retinal vascular occlusions.