High-Resolution MRI of Horizontal Gaze Position for Improved Optical Flow Analysis

Abstract

Purpose: Long term goal of the Delft Finite Element Model of Orbital Mechanics is to adapt the model for each individual patient using optical flow analysis (OFA) of MRI scans taken preoperatively. OFA can estimate displacements and deformations of the orbital fat by comparing two MRI datasets in different positions of gaze. However, this MRI data is marred by involuntary head movements and involuntary eye movements. We obtained high resolution data by limiting head and eye movements. Methods: A bite board of PVC with dental thermoplast was attached to a stiff MDF frame that was mounted rigidly to the MRI gantry. To track head movements, MRI markers were used to detect inadvertent head movement. A LED was rotated at equidistance in front of the dominant eye in 15 directions of gaze, from 35 degrees left gaze to 35 degrees right gaze with steps of 5 degrees. The other eye was covered. Pick-up coils were attached to the frame. Results: Two 23-year-old males were placed supine in the MRI scanner with a dental-impression bite board. For 2 minutes 3D T1 weighted scans were made with a Sigma Excite 3.0T MRI scanner. The successive datasets were analyzed to determine any head movement. With registration of the markers displacements between successive datasets were found to be less than 0.1 mm in transversal, 0.5 mm in temporal and 0.3 mm in vertical direction. The subjects were able to focus on the LED and were able to keep their eye fixated in the applied direction of gaze: resolution of the scans in extreme left and right gaze was equal to that of the scan made in primary gaze. Conclusions: Using this approach high resolution MRI data sets were obtained and the data sets had sufficient resolution to make high resolution OFA of the deformation of orbital fat possible (see accompanying abstract by de Vries et al.).

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