MOTION-RESOLVED 3D MAGNETIC RESONANCE IMAGING OF THE HUMAN EYE

Abstract

Purpose : Eye-movements pose major challenges for the use of MRI techniques in ophthalmology, as they introduce motion artefacts and preclude the applicability of standard procedures in the clinic. We ideated and tested a MR imaging framework that demonstrates the feasibility of motion-tracking and retrospective motion-resolved 3D isotropic image reconstruction of the eye dynamics.

Methods : Data were acquired from N=3 healthy adult volunteers on a 3T clinical MRI scanner (MAGNETOM Prisma^fit, Siemens Healthcare AG), using a prototype uninterrupted gradient recalled echo (GRE) sequence with lipid-insensitive binomial off-resonant RF excitation (LIBRE) for fat suppression. The acquisition used a 3D radial phyllotaxis sampling pattern with spiral trajectories rotated by the golden-angle for uniform k-space coverage. The field-of view was (192mm)³ with 1mm³ isotropic resolution. Eye movements were tracked using an eye-tracking system (EyeLink 1000Plus) synchronized with the MRI scanner via Syncbox (NordicNeuroLab). Sixteen distinct visual stimuli (gray circle at different positions on a black background) were presented to each volunteer. Each stimulus had a duration of 5 seconds and was repeated 6 times during the experiment, for a total of 96 trials opportunely randomized to ensure uniform sampling distribution of the readouts in k-space. The post-processed Eye-tracker data were used for binning the time intervals of each motion state and to match the k-space readouts corresponding to the same stimulus presentation. Motion-resolved 5D image reconstruction (x-y-z-α-β dimensions, where α and β represent the eye angular rotations in the up-down and left-right directions) was performed using a k-t sparse SENSE algorithm exploiting sparsity both along the α and β directions (Fig. 1).

Results : 3D motion-resolved images of the eye with 1mm³ isotropic resolution were successfully acquired and reconstructed in all volunteers. Eye-motions across the presentation of the different visual stimuli were clearly reconstructed (Fig. 2) void of motion artifacts.

Conclusions : The proposed protocol allows the tracking and retrospective resolving of eye motions to overcome the limitations of standardized eye-acquisitions using MRI. Future developments of the protocol might challenge the major hurdle for MRI in ophthalmology, which may open new directions in clinical as well as fundamental visual neuroscience research.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.