Abstract
Purpose :
To produce a high resolution (250μm isotropic), 3-D images of human highly myopic eyes while minimizing eye movements via a novel super-resolution MRI (srMRI)acquisition and processing pipeline with significantly lowered scan times.
Methods :
Twenty-two eyes of 11 emmetropic subjects, 25 eyes of 14 subjects with myopia (with vision > 20/40 in >1 eye) with no prior eye medical history or surgeries aside from cataracts underwent IOLMaster biometry and srMRI imaging (3T, 8-channel head coil). A fat-suppressed, axial T2-weighted volumetric scanning sequence with four 90-second scans was acquired using various slice orientations resulting in 4 non-overlapping voxels. Images underwent registration, thresholding, upsampled with tri-linear interpolation producing isotropic voxels (FSL and Matlab). The coronal and axial acquisitions were then co-registered, averaged together and re-registered to achieve a resolution of 0.25 x 0.25 x 0.25 mm. The axial length from the anterior lens surface to the ILM was then calculated. Moreover, in order to quantify motion artifacts, we measured the frequency of blinks and saccades, two measures that indicate that the subject was unable to maintain fixation with eye tracking data over 25 minutes (EyeBrain, NeuroLite, 5-min-blocks with 1-min washout x 5 gazes) that was collected from 11 myopic subjects correctable to 20/20. Ages ranged from 22.5 to 84.7 years old, 60% female with axial lengths ranging from 22.4 to 33.2 mm.
Results :
In terms of eye-tracking data, over the course of the 25-minute-long study, there was a steady increase the total time the eyes were closed to approximately 12 sec (40%) of each block. The frequency of saccades similarly increased from ~0.01 to ~0.12 saccades per sec. Both results indicate that MR imaging of the globe would benefit from reduced scan time. Comparing the axial lengths measured by SR-MRI with estimates by IOLMaster, the resulting slope was 1.037 (p = 4 x 10-29), which was not significantly different from a slope of 1 (p = 0.28). The residuals were heteroscedastic increasing exponentially with axial length (p = 2 x 10-5) with a rate constant of 5.8 mm.
Conclusions :
A novel super-resolution magnetic resonance imaging acquisition and processing pipeline were used to acquire high resolution images of the whole eye with significantly lowered scan times, which is key in reducing motion artifacts.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.