Quantified elasticity mapping of retinal tissue using acoustic radiation force optical coherence elastography

Abstract

Purpose : Early diagnosis of age-related macular degeneration (AMD) remains a challenge due to limitations in functional imaging modalities in clinics today. It has been shown that the elasticity of the retina is altered during the onset of AMD due to drusen formation and neovascularization. This study shows the feasibility of using acoustic radiation force optical coherence elastography (ARF-OCE) to probe the elasticity of retinal layers to aid in the diagnosis of AMD.

Methods : We report on a minimally invasive ARF-OCE system that uses ARF excitation, and optically detects the displacement of the tissue spatially and in response to different frequencies. First, silicone phantoms are tested to validate the Voigt model relationship between the frequency response and the elastic modulus. Next, fresh ex vivo pig eyes were enucleated, and the displacement was recorded in 12 porcine retinas, in a 3 mm by 1 mm region on the temporal side, 2 mm from the optic disc. Segmentation is performed on the optical coherence tomography (OCT), such as in Figure 1A, and projected on to the displacement map, at 64 locations. Finally, the elastogram is generated using the frequency response, and a weighted average of the thickness and displacement for each layer across all areas.

Results : The OCE in Figure 1B shows the variation in displacement between the photoreceptor and ganglion sides of the retina. The elasticities of the layers are calculated and averaged across 64 scans (regions i. 1.33±0.37 kPa, ii. 2.73±0.82 kPa, iii. 7.7±2.26 kPa, iv. 25.9±7.36 kPa) and elastograms are generated for the corresponding location, shown in Figure 1C. The standard deviation is large for high strain regions due to small displacement. The OCT layers correlate to the H&E staining of the retina, where five distinct layers are matched in Figure 1D.

Conclusions : Our results validate the capability of ARF-OCE to quantify the elastic modulus of the retina. Only 2 samples were analyzed due to retinal detachment and other postmortem changes, so further confirmation in an in vivo model is required. This study is a potential stepping stone to clinical studies, where the elastogram can perhaps aid in the diagnosis of retinal diseases.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.