MHz swept-source optical coherence tomography with a 90 degree field of view

Abstract

Purpose : The field of view (FOV) of commercially available optical coherence tomography (OCT) systems is typically limited to 30deg. Images from ultra-wide FOV color fundus cameras have however shown that examining the peripheral regions of the retina may impact the assessment of severity of disease. In this study we demonstrate 90deg FOV OCT B-scans and enface images acquired in less than 4s. Sampling such a FOV even with the fastest commercially available OCT systems would take over a minute and be very burdensome to the patients.

Methods : We developed a clinical 1060nm swept-source OCT (SS-OCT) prototype capable of acquiring 1.7million A-scans per second (~17x faster than the fastest commercial OCT systems) over a depth range in tissue of 5mm and an axial resolution of 12um in tissue. To broaden the FOV, we designed wide angle optics that enable a FOV of 90deg . A lens design which accounted for modelled peripheral aberrations allowed us to maintain good image quality even in the periphery. 90deg volumes containing 2560x2560 A-scans were acquired in less than 4s. This sampling supports the system’s optical lateral resolution of 20um over the entire FOV. The isotropic sampling enabled the extraction of virtual B-scans along arbitrary, user selectable traces throughout the volume. Due to the dense sampling we could even average neighboring B-scans to generate virtual HD-scans along the same trace.

Results : The system’s large imaging depth allowed us to capture the entire FOV with a single acquisition (Fig 1a). The sensitivity was measured to be 93dB which is sufficient for clinical use. Fig. 1b shows a virtual B-scan, extracted from the volume along the arbitrarily chosen trace shown by the line in Fig. 1a. The dense sampling allowed us to average up to 20 adjacent virtual B-scans to generate a HD scan along the same trace. We compare these images with state of the art images from commercial systems, to illustrate the benefit of larger FOV, imaging depth and speed.

Conclusions : The large FOV may provide otherwise hidden diagnostic information and the dense sampling may enable new clinical workflows, where a comprehensive volume is captured high quality B-scans may be extracted at arbitrary locations and orientations retrospectively.

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

 

Fig 1 a) fundus projection of a 90deg OCT volume acquisition; b) virtual arbitrary B-scan extracted from the 90deg OCT volume along the blue line in a); c) virtual arbitrary HD-scan