Phase stable swept-source optical coherence tomography with active mode-locking laser for contrast enhancements of retinal angiography

Kwan Seob Park,Sang-Won Lee,Hwidon Lee,Tae Joong Eom,Eunwoo Park,Hyun-Ji Lee

doi:10.1038/s41598-021-95982-9

Abstract

Swept-source optical coherence tomography (SS-OCT) is an attractive high-speed imaging technique for retinal angiography. However, conventional swept lasers vary the cavity length of the laser mechanically to tune the output wavelength. This causes sweep-timing jitter and hence low phase stability in OCT angiography. Here, we improve an earlier phase-stabilized, akinetic, SS-OCT angiography (OCTA) method by introducing coherent averaging. We develop an active mode-locking (AML) laser as a high phase-stable akinetic swept source for the OCTA system. The phase stability of the improved system was analyzed, and the effects of coherent averaging were validated using a retina phantom. The effectiveness of the coherent averaging method was further confirmed by comparing coherently and conventionally averaged en face images of human retinal vasculature for their contrast-to-noise ratio, signal-to-noise ratio, and vasculature connectivity. The contrast-to-noise ratio was approximately 1.3 times larger when applying the coherent averaging method in the human retinal experiment. Our coherent averaging method with the high phase-stability AML laser source for OCTA provides a valuable tool for studying healthy and diseased retinas.

Highlights

Swept-source optical coherence tomography (SS-OCT) is an attractive high-speed imaging technique for retinal angiography
Interference signals measured from a cover glass of thickness 330 μm were analyzed to determine the wavelength-sweeping repeatability of the active mode-locking (AML) laser
By taking advantage of the stable OCT signal obtained with the AML laser, the coherent averaging method (cohAvg) method was introduced to obtain a contrast-improved OCT angiography (OCTA) image of the human retinal vasculature, which is essential in ophthalmology

Summary

Introduction

Swept-source optical coherence tomography (SS-OCT) is an attractive high-speed imaging technique for retinal angiography. This akinetic laser source is capable of linear wavelength sweeping in the 1060 nm, 1310 nm, and 1550 nm wavelength bands for biological tissue imaging; further, these characteristics have been demonstrated by OCT imaging of the human retina, skin, tooth, and face as well as mouse b rain[5,6,7,8,9] These lasers have excellent phase stability and offer advantages, such as large coherence length and negligible sensitivity roll-off, as light sources for swept-source OCT angiography (OCTA) s ystems[7,8,9,10]. There are no known reports on the characteristics of swept-source AML lasers for enhancing the performance of the OCTA imaging system

Methods

Results

Conclusion