A clinical MHz swept-source OCT prototype for ultra-widefield imaging

Abstract

Purpose : While research optical coherence tomography (OCT) systems with MHz A-scan rates have been presented in the past, the clinical value of such high acquisition rates is still poorly understood. Clinical studies with significant sample sizes have so far been difficult due to the complexity of such high-speed systems. We present a versatile, easy to operate clinical prototype, capable of A-scan rates up to 1.7MHz and suitable for anterior as well as posterior segment imaging with different field of views (FOV) and spatial resolutions.

Methods : We developed a clinical 1060nm swept-source OCT (SS-OCT) prototype capable of acquiring 1.7 million A-scans per second over a depth range in tissue of up to 6mm and an axial resolution of up to 9μm in tissue. The lateral resolution can be doubled by a beam expander at the click of a button. We designed two magnetically attachable add-on lenses to expand the field of view (FOV) on the retina up to 90° and to enable telecentric scanning of the anterior segment. To ensure the prototype can be operated independently by clinical staff, we added alignment aids such as a fundus view, an iris view, a motorized chin rest, reference delay and polarization control.

Results : Fig.1a shows the en face projection of a 90° OCT scan, a FOV comparable to that of state-of-the-art wide field fundus cameras. A 90° B-scan can be seen in Fig.1b. A volume rendering of a full anterior segment is shown in Fig.1c. In Fig.2 we present the prototype’s wide field and microscopic OCT angiography (OCTA) capabilities. A 12mmx12mm scan acquired within only 2.5s is shown in Fig. 2a. A 65° FOV OCTA scan can be seen in Fig.2b, where the blue magnification box highlights that despite the large FOV, the avascular zone can still be resolved. Fig.2c shows OCTA acquisitions of the choriocapillaris with enhanced lateral resolution. While individual capillaries are even resolved in the 12mmx12mm scan, the denser sampled overlaid scan in the blue box shows that contrast can still significantly improved by increasing the sampling density.

Conclusions : The versatility and ease of use of the presented prototype may enable a thorough investigation of the clinical value of MHz A-scan rates through additional clinical studies.

This is a 2020 Imaging in the Eye Conference abstract.

 

Fig 1. a) 90° retina OCT enface image, b) 90° OCT retina B-scan, c) Volume rendering of anterior segment scan

 

Fig. 2. a) 12mmx12mm retina OCTA scan, b) 65° retina OCTA scan, c) 12mmx12mm choriocapillaris OCTA scan