Widefield simultaneous fluorescein/indo-cyanine green angiography using a slit-scanning ophthalmoscope

Abstract

Purpose : Simultaneous recording of fluorescein angiography (FA) and indo-cyanine green angiography (ICGA) can streamline clinical angiography workflow. Many conventional fundus cameras can acquire FA and ICGA images separately; simultaneous capture of both is performed clinically using confocal scanning laser ophthalmoscopes. An alternative to these technologies is the slit-scanning ophthalmoscope, which can provide clear fundus imaging over a wide field-of-view (FOV) using broadband light. In this study, we describe the application of such an instrument to provide simultaneous FA/ICGA over a 90° FOV, with accurate spatial and temporal co-registration of detail across modalities.

Methods : Subjects were administered a mixture of fluorescein and indocyanine-green dyes. A slit-scanning ophthalmoscope (CLARUS^TM 700, ZEISS, Dublin, CA) with prototype software was used for imaging. During each image capture, a strip of rapidly-alternating blue-green (470-510 nm) and infrared (790 nm) illumination was swept from inferior to superior retina (as illustrated in Figure 1) in approximately 150ms. Dual-bandpass filters enabled excitation and detection of fluorescence for both dyes through a common optical path, while a single image sensor rapidly recorded a sequence of discrete acquisitions. Widefield 90° FA and ICGA images were then assembled. A false-color fusion method was employed to combine the images into a single picture with joint color contrast.

Results : Figure 2 illustrates the generation of simultaneous angiograms. FA and ICGA image details are inherently co-aligned, with no need for registering the images in post-processing, due to the common optical path. Furthermore, the interleaved scan and quasi-simultaneous recording of data ensure that the images are temporally co-registered.

Conclusions : Slit-scanning ophthalmoscopes can provide widefield simultaneous FA/ICGA. Accurate spatial and temporal registration of FA and ICGA details over a wide FOV facilitates image interpretation and provides a compact data format that potentially could be amenable to the development of image analytics.

This is a 2020 Imaging in the Eye Conference abstract.

 

Figure 1. (A) Excitation and detection paths through the eye; FA and ICGA stripe illumination is rapidly alternated (B) and swept jointly from inferior to superior retina over the 90° FOV (C).

 

Figure 2. Assembly and color fusion of widefield FA/ICGA angiograms, showing spatially and temporally co-registered details.