New vista for OCTA

[caption id="attachment_5818" align="alignnone" width="750"] VISTA visualisation in a 30-year-old proliferative diabetic retinopathy patient taken over a 3mm × 3mm field of view (red indicates faster blood flow speeds; blue indicates slower speeds). Courtesy OCT Research Group, MIT-NEEC[/caption] Variable interscan time analysis (VISTA) is a step towards quantitative optical coherence tomography angiography (OCTA) that allows determination of relative blood flow speeds. As a next innovation, the VISTA developers have created ‘VISTA visualisation’, a method for mapping the VISTA data into a colour-coded format to make image interpretation intuitive and easy for clinicians. Speaking on behalf of his colleagues, Stefan Ploner BSc presented the techniques at the 2016 annual 
meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Seattle, USA. “Although OCTA allows visualisation of ocular blood flow, it provides little information about blood flow speed, and that is an important limitation considering that progression of many retinal diseases is thought to involve a gradation of flow impairment and not just vascular loss,” said Mr Ploner, who is affiliated both with the Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology (MIT), Cambridge, USA, and the Friedrich-Alexander-University Erlangen-Nürnberg, Germany. “The core VISTA algorithm provides the theoretical framework for using OCTA to resolve different blood flow speeds, and we believe it is a promising tool for studying and eventually aiding in the treatment of ocular disease. VISTA visualisation bridges the gap between the engineering lab and the clinic by transforming the VISTA output into a readily understandable form. Our long-term technical goal is to extend the algorithm to achieve truly quantitative OCTA,” he said. Currently, VISTA is limited to measuring a marker of relative blood flow speed, and does not provide measurement of absolute blood flow speed. VISTA resolves blood flow speeds by varying the interscan time between repeated B-scans. The VISTA visualisation algorithm transforms the VISTA data to a single value that describes relative blood flow speed and maps the value into an image in which the colour of a vessel indicates the relative blood flow speed. COLLABORATION Mr Ploner illustrated VISTA visualisation with several representative flow maps. Showing the image from an eye with non-proliferative diabetic retinopathy, he highlighted the presence of slow blood flow through capillary loops. “This observation provides clinical validation that the algorithm is doing what we expect,” he said. Mr Ploner also presented VISTA flow maps from eyes with proliferative diabetic retinopathy, exudative age-related macular degeneration, and geographic atrophy (GA). “VISTA was first applied for imaging the choriocapillaris in GA, where it was leveraged to look at subtle blood flow impairment occurring at the GA borders (Choi W et al, Ophthalmology 2015;122(12):2532-2544). The next step is to run larger cohort studies of patients with GA and other diseases to investigate what insights can be uncovered with VISTA,” he told EuroTimes. The development of VISTA and VISTA visualisation represents a collaboration between teams of clinicians, optical engineers and computer scientists at MIT and the New England Eye Centre, Boston, USA; Bascom Palmer Eye Institute, Miami, USA; and the Friedrich-Alexander-University Erlangen-Nürnberg, Germany. Stefan Ploner: Stefan.ploner@fau.de