Phase-variance OCT a promising alternative to fluorescein angiography

Issue: January 25, 2014

Phase-variance optical coherence tomography enabled high-resolution automated imaging of retinal and choroidal microvasculature without intravenous injection of dye, according to a study.

The new technology is not invasive in contrast to fluorescein angiography (FA), the gold standard method of microvasculature imaging in patients with age-related macular degeneration and diabetic retinopathy, the study authors said.

“In terms of screening purposes, it’s difficult to screen patients with proliferative diabetic retinopathy. It can be challenging. If we could do it in an automated fashion using PV-OCT, that would be a huge advantage,” corresponding author Daniel M. Schwartz, MD, professor of clinical ophthalmology at University of California, San Francisco, said in an interview with Ocular Surgery News. Schwartz and co-authors from California Institute of Technology and University of California, Davis, are developing phase-variance optical coherence tomography (PV-OCT).

PV-OCT uses data normally acquired but not used during spectral-domain OCT imaging. It identifies regions of motion between consecutive B-scans that are contrasted with less mobile regions. In the retina and choroid, the regions with motion correspond to vasculature, and the vessels are distinct from other retinal tissues that are static.

Daniel M. Schwartz

Unlike Doppler OCT, PV-OCT can achieve time separations between phase measurements to visualize slow microvascular flow, Schwartz and colleagues said.

“We learn more about the status of the retinal microvasculature [with PV-OCT] than with the fluorescein angiography,” Schwartz said. “The software analysis of the spectral-domain OCT data allows us to generate angiographic images that reveal more about the microvasculature in the retina and the choroid than conventional fluorescein angiography or ICG angiography.”

The study was published online ahead of print in Ophthalmology.

Subjects and methods

The study included four subjects who underwent retinal vascular imaging with FA and PV-OCT: one healthy subject, one subject with dry AMD, one subject with exudative AMD and one subject with nonproliferative diabetic retinopathy.

Software data processing of the entire cross-sectional image from consecutive B-scans was used to generate PV-OCT images. The investigators calculated phase variance through the variance of motion-corrected phase changes captured within multiple B-scans at the same position. Repeating the calculations over the entire volumetric scan generated a three-dimensional PV-OCT image of the vasculature.

“It’s basically automated detection, so you’ll be able to image neovascularization and regions of capillary non-perfusion using OCT rather than having to have a skilled clinician look with the biomicroscope trying to detect these abnormalities. OCT has already allowed us to very precisely depict macular edema, but what we haven’t been able to do is depict neovascularization,” Schwartz said. “I think the most important thing for us is going to be visualization of neovascularization in proliferative diabetic retinopathy. We’re working on that now.”

Results and conclusions

PV-OCT noninvasively provided a two-dimensional depth color-coded map of the retinal and choroidal vasculature. It imaged the choriocapillaris with better resolution of microvascular detail. Areas of geographic atrophy and choroidal neovascularization imaged by FA were imaged on PV-OCT.

Both FA and PV-OCT showed regions of capillary nonperfusion from diabetic retinopathy.

“For the first time, we show in this paper that we can image the choriocapillaris as well as the other layers of the choroid and show those vascular layers in one image,” Schwartz said. “It will allow us to evaluate the role of the choriocapillaris in such diseases as dry and wet macular degeneration and possibly also glaucoma.”

FA and PV-OCT images of microaneurysms did not agree completely.

“Our hypothesis is that it has to do with the depth of the imaging plane. We think we’ll be able to capture all of the microaneurysms that are in the retinal PV-OCT images at various planes of the retinal capillaries,” Schwartz said. “All of those planes are shown simultaneously in a fluorescein angiogram. We think that depth of imaging will allow us to get better visualization using the PV-OCT compared to FA, but that is yet to be proven.” – by Matt Hasson

Reference:

Schwartz DM, et al. Ophthalmology. 2013;doi:10.1016/j.ophtha.2013.09.002.

For more information:

Daniel M. Schwartz, MD, can be reached at Box 0730, Department of Ophthalmology and Vision Science, University of California, San Francisco, CA 94143; email: dan.schwartz@ucsf.edu.
Disclosure: Schwartz, Fingler and Frazer hold an issued patent on the PV-OCT technology. They also hold founders’ shares in a company with an interest in the technology. The remaining authors have no relevant financial disclosures.