Abstract
Purpose :
Optical coherence tomography angiography (OCT-A) is an en face imaging modality that highlights the vascular abnormality. On the other hand, tissue light attenuation (TLA) can be a direct indicator or tissue scattering abnormalities that would be sensitive to the thickening of the retinal pigment epithelium (RPE), hyperreflective foci, and choroidal neovascularization (CNV). While OCT-A is an en face modality, TLA should have been interpreted in a depth-resolved manner. Hence, these two had to be used separately. This presentation demonstrates a new en-face-image-formation method that fuses OCT-A and TLA signals and gives an en face image being sensitive to the vasculature and tissue scattering abnormalities.
Methods :
The custom-made 1.0-µm swept-source OCT, similar to a commercially available SS-OCT, was used. Depth-resolved cumulative TLA (cTLA), which is the total amount of light attenuation occurred from the surface to the particular depth of the tissue, is computed from the OCT. The cTLA and 3D OCT-A volumes are fused into a pseudo-color tomographic volume. The cTLA defines the pixel color, and the OCT-A defines the pixel brightness. An en face pseudo-color image (attenuation-and-flow image; AAF) is obtained by projecting along with depth. In this en face image, the vessels are appeared with different colors according to the total amount of light attenuating materials above the vessel as blue-red-yellow (more to less attenuating material).
Results :
Figure 1 shows en face images of a choroidal neovascularization (CNV) subject. The en face OCT (Fig. 1 A) and OCT-A (entire depth, Fig. 1 B) visualize the distributions of attenuation difference and vasculature. The en face AAF image (Fig. 1 C) visualizes the light attenuation property of the tissue, vasculature, and, the relative depth position of them. At the CNV location, some parts of the vessels appear in red. It suggests that highly attenuating materials do not exist above the vessel. And, these red-color vessels collocate with the hyper-fluorescence of fluorescein angiography (Fig 1D).
Conclusions :
The en face AAF image was found to visualize the tissue attenuation property and vessel abnormality successfully. Since this imaging method does not require special hardware, it can be quickly applied to the current daily diagnostic routine.
This is a 2020 Imaging in the Eye Conference abstract.