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B. Sander, T.M. Joergensen, M. Larsen; Improved OCT Imaging With a New Averaging Method . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2572.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the effect on image quality of a new averaging method for OCT3 scans Methods: A dominant source of noice in OCT is the signal from nearby scatteres in the measuring volume of the OCT scan. Repeated OCT–scans (Stratus, Carl Zeiss, Meditec) were obtained with 512 points per 6mm line scan in the line–mode, approximately 15 times. An averaging algoritm was applied to reduce noise (speckle) with a robust correlation algoritm using a maximising a least square measure of the diffence between corresponding A–scans. For detailed examination the images were shown in gray and color scale. The method was evalated on healthy subjects, patients with diabetic macular edema, macular hole and central serous chorioretinopathy. Results: The averaged images showed a distinctive appearance and separation of the inner and middle retinal layers in comparison to standard images, ie. the high reflectance of the plexifom layers, the external limiting membrane and the junction between inner and outer photoreceptor segments was improved in contrast against the low–reflecting nuclear layers. Also, the outer photoreceptor and retinal pigment epithelium (RPE) layers showed more details than the standard image and 3 hyperreflective and two hyporeflective layers are now clearly discernible in the outer hyperreflective layer of the OCT scan. From cases of healthy subjects and chorideal serous retinopathy the 3 hyperreflective layers of the outer OCT band can now be attributed to the junction of inner/outer photoreceptor segments, the interdigitising outer photoreceptor segments / RPE villi and the outermost layer the cell bodies of the RPE. Whether or not a signal from the choriocapillaris is included in this outermost layer has yet to be determinded. Conclusions: Averaging of OCT3/stratus scans improves the visual quality considerably and allows a detailed interpretation of the retinal layers superior to standard scans and the intraretinal location of pathological changes. Averaged images are in particular useful to study whether the outer parts of photoreceptor layers or defects of the retinal pigment epithelium is present in the individual patient.
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