Objective: To determine whether multiple B-scan averaging improves the quality of spectral-domain optical coherence tomography (SD OCT) images of the retina.
Design: Prospective cross-sectional study.
Participants: One hundred one eyes of 84 patients with various retinal diseases.
Methods: A prototype SD OCT system was used with a sensitivity of 98 decibels, air axial resolution of 6.1 mum, and acquisition rate of approximately 18 700 axial scans per second. To evaluate multiple B-scan averaging, a set of 12 B-scan images was obtained at the identical retinal location and the multiple scans were averaged using custom software; some images containing lateral eye motion were rejected. Objective differences in image quality were measured by comparing the contrast-to-noise ratios (CNRs) for key retinal structures in unenhanced and enhanced images using non-repeated-measures analysis of variance and the Dennett post hoc test. Subjective differences in image quality were evaluated by asking trained ophthalmologists independently to rank pairs of unenhanced and enhanced SD OCT images on a 5-point scale (upper or lower image definitely better, slightly better, or equal) and analyzing results using the Scheffe method for paired comparisons.
Main outcome measures: Contrast-to-noise ratio in enhanced versus unenhanced SD OCT images, expert comparison of image quality, and retinal pathologic features in enhanced versus unenhanced SD OCT images.
Results: Averaging >4 SD OCT scans achieved significant improvement in CNR and also improved ophthalmologists' ability to distinguish retinal structures. More than 4 scans could be averaged for 100 (99%) of the 101 eyes with retinal diseases in this study. Averaging >4 SD OCT scans improved visualization of structures, such as abnormalities in the photoreceptor layer and sub-retinal pigment epithelium (RPE) lesions, that could not be identified clearly in single-scan SD OCT images because of various retinal pathologic features. These included intraretinal lesions that mask the underlying structures, such as cystoid macular edema and retinal hemorrhage, and inward shifting of the sensory retina because of pigment epithelial detachment and lesions beneath the RPE.
Conclusions: Multiple B-scan averaging is an easy and practical method to improve the quality of retinal images obtained by SD OCT and thereby to improve the diagnosis and management of retinal diseases.