Creation of Composite OCT3 Image

Abstract

Abstract: : Purpose: Creating a composite image out of multiple images scanned at the same location is a widely used technique to reduce variability. The purpose of this study was to create composite optical coherence tomography (OCT; StratusOCT, Carl Zeiss Meditec, Inc., Dublin, CA) images and to assess the effect of composite image creation on nerve fiber layer (NFL) thickness measurement. Methods: Stratus OCT fast NFL scan images (a set of 3 individual images with 256 sampling points) were obtained on normal eyes 3 times per day on each of 3 separate days. Composite images were created out of 3 images of each set by aligning to the internal limiting membrane and calculating a mean reflectivity value for each corresponding pixel. A histogram of individual A–scans was normalized to an arbitrary standard histogram to compensate variable pixel reflectance. Composite image creation and NFL thickness measurement were performed using a software program of our own design. NFL thickness was measured on both individual images and composite images. In a manner similar to that of the commercial OCT software, mean NFL thicknesses were calculated mathematically for each set with individual image analysis and then compared with NFL thickness measurements on the corresponding composite images. Results: 45 composite images were created out of 135 individual images of 5 normal volunteers (mean age 31.4 ± 9.1 years). NFL thickness was thicker with composite analysis than with mathematical mean thickness (110.3 ± 10.3 µm vs 102.1 ± 11.2 µm, p<0.001, paired t–Test). Overall coefficient of variation was smaller with composite analysis than mathematical mean thickness (4.0 ± 2.2% vs 5.6 ± 2.5%, p=0.035). Conclusions: OCT NFL thickness measurement reproducibility improved with composite image analysis. Composite image creation may reduce scan by scan variability yielding more reproducible NFL measurements.

Keywords: image processing • imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)