Phase-domain processing of optical coherence tomography images

In optical coherence tomography (OCT), images are usually formed from the e nvelope of the measured interference signal. Computation of the absolute ma gnitude of the signal for measurement of the envelope is a nonlinear proces s that destroys phase information. This study explores the idea of recordin g and processing the phase of the OCT interference signal before calculatio n of the magnitudes for display. Processing the partially coherent OCT sign als in the complex domain provides the opportunity to correct phase aberrat ions responsible for speckle noise in OCT images. We describe an OCT system that incorporates a quadrature-demodulation scheme for accurate recording of the phase and amplitude of OCT signals from single or multiple detectors . A speckle-reduction technique that works in the complex domain, called th e zero-adjustment procedure (ZAP), is investigated as an example of complex -domain processing. After demonstrating its speckle-correction properties m athematically and in numerical simulations, we apply ZAP to OCT images of l iving skin. The results show that ZAP reduces speckle contrast in regions w here scatterer density is high and expands the range of gray values in the image. However, as presently implemented, ZAP tends to blur sharp boundarie s between image features. (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(99)01501-4].