This paper reviews the state of the art of optical coherence tomography (OCT), an interferometric imaging technique that provides cross-sectional views of the subsurface microstructure of biological tissue. Following a discussion of the basic theory of OCT, an overview of the issues involved in the design of the main components of OCT systems is presented. The review concludes by introducing new imaging modes being developed to extract additional diagnostic information.

Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.