CONTRAST LIMITS OF COHERENCE-GATED IMAGING IN SCATTERING MEDIA

The fundamental difference between time-resolved and coherence-gated i maging modalities in scattering media is analyzed in terms of their op tical transfer functions. The effectiveness of coherence gating for mu ltiple-scattering rejection is shown by imaging a 100-mu m-thick razor blade hidden in the scattering phantoms (i.e., Intralipid suspensions ) with different scattering coefficients. We found that the imaging co ntrast is limited by multiple scattering and speckle effects in high-s cattering media, and the measured effective penetration depth of optic al coherence tomography is approximately equal to six mean free paths under the experimental conditions of a numerical aperture of less than 0.1 and a scattering anisotropy of approximately 0.8. (C) 1997 Optica l Society of America.