Monte Carlo simulation studies of optical coherence tomography (OCT) and optical Doppler tomography (ODT)

A Monte Carlo simulation model has been developed to study how OCT and ODT imaging results are influenced by multiple scattering effects. For shallow optical depths [less than 3 mean free path (mfp) units] in intralipid (g equals 0.7), the number of detected backscattered photons was found to follow the extinction-single-backscatter model, and accurate mean values and small standard deviations for axial and lateral point spread functions were observed. For deeper depths, the positional accuracy and precision of backscatter was rapidly lost, and the number of detected photons no longer decreased with increasing focus depth in the nonabsorbing medium. For strongly forward-directed scattering in blood (g equals 0.99), depth profiles of the number of detected backscattered photons only approached the extinction-single- backscatter model for very shallow depths (optical depth less than 2 mfp units, metric depth less than 13 micrometers). However, quite accurate and precise point spread functions were observed even for large optical depths (40 mfp units). Doppler detection of blood flow was studied by simulating a 100 micrometer diameter horizontal blood vessel placed 200 micrometers below the surface in 2% intralipid. Simulated depth profiles of average Doppler frequency demonstrated good accuracy in absolute velocity values and localization of flow boundaries (3 - 4% deviation). Doppler frequency noise was observed in backscattering from regions underneath the vessel.