ACCURACY AND NOISE IN OPTICAL DOPPLER TOMOGRAPHY STUDIED BY MONTE-CARLO SIMULATION

A Monte Carlo model has been developed for optical Doppler tomography (ODT) within the framework of a model for optical coherence tomography (OCT). A phantom situation represented by blood Bowing in a horizonta l 100 mu m diameter vessel placed at 250 mu m axial depth in 2% intral ipid solution was implemented for the Monte Carlo simulation, and a si milar configuration used for experimental ODT measurements in the labo ratory. Simulated depth profiles through the centre of the vessel of a verage Doppler frequency demonstrated an accuracy of 3-4% deviation in frequency values and position localization of flow borders, compared with true values. Stochastic Doppler frequency noise was experimentall y observed as a shadowing in regions underneath the vessel and also se en in simulated Doppler frequency depth profiles. By Monte Carlo simul ation, this Doppler noise was shown to represent a nearly constant lev el over an investigated 100 mu m interval of depth underneath the vess el. The noise level was essentially independent of the numerical apert ure of the detector and angle between the flow velocity and the direct ion of observation, as long as this angle was larger than 60 degrees. Since this angle determines the magnitude of the Doppler frequency for backscattering from the flow region, this means that the signal-to-no ise ratio between Doppler signal from the flow region to Doppler noise from regions underneath the flow is improved by decreasing the angle between the flow direction and direction of observation. Doppler noise values from Monte Carlo simulations were compared with values from st atistical analysis.