Time resolved breast transillumination: analytical, numerical and experimental study
This work is mainly dedicated to the study of light transport through biological tissues and particularly the propagation of a light pulse. This study does not take into account the nonlinear properties of biological tissues. Different approaches were planned and then compared in order to understand and describe the physical phenomenon as well as possible. The analytical approach based on the Boltzmann transport equation gives satisfactory results for the qualitative description of the transmission of a collimated beam, but lacks precision for the quantitative determination. Nevertheless, the analytical consideration remains a useful approach to predict the behaviour of light propagating through tissues and a versatile method for this kind of study. A Monte-Carlo simulation has been developed to predict the quality of time resolved images of the breast by transillumination. The smallest diameter of a detectable carcinoma located in the breast has been computed. The simulation suggests that time-resolved imaging of the breast is possible and invaluable in the near infra-red (NIR) by transillumination. The enhancement of the transfer function by the introduction of time resolved detection is limited by the contribution of noise at short gating times. The estimated diameter of the smallest detectable sphere is derived from the image quality index theory (or IQI theory) and its value is around 4 [mm] for a 40 [mm] thick breast. The simulated images of a sphere (approximating the carcinoma) within a homogeneous medium (approximating the surrounding tissue) show a significant improvement of the image with short gating time. Experimental trials with a streak camera have confirmed our model, and the gating of the signal has been shown to be possible with an ultrafast electro-optic modulator based on the travelling wave principle.