Analysis of Short Pulse Laser Interaction With Tissues for Tumor Detection

The objective of the work is to perform both experimental and numerical analysis of short pulse laser interaction with tissue medium with the goal of tumor / cancer diagnostics. Short pulse laser probing techniques for diagnostics have distinct advantages over very large pulse width or continuous wave lasers primarily due to the additional information conveyed by the temporal distribution of the optical signals. For short pulse laser source, the shape of output signal is a function of the optical properties of the medium and hence the scattered optical signal provides information about the medium characteristics. Two laser systems are used: a mode-locked short pulse laser (wavelength = 514 nm and pulsewidth = 200 ps) and a frequency doubled diode short pulse laser (wavelength = 776 nm and pulsewidth = 1.3 ps). The scattered optical signals are measured with a Hamamatsu streak camera. First in vitro experiments are performed on mouse skin tissue samples injected with India ink in order to simulate presence of inhomogeneities. Finally, in vivo imaging is performed on anaesthetized rats with tumorogenic agents injected inside skin tissues and on anaesthetized mouse with mammary tumors. Both the temporal and the spatial profiles of the scattered reflected optical signals are compared with the numerical modeling results obtained by solving the transient radiative transport equation using the discrete ordinates technique. The goal is to demonstrate the feasibility of the time-resolved technique in detecting tumors in animal model.