Development of diffuse optical imaging systems for clinical applications

Diffuse optical imaging system is emerging as a feasible biomedical imaging modality in many clinical applications such as imaging of brain, breast, limb and joint. The harmless near-infrared light is used for measuring local changes of oxyhemoglobin and deoxyhemoglobin concentrations in tissue. Since the diffuse photon has an e^-1 penetration depth on the order of 0.5 cm, near-infrared around 800 nm wavelength can penetrate several centimeters into human breast tissue. Diffuse optics offers ability for probing absorption and scattering properties of human breast tissues and it also can provide lesion detection with abnormality monitoring. In a diffuse optical system, sources and detectors are placed around the object to be monitored in various geometric configurations. Since it is difficult to directly measure the photon migration in tissue, Monte Carlo simulation is a good tool for the estimation of the optical pathway with various source-detector separations in human breast tissues. Besides, image reconstruction in DOT is an important issue that involves both the forward and the inverse problems. The diffusion equation is usually used to solve the forward problem and provides a good prediction of light distribution on the basis of presumed parameters for both th e light source and the object. However, the early-arrived photon without strong scattering is ignored in the diffusion equation and it deteriorate reconstructed image in superficial subsurface region of tissue. Although the inverse problem is ill-posed, recovering imaging information based on time resolved diffuse reflectance is possible in Monte Carlo simulation.