Abstract

Based on the probability of a given number of scatterings for photons transmitted through a tissue slab with a unity anisotropy factor, the minimum number of scatterings required for optical imaging of tissues in the transmission mode was estimated. For breast tissue imaging with visible or near infrared light, ballistic imaging is possible only for thicknesses less than 42 mean free paths, which is 0.14 cm for breast adipose tissue at 700 nm wavelength (scattering coefficient is 300 cm^–1). For a 5-cm thickness, at least 1100 scattering events must be allowed to receive on average a single transmitted photon from 10-18 input photons (about 1-J visible light). Monte Carlo simulations have shown that the anisotropy of traveling direction of photons after i scatterings decays exponentially with i. The photons that are launched in the same direction will travel practically isotropically after 3/(1–g) scatterings, where g is the anisotropy factor of the tissue. For the breast adipose tissue with g equal to 0.97, 3/(1–g) is 100.

© 1994 Optical Society of America