Abstract

Imaging one type of tissue in another by using light has potential applications in imaging tumors and other diseased tissues that differ .from their surrounding medium in terms of their optical properties. A successful optical imaging method may provide an alternative to conventional mammography, which uses harmful x-rays. Strong random multiple-scattering in tissues renders conventional trans illumination techniques using cw light ineffective. However, the limitations of steady-state transillumination can be overcome by using ultrashort laser pulses and time-resolved detection methods. When ultrashort laser pulses are incident on a slab of scattering medium, the transmitted pulses consist of a ballistic component,¹ a diffuse component, and a snake component.² The ballistic component retaining the coherence of the incident photons is the most suitable for imaging. This component is too weak to be detected in most cases as it decreases exponentially with the thickness of the sample. The diffuse photons do not provide enough information about any particular path since they traverse various different paths in the medium. On the other hand, since the snake photons travel along zig-zag paths slightly off the straight line path, they can provide enough information about the optical properties of the scattering medium along this path and about any foreign object lying on it.

© 1993 Optical Society of America