Professor Hanli Liu
Joint Program in Biomedical Engineering
The University of Texas at Arlington and
The University of Texas Southwestern Medical Center at Dallas
4 PM, Friday, Nov. 14, 1997
Note unusual schedule
Room 101, Olin Physical Laboratory
When tissue is illuminated with near infrared (NIR) light, the light will be either absorbed by various chromophores, such as hemoglobin, or highly scattered by tissue cells and intracellular organelles, such as mitochondria. Recent development of NIR spectroscopy and imaging affords new mechanisms for clinical monitoring and diagnosis of tissue property, structure, and function. The theoretical basis for the technology is the diffusion approximation to the photon transport equation, which has been proved as a good mathematical model for photon migration in tissue. Technically, any of three classes of devices using pulsed, intensity-modulated, and continuous light can be coupled to optical fibers/fiber bundles for light delivery to and collection from the tissues under study. In the time-domain case, picosecond laser pulses are broadened by the turbid tissue, and then can be detected by a single photon counting system. In the frequency-domain system, the phase of intensity-modulated light will be delayed because of scattering of the tissue, and the phase delay can be measured by either a homodyne or heterodyne system. Finally, in the continuous light case, a change in light intensity caused by light absorption can directly reflect a change in blood oxygenation in tissue. If multiple measurements are performed using any of these three systems, it is possible to reconstruct an optical image for hidden objects. Several examples of both in vitro and in vivo studies using these techniques will be present, showing a significant value of the techniques to clinical use, such as tumor detection and brain oxygenation monitoring.