Imaging tissue response to electrical and photothermal stimulation with nanometer sensitivity

Background and Objectives: Tissue response to thermal, electrical, or, chemical stimuli are important in the health and survival of tissue. We report experimental results to assess tissue response to various stimuli using a low coherence differential phase interferometer. Study Design/Materials and Methods: The optical system utilized to measure tissue response is a novel fiber-based phase sensitive optical low coherence reflectometer (PS-OLCR). Inasmuch as the PS-OLCR works with back-reflected light, noninvasive sensing of tissue response to stimuli is possible. In addition to high lateral (similar to10 mum) and longitudinal (similar to10 mum) resolution, PS-OLCR can measure sub-wavelength changes in optical path-length (Angstrom/ nanometer range) by extracting the phase difference between. interference fringes in two channels corresponding to orthogonal polarization modes. Results: When light spatially splits into two polarization states, precise analysis of surface topography, or tissue surface response such as swelling or collapse are possible. Time resolved measurements of nanometer-scale path length changes in response to electrical and thermal stimuli are demonstrated using longitudinally delayed polarization channels. Conclusions: Since PS-OLCR is a useful tool to detect ultra-small path length changes, the system has potential to aid scientists in investigating important phenomena in biomaterials :and developing useful diagnostic and therapeutic imaging modalities. Applications include tissue surface profilometry, measurement of tissue, and cell response to various stimuli, high-resolution intensity and phase imaging. (C) 2003 Wiley-Liss, Inc.