Using a polarization sensitive Michelson interferometer, we measure two-dimensional images of optical birefringence in bovine tendon as a function of depth with a technique known as Optical Coherence Tomography (OCT). Detection of the polarization state of the signal, formed by interference of backscattered light from the sample and a mirror in the reference arm, gives the optical phase delay between light that has propagated along the fast and slow axes of the birefringent tendon. Images showing the change in birefringence in response to laser irradiation are presented. The technique allows rapid non-contact investigation of tissue structural properties through two-dimensional imaging of birefringence.

T-cell contact with antigen-presenting B cells initiates an activation cascade which includes an increase in T-cell intracellular calcium and leads to T-cell proliferation and differentiation. We studied cell-cell contact requirements for T-cell activation using an optical trap to control the orientation of T-cell/B-cell pairs and fluorescence microscopy to measure subsequent T-cell [Ca2+]i response. B cells or beads coated with antibodies to the T-cell receptor (TCR) are trapped with a titanium-sapphire laser and placed at different locations along the T-cell, which has a polarized appearance defined by die shape and direction of crawling. T-cell [Ca2+]i is detected as an emission shift from the combination of fura-red and Oregon-green, two cytoplasmic [Ca2+] indicators. T cells which are presented antigen at the leading edge have a higher probability of responding and a shorter latency of response than those contacting B-cells or beads with their trailing end.