Catheter based instrument for simultaneous OCT imaging and fluorescence spectroscopy

We have developed an imaging device that provides cross-sectional imaging as well as fluorescence spectroscopy. The first application of this device is to differentiate healthy arterial wall from atherosclerotic plaque. Optical coherence tomography (OCT) provides two-dimensional imaging. OCT images have an imaging length and depth of 1-2 millimeters and 15 micron resolution. Laser induced fluorescence (LW) spectroscopy provides histochemical information. Due to high absorption of excitation wavelengths the fluorescence spectra is integrated from tissue only 200 microns deep. The OCT portion of the device is based on a Michelson interferometer. A superluminescent diode provides light at 1300 nm with 49 nm spectral width, and a galvanometer mounted retroreflector allows the reference arm length to be modulated. A helium cadmium laser provides the excitation source with wavelengths of 325 and 442 nm. In one instrument design, a series of dichroic mirrors is used to combine light from the OCT and LIF systems. In another design, OCT, excitation and emission fibers are combined into the same custom-built catheter for the delivery and collection of light. Preliminary data show that OCT images and LIF spectra give complementary information from normal and atherosclerotic portions of arterial wall.