Near-Infrared Optical Tomography in Endoscopy-Geometry

N ear-infrared (NIR) optical tomography is a non-invasive diagnostic imaging technique that has the potential of acquiring unique tissue-specific contrast. The high contrast of NIR optical tomography originates from the stronger light attenuation by hemoglobin relative to water in parenchymal tissue, as well as the distinct spectral differences of hemoglobin between the oxygenated and deoxygenated states. Contrast as high as 300 percent has been demonstrated in NIR tomography for vascular densities of 2 percent, due to increased vascularity in malignant tissues.1 Such high bloodbased contrast means that pathognomic diagnosis for cancer detection and hemodynamic imaging are quite feasible. Over the past two decades, NIR optical tomography has advanced steadily by finding key applications in the characterspectrometer and CCD in the detection. This design enables both the probing in endoscopy-geometry and the rapid sampling for NIR optical tomography. The inset image in the figure shows an example of this endoscopy-geometry NIR tomography imaging, obtained from inside avian rectal tissue ex vivo, sampled at an 8Hz frame rate. The walls of the rectal tissue were quite uniform in terms of light absorption; therefore, we injected a tiny amount of exogenous absorption agent made by diluted India ink into the rectal wall to demonstrate the principle. The endoscope NIR probe was then inserted into the rectum and the NIR imaging plane was placed at the region of extraneous absorption agent. The reconstructed image reveals excellent contrast of the occlusion over the ex vivo background tissue. In summary, we demonstrated the first implementation of NIR optical tomography in endoscopy imaging geometry. This innovative technique presents a new paradigm for non-invasive tissue-specific cancer detection in internal organs, including the prostate, colo-rectum and cervix. t