Abstract
A side-viewing, 2.3-mm diameter oblique incidence reflectometry endoscope has been designed to obtain optical property measurements of turbid samples. Light from a single-mode fiber is relayed obliquely onto the tissue with a gradient index lens-based distal optics assembly and the resulting diffuse reflectance profile is imaged and collected with a 30,000 element, 0.72 mm clear aperture fiber bundle. Sampling the diffuse reflectance in two-dimensions allows for fitting of the reflected intensity profile to a well-known theoretical model, permitting the extraction of both absorption and reduced scattering coefficients of the tissue sample. Models and measurements of the endoscopic imaging system are presented in tissue phantoms and in vivo mouse colon, verifying the endoscope's capabilities to accurately measure effective attenuation coefficient and differentiate diseased from normal colon.
Highlights
Using FRED analysis tools, irradiance plots were obtained at the analysis surfaces in the full oblique incidence reflectometry (OIR) endoscope models, the offset and effective attenuation coefficients extracted, and the absorption and reduced scattering coefficients computed
The most unique aspect of this endoscope is the concept of using a 2-D fiber bundle to collect diffuse reflectance from only one side of the angled incident illumination, and using image gradients to estimate the location of the diffuse reflectance peak
All that is needed to create angled illumination is to place the illumination fiber off the central optical axis. Such endoscopes can be forward looking or side-looking with the addition of a right-angle prism or other reflecting surface. An advantage of this technique is that it requires the use of only one wavelength of illumination
Summary
The most common method of evaluating tissue properties is through integrating sphere measurements,[12] though this setup is usually limited to thin ex vivo tissue samples. Through implementation of diffusion theory, which is valid for observation points far from the light source, optical fiber bundles[13] and video reflectometers[14] have been used to measures a tissue’s diffuse reflectance profile and compute optical properties. These single wavelength implementations utilized a normally incident light source and either measured only the effective attenuation coefficient, μeff, or assumed absorption in the tissue to be negligible while measuring only μs[0]
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