Colorectal cancer (CRC) is the third most common and the second most deadly type of cancer worldwide. Developing new technologies for accurate CRC detection/delineation for resection during microsurgery requires unveiling tissue biochemical and microstructural changes associated with carcinogenesis. These changes can be probed by diffuse reflectance spectroscopy (DRS), which is capable of extracting tissue chromophore concentrations and scattering parameters. Previous CRC studies have been mostly restricted to chromophores in the visible region and analytical light diffusion models. In this study, we extended this wavelength range to 350–1919 nm and used the range between 450–1590 nm to extract tissue biochemical and microstructural parameters. This extraction was performed by using DRS spectral fitting based on a reflectance look-up table built using Monte Carlo simulations of light propagation in tissues. Tissue parameters were used as an input to classification and regression tree algorithm to estimate parameter thresholds leading to best tissue differentiation for CRC detection/delineation. Differentiation between mucosa and tumor tissues was based on 2889 diffuse reflectance spectra from fresh ex vivo tissue samples from 47 subjects. All analyses were performed to investigate data of superficial tissue up to 1.1 mm and deeper tissue layers up to 1.8 mm. The most important parameters for CRC detection were total lipid content, water content, reduced scattering amplitude, Mie scattering power, and microvascular parameters. We not only confirmed the importance of these parameters with metrics in addition to statistical tests and classification models of our previous studies, but also extended the motivation of achieving successful tissue classification with an area under the receiver operating characteristic curve (AUC) higher than 90% with interpretable DRS spectral fitting parameters. Our analysis may have important clinical applications for the rapid diagnosis of colorectal neoplasia.
Tissue biomolecular and microstructure profiles for optical colorectal cancer delineation suggest mucosa and tumors can be differentiated mainly based on lipid, water, tissue scattering properties and microvascular parameters.
The development of photomedical modalities for diagnostics and treatment has created a need for knowledge of the optical properties of the targeted biological tissues. These properties are essential to plan certain procedures, since they determine the light absorption, propagation and penetration in tissues. One way to measure these properties is based on diffuse reflectance spectroscopy (DRS). DRS can provide light absorption and scattering coefficients for each wavelength through a non-invasive, fast and in situ interrogation, and thereby tissue biochemical information. In this study, reflectance measurements of ex vivo mice organs were investigated in a wavelength range between 350 and 1860 nm. To the best of our knowledge, this range is broader than previous studies reported in the literature and is useful to study additional chromophores with absorption in the extended wavelength range. Also, it may provide a more accurate concentration of tissue chromophores when fitting the reflectance spectrum in this extended range. In order to extract these concentrations, optical properties were calculated in a wide spectral range through a fitting routine based on an inverse Monte-Carlo look-up table model. Measurements variability was assessed by calculating the Pearson correlation coefficients between each pair of measured spectra of the same type of organ.
Scattering property of Intralipid is widely used for calibration and simulation of turbid media, especially biological tissues, in optical spectroscopic studies. The desired phantom turbidity level matching that of target tissue scattering properties is vital in the right preparation of phantoms mimicking the tissue. A simplified two fiber oblique illumination-collection geometry setup is used along with iterative inverse Monte Carlo simulations on the diffuse reflectance obtained experimentally for estimating the reduced scattering coefficient (μś) of Intralipid-20% for wavelengths ranging from 500 nm to 880 nm. Basic Monte Carlo for Multi Layered media (MCML) code is modified to incorporate the two fiber inverse model of diffuse reflectance with oblique broadband illumination and perpendicular collection of diffusively reflected light from the sample. Wavelength dependent true phase function of Intralipid is incorporated in the model and a semi-empirical concentration scaling methodology is used to obtain volume concentration dependence on the μś. In the inverse modelling, the modified Twersky equation for correlated scattering has been used to obtain the μś profile of Intralipid-20% for its volume concentration ranging from 16% to 100%. The results are shown to be in good agreement with the optical characterization studies of Intralipid-20% involving bulkier instrumentation for the wavelength range under consideration. The study presented in this paper gives an insight for an in vivo fiber based methodology for quantifying the variation of optical scattering during tissue malignancy.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.