Lipofuscin-Type Pigment as a Marker of Colorectal Cancer

Abstract

The study of the optical properties of biological tissues for a wide spectral range is necessary for the development and planning of noninvasive optical methods to be used in clinical practice. In this study, we propose a new method to calculate almost all optical properties of tissues as a function of wavelength directly from spectral measurements. Using this method, and with the exception of the reduced scattering coefficient, which was obtained by traditional simulation methods, all the other optical properties were calculated in a simple and fast manner for human and pathological colorectal tissues. The obtained results are in good agreement with previous published data, both in magnitude and in wavelength dependence. Since this method is based on spectral measurements and not on discrete-wavelength experimental data, the calculated optical properties contain spectral signatures that correspond to major tissue chromophores such as DNA and hemoglobin. Analysis of the absorption bands of hemoglobin in the wavelength dependence of the absorption spectra of normal and pathological colorectal mucosa allowed to identify differentiated accumulation of a pigment in these tissues. The increased content of this pigment in the pathological mucosa may be used for the future development of noninvasive diagnostic methods for colorectal cancer detection.

Spectral Optical Properties of Rabbit Brain Cortex between 200 and 1000 nm

“…The optical properties of biological tissues are unique to those tissues and provide means for their identification. The estimation of their wavelength dependence allows the identification of biological components in tissues and the discrimination of pathologies [1]. There are various optical properties, but the most commonly used to characterize a biological tissue are the refractive index (RI), the absorption coefficient (µ a ), the scattering coefficient (µ s ) or the reduced scattering coefficient (µ s ) and the scattering anisotropy (g) [2,3].…”

“…This means that a fast way to obtain the optical properties of a tissue for a wide spectral range is necessary. As recently published [1,9], if some spectral measurements from the tissue samples are available, certain equations can be used for a fast calculation of such properties. If the absorption properties of a tissue are considerably higher than its scattering properties, the Bouguer-Beer-Lambert law can be used to describe such an absorption-dominated medium [10]:…”

“…For any slab-form tissue sample that is irradiated by a light beam of intensity I 0 (λ), three optical phenomena will occur [2]: transmittance, reflectance and absorbance. If we can measure the total transmittance (T t ) and total reflectance (R t ) spectra from such a sample, its A(λ) can be calculated using the following relation [1,9]:…”

“…(3) Equation ( 3) can be used to calculate A(λ) for any sample that contains major absorption, major scattering, or a combination of absorption and scattering properties. When combining Equations (2) and (3), it is possible to calculate µ a (λ) from such T t and R t spectra that were measured from a tissue slab sample [1]:…”

“…where T t (λ) and R t (λ) are represented as ratios of total intensity of transmitted and reflected light measured with the corresponding integrating spheres to intensity of the incident light I 0 (λ), respectively; µ a (λ) is calculated in cm −1 (or mm −1 ), depending on the units used to measure d (cm or mm). Since biological tissues are dominated by light scattering properties, once µ a (λ) is calculated with Equation (4), and if collimated transmittance (T c ) spectra from the tissue are available, then the following form of the Bouguer-Beer-Lambert law can be used to calculate µ s (λ) for the same wavelength range [1][2][3]:…”