Effect of bile absorption coefficients on the estimation of liver tissue optical properties and related implications in discriminating healthy and tumorous samples

Abstract

We investigated differences between healthy tissue and metastatic tumor from ex vivo human partial liver resections using diffuse optical spectroscopy with a fiber optic probe. We extracted various physiological and morphological parameters from the spectra. During evaluation of the residual between the measurements and a fit model based on diffusion theory, we found that bile is an additional chromophore absorbing in the visible wavelength range that was missing in our model. Consistency of the residual with the absorption spectrum of bile was noticed. An accurate measurement of the absorption coefficient of bile from various human bile samples was performed and implemented into the fit model. Having the absorption coefficient of bile as a priori knowledge in the model showed a clear improvement in terms of reducing the fitting discrepancies. The addition of this chromophore yields significantly different estimates of the amount of blood. Furthermore, the estimated bile volume fraction and reduced scattering amplitude turned out to be two main relevant discriminators between normal and metastatic liver tissues.

Diffuse reflectance spectroscopy of human liver tumor specimens - towards a tissue differentiating optical biopsy needle using light emitting diodes

“…3 suggest that the optical properties of tissue types contain the most discriminative information for tissue classification in the VIS wavelength range between 450 nm and 750 nm. These findings are similar to those that have been reported for different ex vivo studies on human liver tissue of tumor patients with primary cancer [14], as well as with liver metastases [17][18][19].…”

“…These observations originate from different chromophores for both primary and secondary tumor types. Since metastases consist of abnormal cells with their origin in other organs, the amount of bile with high absorption between 400 nm and 500 nm is low [17,18,31]. Extracted from diffuse reflectance spectra, Nachabé et al [18] have shown that the amount of bile in metastatic tumor tissues is 80% lower than in healthy liver tissue.…”

“…Since metastases consist of abnormal cells with their origin in other organs, the amount of bile with high absorption between 400 nm and 500 nm is low [17,18,31]. Extracted from diffuse reflectance spectra, Nachabé et al [18] have shown that the amount of bile in metastatic tumor tissues is 80% lower than in healthy liver tissue. Although, primary liver cancer cells can produce bile, the diffuse reflectance spectra show comparable results of absorption in the wavelength range between 400 nm and 500 nm with spectra of metastases [14].…”

“…The selection of used LEDs was based on publications by Nachabé et al [18] and Bydlon et al [26]. They summarized wavelength-dependent absorption characteristics of various chromophores with their relevance for the liver and effect on optical properties after tumorous changes.…”

“…Spectroscopic detection of malignant tumors in liver specimens has been successfully performed for primary liver cancer [14] and liver metastases in humans [15][16][17][18][19] as well as in animal models [20,21]. In a clinical ex vivo study by Evers et al [17] liver specimen of 24 patients who underwent surgery for colorectal liver metastases were analyzed with DRS in the visible (VIS) and near infrared (NIR) spectral range.…”