Determination of continuous complex refractive index dispersion of biotissue based on internal reflection

Abstract

The complex refractive index dispersion (CRID), which contains the information on the refractive index dispersion and extinction coefficient spectra, is an important optical parameter of biotissue. However, it is hard to perform the CRID measurement on biotissues due to their high scattering property. Continuous CRID measurement based on internal reflection (CCRIDM-IR) is introduced. By using a lab-made apparatus, internal reflectance spectra of biotissue samples at multiple incident angles were detected, from which the continuous CRIDs were calculated based on the Fresnel formula. Results showed that in 400-to 750-nm range, hemoglobin solution has complicated dispersion and extinction coefficient spectra, while other biotissues have normal dispersion properties, and their extinction coefficients do not vary much with different wavelengths. The normal dispersion can be accurately described by several coefficients of dispersion equations (Cauchy equation, Cornu equation, and Conrady equation). To our knowledge, this is the first time that the continuous CRID of scattering biotissue over a continuous spectral region is measured, and we hereby have proven that CCRIDM-IR is a good method for continuous CRID research of biotissue.

Wavelength dependence of the refractive index of human colorectal tissues: comparison between healthy mucosa and cancer

“…Considering the visible wavelength range, our experimental data is much approximated to data presented in literature [4]. Since the lowest laser wavelength we used in our measurements was 401.4 nm, we have verified that both Cornu and Conrady equations are the best to fit the decaying RI behavior with wavelength that is described in literature for biological tissues [21,23]. Cauchy's equation allows for good RI fittings for wavelengths above 450 nm, as demonstrated by authors of Ref.…”

“…(6). For ultraviolet wavelengths, our data seems to have more consistent wavelength decay as described in literature [21,23]. Such difference is visible, since we have used a laser with 401.4 nm in our measurements.…”

“…According to literature, there are three equations that are commonly used to fit the RI of biological tissues -the Cauchy equation (equation 6), the Cornu equation (equation 7) and the Conrady equation (equation 8) [21,23]:…”

Water Content and Scatterers Dispersion Evaluation in Colorectal Tissues

“…After obtaining the mean RI values from each type of tissue at these wavelengths, we have used CFTOOL in MATLAB TM to fit that data with the curves that are commonly used for biological tissues [34][35]. For all tissues we obtained the corresponding dispersion curves between 400 and 1000 nm and the best data fitting was found with the Cornu equation [34][35]:…”

Measurement of refractive index of hemoglobin in the visible/NIR spectral range

“…Because of tissue heterogeneity, n is always known as the effective or average RI. 24,26 According to the classical theory of light dispersion, the components of the complex RI of molecular structures can be written as [21][22][23][24][25] E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 0 2 ; 3 2 6 ; 4 1 0…”