In vivo absorption and scattering spectroscopy of biological tissues

Abstract

Different approaches for absorption and scattering spectroscopy of living tissues are discussed. In particular, a unique system for time-resolved reflectance and transmittance spectroscopy is presented, capable of acquiring in vivo absorption and scattering spectra of diffusive media between 600 and 1000 nm. A review of typical spectra obtained from a variety of tissue structures is shown, including female breast, forearm, abdomen, and forehead. A second-level analysis of the measured spectra permits an estimation of the concentrations of the key tissue absorbers, as well as of the Mie-equivalent scattering radii. Further, absorption and scattering spectra can be used to estimate the penetration depth of light in tissues as a function of wavelength, which is a crucial parameter in view of the possible application of optical in vivo molecular imaging in clinical diagnosis. Finally, an example of the applicability of the methodology to other biological media such as fruits and vegetables is shown.

Susceptibility of Candida albicans to photodynamic therapy in a murine model of oral candidosis

“…48 Despite these considerations, it is known that light penetration into the tissue is proportional to its wavelength when considering the UV-near infrared range, i.e., the longer the wavelength, the deeper is the light penetration. [49][50][51][52] The shorter wavelengths are better absorbed by biological molecules, i.e., the greater part of light intensity is absorbed by the superficial tissue layers and as a consequence, lower penetration is observed. Whereas, photons in the red and infrared range are less absorbed by the biological chromophores and a higher light penetration is achieved.…”

Transabdominal near infrared oximetry of hypoxic stress in fetal sheep brain in utero

“…In the top layer, d was fixed based on thickness measurements of the maternal skin, fetal skin, and fetal skull postmortem. The background a bg ( ), the scattering properties A and b, the baseline THC of both layers, and the baseline StO 2 of the top layer were assumed based on values reported in the literature (35)(36)(37). The StO 2 values of the bottom layer were obtained from the hemoximeter measurements during the normoxic baseline in each cycle.…”

Reporter systems forin vivotracking of lactic acid bacteria in animal model studies

“…54 Endogenous chromophores such as hemoglobin, keratin and collagen absorb light within tissues in the visible spectrum (400-760 nm). 55 Generally, the absorption of wavelengths longer than 600 nm (red part of the spectrum) by endogenously produced fluorophores is reduced, allowing the propagation of red light through several centimeters of tissue. 56,57 In many applications, the use of fluorescent proteins such as DsRed is hampered by a slow maturation time, photobleaching, oligomerization, brightness of the chromophore and cell toxicity.…”

“…Hemoglobin serves as one of the most significant causes of light absorption in animals. 55 While hemoglobin absorbs light in the visible spectrum (400-760 nm), longer wavelengths of light (above 600 nm) propagate through mammalian tissue more readily. 56 Furthermore, melanin influences the absorption of light in animals with dark fur.…”