Measurement of tissue optical properties in a wide spectral range: a review [Invited]

Abstract

A distinctive feature of this review is a critical analysis of methods and results of measurements of the optical properties of tissues in a wide spectral range from deep UV to terahertz waves. Much attention is paid to measurements of the refractive index of biological tissues and liquids, the knowledge of which is necessary for the effective application of many methods of optical imaging and diagnostics. The optical parameters of healthy and pathological tissues are presented, and the reasons for their differences are discussed, which is important for the discrimination of pathologies and the demarcation of their boundaries. When considering the interaction of terahertz radiation with tissues, the concept of an effective medium is discussed, and relaxation models of the effective optical properties of tissues are presented. Attention is drawn to the manifestation of the scattering properties of tissues in the THz range and the problems of measuring the optical properties of tissues in this range are discussed. In conclusion, a method for the dynamic analysis of the optical properties of tissues under optical clearing using an application of immersion agents is presented. The main mechanisms and technologies of optical clearing, as well as examples of the successful application for differentiation of healthy and pathological tissues, are analyzed.

Transcranial photobiomodulation for brain diseases: review of animal and human studies including mechanisms and emerging trends

“…Mitrofanis’ group showed that the neuroprotective benefits of tPBM (670 nm) were more effective in the BALB/C strain than in the C57BL/6 strain. This could be attributed to deeper photon penetration, far into the brain from the skin in the BALB/C mice 89 , 225 . They also discovered that the neuroprotective effects of tPBM existed in the SNc region but not in the periaqueductal grey matter (PaG) and zona incerta-hypothalamus (ZI-Hyp) regions.…”

Monitoring of optical properties of tumors during laser plasmon photothermal therapy

“…We used the average refractive index for all tissues for MC simulations, equal to 1.37 in the visible and near-infrared spectral ranges [32]. For more accurate estimates, it is necessary to consider the refractive indices' values for different tissue layers, their dispersion, and temperature dependencies [37,38]. Optical parameters of all tissues were calculated for each animal and then averaged by groups.…”

Hemispherical Rutile Solid Immersion Lens for Terahertz Microscopy with Superior 0.06–0.11λ Resolution

“…PG and its aqueous solutions were common hyperosmotic agents in the immersion optical clearing of tissues in the visible, infrared, and even THz bands. [68][69][70] In refs. [64,71], their optical properties were studied (among other liquids), aimed at selecting the optimal agents for the tissue immersion optical clearing in the THz range.…”