Immersion optical clearing of biological tissues in the THz range
Daria S. Ustiantseva¹, Daria R. Il'enkova¹, Valery V. Tuchin², Nikita V. Chernomyrdin¹, Kirill I. Zaytsev¹; ¹Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia; ²Saratov State University, Saratov, Russia.
Abstract
The penetration depth of terahertz (THz) waves into hydrated biological tissues is limited by hundreds of microns due to strong absorption by tissue water, allowing probing of only superficial tissues. Immersion optical clearing (IOC) increases THz penetration by replacing free tissue water with a hyperosmotic agent featuring much less THz absorption via bimodal diffusion. While IOC is widely used in ultraviolet, visible, and infrared ranges, its THz potential is still to be comprehensively analyzed. Previously, we studied THz optical properties and diffusion coefficients of hyperosmotic agents to select optimal ones. In this work, we continue tissue IOC research in the THz range, focusing on real biological tissues ex vivo and selected optimal agents. Two laboratory setups were assembled. The first relies on reflection-mode backward wave oscillator spectroscopy to study THz reflectivity of tissues ex vivo during IOC, retrieving optical properties and diffusion coefficients from Fabry-Pérot resonances. The second measures collimated transmission spectra of tissues ex vivo in the visible range during IOC to quantify diffusion coefficients, forming a reference to verify THz measurements. Pilot studies show consistency of diffusion coefficients retrieved from visible and THz data, and considerable reduction of THz-wave absorption upon IOC. These results demonstrate high potential of IOC in the THz range, opening broad prospects for systematic research, though more agents and tissue types are to be examined.
Speaker
Ustiantseva Daria Sergeevna
Prokhorov General Physics Institute of the Russian Academy of Sciences
Russia
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