Terahertz scattering in biological tissues: spherical and cylindrical scatterers

Abstract

Most applications of terahertz (THz) radiation in medical diagnostics assume that tissues are optically isotropic and homogeneous and can be described within the effective medium theory (EMT) formalism. Meanwhile, recent research demonstrated the wavelength-scale heterogeneity and birefringence of various biological tissues, which can't be accounted for within the EMT framework. This facilitated further research into THz wave transport in soft tissues.
The first stage of our research involved the creation of a phantom to simulate connective tissue with single fat cells. The developed phantom consisted of silicon dioxide microspheres in gelatin solution. Analytical calculation based on Lorenz-Mie theory predicts a non-Rayleigh scattering regime and challenges the applicability of the EMT. However, we theoretically discovered and experimentally confirmed that EMT can determine the effective optical properties of that phantom over a wide limit of scatterer diameters (d ≤ 0.47λ) and volume fractions (fv ≤ 0.2) in cause of strong attenuation of THz waves in the medium.
The second stage devoted creating a phantom to simulate such tissues as muscle, tendon, and nerve fibers. The developed phantom consisted of a single-row PVDF grating filled with gelatin solution. Analytical calculation similarly predicts a non-Rayleigh scattering regime and independence of polarization. However, experimental data demonstrated the polarization-dependent transmission spectra. EMT allows for a description of the interaction of only TM-polarized radiation with this phantom over a wide range of parameters (d ≤ 0.7λ, fv ≤ 0.2). This necessitates the development of a polarization-dependent model to describe radiative transfer in such systems

Speaker

Anna S. Kucheryavenko
Osipyan Institute of Solid State Physics of the Russian Academy of Sciences
Russia

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