Abstract-Terahertz dielectric spectroscopy of human brain gliomas and intact tissues ex vivo: double-Debye and double-overdamped-oscillator models of dielectric response

 

A. A. Gavdush, N. V. Chernomyrdin, G. A. Komandin, I. N. Dolganova, P. V. Nikitin, G. R. Musina, G. M. Katyba, A. S. Kucheryavenko, I. V. Reshetov, A. A. Potapov, V. V. Tuchin, K. I. Zaytsev,

 Ex vivo THz complex dielectric permittivity 𝜀̃$\tilde{\epsilon }$ of the intact tissues, edematous tissues and gliomas of the human brain: (a),(b) measured real 𝜀′${\epsilon }^{\prime }$ and imaginary 𝜀″${\epsilon }^{″}$ dielectric permittivity parts for the intact brain tissues, as compared with the DD (Eq. (3)) and DO (Eq. (4)) models; (c)–(l) the same data for the edematous tissues and gliomas; (m) the DD model parameters for water and tissues, from which parameters of the DO model can be calculated using Eq. (5). In (a)–(l), dielectric properties of tissues are compared with the DD model of liquid water from Ref. [42]. Here, GI$\text{I}$–GIV$\text{IV}$ stands for the WHO Grade I$\text{I}$–IV$\text{IV}$ gliomas.

https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-12-1-69&id=444278

Terahertz (THz) technology offers novel opportunities in the intraoperative neurodiagnosis. Recently, the significant progress was achieved in the study of brain gliomas and intact tissues, highlighting a potential for THz technology in the intraoperative delineation of tumor margins. However, a lack of physical models describing the THz dielectric permittivity of healthy and pathological brain tissues restrains the further progress in this field. In the present work, the ex vivo THz dielectric response of human brain tissues was analyzed using relaxation models of complex dielectric permittivity. Dielectric response of tissues was parametrized by a pair of the Debye relaxators and a pair of the overdamped-oscillators – namely, the double-Debye (DD) and double-overdamped-oscillator (DO) models. Both models accurately reproduce the experimental curves for the intact tissues and the WHO Grades I–IV gliomas. While the DD model is more common for THz biophotonics, the DO model is more physically rigorous, since it satisfies the sum rule. In this way, the DO model and the sum rule were, then, applied to estimate the content of water in intact tissues and gliomas ex vivo. The observed results agreed well with the earlier-reported data, justifying water as a main endogenous label of brain tumors in the THz range. The developed models can be used to describe completely the THz-wave – human brain tissues interactions in the frameworks of classical electrodynamics, being quite important for further research and developments in THz neurodiagnosis of tumors.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-FDTD-modelling of terahertz solid immersion microscopy

V. A. Zhelnov,  N. V. Chernomyrdin, A. S. Kucheryavenko,  I. N. Dolganova,  G. M. Katyba,  K. I. Zaytsev,

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11164/111640H/FDTD-modelling-of-terahertz-solid-immersion-microscopy/10.1117/12.2532389.short

Terahertz (THz) solid immersion microscopy is a novel THz imaging modality, which provides both a sub- wavelength spatial resolution and a high energy efficiency, thanks to the absence of sub-wavelength apertures and probes in an optical scheme. In this work, we apply the finite-difference time-domain technique for solving the Maxwell's equations in order to analyze the performance of our original THz SIL arrangement. Namely, we estimate the theoretical limits for the spatial resolution and the depth of field of our optical system, as well as specify the confidential intervals for the alignment of optical elements. The observed results demonstrate the resolution of 0:15λ and the depth of field of 0:12λ(λ is an electromagnetic wavelength), justifying advanced performance of our THz SIL.

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Wide-Aperture Aspheric Optics for Formation of Subwavelength Caustics of a Terahertz Electromagnetic-Radiation Beam

N. V. Chernomyrdin, A. O. Shchadko, S. P. Lebedev, I. E. Spektor, V. L. Tolstoguzov, A. S. Kucheryavenko, K. M. Malakhov, G. A. Komandin, V. S. Gorelik, K. I. Zaytsev

https://link.springer.com/article/10.1134%2FS0030400X18030086

A wide-aperture aspheric lens for focusing a terahertz electromagnetic-radiation beam in a circle of the subwavelength size is proposed. The calculation of the lens and the estimation of size of created caustic were carried out using computational methods of geometric optics and electrodynamics. The lens is made of high-density polyethylene with the help of a turning machine. For experimental estimation of the spatial resolution provided by the lens, a THz imaging system based on raster scanning of the object’s surface was created. The imaging system was used in combination with wide-aperture THz optics to record images of the streak plates with different spatial frequencies. Analysis of the experimental data showed that the aspheric lens allows the resolution of two objects spaced at a distance of 0.95λ, providing contrast of 15%. The proposed THz optics is superior to classical THz spherical lenses and off-axis parabolic mirrors, greatly expanding the capabilities of THz-spectroscopy methods and imaging.