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

Abstract

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.

Cellular effects of terahertz waves

“…Obviously, such safe limits should account for not only the thermal THz-wave effects (as the common ICNIRP standards do) 40 , 192 , 193 but also for the nonthermal. Development of the THz dosimetry is of crucial importance for biomedical applications of THz technology in such demanding branches as label-free diagnosis of malignant and benign neoplasms, 3 , 4 , 8 – 16 sensing of glycated tissues and blood in context of diabetes diagnosis, 1 , 19 – 21 determining the degree of traumatic injuries 22 and viability 30 of tissues, and even emerging methods of single cells, microorganisms, bacteria, and viruses sensing. 286 – 291 Also, THz dosimetry is of crucial importance for the rapidly developing 6G wireless communications that will reportedly span sub-THz and THz frequencies.…”

“…To mitigate this drawback, the double-overdamped oscillator model was applied to describe the THz dielectric response of tissues in Ref. 15 . As compared with the double-Debye model, a pair of the overdamped oscillators provides almost equal dielectric curves and in the analyzed THz range but predicts considerably lower losses at high frequencies and, thus, satisfies the sum rule.…”

“…1 ), has been observed during the past few decades, 1 – 5 driven by rapid progress in THz technology. 6 , 7 Numerous research papers demonstrate the potential of THz technology in label-free early noninvasive, least-invasive, and intraoperative diagnosis of malignant and benign neoplasms with different nosologies and localizations, 3 , 4 , 8 – 18 sensing of glycated tissues and blood in the context of diabetes diagnosis, 1 , 19 – 21 determining the degree of traumatic injuries, 22 – 25 hydration levels, 26 – 29 and viability 30 of tissues. Along with the diagnostic applications, THz technology holds strong potential in therapeutics, 31 , 32 for example, in nonthermal regulation in expression of genes associated with cancer and inflammatory diseases.…”

Diagnosis of Glioma Molecular Markers by Terahertz Technologies

“…THz radiation interaction with tumor tissue can be analyzed using the effective complex dielectric constant, which is a well-known model of the dielectric medium [25,[126][127][128][129].…”

The Application of Terahertz Time-Domain Spectroscopy to Identification of Potato Late Blight and Fusariosis

“…In the last decade, the terahertz spectroscopy method has demonstrated high information content in a wide range of applications: material analysis, monitoring of various technological processes, biomedicine, food chemistry and agriculture to determine the nutritional value of seeds [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. It should be noted that THz spectra are most informative when analyzed substances in crystalline form.…”