The terahertz optical properties of composites with poly vinyl chloride (PVC) nanofibers and polypropylene (PP) were investigated. To evaluate the influence of PVC content, we measured the composites under conditions where the content of PVC nanofibers was controlled. We found that the refractive indices increase with the decrease of PVC nanofiber content. We also found that highly aligned PVC nanofibers bring birefringence to the composites. The proposed PVC-PP composites are promising materials for terahertz optics.
At present, due to the rapid development of THz technology in medical applications, it becomes urgent to develop stable test objects (phantoms) for calibration, optimization of the operation of devices, and verification of the research methods used. In this work, a five-component phantom has been developed based on water, glycerin, starch, bentonite, and gelatin, and it was shown that these phantoms can be used as indicators of the level of dehydration of the renal tumor tissue. The mechanical properties of the phantom were investigated, the dispersions of the refractive index and absorption coefficient of the biocomposite were determined in the range from 0.2 to 1 THz. To simulate the optical parameters of a phantom depending on the concentration of inclusions, an iterative method was developed and it was found that this method makes it possible to simulate the optical parameters of a phantom at low concentrations of bentonite. It is shown that in the structure of a five-component phantom, during fabrication, clusters of starch particles are formed, and the resonant interaction of the incident THz radiation with cluster particles leads to the excitation of whispering gallery modes.
Significance: A new concept of a biotissue phantom for terahertz (THz) biomedical applications is needed for reliable and long-term usage.
Aim: We aimed to develop a new type of biotissue phantom without water content and with controllable THz optical properties by applying graphite powders into a polyvinyl chloride plastisol (PVCP) matrix and to give a numerical description to the THz optical properties of the phantoms using the Bruggeman model (BM) of the effective medium theory (EMT).
Approach: The THz optical properties of graphite and the PVCP matrix were measured using THz time-domain spectroscopy, which works in the frequency range from 0.1 to 1 THz. Two phantoms with 10% and 12.5% graphite were fabricated to evaluate the feasibility of describing phantoms using the EMT. The EMT then was used to determine the concentration of graphite required to mimic the THz optical properties of human cancerous and healthy oral tissue.
Results: The phantom with 16.7% of graphite has the similar THz optical properties as human cancerous oral tissue in the frequency range of 0.2 to 0.7 THz. The THz optical properties of the phantom with 21.9% of graphite are close to those of human healthy oral tissue in the bandwidth from 0.6 to 0.8 THz. Both the refractive index and absorption coefficient of the samples increase with an increase of graphite concentration. The BM of the EMT was used as the numerical model to describe the THz optical properties of the phantoms. The relative error of the BM for the refractive index estimation and the absorption coefficient is up to 4% and 8%, respectively.
Conclusions: A water-free biotissue phantom that mimics the THz optical properties of human cancerous oral tissue was developed. With 21.9% of graphite, the phantom also mimics human healthy oral tissue in a narrow frequency range. The BM proved to be a suitable numerical model of the phantom.
To evaluate, calibrate equipment, and check the safety of THz devices etc, biotissue phantom is needed for these purposes. Although various researches about biotissue phantom using water have been done, such phantoms are not ideal. Because of the evaporation of water, the optical properties of a phantom change as the time goes by, since THz radiation is very sensitive to the water concentration of the sample. We chose graphite as the substitute of water, and therefore the water-free biotissue phantom was developed to mimic the similar optical properties as human tissues. In order to determine the concentration of each component precisely, quantitative analysis is needed. In this work, we used several mathematical models of the effective medium theory, including the Polder and van Santen model, the Landau, Lifshitz, Looyenga model, the model of complex refractive index, and the Bruggeman model, to study the influence of different graphite concentrations on the refractive index of the water-free biotissue phantom. Phantoms with different graphite concentrations were simulated and 3 phantoms with different graphite concentrations were produced to evaluate the reliability of each model. The fabricated phantoms were then compared with stomach tissues. The result also shows the promise that by using the proper mathematical model, correct concentration can be calculated for other tissue phantom.
This paper presents qualitative analysis of terahertz time-domain spectroscopy application for cancer diagnosis by measurement of the optical properties and spectral characteristics of cancer cells. For this purpose, the cultivation of two cancer cells, U-251 (glioblastoma brain) and A549 (lung adenocarcinoma), were carried out, then their refractive index, absorption coefficient and dielectric constant were measured, and the optical properties of tumor cells were compared with the optical properties of healthy cells (fibroblasts). Tumor cells contain more OH-components in comparison with healthy cells. Since terahertz radiation is heavily absorbed by water, there are differences in the spectra of healthy and oncological cells. To obtain the optical properties and spectral characteristics of the researched objects, a terahertz time-domain spectroscopy method in the transmission mode was used. The researched cell lines were cultured in vitro. Optical properties and spectral characteristics of the samples were calculated by the thin film method and Fourier transform. The results show the differences of refractive index, absorption coefficient and dielectric permittivity between the oncological cell lines U- 251, A549 and the healthy cells in the frequency range 0.2-1 THz. It was found that cancer cells have higher values of refractive indices and absorption coefficients than those of healthy cells. Brain glioblastoma (U-251) has a transmission peak at the frequency of 0.24 THz. The results obtained in this work can form the basis for the diagnosis of brain and lung cancer with the use of terahertz time-domain spectroscopy.
The glucose level of blood can be obtained by terahertz time-domain spectroscopy using refractive index measurement method. The detected refractive indices vary from person to person since the impact of bilirubin and creatinine wasn’t considered. 14 human blood samples were tested using terahertz time-domain spectroscopy. The experiment results show that under the certain concentration of glucose, the refractive index of blood decreases with the increase of bilirubin and creatinine concentration, and thus the concentration of other blood components may also influence on the refractive index of blood. The feasibility of using terahertz time-domain spectroscopy to determine the level of glucose, bilirubin and creatinine qualitatively and quantitatively is provided.
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