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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.

With the fast development of terahertz technology in medical diagnosis and monitoring, it has become important to investigate the application of THz radiation in the cancer treatment assessment during the therapy. In this paper, a buccal drug delivery system is studied as the first step towards this application. The drug delivery system is based on a gelatin-starch biopolymer matrix filled with plasticizing glycerol and various contents of reinforcing particles of bentonite clay. The biopolymers were subjected to morphology analysis using optical microscopy, analysis of mechanical tensile properties, and analysis of terahertz optical properties, followed by a theoretical approach of the experiment. The results show a visible effect of the bentonite content on both of the mechanical and terahertz optical properties of the biopolymer. These findings allow us to confirm the feasibility of using THz radiation for cancer assessment during therapies. The proposed biopolymer also has the potential to be applied as a substrate when carrying out in-vivo optical property measurement of biotissue in terahertz frequency range.

Subject of Research.The paper presents the study of blood biochemical composition (bilirubin, creatinine, triglycerides, uric acid) effect on its optical properties, refractive index and absorption coefficient, in terahertz frequency range. Method. To obtain the values of the refractive index and the absorption coefficient, the method of terahertz time-domain spectroscopy was used in the transmission mode. Concentrations of total bilirubin, creatinine and triglycerides were measured in blood serum by the colorimetric method, the pseudokinetic method and the enzymatic method, respectively. The glucose level was determined in blood plasma by the enzyme method. All measurements of blood component concentrations were carried out at the Almazov National Medical Research Centre. Main Results. The optical properties of blood with various biochemical composition were obtained using terahertz time-domain spectroscopy at the frequency of 0.4THz. It is shown that the refractive indices and the absorption coefficients of blood decrease with an increase in the concentration of bilirubin and creatinine. It has also been found that with an increase in the concentration of uric acid and triglycerides, the refractive index of blood increases and the absorption coefficient of blood decreases, respectively. The correlation between the refractive index and the concentration of triglycerides and the correlation between the blood absorption coefficient and the concentration of uric acid were not revealed. Practical Relevance. The observed correlations between the concentrations of blood components and the optical properties are useful in the development of a new technique for blood analysis.

Composite mediums are being used broadly nowadays. To design a desired composite medium, its theoretical properties should be calculated beforehand so its behavior can be expected. To find out the proper calculation methods in the terahertz regime, several mathematical models were used to calculate the theoretical optical properties of different composite materials. These properties were compared with the experiment data which is obtained from terahertz time-domain spectroscopy or from the reference papers. The result shows that to choose reliable mathematical model, the shape and size of each component need to be taken into account.

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.

The optical properties of the polymer composites consisting of polyvinyl chloride nanofibers and polypropylene films in the frequency range of 0.2–1.0 THz were studied, and the mechanical properties of polyvinyl chloride nanofibers and the structure porosity were investigated. An iterative mathematical model based on effective medium theory was used to describe the effective refractive index and absorption coefficient of the polymer composites. The permittivity tensors of the composites were calculated using the Rytov method. We found that the refractive indices of the composites increased with the increase of polypropylene contents, while absorption coefficients remained the same. The polarization-dependencies of THz optical properties of the composites were relatively low. The proposed composites have the potential to be used as materials for terahertz optical components.

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.

PVC-based water-free phantoms with silicon and zinc oxide nanoparticles were fabricated for mimicking biotissues in the terahertz frequency range. Terahertz time-domain spectroscopy (TDS) was used to obtain the refractive indices and absorption coefficients of the phantoms. Their optical properties were compared with those of real biotissues from published data. The results show that the phantoms are able to mimic human skin, paraffin-embedded glioma and paraffin-embedded healthy brain tissue by their optical properties. The refractive index of the phantoms can be controlled by changing the concentration of the nanoparticles.

2 Faculty of Math and Natural Science, Kalashnikov Izhevsk State Technical University, Izhevsk, 426069, Russian Federation Photoplethysmography is a simple technology with low-cost. It can be used to detect blood volume changes in the microvascular. Because the photoplethysmographic devices, which are produced by this technology, are portable and noninvasive, and the data which is received consists of many physiological information of human body, this technology can give great convenience to clinical diagnostic and personal daily health monitoring. This is why it has very broad application prospects. Photoplethysmogram usual y consists of an AC component which depends on the blood volume changes in cardiac system, and a DC component which is decided by respiration, tissue, inherent components of blood. Although the origin of the photoplethysmographic signal are being researched stil , we can get many valuable information of cardiac system.

A convenient method has been developed for the preparation of a variety of 2-mercaptobenzothiazoles from 2-haloanilines and CS2 mediated by metal sulfide. In this reaction, 2-haloanilines reacted with CS2 in the presence of Na2S · 9H2O to form 2-mercaptobenzothiazoles. Na2S · 9H2O functioned both as an activator of CS2 and as a base. Furthermore, NMR analysis was used to identify the different reaction mechanisms of 2-haloanilines and CS2 mediated by Na2S or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), which demonstrated that Na2S interacted only with CS2, while DBU reacted with both 2-iodoaniline and CS2.