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This article describes possibilities of multifractal analysis application to evaluate the short-term signals of brain microwave radiation recorded by the Radiophysical complex MRTHR for a group of psychologically healthy patients. Limitations of the multifractal fluctuation analysis method for evaluation of the fluctuation processes of brain regulation are considered. For this purpose, time series of two channels of microwave radiation of the parietal areas of human brain were processed. The results define the limits of applicability of the multifractal detrended fluctuation analysis (MFDFA) method by the time window from 10 to 70 s and correspond to the two independent areas of periods of fluctuations of brain microwave radiation with different physiological nature that were justified by other methods. The obtained estimations prove the multifractal nature of the brain microwave radiation signals. These findings suggest that diagnostic possibilities of the modernized Radiophysical complex MRTHR can be increased with the usage of the multifractal analysis to functional studies of the microwave radiation signals of the brain.

In the article, the characteristics of antenna-applicators (AA) for the contact microwave radiometers are analyzed. The bow-tie AA (in which the near-field and transition regions better match with the feeder in a wide frequency band) is preferred for monitoring the brain microwave radiation. Modelling these bow-tie AA with contact pins was conducted. The simulation results have confirmed that the increase in length of the pins up to 5 mm reduces the characteristic impedance similar to that of flat AA. Meanwhile, increased thickness of the vibrator does not degrade receiving properties of the AA. The modelling results are confirmed by laboratory studies that have examined the characteristics of the bow-tie AA with pins and flat AA without pins. It is shown that the introduction of designed AA with pins significantly reduced the impact of hair on the matching of the AA and body. In the study of changes in the characteristics of AA for 30 min, the change rate matching such antennas with the brain tissue changes by less than two times compared with that matching AA without pins.

Background and Objective The influence of biophysical parameters on the formation of microwave radiation of the human head is poorly studied. Existing approaches to modeling microwave radiation of the human head have limitations associated with simplifying the geometry of human anatomy. The article proposes methodological solutions for numerical modeling of microwave radiation of the brain biological tissues using the geometry obtained from MRI data. Methods The geometrical characteristics of biological tissues in model are determined using an MRI image of the head. The methodology proposed in the article allows simulation of a human body voxel models performed the Pennes bio-heat transfer equation using the Fenix software package. Results Modeling evaluations have shown that anatomical tissues heterogeneities on the surface of the head form temperature gradient of up to 2.0 K, and changes of the microwave radiation up to 0.3 K. Conclusions Verification data made by IR thermograph practically coincide with the results of numerical modeling. The fluctuations of the brain microwave radiation are not only the result of thermal processes in its tissues, but are determined by the dynamics of its thermoregulation processes and are an indicator of changes in the physiological processes occurring in it.

In this study, organizational principles of the radiophysical complex are proposed for simultaneous measurements of the brightness temperature fluctuations of the human brain and parameters of the autonomic nervous system. A new structure of the medical microwave radiothermograph is suggested based on the parametric compensation of losses in the circuit elements of the thermobalance. The aim of this article is to justify the structural organization of the radiophysical complex for the recording and joint real-time analysis of processes of the microwave radiation formation in the brain tissue and characteristics of the autonomic nervous system. Description of the radiophysical complex MRTHR with realization of these principles is presented. The peculiarity of the proposed radiophysical complex is in passive elements that do not contain electronic nodes and blocks and are inside the shielded cabin. In order to increase the accuracy of the brightness temperature of the deep brain structures measurement in the radiophysical complex a new structure is implemented. This structure of the medical microwave radiothermograph is based on the parametric compensation of losses in the circuit elements of the thermobalance.

The paper presents the results of dependency assessments of the spectral and multifractal analysis of the brain microwave radiation signals. Twenty neurology healthy volunteers participated in study. The biomedical signals formed by the dual-channel microwave radiometer. The research method used a machine-learning algorithm that allows predicting relation between the spectral power and the Hurst exponent. Compare the distribution of possible functions with data obtained from different channels were present. The results obtained allowed to demonstrate the absence interrelation between spectral and multifractal estimates of the brain microwave radiation signals.

In paper discusses study spectral characteristics fluctuations of the brain microwave radiation for estimation changes the metabolic production in the brain tissues. Computer simulation of this problem showed that frequency band ranging from 650 to 850 MHz is optimal. The results based on the analysis phenomenological models of the brain tissues radiation and thermodynamic processes in it, and, also, on the experimental data obtained with the measuring system the Radiophysical complex. The fluctuation of the brain microwave radiation in the frequency band from 0.02 Hz to 0.013 Hz characterized mainly liquid circulation in the intercellular and intracellular spaces of the brain tissue. In the frequency band below 0.013 Hz, these fluctuations defined mainly by thermodynamic changes in the tissues.

In the paper, features of the brain microwave radiation measurements are considered. Influence of the contact pins addition on the antenna matching with head surface (changes of the reflection coefficient) is studied. Estimates of human head modelling with contact antenna-applicator are presented. Results of the investigations show that fluctuations of electromagnetic field in the near-field region is defined by magnetic component and depend on functional processes in the human brain.

The principles of processing signals of Radiophysical complex MRTHR for studying the role of autonomic regulation in the formation of the brain microwave radiation during the treatment process are presented. The feature of this complex is the possibility of registration and analysing the non-stationary short-term time series of the brain microwave radiation and heart rate variability signals. The processing is implemented via the method of multifractal cross-correlation analysis. The results of the fluctuation and cross-correlation Hurst exponent estimations of these signals are shown. The estimates for a group of relatively healthy patients have low levels of systemic discrepancy. For the patients group with ischemic stroke before treatment the systematic discrepancy of estimations are significantly larger than those of healthy patients. After rehabilitation course, the discrepancy between these estimates are reduced. Copyright © 2016 by SCITEPRESS - Science and Technology Publications, Lda. All rights reserved.

The features of the application of multifractal analysis to assess the interrelation of the short-term signals of microwave radiation of the human brain and heart rate variability (HRV) are described. Data are presented for periods (20, 40) s of microwave radiation signals and periods (6.5, 25) s of HRV showing low level of systematic divergence. Similar properties for periods (50, 70) s of microwave radiation signals and periods (25, 300) s of HRV are found. The results indicate the interface between microwave radiation fluctuations of the human brain and HRV signals, which represent autonomic nervous system activity.