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Brain temperature (BT) is a crucial physiological parameter used to monitor cerebral status. Physical activities and traumatic brain injuries (TBI) can affect BT; therefore, non-invasive BT monitoring is an important way to gain insight into TBI, stroke, and wellbeing. The effects of BT on physical performance have been studied at length. When humans are under extreme conditions, most of the energy consumed is used to maintain the BT. In addition, measuring the BT is useful for early brain diagnostics. Passive microwave radiometry (MWR) measures the intrinsic radiation of tissues in the 1–4 GHz range. It was shown that non-invasive passive MWR technology can successfully measure BT and identify even small TBIs. Here, we review the potential applications of MWR for assessing BT.

Passive microwave radiometry (MWR) is a measurement technique based on the detection of passive radiation in the microwave spectrum from different objects. This radiation in equilibrium is known to be proportional to the thermodynamic temperature of an emitting body. We hypothesize that living systems feature other mechanisms of emission that are based on protein unfolding and water rotational transitions. To understand the nature of these emissions, microwave radiometry has been used in several in vitro experiments. In our study, we performed pilot measurements of microwave emissions from egg whites during denaturation induced by ethanol. Egg whites are 10% proteins such as albumins, mucoproteins, and globulins. We found a novel phenomenon that microwave emissions changed without a corresponding change of the water thermodynamic temperature. increase 100 times faster than thermodynamic temperature. We have also found striking differences between microwave emission and thermodynamic temperature kinetics. Therefore, we hypothesize that these two processes are unrelated, contrary to what was thought before. It is known that some pathologies like stroke or brain trauma feature increased microwave emissions. We hypothesize that this phenomenon originates from protein denaturation and is not related to the thermodynamic temperature. So, our finding could explain first time the reason for microwave emissions increase after trauma and postmortem. It could be used for the development of novel diagnostics methods. The MWR method is inexpensive, and it does not require fluorescent or radioactive labels. It can be used in different areas of basic and applied pharmaceutical research, including kinetics studies in biomedicine.

The World Health Organization (WHO) declared COVID-19 as a global pandemic. It becomes clear that the virus is spreading mostly deadly due to limited access to diagnostics tests and equipment. Traditional radiography and CT remain the main methods of the initial examination of the chest organs. Now, most of the diagnostics has been focused on PCR, chest X-Ray/CT manifestations of COVID-19. However, there are problems with CT due to infection control issues, the inefficiencies introduced in CT room decontamination, and lack of CT availability in LMIC (Low Middle Income Countries). Passive microwave radiometry (MWR) is a cheap, non-radioactive and portable technology. It has already been used for diagnostics of cancer, and other diseases. We have tested if MWR could be used for early diagnostics of pulmonary COVID-19 complications. This was a randomized controlled trial (195 subjects) to evaluate the effectiveness of diagnostics using MWR in patients with pneumonia caused by COVID-19 while they are in hospitals of Kyrgyzstan, and healthy individuals.We have measured skin (IR) and internal (MWR) temperatures by recording passive electromagnetic radiation through the chest wall in the projection of the lungs at 30 symmetrical points on both sides. Pneumonia and lung damage were diagnosed by X-RAY/CT scan and doctor final diagnosis (pn+/pn-). COVID-19 was determined by PCR test (covid+/covid-). The best results were obtained between pn-/covid- and pn+/covid+ groups with sensitivity 92% and specificity 75%.Overall, the study suggests that the use of MWR is a convenient and safe method for screening diagnostics in COVID-19 patients with suspected pneumonia. Since MWR is an inexpensive, it will ease the financial burden for both patients and the countries, especially in LMICSummary statementCategorization of COVID-19 caused pneumonia suspicion by MWR has good diagnostic perspectives. It could be done in clinics or for mass screening to identify potential COVID-19 patients with lung complications.BackgroundThe use of chest CT for COVID-19 and PCR diagnosis in healthcare settings with limited PCR and CT capacity is controversial. MWR categorization of the level of COVID-19 suspicion of lung complications might improve diagnostic performance.PurposeTo investigate the value of MWR in addition to CT and COVID-19 PCR scans and to determine its diagnostic performance in individuals with COVID-19 symptoms during hospital admission and rehabilitation.Materials and MethodsIn this trial (Kyrgyz Committee Clinical Trial Number: 01-2/141 27 May 2020), from June, 1 2020 to August, 1 2020, we performed parallel MWR, PCR and CT tests, for individuals with COVID-19 admitted to the hospital for medical emergencies related to COVID-19 and pneumonia suspicion. Siemens Ecoline CT scanner, and HITACHI, Radnext 50 Chest X-Ray was used. RT-PCR test were done using “DNA technology” company https://www.dna-technology.ru/equipmentpr/nabory-reagentov-dlya-pcr-infekcii-respiratornogo-trakta/sars-cov-2sars-cov). For MWR and IR measurements RTM-01-RES was used MMWR LTD, UK (www.mmwr.co.uk)ResultsThis was a randomized controlled trial to evaluate the effectiveness of diagnostics of COVID-19 (covid-/covid+) and pneumonia (pn+/pn-) using passive microwave radiometry (MWR) in patients while they are in hospital, and healthy individuals. We have measured internal (MWR) and skin (IR) temperature on 195 subjects. 149 of them were hospitalized with pneumonia symptoms to Medical center of KSMA and BICARD clinic. Pneumonia and lung damage were diagnosed by X-RAY/CT scans and radiologists lung damage assessment (pn+/pn-). COVID-19 was determined by PCR test (covid+/covid-). The best diagnostics results were obtained between pn-/covid- and pn+/covid+ groups with sensitivity 92% and specificity 75%.ConclusionThe study suggests that the use of MWR is a convenient and safe method for screening diagnostics in COVID-19 patients with suspected pneumonia. Since MWR is inexpensive, it will ease the financial burden for both patients and the countries, especially in LMIC.

The physical basis of microwave radiometry and the construction and technical characteristics of different types of antenna applicators used in medical radiometers are discussed. We present results obtained during the development and the potential uses of new types of antenna applicators in different areas of medicine.

This paper presents a new circuit of the miniature microwave radiometer for wearable devices, which can be used to monitor the core body temperature (CBT) of internal human tissues continuously 24/7. The measurement results of the proposed device, as opposed to the known miniature wearable radiometers, remain unchanged when the impedance of the examined area varies. We have derived an analytical expression for radiometer measurement error based on parameters of device components. This formula allows accuracies to be estimated and optimal parameters of the circuit to be selected to minimise measurement error at a design stage. It is shown that measurement error is independent of the antenna reflection coefficient and the temperature of the radiometer front-end. A prototype of the single-channel miniature radiometer has 32 х 25 х 14 mm3 dimensions and USB interface communication with PC. A 28-hour run of the device has shown that it is highly stable, and a maximum drift in temperature is 0.15 ̊C. Operating frequency range was 3400-4100 MHz, supply voltage - 5V; power supply of the radiometer in measurement mode is 210 mA; time constant of the radiometer without being averaged is 0.6 sec, at the same time, standard deviation δ = 0.17 ̊С, with further averaging during 4 sec δ=0.052 ̊С, with averaging during 30 sec δ =0.017 ̊C; when there were input reflections R2=0.25, an error in measuring brightness temperature shifted by 0.2 ̊ C; with 10 ̊C variations in ambient temperature the shift was 0.15 ̊C. Introduction of self-contained power supply and wireless communication with smartphone have made it possible to use the proposed radiometer as a wearable device to monitor the temperature of internal tissues and CBT during human activities.