## 1 Introduction  
Temperature distributions inside biological tissues/organs and on the human body surface can be a source of important information about the functional state of the organism and negative processes associated with the development of disease at the earliest stages [1, 2, 3, 4, 5, 6]. Measurement of passive radiation in the microwave range is a simple, non-invasive, cheap, and fairly accurate method for determining temperature distributions inside biological tissues [2, 7, 8]. This approach is called microwave radiometry (MWR). Other terms used in the literature to refer to this method--for example, microwave thermography, microwave thermometry, microwave radiometry, and microwave thermographic--and such studies of internal temperature began more than 40 years ago on examples of the breast [9, 10], knee joint [11], head, and neck [7]. Significant advances in the use of microwave radiometry are associated with the diagnosis of breast cancer [1, 2, 5, 6, 10, 12, 13, 14]. A positive outcome of breast cancer treatment is determined by the earliest possible diagnosis, covering a significant part of the population [15]. Because breast oncology dominates in women's mortality from cancer,the organization of mass early diagnosis and screening is a priority, which requires reliable algorithms for processing thermometric data. Various aspects of the application of microwave radiometry methods are actively discussed in a number of reviews [6; 16; 17; 18; 19; 20]. Machine learning and the application of the full range of artificial intelligence algorithms are powerful tools for processing medical measurement data [4; 14; 21; 22; 23]. Convolutional neural networks can automatically detect signs of breast cancer in thermal images with up to 98.95 percent accuracy [14]. Microwave imaging technology makes it possible to monitor the progress of a disease in quasi-real time, such as brain stroke [24; 25]. Microwave radiometry provides clinical monitoring of brain temperature distribution during surgical procedures [3]. A particular task is the visualization of temperature fields during thermal therapy based on microwave ablation at frequencies of 300 MHz-300 GHz with local heating up to 60 \({}^{\circ}\)C and even higher in real time mode. This method allows for destroying malignant tumors and their metastases. The procedure uses an antenna needle that is inserted into the tumor node and emits microwaves, resulting in intense localized heating [26]. This approach makes it possible to successfully treat a tumor up to 0.5 cm [27; 28]. The target therapeutic temperature range is 39-45 \({}^{\circ}\)C for a more gentle effect on tumors and surrounding tissues, which is limited by the risk of vascular damage [17]. The advantages and disadvantages of microwave thermometry for medical diagnostic tasks are highlighted below. Advantages [3; 4; 8; 29; 30; 31]:  
Non-invasive method;  
Very fast temperature measurement;  
Inexpensive method;  
No contraindications;  
No restrictions on the procedure frequency;  
It is possible to measure both the thermodynamic temperature \(T\) and local changes in the electromagnetic characteristics of the biological tissue (primarily the electrical conductivity), as MWR measures the brightness temperature \(T_{B}\) by the electric field;  
The device for measuring brightness temperature is a portable system. Disadvantages [32; 31]:  
Low accuracy of building temperature fields compared to the resolution of structures when using ultrasound, tomography, mammography, or magnetic resonance elastography;  
Poor spatial error in measuring the brightness temperature in the plane and along the depth of the tissue;  
The MWR method determines only the brightness temperature \(T_{B}\), which requires additional data processing to relate to the real thermodynamic temperature \(T\) and is model-dependent;  
Restrictions on the air temperature in the room where measurements are taken.