Thermography

All bodies whose temperature is above absolute zero emit radio waves of a continuous frequency spectrum (thermal radio emission). The intensity of thermal radiation is proportional to the temperature of the body.

Medical thermography is a method of recording the natural thermal radiation of the human body in the invisible infrared region of the electromagnetic spectrum. Thermography determines the characteristic "thermal" picture of all areas of the body. In a healthy person, it is relatively constant, but changes in pathological conditions. Thermography is an objective, simple and absolutely harmless method, the use of which has no contraindications.

Preparation of the patient for thermography involves discontinuing medications that affect blood circulation and metabolic processes. There should be no ointments or cosmetics on the body surface. The patient is prohibited from smoking 4 hours before the examination. This is especially important when studying peripheral blood flow. Thermography of the abdominal organs is performed on an empty stomach. A constant temperature (18-20 °C) and humidity (55-65%) are maintained in the room. The body part being examined is uncovered, after which the patient adapts to the room temperature for 10-15 minutes, and for examination of the hands and feet - 30 minutes. Depending on the objectives of the study, thermography is performed in different patient positions and projections.

Thermography allows for an accurate and quick assessment of the intensity of PC radiation from the surface of the human body, to detect changes in heat production and heat transfer in various areas of the body and thereby to identify disturbances in blood flow and innervation, symptoms of developing inflammatory, oncological and some occupational diseases.

The human body temperature is considered constant. However, this constancy is relative. The temperature of the internal organs is higher than the temperature on the body surface. When the environment changes, the temperature changes depending on the physiological state of the body.

Due to the extremely developed vascular network in the skin and subcutaneous tissue, the indicators of superficial blood flow are an important indicator of the state of internal organs: when pathological processes develop in them, a reflex change in superficial blood flow occurs, which is accompanied by a change in heat transfer. Thus, the main factor determining skin temperature is the intensity of blood circulation.

The second mechanism of heat generation is metabolic processes. The degree of expression of metabolism in tissue is determined by the intensity of biochemical reactions: as they intensify, heat production increases.

The third factor determining the thermal balance in surface tissues is their thermal conductivity. It depends on the thickness, structure, and location of these tissues. In particular, the heat transfer of the human body is determined by the condition of the skin and subcutaneous fat: their thickness, development of the main structural elements, and hydrophilicity.

Normally, each area of the body surface has a characteristic thermal relief. The temperature above large blood vessels is higher than in the surrounding areas. The average skin temperature is 31-33 °C, but it varies in different parts of the body - from 24 °C on the thumb to 35 °C in the sternal fossa. However, the skin temperature is usually the same on symmetrical areas of the body, the difference here should not exceed 0.5-0.6 °C. Physiological asymmetry on the limbs fluctuates from 0.3 to 0.8 °C, and on the anterior abdominal wall does not exceed 1 °C. Women experience periodic changes in the temperature relief of some parts of the body (mammary glands, abdominal area) due to the menstrual cycle, so thermography of these areas is recommended for them on the 6th-8th day of the cycle. Significant changes in the temperature relief occur in many pathological conditions. In this case, hyper- or hypothermia zones appear, the normal vascular pattern is disrupted, and thermal asymmetry is recorded on the body or limb.

There are three types of thermography: liquid crystal thermography, infrared thermography and radiothermography (microwave thermography).

Liquid crystal thermography is based on the property of liquid crystals to change color depending on the change in temperature. Special devices have been developed in which the screen is covered with a liquid crystal composition. During thermography, the screen is brought closer to the part of the body being examined. The color of the image is used to judge the temperature of the surface tissues using a calorimetric ruler.

Infrared thermography is the most common method of thermography. It allows you to get an image of the thermal relief of the body surface and measure the temperature on any part of the body surface with an accuracy of tenths of a degree. Infrared thermography is carried out using special devices - thermographs (thermal imagers).

Each area of the surface being examined, depending on its temperature, is represented on the thermograph screen as a lighter or darker area or has a conventional color. The image can be viewed on the screen (thermoscopy) or recorded on photochemical paper to obtain a thermogram. Using a graduated scale and a thermal control emitter ("black body"), it is possible to determine the absolute temperature on the skin surface or the temperature difference in different areas of the body in a contactless manner, i.e. perform thermometry.

Qualitative analysis of thermograms consists of a general examination of the image, study of the temperature relief and distribution of hot and cold zones. In such visual analysis, special attention is paid to identifying hyper- and hypothermia zones and disturbances in the structure of the vascular pattern, assessing the extent of the hyper- or hypothermia area (limited, extended, diffuse), its localization, size, shape, and outline. Disturbances in the vascular pattern are manifested by changes in the number, location and caliber of vascular branches.

Quantitative analysis makes it possible to clarify the results of the visual analysis of the thermogram and determine the difference in temperatures of the examined area and the surrounding tissues or a symmetrical area. In a healthy person, the thermogram of each area of the body has a characteristic appearance. In inflammatory processes, a hyperthermia zone is determined, corresponding to the infiltration area, having a heterogeneous structure, while the difference in temperatures with the surrounding tissues is 0.7-1 ° C in chronic inflammation, 1 -1.5 ° C in acute inflammation and over 1.5 - 2 ° C - in a purulent-destructive process. In particular, thermography is useful in assessing the activity of arthritis and bursitis, determining the boundaries of a burn lesion or frostbite zone.

A malignant tumor is characterized by a zone of intense hyperthermia (2-2.5 °C higher than the temperature of the symmetrical area). The structure of the hyperthermia area is uniform, its contours are relatively clear, and dilated vessels are visible. In case of arterial circulation disorders (angiospasm, narrowing or complete stenosis of the vessel), a hypothermia zone is determined, which by location, shape and size corresponds to the area of decreased blood flow. In case of venous thrombosis, thrombophlebitis, post-thrombophlebitic syndrome, on the contrary, a zone of increased temperature is usually noted in the corresponding area. In addition, in case of blood flow disorders, a change in the usual vascular pattern characteristic of a given anatomical region is observed,

Radiothermometry is the measurement of the temperature of internal organs and tissues by studying them yourself. It has long been known that humans are sources of radio emission. The first to use the registration of this radiation for medical diagnostics was A. Barrett and P. Myers in 1975.

Radiothermometry measures the temperature of tissue at different depths using a microwave radiometer. If the skin temperature in a given area is known, the temperature at any depth can be calculated. This can also be achieved by recording the temperature at two different wavelengths. The value of the method is reinforced by the fact that the temperature of deep tissues is constant on the one hand, and changes almost instantly under the influence of certain medications, particularly vasodilators. This makes it possible to conduct functional studies, for example, when deciding on the level of amputation in the case of vascular occlusion of the extremities.