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 a human body in the invisible infrared region of the electromagnetic spectrum. Thermography defines a characteristic "thermal" picture of all areas of the body. In a healthy person, it is relatively constant, but with pathological conditions varies. Thermography - an objective, simple and absolutely harmless method, to the application of which there are no contraindications.
Preparation of the patient for thermography provides for the abolition of drugs that affect blood circulation and metabolic processes. On the surface of the body there should be no ointments and cosmetics. The patient is forbidden to smoke 4 hours before the test. This is especially important in the study of peripheral blood flow. The thermography of the abdominal cavity is performed on an empty stomach. The cabinet is kept at a constant temperature (18-20 ° C) and humidity (55-65%). The investigated part of the body is exposed, after which the patient adapts to the room temperature for 10-15 minutes, and in the study of brushes and feet, 30 minutes. Depending on the research tasks, the thermography is performed in different patient positions and projections.
Thermography allows you to accurately and quickly assess the intensity of PC radiation from the surface of the human body, to detect changes in heat production and heat transfer in the areas of the body, and thereby detect violations of blood flow and innervation, the symptoms of developing inflammatory, oncological and certain occupational diseases.
The temperature of the human body is considered to be constant. However, this constancy is relative. The temperature of the internal organs is higher than the temperature on the surface of the body. When the environment changes, the temperature changes depending on the physiological state of the organism.
In connection with the highly developed vasculature in the skin and subcutaneous tissue, surface blood flow indicators are an important indicator of the state of internal organs: when pathological processes develop in them, a reflex change in the surface blood flow occurs accompanied by a change in heat transfer. Thus, the main factor determining the temperature of the skin is the intensity of the blood circulation.
The second mechanism of heat formation is metabolic processes. The degree of expression of metabolism in the tissue is due to the intensity of biochemical reactions: with their increase, heat production increases.
The third factor that determines the heat balance in the surface tissues is their thermal conductivity. It depends on the thickness, structure, location of these tissues. In particular, the heat transfer of the human body is determined by the state of the skin and subcutaneous fatty tissue: their thickness, the development of the basic structural elements, hydrophilicity.
Normally, each area of the body surface has a characteristic thermal relief. Above the large blood vessels, the temperature is higher than in the surrounding areas. The average skin temperature is 31-33 ° C, but it is different in different parts of the body - from 24 ° C on the thumb to 35 ° C in the sternal fossa. However, the temperature of the skin, as a rule, is the same in the symmetrical parts of the body, the difference here should not exceed 0.5-0.6 ° C. Physiological asymmetry on the limbs ranges 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 certain parts of the body (mammary glands, abdominal region) in connection with the menstrual cycle, therefore, they are recommended to perform the thermography of these areas on the 6th-8th day of the cycle.Significant changes in the temperature relief occur in many pathological conditions, with zones of hyper- or hypothermia appearing, normal vascular patterns disrupted, gistriruetsya thermal asymmetry in the body or limbs.
Three methods of thermography are solved: 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 temperature change. Special devices have been developed in which the screen is covered with liquid crystal composition. In the process of thermography, the screen is closer to the part of the body being examined. By coloring the image with a calorimetric ruler, the temperature of the surface tissues is judged.
Infrared thermography is the most common method of thermography. From allows you to obtain 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 with the help of special instruments - thermographs (thermal imagers).
Each section of the surface under study, depending on its temperature, is presented on the thermograph screen with a lighter or darker area or has a conventional color. The image can be viewed on the screen (thermoscopy) or fixed on photochemical paper and get a thermogram. With the help of a graduated scale and a thermal control radiator ("blackbody"), it is possible to determine the absolute temperature on the surface of the skin or the temperature difference at different parts of the body, ie, without contacting the skin. Perform thermometry.
Analysis of thermograms at a qualitative level consists in a general examination of the image, study of the thermal relief and distribution of hot and cold zones. With this visual analysis, special attention is paid to identifying zones of hyper- and hypothermia and disturbing the structure of the vascular pattern, assessing the extent of the hyper- or hypothermia site (limited, extended, diffuse), its localization, size, shape, shape. Violations of the vascular pattern are manifested by a change 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 to determine the temperature difference between the area under investigation and the surrounding tissues or a symmetrical site. In a healthy person, the thermogram of each area of the body has a characteristic appearance. In inflammatory processes, the hyperthermia zone corresponding to the infiltration region having a non-uniform structure is determined, with a difference in temperature with the surrounding tissues 0.7-1 ° C in chronic inflammation, 1-1.5 ° C with acute and more than 1, 5 - 2 ° C - with a purulent-destructive process. In particular, thermography is useful in assessing the activity of arthritis and bursitis, determining the boundaries of a burn injury or a zone of frostbite.
A malignant tumor is characterized by a zone of intense hyperthermia (2-2.5 ° C above the temperature of the symmetrical region). The structure of the hyperthermia section is homogeneous at the same time, its contours are relatively clear, and extended vessels are visible. When the arterial blood flow is disturbed (angiospasm, constriction or complete stenosis of the vessel), a hypothermia zone is determined, which by location, shape and size corresponds to the area of blood flow decrease. In venous thrombosis, thrombophlebitis, post-thrombophlebitis syndrome, on the contrary, in the corresponding area, an area of elevated temperature is usually noted. In addition, with blood flow disorders, there is a change in the usual vascular pattern characteristic of this anatomical region,
Radiometrometry is the measurement of the temperature of internal organs and tissues for their own study. It has long been known that a person is a source of radio emission. For the first time the registration of this radiation for medical diagnostics was applied by A. Barrett and P. Myers in 1975
With radio thermometry, the tissue temperature is measured at different depths using a microwave radiometer. If the temperature of the skin is known in this area, then it is possible to calculate the temperature at any depth. This can also be achieved by recording the temperature at two different wavelengths. The value of the method is supported by the fact that the temperature of deeply located tissues, on the one hand, is constant, and on the other - almost instantly changes under the influence of certain drugs, in particular vasodilating drugs. This makes it possible to conduct functional studies, for example, when deciding the question of the level of amputation in the occlusion of the vessels of the extremities.