Scintigraphy is the acquisition of images of the patient's organs and tissues by recording on a gamma camera the radiation emitted by an incorporated radionuclide.
The physiological essence of scintigraphy is organotropic RFP, i.e. The ability to selectively accumulate in a certain organ - accumulate, stand out or pass through it in the form of a compact radioactive bolus.
Gamma camera is a complex technical device, saturated with microelectronics and computer technology. A scintillation crystal (usually sodium iodide) of large dimensions, up to a diameter of 50 cm, is used as the detector of radioactive emissions. This ensures that radiation is simultaneously registered over the whole part of the body being examined. The gamma quanta emitted from the body cause light flashes in the crystal. These flares are detected by several photomultipliers, which are uniformly located above the surface of the crystal. Electric pulses from the PMT through the amplifier and discriminator are transmitted to the analyzer unit, which forms a signal on the display screen. In this case, the coordinates of the glowing on the screen exactly correspond to the coordinates of the light flare in the scintillator and, consequently, the location of the radionuclide in the organ. Simultaneously with the help of electronics the moment of occurrence of each scintillation is analyzed, which makes it possible to determine the time of radionuclide passage through the organ.
The most important component of the gamma camera is certainly a specialized computer that allows you to produce a variety of computer image processing: allocate on it fields of interest - so-called zones of interest - and conduct various procedures in them: measurement of radioactivity (general and local) or its parts, the study of the rate of propagation of the RFP in this field. With the help of a computer, you can improve the quality of the image, highlight the interesting details on it, for example the feeding organs of the vessels.
In the analysis of scintigrams, mathematical methods, system analysis, chamber modeling of physiological and pathological processes are widely used. Naturally, all received data is not only displayed, but can also be transferred to magnetic media, transmitted over computer networks.
The final step in scintigraphy is usually to create a hard copy of the image on paper (using a printer) or a film (using a camera).
In principle, each scintigram to some extent characterizes the function of the organ, since RFP accumulates (and is allocated) mainly in normal and actively functioning cells, therefore the scintigram is a functional anatomical image. This is the uniqueness of radionuclide images, which distinguishes them from those obtained by X-ray and ultrasound research, magnetic resonance imaging. Hence the basic condition for the appointment of scintigraphy - the organ under investigation must necessarily be at least to a limited extent functionally active. Otherwise, the scintigraphic image does not work. That is why it is senseless to prescribe a radionuclide study of the liver in a hepatic coma.
Scintigraphy is widely used in almost all areas of clinical medicine: therapy, surgery, oncology, cardiology, endocrinology, etc. - where a "functional image" of the body is needed. In the event that one picture is taken, this is a static scintigraphy. If the task of radionuclide research is to study the function of the organ, then a series of scintigrams with different time intervals are performed, which can be measured in minutes or seconds. Such serial scintigraphy is called dynamic. After analyzing the received series of scintigrams on the computer, selecting the whole organ or a part of it as the "zone of interest", one can obtain on the display a curve showing the passage of the RFP through this organ (or part of it). Such curves, constructed on the basis of the results of a computer analysis of a series of scintigrams, are called histograms. They are designed to study the function of the organ (or part of it). An important advantage of histograms is the ability to process them on a computer: smooth out, isolate individual constituent parts, summarize and subtract, digitize and subject to mathematical analysis.
In analyzing scintigrams, mostly static, along with the topography of the organ, its size and shape determine the degree of uniformity of its image. Areas with increased accumulation of RFP are called hot foci, or hot nodes. Usually they correspond to excessively active parts of the body - inflammatory altered tissues, certain types of tumors, zones of hyperplasia. If, on the synthigram, the region of reduced accumulation of RFP is detected, then, it means that there is some volumetric formation that replaced the normally functioning organ parenchyma-the so-called cold nodes. They are observed with cysts, metastasis, focal sclerosis, some tumors.
The RFPs selectively accumulating in tumor tissue are synthesized. They are tumorotropic RFP, which are included mainly in cells that have high mitotic and metabolic activity. Due to the increased concentration of RFP, the tumor will appear on the scintigram as a hot focus. This technique is called positive scintigraphy. A number of RFPs have been created for it.
Scintigraphy with labeled monoclonal antibodies is called immunoscintigraphy.
A type of scintigraphy is a binuclide study, i.e. Obtaining two scintigraphic images using simultaneously introduced RFP. Such a study is carried out, for example, for a more distinct allocation of small parathyroid glands against a background of a more massive tissue of the thyroid gland. For this purpose, two RFPs are simultaneously administered, one of which is 99m T1 chloride, accumulates in both organs, the other 99m Tc-pertechnetate only in the thyroid gland. Then, using the discriminator and the computer, the second (total) image is subtracted from the first image (i.e. Perform the procedure of subtraction, resulting in the resulting isolated image of the parathyroid glands.
There is a special type of gamma camera, designed to visualize the entire body of the patient. In this case, the camera sensor moves over the patient being examined (or, conversely, the patient moves under the sensor). The resulting scintigram will contain information on the distribution of RFP in the whole body of the patient. In this way, for example, an entire skeleton is obtained, revealing hidden metastases.
To study the contractile function of the heart, gamma cameras equipped with a special trigger device are used, which, under the control of an electrocardiograph, includes a scintillation camera detector in strictly prescribed phases of the cardiac cycle-systole and diastole. As a result, after computer analysis of the information received, two images of the heart appear on the display screen - systolic and diastolic. By combining them on the display, you can study the contractile function of the heart.
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