Scintigraphy

Scintigraphy is the production of images of a patient's organs and tissues by recording the radiation emitted by an incorporated radionuclide on a gamma camera.

The physiological essence of scintigraphy is the organotropism of the radiopharmaceutical, i.e. its ability to selectively accumulate in a specific organ - to accumulate, be released or pass through it in the form of a compact radioactive bolus.

A gamma camera is a complex technical device, saturated with microelectronics and computer technology. A scintillation crystal (usually sodium iodide) of large dimensions - up to 50 cm in diameter - is used as a detector of radioactive radiation. This ensures that radiation is simultaneously recorded over the entire examined part of the body. Gamma quanta emanating from the organ cause light flashes in the crystal. These flashes are recorded by several photomultipliers, which are evenly distributed over the surface of the crystal. Electrical impulses from the photomultiplier are transmitted through an amplifier and discriminator to the analyzer unit, which forms a signal on the display screen. In this case, the coordinates of the point glowing on the screen exactly correspond to the coordinates of the light flash in the scintillator and, consequently, the location of the radionuclide in the organ. At the same time, the moment of occurrence of each scintillation is analyzed using electronics, which makes it possible to determine the time of passage of the radionuclide through the organ.

The most important component of a gamma camera is, of course, a specialized computer, which allows for a variety of computer image processing: highlighting noteworthy fields on it - the so-called zones of interest - and performing various procedures in them: measuring radioactivity (general and local), determining the size of an organ or its parts, studying the speed of passage of radiopharmaceuticals in this field. With the help of a computer, it is possible to improve the quality of an image, highlight interesting details on it, for example, vessels feeding an organ.

When analyzing scintigrams, mathematical methods, system analysis, chamber modeling of physiological and pathological processes are widely used. Naturally, all the data obtained are not only displayed on the screen, but can also be transferred to magnetic media and 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 film (using a camera).

In principle, each scintigram characterizes the function of an organ to a certain extent, since the radiopharmaceutical accumulates (and is released) mainly in normal and actively functioning cells, therefore a scintigram is a functional-anatomical image. This is the uniqueness of radionuclide images, which distinguishes them from those obtained during X-ray and ultrasound examinations, magnetic resonance imaging. Hence the main condition for prescribing scintigraphy - the organ being examined must be functionally active to at least a limited extent. Otherwise, a scintigraphic image will not be obtained. That is why it is pointless to prescribe a radionuclide study of the liver in hepatic coma.

Scintigraphy is widely used in almost all areas of clinical medicine: therapy, surgery, oncology, cardiology, endocrinology, etc. - where a "functional image" of an organ is needed. If one image is taken, it is static scintigraphy. If the goal of the radionuclide study is to study the function of the organ, a series of scintigrams is taken at different time intervals, which can be measured in minutes or seconds. Such serial scintigraphy is called dynamic. After analyzing the resulting series of scintigrams on a computer, selecting the entire organ or part of it as the "zone of interest", you can get a curve on the display showing the passage of the radiopharmaceutical through this organ (or part of it). Such curves, constructed on the basis of the results of computer analysis of a series of scintigrams, are called histograms. They are intended to study the function of an organ (or part of it). An important advantage of histograms is the ability to process them on a computer: smooth them, isolate individual components, sum and subtract, digitize and subject them to mathematical analysis.

When analyzing scintigrams, mainly static ones, along with the topography of the organ, its size and shape, the degree of homogeneity of its image is determined. Areas with increased accumulation of the radiopharmaceutical are called hot spots or hot nodes. They usually correspond to excessively actively functioning areas of the organ - inflammatory tissues, some types of tumors, hyperplasia zones. If an area of decreased accumulation of the radiopharmaceutical is detected on the scintigram, then this means that we are talking about some kind of volumetric formation that has replaced the normally functioning parenchyma of the organ - the so-called cold nodes. They are observed in cysts, metastases, focal sclerosis, and some tumors.

Radiopharmaceuticals have been synthesized that selectively accumulate in tumor tissue - tumorotropic radiopharmaceuticals, which are included mainly in cells with high mitotic and metabolic activity. Due to the increased concentration of radiopharmaceuticals, the tumor will appear on the scintigram as a hot spot. This research method is called positive scintigraphy. A number of radiopharmaceuticals 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 administered radiopharmaceuticals. Such a study is conducted, for example, to more clearly distinguish small parathyroid glands against the background of more massive thyroid tissue. For this purpose, two radiopharmaceuticals are administered simultaneously, one of which - ^99m T1-chloride - accumulates in both organs, the other - ^99m Tc-pertechnetate - only in the thyroid gland. Then, using a discriminator and a computer, the second is subtracted from the first (summary) image, i.e. a subtraction procedure is performed, as a result of which a final isolated image of the parathyroid glands is obtained.

There is a special type of gamma camera designed to visualize the patient's entire body. The camera sensor moves above the patient being examined (or, conversely, the patient moves under the sensor). The resulting scintigram will contain information about the distribution of the radiopharmaceutical throughout the patient's entire body. In this way, for example, an image of the entire skeleton is obtained, revealing hidden metastases.

To study the contractile function of the heart, gamma cameras are used, equipped with a special device - a trigger, which, under the control of the electrocardiograph, turns on the scintillation detector of the camera in strictly specified phases of the cardiac cycle - systole and diastole. As a result, after a 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, it is possible to study the contractile function of the heart.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ]