Radionuclide study of the kidneys

Radonuclide methods have firmly entered the practice of urological and nephrological clinics. They allow you to detect kidney function disorders in the initial stages, which is difficult to carry out using other methods. The clinicians are attracted by the physiologicity of the radioindication method, its relative simplicity and the possibility of repeated studies during the treatment of the patient. It is also important that radionuclide compounds can be applied in patients with increased sensitivity to radiomatic substances. Depending on the tasks of the study from the group of nephrotropic RFP, one of the radionuclide indicators is chosen.

^99MTc-dtpa is chosen with glomeruli, ⁹⁹Tc-mag-3 and i-hippuran are also filtered mainly tubular cells. Thus, all these three RFPs can be used to study the functions of the kidneys - glomerular filtration and tubular secretion. Such a study is called "renography." Two other drugs-^99MTc-dmsa and ^99mTS-glucogeptonate for a relatively long time are accumulated in functioning tubular cells, so they can be used for static scintigraphy. After intravenous administration of these drugs, they are held in the canal of the kidney epithelium for several hours. The maximum accumulation is noted 2 hours after the injection. Therefore, at this time, scintigraphy should be carried out. They usually take several pictures: in the direct projection of the front and behind, in lateral and oblique projections.

Changes in the renal parenchyma associated with the loss of its function or the replacement of its fabric with pathological formations (tumor, cyst, abscess) lead to the appearance of “cold” foci on the scintigram. Their localization and dimensions correspond to areas of non-functioning or absent renal tissue. Static scintigraphy can be used not only to detect volumetric processes in the kidney, but also to diagnose stenosis of the renal artery. For this purpose, a sample with captopril is performed. Static scintigraphy is performed twice - before and after intravenous administration of the specified drug. In response to the introduction of captopril, the scintigraphic image of the kidney, “covered” with stenosis, is the so-called drug nephrectomy.

The readings for the radionuclide study of the kidneys - renography are much wider. As you know, the total kidney function is the following private functions: renal blood flow, glomerular filtration, tubular secretion, tubular reabsorption. All these aspects of the activity of the kidneys can be studied using radionuclide techniques.

Important in the clinic of internal diseases is the definition of renal plasmotok. This can be done by studying the clearance, i.e. The speed of cleansing the kidneys from substances completely or almost completely removed when blood flow through the kidney. Since cleansing from these substances does not occur in the entire counting parenchyma, but only in its functioning part, which is about 90 %, the renal clearance determined by the cleansing method is called “Effective renal plasma plasma”. As the RFP, hippuran is used, stained ¹³¹I. After intravenous administration, a small amount of this RFP measure its concentration in the blood 20 minutes after injection and compared with the level of radioactivity according to a special formula. In healthy people, effective renal plasmaids is 500-800 ml/min. The selective decrease in effective renal plasmotok is observed with arterial hypertension, heart and acute vascular insufficiency.

In the study of the functional state of the kidneys, an important place is assigned to determine the speed of glomerular filtration. For this purpose, substances that are not subjected to channel reabsorption, tubular secretion, destruction and not formed in tubules and urinary tract are used. Such substances include inulin, mannitol and to some extent creatinine. The definition of their concentration in the laboratory is difficult. In addition, for him it is necessary to collect urine that has been released for certain periods of time.

The radionuclide method made it possible to significantly simplify the assessment of glomerular filtration. The patient is administered intravenously ^99MTc-dtpa. Since this drug is released exclusively by glomerular filtration, having determined the rate of blood cleansing from the RFP, you can calculate the intensity of the filtration function of the kidneys. Typically, the concentration of these RFP in the blood is determined twice: 2 and 4 hours after intravenous administration. Then, the speed of glomerular filtration is calculated according to a special formula. Normally, it is 90-130 ml/min.

In the nephrological clinic, they attach the value to another indicator of the function of the kidneys - filtration fraction. This is the ratio of the speed of glomerular filtration to the speed of effective renal plasmotok. According to the results of a radionuclide study, the normal value of the filtration fraction is an average of 20 %. An increase in this indicator is observed with arterial hypertension, and a decrease in glomerulonephritis and exacerbation of chronic pyelonephritis.

A common way to evaluate the function of renal parenchyma is dynamic scintigraphy, or renography. At the same time, they use ¹³¹I-hippuran or ^99MTc-mag-3. The study is carried out on a gamma camera. Typically, the duration of the study is 20-25 minutes, and in case of impaired renal function-up to 30-40 minutes. On the display screen, 4 “zones of interest” (both buds, aorta and bladder) are chosen and curves are built on them - renograms that reflect the function of the kidneys.

First, the RFP, introduced intravenously, is brought with blood to the kidneys. This determines the rapid appearance and significant increase in the intensity of radiation over the kidneys. This is the first phase of the renographic curve; It characterizes the perfusion of the kidney. The duration of this phase is approximately 30-60 s. Of course, this segment of the curve reflects the presence of a radionuclide not only in the vascular channel of the kidneys, but also in the peripochial tissues and soft tissues of the back, as well as the beginning transit of the RFP into the lumen of the tubules. Then the number of RFP in the kidneys gradually increases. The curve on this segment is less steep - this is its second phase. The contents of the tubules decrease, and within a few minutes there is a approximate equilibrium between the receipt and excretion of the RFP, which corresponds to the top of the curve (T Max - 4-5 minutes). From the moment when the concentration of the RFP in the kidney begins to decrease, i.e. The outflow of the RFP prevails over the admission, the third phase of the curve is noted. The duration of the half-life of the RFP from the kidneys of different people is different, but on average it ranges from 5 to 8 minutes.

To characterize the renographic curve, three indicators are usually used: the time for achieving the maximum of radioactivity, the height of its maximum rise and the duration of the half-life of the RFP from the kidney. In case of violation of the function of the kidneys and urinary tract, the renographic curves change. We indicate 4 of the characteristic option of curves.

• The first option is a slowdown in the receipt of the RFP in the "zone of interest" of the kidney. This is manifested by a decrease in the height of the curve and the lengthening of its first two phases. This type is observed with a decrease in blood flow in the kidney (for example, with narrowing the renal artery) or a decrease in the secretory function of the tubules (for example, in patients with pyelonephritis).
• The second option is a slowdown in the breeding of the RFP by the kidney. At the same time, the steepness and duration of the second phase of the curve increase. Sometimes for 20 minutes the curve does not reach the peak and does not come the subsequent recession. In such cases, they talk about the obstructive type curve. In order to distinguish the true obstruction of the urinary tract with a stone or other mechanical obstacle from dilatation ungity, a diuretic agent, such as Lazix, is intravenously administered. When obstructing urinary tract, the introduction of a diuretic is not reflected on the shape of a curve. In cases of functional delay in the transit of the RFP, an immediate decline in the curve occurs.
• The third option is a slow intake and excretion of the RFP from the kidneys. This is manifested by a decrease in the total height of the curve, deformation and elongation of the second and third segments of the renogram, the absence of a clearly expressed maximum. This option is observed mainly for chronic diffuse kidney diseases: glomerulonephritis, pyelonephritis, amyloidosis, and the severity of the changes depends on the severity of kidney damage.
• The fourth option is a repeated rise in renographic curve. It is observed with bubble-memorial reflux. Sometimes this option is detected with ordinary scintigraphy. If it is not there, but on the basis of clinical data, reflux is suspected, then at the end of renography the patient is offered to urinate in a lining ship. If a new rise occurs on the curve, then this means that the urine radionuclide from the bladder returned to the ureter and then to the renal pelvis.

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