Radioisotope renography

The dynamic Nierenszintigrafie with MAG3 is a diagnostic procedure in nuclear medicine and is used for kidney function test. MAG3 is mercaptoacetyltriglycine or mercaptoacetylglycylglycylglycine. The method has become a standard method and (eg " Oberhausen " ) displaces other methods. MAG -3 was developed in 1986 at the University of Utah by Alan R. Fritz Berg, Sudhakar Kasina and Dennis Eshima. The phase III trials were successfully completed in 1988. Significant work on the use of MAG -3 among others to Clearanceberechnung in children using the single -sample Bubeck method were supplied by Bernd Bubeck, who also established the concept of tubular extraction rate (TER).

Background

The ideal substance for Funktionsszintigrafie expected to accumulate quickly and strongly in the kidney and are excreted without parenchymal retention in the urine, so as to judge tissue and cavity system of the kidneys. In addition, it should be possible completely removed per kidney passage. The substance should be markable beyond with a gamma emitter, which is well represented with the help of gamma cameras and results in a low radiation exposure to the patient.

The clearance determination with o -iodo- hippuric acid (abbreviated OJH ) is still the gold standard in nuclear medicine because his biological precipitation behavior is nearly ideal for the question of the Clearancebestimmung. It is excreted faster than any other known radiopharmaceutical. However, the 131I used in radiopharmaceutical OJH has a beta radiation component and a relatively long half-life of 8 days, resulting in a high radiation exposure with it. The radiation hygienic far more affordable version with 123I is far more expensive and difficult than the technetium tracers in procurement. OJH is therefore used today any more.

99mTc- MAG3 improved the image quality of Nierenszintigrammen because the radionuclide 99mTc by its lower photon energy (140 keV instead of 364 keV) meets the imaging properties of gamma cameras. In addition, the radiation exposure is through the investigation because of the elimination of the beta component and because of with 6 hours significantly shorter half-life of 99mTc considerably lower than when using OJH. For the same injected activity, the radiation exposure of the kidneys ( organ dose) by a factor of 3.6 and the " Effective dose equivalent" are ( ICRP 1979) by a factor of 6.2 lower. The latter is about 0.8 mSv using 100 MBq of 99mTc- MAG3.

Indication

The Nierenszintigrafie with MAG3 is used to display, the perfusion and function monitoring of renal cases of suspected injury or impairment of renal function.

The investigation

Preparation

Children to a pint of their favorite beverage, adults should 10 ml / kg body weight liquid drink. Children and adults should empty the bladder before study initiation.

Dosage

For combined perfusion and Funktionsszintigrafie is used in adults an activity of 150-200 MBq 99mTc- MAG3 in children 4 MBq per kg body weight may be administered. In a pure Funktionsszintigrafie 60-80 MBq in adults and 1-2 MBq / kg body weight in children. Quantitatively Clearancebestimmung without camera measurement 10-20 MBq be used.

Examination process

The total scan time is about an hour. After finding the medical history (anamnesis) the injection of the radiopharmaceutical is done. This should be injected quickly as possible and in a small volume bolus followed by 10-20 ml of isotonic saline immediately following and with the maximum possible pressure. Now follows the total 30-minute recording using a gamma camera.

It is usually a combined perfusion and Funktionszintigraphie performed: During the first 60 minutes of each one-second recordings are made (dynamic Perfusionsaufnahme ). In two minutes is acquired with one image per 5 seconds, and after 20 minutes to one minute recordings are created (function recording). The patient is sitting normally, the head of the gamma camera is located on the patient's back. While recording one or two blood samples are performed. If necessary. can be administered to stimulate kidney function while recording a diuretic. After the end of the recording, the patient should urinate and after perform shooting while lying down (camera head also fitting to the back) should be able to assess such a possible change in position of the kidneys.

Evaluation

For evaluation, ROIs are placed over both kidneys, a aortic and an underground region. The underground area is ideally located outside of large vessels and outside of the liver and spleen, ideally between both kidneys. Using the two - kidney ROIs are created from minute one to separate Perfusionskurven. The aortic ROI is used to control the bolus quality. The underground ROI is used exclusively for the calculation page.

Time 0 for all calculations is set manually using a marker. It is defined as the base of the first ascending kidney ROI curve. The curves of the underlying raw data are smoothed with a conventional method; function curves generated over the entire course of the examination are based on the calculation of the functional portion of both kidneys. The calculation is based on the determined 60-100 seconds after the rise in the curve in the time interval data. This avoids that the side portion of a congested kidney is overestimated; as the time of possible variations in activity of the underground ROI is outside this time window and goes therefore not distorting in the calculation.

The clearance index, given in cps / MBq ( counts per second per Megabecquerel ), calculated as follows:

With

F1 = integral part of the slope triangle from kidney curve 1 F2 = integral part of the slope triangle from kidney curve 2 Di = activity at time of injection   = Time interval is integrated over the fac = attenuation correction factor with μ = 1.53 eμs [cm -1] (absorption coefficient for 99mTc) s = distance Kidney skin surface [cm ] 10x = scaling factor with x = 0 .2

Result

The Nierenszintigrafie with MAG3 is used for perfusion, the function and clearance determination of both kidneys, absolute or relative before and after an intervention (eg, chemotherapy). In addition, it provides the body sizes indicates merger, hiking or congestive or double kidneys and represents a possibly existing urinary obstruction dar. Using the MAG -3 clearance can determine the tubular extraction rate TER in adults and children.