Kidney scintigraphy with MAG3

Dynamic kidney scintigraphy with MAG3 is a diagnostic procedure in nuclear medicine and is used to test kidney function ( kidney scintigraphy ). MAG3 stands for mercaptoacetyltriglycine or mercaptoacetylglycylglycylglycine. The procedure has established itself as a standard procedure and has displaced other methods (e.g. "to Oberhausen"). MAG-3 was developed in 1986 at the University of Utah by Alan R. Fritzberg, Sudhakar Kasina and Dennis Eshima. The phase III tests were successfully completed in 1988. Essential work on the use of MAG-3 u. a. for the calculation of clearance in children using the single-sample Bubeck method were provided by Bernd Bubeck, who also established the term tubular extraction rate (TER).

background

The ideal substance for functional scintigraphy should accumulate rapidly and strongly in the kidneys and be excreted in the urine without parenchymatic retention in order to be able to assess the tissue and cavity system of the kidneys. In addition, it should be removed as completely as possible per kidney passage. In addition, it should be possible to mark the substance with a gamma emitter, which can be easily displayed with the aid of gamma cameras and leads to a low radiation exposure of the patient. Non-radiating molecules are radioactively labeled to meet these conditions.

The clearance determination with o-iodine- hippuric acid (abbreviated OJH) is the gold standard in nuclear medicine to this day , since its biological excretion behavior is almost ideal for the question of clearance determination. It is cleared faster than any other known radiopharmaceutical. The ¹³¹ I used in the radiopharmaceutical OJH , however, has a beta radiation component and a comparatively long half-life of 8 days, which results in a high level of radiation exposure. The version with ¹²³ I, which is far cheaper in terms of radiation hygiene, is far more expensive and more difficult to procure than the technetium tracer. OJH is therefore rarely used today.

^99m Tc -MAG3 improved the image quality of kidney scintigrams, since the radionuclide ^99m Tc, with its lower photon energy (140 keV instead of 364 keV),complies with the imaging properties of gamma cameras. In addition, the radiation exposure due to the examination isconsiderably lower than when using OJHdue to the omission of the beta component and the significantly shorter half-life of ^99m Tc of6 hours. With the same injected activity, the radiation exposure of the kidneys ( organ dose ) islowerby a factor of 3.6 and the “ effective dose equivalent ” (according to ICRP 1979) is lower by a factor of 6.2. The latter amounts toapprox. 0.8 mSvwhen using 100 MBq ^99m Tc-MAG3.

indication

The kidney scintigraphy with MAG3 is used to display, perfusion and function control of the kidneys in case of suspected damage or impairment of kidney function. One-sided kidney damage in particular can be quantified, but the informative value in the case of systemic kidney diseases is considered to be low.

The investigation

preparation

Children should drink half a liter of their favorite drink, adults should drink 10 ml / kg of liquid. Children and adults should empty the urinary bladder before starting the examination. Baby milk does not count as a drink, but as a food.

dosage

With combined perfusion and functional scintigraphy, an activity of approx. 100 MBq ^99m Tc-MAG3 is administered in adults and 4 MBq per kg body weight in children. In a pure functional scintigraphy, 60–80 MBq / kg body weight are administered in adults and 1–2 MBq / kg body weight in children. For a purely quantitative clearance determination without camera measurement, 10–20 MBq are used.

Investigation process

The total duration of the examination is about an hour. After determining the medical history ( anamnesis ), the radiopharmaceutical is injected. This should be injected quickly and, if possible, in a small-volume bolus , followed by 10–20 ml of isotonic saline solution immediately afterwards and with the maximum possible pressure. This is followed by a 30-minute recording with the help of a gamma camera.

A combined perfusion and functional scintigraphy is usually carried out: During the first minute, 60 images, each lasting one second, are made (dynamic perfusion image). In minute two, one image is acquired every 5 seconds and then, up to minute 20, one-minute recordings are made continuously (function recording). The patient is usually seated with the head of the gamma camera resting on the patient's back. One or two blood samples are taken during admission. Possibly. a diuretic may be given during admission to stimulate kidney function. After the end of the exposure, the patient should urinate and then an exposure should be made lying down (camera head also resting on the back) in order to be able to assess a possible change in the position of the kidneys.

evaluation

For evaluation, ROIs are placed over both kidneys, over a section of the aorta and over an underground region. The underground region is ideally located outside large vessels and outside the liver and spleen, ideally between both kidneys. With the help of the two kidney ROIs, separate perfusion curves are created from minute one. The aortic ROI is used to control the bolus quality. The underground ROI is used exclusively for the side calculation.

Time 0 for all calculations is set manually with the help of a marker. It is defined as the base of the first ascending kidney ROI curve. The raw data on which the curves are based are smoothed using a conventional method; Function curves generated over the entire examination process are the basis for calculating the functional share of both kidneys. The calculation is based on the data determined in the time interval 60–100 seconds after the curve rise. This avoids overestimating the side portion of a congested kidney; Likewise, the point in time of possible activity fluctuations in the background ROI lies outside this time window and for this reason is not included in the calculation in a falsifying manner.

The clearance index, given in Cps / MBq (counts per second per megabecquerel), is calculated as follows:

${\displaystyle {\frac {(F_{1}+F_{2})}{D_{i}\!\ \delta t}}f_{AC}\!\ 10^{x}}$

With

F ₁ = partial integral of the slope triangle below the kidney curve 1
F ₂ = partial integral of the slope triangle below the kidney curve 2
D _i = activity at the time of injection = time interval over which the integration takes place f _ac = attenuation correction factor e ^µs with µ = 1.53 [cm ⁻¹ ] ( Absorption coefficient for ^99m Tc) s = distance kidney - skin surface [cm] 10 ^x = scaling factor with x = 0..2
${\displaystyle \delta t}$

Result

The kidney scintigraphy with MAG3 is used to determine the perfusion, function and clearance of both kidneys in absolute terms or in comparison before or after an intervention (e.g. chemotherapy). In addition, it provides the organ sizes, shows merging, migrating, congested or double kidneys and shows any urinary outflow disorder. With the help of MAG-3 clearance, the tubular extraction rate TER can be determined in adults and children. Statements on glomerular filtration are not possible. Absolute values ​​for a tubular extraction (with the unit ml / min) of the tracer used are of no relevance in everyday clinical practice. The result of the dynamic kidney scintigraphy with MAG3 is the ratio of both kidneys (always with the sum 100%) with regard to the excretion of the test substance via the kidney tubules ; these work independently of the podocytes and glomeruli . However, no statements can be made about normal or pathological tubular function either, because the task of the tubules is reabsorption and not the opposite secretion .

Individual evidence

1. ^ Alan R. Fritzberg, S. Kasina, D. Eshima, DL Johnson: Synthesis and biological evaluation of technetium-99m MAG3 as a hippuran replacement . In: J. Nucl. Med . 27, No. 1, 1986, pp. 111-6. PMID 2934521 .
2. ↑ A. Taylor, D. Eshima, N. Alazraki: 99mTc-MAG3, a new renal imaging agent: preliminary results in patients . In: Eur J Nucl Med . 12, No. 10, 1987, pp. 510-4. doi : 10.1007 / BF00620476 . PMID 2952506 .
3. ↑ AA Al-Nahhas, RA Jafri, KE Britton et al. : Clinical experience with 99mTc-MAG3, mercaptoacetyltriglycine, and a comparison with 99mTc-DTPA . In: Eur J Nucl Med . 14, No. 9-10, 1988, pp. 453-62. doi : 10.1007 / BF00252388 . PMID 2975219 .
4. ^ Karl Julius Ullrich , Klaus Hierholzer (ed.): Normal and pathological function of the renal tubule , Verlag Hans Huber , Bern, Stuttgart 1965, 465 pages.
5. ↑ Another view, albeit without justification: Richard Fotter (ed.): Pediatric Uroradiology , 2nd edition, Springer-Verlag, Berlin, Heidelberg 2008, ISBN 978-3-540-33004-2 , pp. 37–51. On page 39, kidney scintigraphy with MAG3 and indirect radioisotope cystography are also combined to determine kidney function.

literature

• Bernd Bubeck: Technetium 99m-MAG-3 for nuclear medicine kidney function diagnostics; Pharmacokinetics and clinical application in comparison with radioiodinated iodohippuric acid , 2nd revised and expanded edition online at Nuklearmedizin.ch (PDF; 67.0 MB).

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