Renal function scintigraphy

Renal function scintigraphy is a method for side-separated imaging of renal function (Risler 2008).

Even today, it is still one of the most common nuclear medical functional examinations (Hoffmann 2002), as it has only a low radiation exposure on the one hand, but on the other hand a high clinical significance with regard to renal function (Radtke 2018).

Synonyms

Radioisotope nephrography; isotope nephrography;

Classification

Renal function scintigraphy is differentiated into two main forms:

• static
• dynamic (Hegele 2015)

Captopril renal scintigraphy has an additional importance (Risler 2008).

Renal function scintigraphy is one of the nuclear medicine examinations. It is a non-invasive method that can be used to detect functional changes in kidney tissue (Kasper 2015).

The radiation exposure is low. In children, renal function scintigraphy is one of the most commonly used nuclear medicine examinations (Keller 2010).

• Indications:
  • Identification of ectopic renal tissue
  • Presence of an X-ray contrast agent allergy
  • Necessity of a side-separated functional diagnosis
  • Ren mobilis outflow obstruction, also known as nephroptosis (the examination can be performed in the supine or sitting position)
  • V. a. a circulatory disorder in anuric transplanted kidney
  • Detection of renal artery stenosis requiring treatment with simultaneous administration of an ACE inhibitor (the sensitivity is between 85 % - 90 %; for comparison: the sensitivity of a spiral CT is 98 % and the specificity 94 %; however, the latter decreases from a creatinine of 1.7 mg / dl [Keller 2010])
  • Reflux diagnostics of the activity collected in the urinary bladder

[Herold 2021)

• As scintigraphy with 99 m Tc- DMSA:
  • Diagnosis of vesicoureteral reflux
  • Detection of renal scars after infection (Kuhlmann 2015)
  • Assessment of excretory function of the individual kidney and also its segments (Tanagho 1992)
  • Assessment of obstructive from non-obstructive dilatations (Tanagho 1992)
  • Assessment of tissue function of the individual kidney
  • Differentiation between functional or obstructive outflow obstruction and assessment of urodynamic relevance after previous administration of a loop diuretic (Keller 2010)
  • Indications of partial function in double kidneys
  • Examination in preparation for living kidney donation
  • for the evaluation of transplant kidneys
  • exclusion or detection of urine leakage
  • Follow-up of surgically treated obstruction
  • Determination of the total clearance

(Eckardt 2009)

• contraindication:
  • Pregnancy
  • Lactation (Keller 2010)
  • Serum creatinine > 3 mg / dl
• strict indication:
  • in children (Risler 2008)
  • Repeat examination in a period of ≤ 3 months (Eckardt 2009).

Nephrolithiasis should be excluded before administration of a diuretic (Eckardt 2009).

More details on the different types of renal scintigraphy:

1. static renal scintigraphy

Static renal scintigraphy shows a snapshot of the functioning renal parenchyma. It also provides information on kidney size, shape and location (Staubach 2013).

The examination is particularly used to visualize renal parenchymal damage (Oberbeck 2021). In paediatrics, static scintigraphy is sometimes used to evaluate scar tissue in cases of pyelonephritis (Porn 2003).

The examination is usually performed with the radiopharmaceutical dimercaptosuccinic acid (DMSA), which is taken up and stored by the epithelium of the proximal tubules. DMSA can be labelled by chelation with the tracer technetium-99m. The nuclide technetium- 99 m is stored for a long time, as excretion is very low (Hegele 2015).

The imaging is done by a gamma camera in 3D.

The radiation exposure is due to the effective half-life is higher than in dynamic scintigraphy and is 380 µGy / Mbq (Benz- Bohm 2005).

2. dynamic renal scintigraphy (also referred to as renal function scintigraphy [Oberbeck 2021]).

In contrast to static scintigraphy, dynamic renal scintigraphy uses rapidly excreted and predominantly tubularly secreted tracers such as MAG3 (technetium-labeled mercaptoacetyltriglycine), Tc- 99m- ethylene- dicysteine, or I-123- hippuran labeled with radioactive iodine- 123.

These tracers are mainly secreted tubularly.

The radiation exposure is lower than in static scintigraphy and is 17 µGy / Mbq (Benz- Bohm 2005).

3 Captopril scintigraphy

Captopril scintigraphy is used to clarify renovascular hypertension and thus a hemodynamically effective renal artery stenosis.

For this purpose, all diuretics and ACE inhibitors are discontinued 3 days before the start of the test and calcium antagonists 1 day before the start of the test. The patient remains fasting and without antihypertensive medication on the day of the examination; only beta-receptor blockers may be taken (Risler 2008).

• Performance of static renal scintigraphy (1):

In static scintigraphy, the patient is injected i. v. with the tracer DMSA. The actual images are then taken 3 - 6 h later (Manski 2019).

• Performance dynamic renal scintigraphy (2):

First, determine body height and weight and renal function parameters. Attach 2 venous indwelling cannulas in both arms (for blood sampling and bolus injection). Hydration with a NaCl solution of 10 ml / kg bw is administered 30 min before the examination. Bladder emptying immediately before the examination (Risler 2008).

The patient is positioned so that both kidneys are in view. This is followed by the collection of 1 ml of empty blood (Risler 2008), then the injection of the tracer and simultaneous start of the recording sequence from usually dorsal (Hegele 2015).

After each 15, 20, 25 min and at the end of the examination, blood samples are taken from unstowed arms (Risler 2008).

If outflow is delayed, additional recordings can be made after micturition and under forced diuresis with an i.v. injected diuretic (e.g. furosemide) (Hegele 2015).

• Performance on captopril scintigram (3):

In patients who have interrupted treatment with an ACE inhibitor, it is recommended to measure blood pressure and pulse before ACE administration and every 10-15 min thereafter.

Venous access with a NaCl infusion should be established in high-risk patients (e.g. history of carotid disease, TIA, apoplexy, angina pectoris, myocardial infarction), as well as in patients who receive the ACE inhibitor i.v. during the examination (Otto 1998).

Tc- 99m- mercapto- acethyltriglycerine (MAG3) or Tc- 99m- diethylene triamine pentaacetic acid (DTPA) are used as radiopharmaceuticals.

(Otto 1998)

The patient receives 25 mg captopril p. o. or i. v., followed by hydration and blood pressure measurement. A prerequisite for the test is systolic values > 140 mm Hg.

One minute before the administration of the radionuclide, the patient receives 10 mg furosemide i. v., followed by the usual scintigraphy (Risler 2008).

The patient should be monitored until there is no longer a tendency to collapse and the standing blood pressure is ≥ 70% of normal (Otto 1998).

• Evaluation static renal scintigraphy (1):

Functional renal tissue is sensitively demonstrated (Manski 2019).

• Evaluation dynamic renal scintigraphy (2):

The evaluation is performed - depending on the question - by the flare-up and decay of the radionuclide (Risler 2008).

With the help of an isotope nephrogram (representation of a time-activity curve) further conclusions can be drawn. This consists of 3 functional phases:

• Perfusion (this shows a rapid increase in activity, this correlates with the perfusion of the kidneys [Manski 2019]).
• Secretion (this is the peak of activity and is reached after about 2 - 5 min [Manski 2019]).
• Excretion (here, there is a gradual decrease in activity, the half-life of which is usually less than 10 min [Manski 2019]).

This allows conclusions to be drawn about various pathologies:

• Decrease in perfusion

The perfusion of the tracer is delayed in the 1st phase compared to the side or compared to the entry of the tracer into the aorta. This gives evidence of a reduction in perfusion (Hegele 2015).

• Calculation of the side-to-side fraction

This is calculated by comparing the nephrograms. This is done by determining the area between the nephrograms and the whole-body curve in the parenchymal phase and then calculating the aspect ratio (Hegele 2015).

• Urinary outflow obstruction

Outflow obstruction is manifested in the excretory phase by a decreased drop in nephrograms. If the outflow obstruction is only moderate, the curve forms a plateau, otherwise the activity increases continuously.

Normally, the ureters are not delineated in the adult images. If they should be recognizable between the kidney and the bladder, this indicates a stenosis in the area of the ureteral orifice or a pronounced reflux from the urinary bladder.

In the case of stenosis in the renal pelvic outlet, the tracer collection is in the renal pelvis. In this case, the ureters cannot be demarcated.

(Hegele 2015)

• Evaluation of captopril scintigram (3):

Curve maxima with a temporal difference of > 2 min and / or depressed or flattened maxima of at least 5% are considered pathological. However, bilateral symmetrical changes sometimes result in false positive findings (Risler 2008).

• Potential sources of error in renal scintigraphy:
  • in the case of bilateral severe damage, the values may lie within the normal range, since the side-separated function of the kidney lies between 45 % - 55 %S
  • subjective assessment of the outflow in individual examiners
  • incorrect positioning
  • movements of the patient
  • insufficient hydration of the patient etc.

(Overbeck 2021)

1. Benz - Bohm G (2005) Pediatric radiology. Thieme Verlag 234 - 235
2. Eckardt J et al. (2009) Recommendations for quality control in nuclear medicine clinic and measurement technology. Schattauer Publishers 159 - 162
3. Hegele A et al. (2015) Urology: intensive course for continuing education. Thieme Verlag 70 - 75
4. Herold G et al (2021) Internal medicine. Herold Publishers 605
5. Hoffmann H et al. (2002) Original examination questions with commentary GK2. Radiology Thieme Verlag
6. Kasper D L et al (2015) Harrison's Principles of Internal Medicine. Mc Graw Hill Education 140
7. Kasper D L et al (2015) Harrison's internal medicine. Georg Thieme Publishers 270
8. Keller C K et al (2010) Practice of nephrology. Springer Verlag 32, 397
9. Kuhlmann U et al (2015) Nephrology: pathophysiology - clinic - renal replacement procedures. Thieme Verlag 542
10. Manski D (2019) The urology textbook. Dirk Manski Publishers 122 - 123
11. Oberbeck M S (2021) The clinical value of 99mTc-MAG3- renal scintigraphy before peptide receptor radionuclide therapy (PRRT) for prediction of therapy-induced renal function loss. Inaugural dissertation for the award of the doctorate of medicine or dentistry, human biology or natural sciences, medical sciences of the faculty of medicine of the Philipps-University Marburg.
12. Otto H J et al (1998) Guideline for the diagnosis of renovascular hypertension based on Taylor AT Jr, et al Procedure Guideline for Diagnosis of Renovascular Hypertension. J Nucl Med 1998; 39: 1297- 1302.
13. Porn U et al (2003) Nuclear medicine renal diagnosis in pediatrics. The nuclear medicine physician (26) 208 - 217.
14. Radtke H et al. (2018) Why does nephrology still need renal scintigraphy today? The Nephrologist (13) 244 - 250
15. Risler T et al (2008) Specialist nephrology. Elsevier Urban and Fischer Publishing 131 - 134
16. Staubach K H et al. (2013) Short textbook foursome small operative subjects: urology, ophthalmology, ENT, orthopaedics. Elsevier Urban and Fischer Publishers 18
17. Tanagho E A et al (1992) Smith Urology. Springer Publishers 666, 669, 675