Renal Scintigraphy – Function, Procedure & Results

What is Renal Scintigraphy?

Renal scintigraphy (also called a kidney scan or renography) is a nuclear medicine imaging technique that uses small amounts of radioactive substances called radiopharmaceuticals to evaluate the function and blood supply of the kidneys. Unlike purely anatomical imaging methods such as ultrasound or computed tomography (CT), renal scintigraphy primarily provides functional information -- showing how well each kidney is working and how blood flows through the renal tissue.

The procedure is performed in nuclear medicine departments and is suitable for patients of all ages, including children and, in exceptional circumstances, pregnant women.

Types of Renal Scintigraphy

Static Renal Scintigraphy (DMSA Scan)

In static renal scintigraphy, the radiopharmaceutical Technetium-99m-DMSA (dimercaptosuccinic acid) is used. It accumulates in functional kidney tissue, providing a detailed image of the renal cortex. This method is primarily used to detect cortical scars, focal defects, or structural anomalies of the kidneys.

Dynamic Renal Scintigraphy (MAG3 or DTPA Scan)

Dynamic renal scintigraphy uses radiopharmaceuticals such as Technetium-99m-MAG3 (mercaptoacetyl triglycine) or Technetium-99m-DTPA (diethylenetriamine pentaacetic acid). These agents are filtered and excreted by the kidneys. A special gamma camera records the process in real time, generating time-activity curves that show how efficiently each kidney produces and drains urine.

Clinical Indications

Renal scintigraphy is used in a variety of clinical situations, including:

• Assessment of split renal function (the percentage contribution of each kidney to total renal function)
• Diagnosis and follow-up of urinary outflow obstruction (e.g., ureteropelvic junction obstruction)
• Evaluation of vesicoureteral reflux (backflow of urine from the bladder into the ureters)
• Detection of renal cortical scars following recurrent urinary tract infections, especially in children
• Monitoring after kidney transplantation
• Diagnosis of renovascular hypertension (high blood pressure caused by renal artery stenosis), often combined with an ACE inhibitor test (captopril renography)
• Assessment of renal function before and after surgical procedures

How the Procedure is Performed

Before the scan, patients are typically asked to drink plenty of fluids to ensure adequate kidney perfusion. The radiopharmaceutical is administered as an intravenous injection into a vein in the arm. The patient then lies on an examination table while a gamma camera positioned above or below the body detects the radiation emitted by the radioactive tracer.

For a dynamic scan, the imaging session typically lasts 20 to 40 minutes. In some cases, a diuretic (such as furosemide) is injected to specifically assess urinary outflow. The static scan is usually performed 2 to 4 hours after injection, once the radiopharmaceutical has sufficiently accumulated in the renal tissue.

Radiation Exposure and Safety

The radiopharmaceuticals used in renal scintigraphy emit only very small amounts of ionizing radiation. The effective radiation dose ranges from approximately 0.5 to 3 millisieverts (mSv) depending on the tracer used and the age of the patient -- comparable to the natural background radiation we are exposed to in everyday life. The radioactive substances are excreted through the kidneys within a few hours to days.

The procedure is generally avoided during pregnancy unless there is an urgent medical indication. Breastfeeding mothers may be advised to temporarily interrupt breastfeeding for a period specified by their physician after the examination.

Interpretation of Results

The analysis of renal scintigraphy provides the following key information:

• Split renal function: Under normal conditions, each kidney contributes approximately 50% to total renal function. Significant deviations may indicate unilateral disease.
• Time-activity curves: A typical curve shows rapid tracer uptake followed by a swift decline as it is excreted. A delayed or plateau-shaped decline may suggest urinary outflow obstruction.
• Perfusion phase: The first few seconds after injection reveal how well the kidneys are being supplied with blood.

Advantages and Limitations Compared to Other Imaging Methods

Renal scintigraphy offers specific strengths and limitations compared to other imaging techniques:

• Advantages: Provides functional rather than purely anatomical information; does not require iodinated contrast agents (which may be problematic in patients with reduced kidney function); well-established procedure with high clinical relevance.
• Limitations: Lower anatomical detail resolution compared to CT or MRI; involves radiation exposure (albeit low); only available in nuclear medicine facilities.

References

1. Piepsz A, Ham HR. Pediatric applications of renal nuclear medicine. Seminars in Nuclear Medicine. 2006;36(1):16-35.
2. Taylor A, Nally J, Aurell M, et al. Consensus report on ACE inhibitor renography for detecting renovascular hypertension. Journal of Nuclear Medicine. 1996;37(11):1876-1882.
3. Shreve P, Gross MD. Renal scintigraphy. In: Henkin RE, ed. Nuclear Medicine. 2nd ed. Mosby; 2006.