Renogram Imaging and Applications

Definition and Purpose

A renogram is a noninvasive nuclear medicine test that evaluates kidney function by tracking the movement of radioactive tracers through the kidneys over time, providing functional information about renal blood flow, filtration, and excretion, as recommended by the American College of Radiology 1, 2
It provides real-time functional data, which complements the anatomical information obtained from other imaging modalities, and has the advantage of not lagging behind actual kidney function changes like serum creatinine levels, according to the American College of Radiology 3, 4, 5, 6

Technetium-99m MAG3 is preferred for evaluating urinary flow and obstruction due to its tubular secretion properties, and is used to assess all three sequential phases of renal function: perfusion, excretion, and urine flow, as indicated by the American College of Radiology 5
Technetium-99m DTPA is excreted by glomerular filtration and is useful for measuring glomerular filtration rate (GFR), but is limited in evaluating obstruction, and can monitor transplant kidney perfusion and GFR, according to the American College of Cardiology and the American College of Radiology 1, 7

Renography is used for assessment of renal transplants, evaluating transplant function and screening for surgical complications, as recommended by the American College of Radiology 1, 5
Captopril-enhanced renography can detect functionally significant renal artery stenosis, which is useful in diagnosing renovascular hypertension, according to the American College of Radiology and the American College of Cardiology 7, 8

Although sensitive for detecting kidney dysfunction, renograms often lack specificity for diagnosing the exact cause of dysfunction, and interpretation may be challenging in patients with poor renal function, dehydration, or bilateral disease, as noted by the American College of Radiology 1, 2, 8
Results should be interpreted in conjunction with clinical findings and other imaging studies, as recommended by the American College of Radiology and the American College of Cardiology 5, 7

MAG3 is designed for renal tubular transport and excretion, with approximately 40-50% extraction fraction through active tubular secretion, and demonstrates rapid renal uptake with minimal background activity compared to DTPA, according to the American College of Radiology 9, 10
The American College of Radiology recommends considering MAG3's primary excretion through the kidneys via MRP2 and MRP4 transporters on the apical membrane of proximal tubule cells, and its superior image quality with less background activity than other renal agents due to efficient tubular extraction, although the strength of evidence for this is not provided 9, 10

True renal uptake should demonstrate all three phases of renal function: perfusion, excretion, and urine flow, as stated by the American College of Radiology, with a moderate strength of evidence 11
Ectopic or abnormal renal tissue would still demonstrate functional phases if viable, according to the American College of Radiology, with a moderate strength of evidence 9, 10