What is a renogram?

What is a Renogram?

A renogram is a dynamic nuclear medicine imaging study that provides functional assessment of kidney perfusion, filtration, and excretion using radiopharmaceuticals to evaluate renal function and detect abnormalities. 1

Definition and Purpose

• A renogram (also called dynamic renal scintigraphy) is a noninvasive nuclear medicine test that evaluates kidney function by tracking the movement of radioactive tracers through the kidneys over time 1
• It provides functional information about renal blood flow, filtration, and excretion, which complements the anatomical information obtained from other imaging modalities 1
• Renography has the advantage of providing real-time functional data, whereas serum creatinine levels lag behind actual kidney function changes 1

Types of Radiopharmaceuticals Used

Two main radiopharmaceuticals are commonly used in renography:

1. Technetium-99m MAG3 (mercaptoacetyltriglycine):

   • Primarily excreted by tubular secretion 2
   • Preferred for evaluating urinary flow and obstruction due to its tubular secretion properties 1
   • Used to assess all three sequential phases of renal function: perfusion, excretion, and urine flow 1
   • Indicated for diagnosis of congenital and acquired abnormalities, renal failure, urinary tract obstruction, and calculi 2

2. Technetium-99m DTPA (diethylenetriaminepentaacetic acid):

   • Excreted by glomerular filtration 1, 3
   • Useful for measuring glomerular filtration rate (GFR) 3, 4
   • Limited in evaluating obstruction as it is not excreted by tubular secretion 1
   • Can monitor transplant kidney perfusion and glomerular filtration rate 1

Renogram Procedure and Analysis

• The procedure involves intravenous injection of a radiopharmaceutical followed by sequential gamma camera imaging of the kidneys 1, 5
• Images are typically acquired over 20-30 minutes to generate time-activity curves (renograms) for each kidney 1, 5
• The renogram curve is analyzed for:
  • Relative uptake between kidneys (split renal function) 2, 3
  • Time to peak activity 5
  • Rate of tracer clearance/washout 6
  • Response to diuretic administration in cases of suspected obstruction 6, 7

Clinical Applications

• Evaluation of renal function: Provides quantitative assessment of total and individual kidney function 2, 3
• Detection of urinary tract obstruction: Diuretic renography can differentiate between true obstruction and non-obstructive dilation 6, 7
• Assessment of renal transplants: Evaluates transplant function and screens for surgical complications 1
• Renovascular hypertension: Captopril-enhanced renography can detect functionally significant renal artery stenosis 1
• Congenital abnormalities: Helps evaluate congenital renal and urinary tract anomalies 2, 7

Special Considerations in Renography

• Diuretic renography: Involves administration of furosemide to differentiate between true obstruction and non-obstructive dilation 6, 7
• Captopril renography: Administration of an ACE inhibitor can help diagnose renovascular hypertension by demonstrating changes in renal function in kidneys with significant renal artery stenosis 1
• Quantitative analysis: Modern techniques allow calculation of absolute renal uptake and GFR from renogram data 5, 3, 4

Limitations and Considerations

• Although sensitive for detecting kidney dysfunction, renograms often lack specificity for diagnosing the exact cause of dysfunction 1
• Interpretation may be challenging in patients with poor renal function, dehydration, or bilateral disease 1, 6
• Results should be interpreted in conjunction with clinical findings and other imaging studies 1
• Proper hydration and standardized protocols are essential for accurate results 6, 7