Renal Scan

Renal Scan  Mag 3

Principle

Numerous drugs are bound and or cleared by the kidneys. A number of technetium-99m labeled radioharmaceuticals are also handled by the kidneys in ways useful for imaging as their mode of excretion isolates certain elements of renal function.  Tc-99m DTPA may be used to measure glomerular function.  I-131 or I-123 Hippuran or Tc-99m DMSA  may be used to visualize and quantitate tubular function.  Tc-99m glucoheptonate is excreted through glomerular filtration and concentrated by the tubular cell.  Tc-99m Mag 3 is used to quantify tubular secretion and glomerular filtration.

Indications

• Evaluation of renal perfusion and function.
• Detection an evaluation of renal collecting system obstruction.
• Information about renal size, location and anatomy
• Obstructive uropathy

Limitations

Results cannot differentiate cysts from tumors. Generalized decreases in uptake can be due to a variety of causes such as ischemia chronic inflammatory disease or chronic obstructive disease

Equipment

• Gamma camera: Large field of view
• Collimator:  Low energy, all purpose, parallel hole.
• Energy window:  25% centered at 140kev

Radiopharaceutical

Intravenous injection of 40-50 mCi   Tc99m-Mag 3  (mercaptoacetyltriglycine)

Patient Preparation and Positioning

• Ideally, the bladder should be empty.
• Mild sedation as needed.
• Position the detector projected dorsally over the kidneys and if possible include a portion of the bladder.

Acquisition protocol

Inject the radiopharmaceutical and acquire dynamic 128 x 128 frames at 5 second intervals for 2 minutes.  Subsequent static images are acquired at 5 minute intervals for 30 to 45 minutes.  Additional static images may be acquired at 1 and 2 hours if necessary. All static images are acquired for 1 minute and motion corrected. In patients with renal insufficiency, delayed images up to 24 hours after radiopharmaceutical administration may improve visualization.

Interpretation

The normal renal scan shows homogenous uptake through out both kidneys. The kidney margins may show some irregularity due to motion artifact (respiration, etc).

Renal tumors, cysts, abscesses and damage due to renal trauma such as rupture or hematomas appear a cold defects.

Diffuse renal disease may give patchy or diffusely decreased uptake of the radiopharnaceutical.

Unilateral renal disease such as artery stenosis will show decrease size and/or decreased uptake.