NucMed Boards Prep
IMAGE INTERPRETATION · RENAL AND GENITOURINARY

UPJ Obstruction on MAG3 Diuretic Renogram

Tc-99m MAG3 diuretic renogram with Lasix at 21 min — right kidney shows prolonged T½ (85.53 min) with persistent tracer retention and rising renogram curve post-furosemide, indicating UPJ obstruction
Tc-99m MAG3 diuretic renogram with Lasix at 21 min — right kidney shows prolonged T½ (85.53 min) with persistent tracer retention and rising renogram curve post-furosemide, indicating UPJ obstruction

Provided clinical image

Question

A Tc-99m MAG3 (mercaptoacetyltriglycine) diuretic renogram is performed to evaluate a dilated right renal collecting system (hydronephrosis) found on ultrasound. The MAG3 scan shows normal tracer uptake by both kidneys, but tracer is retained in the right renal pelvis after furosemide (Lasix) injection and shows a prolonged T½ of 28 minutes (normal <10 min). This is MOST consistent with:

  1. AObstructed right ureteropelvic junction (UPJ) — prolonged T½ after diuretic confirms true mechanical obstruction
  2. BNormal variant dilated collecting system — no obstruction
  3. CRenal artery stenosis
  4. DVesicoureteral reflux
Show the answer and explanation

A. Obstructed right ureteropelvic junction (UPJ) — prolonged T½ after diuretic confirms true mechanical obstruction

Tc-99m MAG3 diuretic renography (Lasix renogram) differentiates obstructed from non-obstructed dilated collecting systems. After IV furosemide, a normal or dilated-but-not-obstructed system drains rapidly (T½ < 10 min). In true mechanical obstruction (UPJ obstruction, ureteral stricture), the tracer cannot drain despite diuretic washout and T½ is markedly prolonged (>20 min = obstructed; 10–20 min = equivocal). A T½ of 28 minutes confirms right UPJ obstruction requiring urologic intervention (pyeloplasty). Tc-99m MAG3 is preferred for renal function assessment as it is tubularly secreted (not filtered like DTPA), providing better image quality even in impaired renal function.

More renal and genitourinary images

Tc-99m DMSA renal cortical scan at 30 min and 3 hours (POST, RAO, LAO views) showing focal cortical defect — renal scarring post-pyelonephritisRenal Cortical Scar on DMSA Scan Tc-99m MAG3 qualitative renal scan (0–30 min sequential images) with renogram curves and quantitative parameters for both kidneysNormal Renal Drainage Half-Time on MAG3 Tc-99m MAG3 qualitative renal scan — renogram function curves: left kidney (red dashed), right kidney (green), bladder (purple dotted)Why MAG3 for Renal Imaging: Tubular Secretion Tc-99m MAG3 qualitative renal scan with quantitative parameters: Right T½ = 22.2 min, residual 30 min = 49.4%; Left T½ = 8.1 min, residual 30 min = 15.9%; equal bilateral differential function (51%/49%)Furosemide Dose for Diuretic Renography Direct radionuclide cystogram — sequential bladder filling frames, post-flow total, post-voiding views, and anterior/posterior bladder prevoid imagesDirect Radionuclide Cystogram Technique Direct radionuclide cystogram — sequential frames during bladder filling and voiding phasesVesicoureteral Reflux on Radionuclide Cystogram
← Motion Correction in MAG3 Renal ScansRenal Cortical Scar on DMSA Scan →

All 130 nuclear medicine images by category →

Practise image interpretation in the app

All 130 images as an interactive quiz, alongside 500 NMTCB and ARRT(N) questions with worked explanations, case studies and timed mock exams. 25 questions are free, no card and no account.

Start free — no card

Download on the App StoreGet it on Google Play