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IMAGE INTERPRETATION · RENAL AND GENITOURINARY

Normal Renal Drainage Half-Time on MAG3

Tc-99m MAG3 qualitative renal scan (0–30 min sequential images) with renogram curves and quantitative parameters for both kidneys
Tc-99m MAG3 qualitative renal scan (0–30 min sequential images) with renogram curves and quantitative parameters for both kidneys

Provided clinical image

Question

A Tc-99m MAG3 renal scan is performed and the renogram analysis shows the following results: Right kidney — Time to Maximum 7.0 min, T½ 22.2 min. Left kidney — Time to Maximum 3.0 min, T½ 8.1 min. The T½ (drainage half-time) is a key parameter in renal scan interpretation. What is the UPPER LIMIT of normal for T½ on a MAG3 renogram?

  1. ALess than 10 minutes — a T½ above 10 minutes suggests impaired drainage and warrants further evaluation with a diuretic
  2. BLess than 5 minutes — any T½ above 5 minutes is considered abnormal and requires furosemide challenge
  3. CLess than 20 minutes — values between 10 and 20 minutes are indeterminate and only values above 20 minutes are considered definitely abnormal
  4. DLess than 30 minutes — the T½ parameter has low specificity and is only clinically meaningful when above 30 minutes on a post-diuretic study
Show the answer and explanation

A. Less than 10 minutes — a T½ above 10 minutes suggests impaired drainage and warrants further evaluation with a diuretic

The T½ (drainage half-time) measures how long it takes for the kidney to clear half of its peak tracer activity. A T½ of less than 10 minutes is considered normal, indicating good urinary drainage. Values between 10–20 minutes are indeterminate, and above 20 minutes is considered obstructed. In this scan, the right kidney's T½ of 22.2 minutes (vs. left at 8.1 min) indicates impaired right-sided drainage. Note: T½ should ideally be measured after furosemide administration to distinguish true obstruction from a dilated non-obstructed system.

More renal and genitourinary images

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 Direct radionuclide cystogram — post-flow total image and post-voiding views showing the bladder before and after urinationWhy Post-Void Images on a Radionuclide Cystogram Tc-99m MAG3 renal scan — composite image, flow curve, renogram curves, and quantitative results showing bilateral abnormal drainage with asymmetric differential functionDifferential Renal Function on MAG3
← Renal Cortical Scar on DMSA ScanWhy MAG3 for Renal Imaging: Tubular Secretion →

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