NephrologyTier 2Topic

Imaging - functional renal scans

Types

Nuclear medicine studies assessing differential (split) renal function and drainage, using radiotracers taken up and excreted by the kidneys
Two main types: DTPA/MAG3 (dynamic, excretory function + drainage) and DMSA (static, cortical scarring/differential function)
Used for split function assessment (e.g. before nephrectomy), suspected obstruction where ultrasound is equivocal, and paediatric reflux nephropathy/scarring assessment

Tracers

MAG3 - actively secreted by renal tubules, cleared efficiently even in reduced renal function - preferred for functional/drainage studies
DTPA - filtered, not secreted; less useful in poor renal function - largely superseded by MAG3
DMSA - binds renal cortical tubular cells, taken up proportionally to functioning cortical mass - a static "structural" image of relative function and focal scarring

Interpretation

MAG3 with diuretic challenge (furosemide) - distinguishes true mechanical obstruction (tracer retained despite diuretic) from a dilated but unobstructed system (tracer washes out)
DMSA - quantifies split (left vs right) function as a percentage; identifies focal cortical scarring (e.g. post-pyelonephritis)

Acting on the result

Guides decisions on nephrectomy (confirming the contralateral kidney has adequate function first)
Guides paediatric reflux/scarring follow-up and surgical decision-making

Indications

Vesicoureteric reflux, PUJ obstruction, unilateral renal artery stenosis, single kidney assessment pre-nephrectomy

Serial use

Serial DMSA can track scarring progression or stability after pyelonephritis episodes in children

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