Renal imaging in nuclear medicine
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Renal imaging in nuclear medicine is a method to assess the kidneys and collecting systems via multiple different radioactive tracers.
Dynamic renal imaging is performed using Tc-99m MAG3 or Tc-99m DTPA, and static renal imaging is performed with Tc-99m DMSA. In addition, Tc-99m DTPA can be used to calculate glomerular filtration rate (GFR) washout without an accompanying imaging study.
Dynamic renal scintigraphy
Dynamic renal studies are able to assess the perfusion to the kidneys, extraction of tracer from the blood and excretion of the tracer through the collecting system. Tc-99m MAG3 is secreted in the distal part of the proximal tubule by active secretion and Tc-99m DTPA is removed from the blood by the glomerulus by filtration 3. While both radiopharmaceuticals provide good images, MAG3 has higher renal extraction and chemical purity and is often the preferred agent for imaging only studies. If the patient requires concurrent GFR measurement, Tc-99m DTPA will be performed.
Indications include evaluation of mechanical renal tract obstruction (including pelviureteric and vesicoureteric junction obstruction), perfusional abnormalities, investigation of declining renal function, calculation of differential renal function and assessment of renal transplants 3. Furosemide (Lasix) is often administered to patients who are being investigated for known or suspected renal tract obstruction or those with poor urine drainage after 10 to 20 minutes 3. Renovascular hypertension or renal arterial stenosis (RAS) can be investigated with the addition of captopril to the imaging protocol 3.
Imaging protocols vary between sites, but will consist of continuous acquisition for a minimum of 25-30 minutes to demonstrate the perfusion, extraction and excretion phases. Delayed planar imaging can be performed if there is a concern for renal tract obstruction. SPECT-CT is not routinely performed as part of the study.
Static renal scintigraphy
Imaging of the renal cortex is achieved following administration of Tc-99m DMSA. While the mechanism of action is unclear, our ability to use it as an imaging agent is partly due to retention in renal tubular cells 3. Renal uptake of DMSA is 45 to 65% in 2 hours after intravenous injection 3.
Indications include evaluation of renal scarring 3 (e.g. reflux nephropathy, prior trauma) or calculation of differential renal function.
Imaging occurs at a delayed time-point, 2-4 hours after radiopharmaceutical administration. Depending on the site, image acquisition may consist of planar images only (with a pin-hole collimator) or SPECT.
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