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DMSA Case 1 Answers

1) Name the radiopharmaceutical and isotope

2,3 dimercaptosuccinic acid is the radiopharmaceutical of choice. It binds to -SH (sulphur hydryl) bearing receptors in the renal tubules to form a complex. Most of these receptors are situated in the proximal tubule. Therefore DMSA imaging visualizes the functioning proximal tubules.

DTPA, MAG-3 or Hippuran may be used but only for measuring uptake function. Technectium-99m is the isotope used in virtually all modern renal imaging.

2) How long from injection to imaging?
3) Why?

Imaging between 3-4 hours is optimal. It is a trade off between allowing maximal renal uptake vs. imaging before the technetium decays & DMSA is excreted by the kidneys. At 3-4 hours, 50% of the injected DMSA is bound to the kidneys

Anterior and posterior views are usually obtained, with obliques providing more information about possible focal defects.

4) What is the accepted range for normal split function?

Normal split function is between 45-55%. If renal function is poor, allow a higher range as the counts are less and therefore less accurate.

5) What are the green and white lines on the right hand images?

These are regions of interest (ROIs) - areas where the counts are measured.

6) What percentage of the radiopharmaceutical is excreted?

The half-life of DMSA is about 1 hour, with ~25% of total amount being excreted into the urine within the first hour. Excretion increases after 6 hours as the DMSA-receptor complexes gradually disassociate and the DMSA is excreted.

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The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.