Tailoring 99mTc-Macroaggregated Albumin Administration to Optimize Patient Dose Reduction

In the ever-changing field of nuclear medicine, best-practice considerations cannot simply go unchallenged for months and years, with the need to minimize radiation exposure to patients highlighted in "as low as reasonably achievable" principles. The Australian Radiation Protection and Nuclear Safety Agency reports that the dose for (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) administered should be 180-200 MBq. An objective of imaging in pulmonary embolism, or indeed any diagnostic procedure involving radiation, is to minimize radiation exposure without sacrificing image quality and diagnostic accuracy. The amount of radiation involved must be considered together with imaging protocols. Our aim was to reduce the amount of (99m)Tc-MAA administered without compromising the diagnostic quality of the scan.

To achieve a ventilation-to-perfusion ratio of 1:4, we ventilated the patient as per standard protocol and then placed intravenous access into the patient. For the perfusion component, 180-200 MBq were prepared in a 2-mL injection. Aliquots of 0.5 mL of (99m)Tc-MAA were administered every 30 s followed by a 5-mL saline flush until the required ventilation-to-perfusion ratio was achieved.

With this protocol, the average administered dose was 105 ± 20.7 MBq (vs. 180 ± 5.3 MBq, P < 0.0001).

By individually tailoring the administered dose, diagnostic quality is maintained while achieving a significant dose reduction.