Tc-99m MAA Injection Technique
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Question
When preparing and injecting Tc-99m MAA for a lung perfusion scan, which of the following is the correct injection technique to ensure proper MAA distribution?
- AInject rapidly as a bolus while the patient is in the upright sitting position
- BInject slowly over 3–5 breathing cycles with the patient SUPINE to ensure even MAA distribution throughout both lungs
- CMix MAA with blood in the syringe before injection to prevent clumping
- DInject into a peripheral vein while the patient performs a Valsalva maneuver
Show the answer and explanation
B. Inject slowly over 3–5 breathing cycles with the patient SUPINE to ensure even MAA distribution throughout both lungs
Tc-99m MAA should be injected SLOWLY (over 3–5 breathing cycles) with the patient in the SUPINE position. Supine injection ensures that blood flow is more evenly distributed between the two lungs (compared to upright, where gravity would direct more flow to the bases). Slow injection prevents transient streaming and ensures the particles distribute proportionally to regional blood flow. Mixing MAA with blood in the syringe is contraindicated as clumping can form larger aggregates. Valsalva maneuver could open a PFO and allow MAA to cross to the systemic circulation.
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