Why is it considered safe to block a portion of the pulmonary circulation with MAA particles in patients with suspected pulmonary embolism (PE)?

Blocking a portion of the pulmonary circulation with macroaggregated albumin (MAA) particles is considered safe primarily because the injected particles only obstruct a small number of precapillary arterioles. MAA particles are specifically designed to have a size that allows them to lodge in the smaller branches of the pulmonary vasculature without causing widespread or significant disruption to blood flow in the lungs. This localized blockage does not typically lead to severe adverse effects because it usually does not compromise the overall blood supply to the lung tissue, allowing for adequate perfusion in other areas.

It is also important to recognize that MAA particles are selectively chosen for this purpose since their size ensures that they can occlude only a limited area of the pulmonary circulation. By blocking just a few vessels, the assessment of lung perfusion can be improved without causing widespread pulmonary ischemia or significant hemodynamic changes. This safety profile is critical in imaging procedures, where the goal is to evaluate conditions such as pulmonary embolism while minimizing potential risks to the patient.