Focal Artifacts and Extraorgan Findings in Pulmonary Perfusion Scintigraphy

Objective: to clarify and systematize the causes of focal and non-organ artifacts capable of acting as diagnostic pitfalls in lung perfusion scintigraphy using 99mTc macroaggregated albumin (MAA), as well as their semiotics, principles, and methods for differentiating from pathological changes.

Material and methods. The outcomes of lung perfusion scintigraphy were analyzed in 1,025 patients who underwent examinations to rule out pulmonary embolism (PE) or thromboembolic factors contributing to diagnosed pulmonary hypertension. The procedure was carried out in a multiplanar mode using twodetector single-photon emission computed tomography (SPECT) scanners while the patient was lying supine, 4–5 minutes after intravenous injection of a radiopharmaceutical (RPh) with an activity level of 111–148 MBq. Lung images were captured in six projections, including anterior, posterior, and four oblique planes. If required, additional screening was performed in combined SPECT/CT mode. The term “artifact” was used to describe isolated perfusion defects that simulate PE, as well as extrapulmonary findings resembling signs of a right-to-left shunt.

Results. Artefact scintigraphic findings corresponding to the above criteria were found in 634 (61.8%) patients. Focal changes (n=618) were classified into “cold” and “hot” based on their scintigraphic presentation. Single “cold” lesions (n=611) were most commonly due to the shielding effect of altered anatomical structures (heart – 493, pulmonary artery trunk – 72, pleural effusion and elevated diaphragm – 41), as well as implanted pacemakers (n=5). “Hot spot” (n=7) obscured thromboembolic perfusion defects because of their high specific radioactivity. The main reason for this artifact is blood ingress into a syringe with 99mTc-MAA during intravenous administration of RPh. Extrapulmonary signs of right-to-left shunt were observed in 14 patients with congenital heart defects and were characterized by concurrent visualization of the kidneys and other organs in the systemic circulation (spleen, liver, thyroid gland). The reason for artefactual intestinal imaging (n=2) was residual radioactivity following prior myocardial perfusion scintigraphy with 99mTc methoxyisobutyl-isonitrile.

Conclusion. Examining the reasons behind the occurrence of focal and extra-organ artifact findings in lung perfusion scintigraphy, as well as associated diagnostic and interpretive pitfalls, will enable the development of an appropriate quality control strategy to reduce the likelihood of false-positive interpretations of PE and systemic pulmonary shunts.

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