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Full history/Diagnosis is available below
Several technical problems commonly affect perfusion studies. "Hot clots" are produced by drawing blood into the syringe containing Tc-99m MAA, forming radioactive clots, and then reinjecting the suspension into the patient. This technical artifact may produce multiple, predominantly centrally located radioactive "clumps" and perfusion defects that mimic pulmonary emboli. This problem may be prevented by gently shaking the syringe to resuspend the particles prior to injection and by administering the radiopharmaceutical without drawing blood into the syringe. These "hot clots" may also be produced by injecting Tc-99m MAA through a vein with thrombophlebitis. Interpretation of the perfusion study with this artifact is difficult (increased likelihood of false- positive) and a repeat perfusion study is recommended 18-24 hours later.
Another common technical problem is the administration of too few Tc-99m MAA particles resulting in quantum mottle. Fewer than 60,000 particles fails to give a homogeneous distribution of radioactivity in the pulmonary vascular bed. With this technical artifact, the perfusion study appears grossly mottled with multiple small perfusion defects bilaterally and a generalized overall decrease in pulmonary perfusion. The most common cause of quantum mottle secondary to too few particles is infiltration of the radiopharmaceutical. Imaging over the injection site confirms infiltration. Repeat perfusion imaging with a second dose may be performed immediately. Perfusion scintigraphy is typically performed with 500,000 particles of MAA, unless the particles are reduced for specific indications (e.g., right-to-left shunt, severe pulmonary hypertension, pediatric patients).
references: 1) Sandler, et al. Diagnostic Nuclear Medicine, 3rd edition, 1996. Williams and Wilkins 2) Datz. Nuclear Medicine: a teaching file, 1992. Mosby Yearbook 3) Datz FL. Gamuts in Nuclear Medicine, 3rd edition, 1995. Mosby Yearbook
References and General Discussion of Ventilation Perfusion Scintigraphy (Anatomic field:Lung, Mediastinum, and Pleura, Category:Other(Artifact))
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