Elimination of artifacts caused by residual radiopharmaceutical activity in injection site in myocardial perfusion imaging on Discovery NM 530c semiconductor gamma camera.

Abstract

Background: Cardiac gamma cameras dedicated for myocardial perfusion imaging (MPI) perform studies faster and acquire higher quality images than traditional cameras. However, they are susceptible to some artifacts. We observed a previously unreported artifact, caused by residual radiopharmaceutical activity in injection site in cubital fossa caught in camera field of view. This study aims to assess the impact of these artifacts on image quality and the possibility of their elimination. Study included 50 male patients referred for MPI using Discovery NM 530c gamma camera, in whom radiopharmaceutical activity in injection site was observed in stress or rest study. In such cases, image acquisition was immediately repeated, with the patient and the camera kept in the same position, after covering the injection site with a special lead shield. Obtained images were assessed by two experienced nuclear medicine physicians using a 0-4 point scale in each segment (where 0-normal perfusion, and 4-complete lack of perfusion). Summed stress, rest and difference scores (SSS, SRS and SDS, respectively) were calculated for the entire myocardium and 3 main vascular territories.

Results: SSS, SRS and SDS were most frequently assessed as abnormal in RCA territory. Radiopharmaceutical activity in injection site was observed more frequently in stress studies (84% of cases). Covering injection site with a shield changed the assessment of SSS, SRS or SDS from normal to abnormal and vice versa in almost 20% of studies. The most frequently affected vascular territories were LAD and RCA. Elimination of the artifact changed final diagnosis in almost 1/5 of patients, most often by eliminating previously visible significant stress-induced perfusion defects (patients in whom such change occurred did not report any cardiovascular events in one-year follow-up).

Conclusions: Artifacts caused by radiopharmaceutical activity in injection site reduce image quality and can potentially generate or hide perfusion defects. They can be observed mainly in patients examined in prone position, after radiopharmaceutical injection in cubital fossa. These artifacts can be eliminated by a lead shield, which can change the final assessment of MPI study in 20% of the patients.