ATTENUATION ARTIFACTS IN SPECT - EFFECT OF WRAP-AROUND LUNG IN 180-DEGREES CARDIAC STUDIES

We estimated that in 75%-90% of PET Rb-82 patients the left lung appea red to wrap around the anterior aspect of the left ventricle. We used clinical PET Rb-82 myocardial perfusion studies as the input to a SPEC T computer simulation model to determine a patients with left lung wra p-around displayed consistent artifacts in reconstructed SPECT images. In particular, we sought an explanation for the hot lateral wall seen in SPECT images from normal female and male patients. Methods: Attenu ated SPECT (TI)-T-201 emission data were simulated from a mid-ventricu lar slice in 10 randomly selected clinical PET Rb-82 studies with left lung wrap-around. In these same cases, the influence of left lung wra p-around was removed by assigning the left lung an attenuation coeffic ient which matched that of the heart. Five randomly selected clinical PET Rb-82 studies without left lung wrap-around were also processed wi th our model. Results: In all 10 cases with left lung wrap-around, rec onstructed SPECT images showed the hot lateral wall artifact with a me an septal-to-lateral wall count ratio of 0.86. With left lung wrap-aro und removed in the same 10 patients, reconstructed images did not show hot lateral wall (mean septal-to-lateral wall count ratio = 1.07). Th e 5 cases without left lung wrap-around did not show hot lateral wall (mean septal-to-lateral wall count ratio = 1.04) and the ratios change d little with the filling of the left lung (mean septal-to-lateral wal l count ratio = 1.05). Conclusion: Results of our PET-to-SPECT compute r simulation model showed that the hot lateral wall artifact found in SPECT myocardial perfusion images was related to the orientation and p ositions of the left ventricle and the left lung.