Simultaneous transmission-emission thallium-201 cardiac SPECT: effect of attenuation correction on myocardial tracer distribution.

UNLABELLED: This study evaluates the effect of attenuation correction on regional myocardial tracer distributions defined by 201TI cardiac perfusion SPECT images obtained from healthy volunteers and patients with coronary heart disease. METHODS: A three-detector SPECT system equipped with an 241Am line source and a fanbeam collimator was used for simultaneous transmission/emission (201TI) tomography on 40 patients and 10 normal volunteers. Uncorrected emission images were reconstructed using filtered backprojection (FBP), whereas the attenuation corrected images were iteratively reconstructed with a regularized, least-squares algorithm utilizing the attenuation map computed from the transmission data. Both sets of images were reoriented into short-axis and vertical long-axis slices. Circumferential profile analysis was applied to both datasets of short-axis slices. RESULTS: The normal volunteers demonstrated improved homogeneity in tracer distribution. For a basal short-axis slice, the lateral-to-posterior activity ratio improved from 1.17 +/- 0.12 for FBP to 1.01 +/- 0.07. Basal attenuation appeared properly compensated as the peak basal-to-apical slice activity gradient along the posterior-inferior wall changed from 1.15 +/- 0.12 for FBP to 1.01 +/- 0.09. The apex of the attenuation corrected images showed a significant decrease in activity relative to the base which appeared consistent with anatomic wall thinning. For the inferior and basal septal regions, the defect severity was slightly less in the attenuation corrected images, but the defects were more sharply defined compared to the FBP image defects. CONCLUSION: These results indicate that attenuation correction is clinically feasible and accurately corrects for photon attenuation. Clinical validation, however, is necessary to define the diagnostic benefits.