Evaluation of simultaneous acquisition of transmission and emission data on thallium-201 myocardial SPECT

A three-detector SPECT system equipped with a 99mTc line source and a fan-beam collimator was used for simultaneous transmission and emission data acquisition. All three detectors were equipped with fan-beam collimators. 201Tl myocardial scintigraphy was performed on phantom study and 19 patients. Transmission images, uncorrected and corrected emission images were iteratively reconstructed with a EM-ML algorithm. Attenuation map computed from the transmission data was utilized for the attenuation correction. For the phantom study, circumferential profile analysis was applied to both datasets of horizontal long-axis slices through the center of the phantom. The maximum profile value in the circumferential profile set to 100% in the normalized uncorrected and corrected profiles. The uncorrected circumferential profiles from cardiac insert model 7070 and RH-2 cardiophantom showed decrease in activity in basal regions which appeared improvement in the attenuation corrected profiles. In clinical study, the inferior-to-anterior actively ratio, changed from 0.78±0.10 to 0.97±0.11 on stress images in patients with inferior ischemia and from 0.96±0.12 to 1.15±0.13 on 4 hour delayed or rest images in normal cases. The antero-apical wall of the attenuation corrected images, however, showed a decrease in activity relative to the inferior wall in normal cases. The increase in activity in inferior wall on attenuation corrected images was observed frequently in clinical study but not in phantom study. A presence of scatter from the liver or bowels may cause the increase in activity in the inferior wall in clinical study. In conclusion, transmission scan is one of the useful methods for the attenuation correction. Scatter correction, however, is also necessary to make an accurate attenuation corrected images. (K.H.)