Attenuation correction of PET cardiac data with low-dose average CT in PET/CT.

We proposed a low-dose average computer tomography (ACT) for attenuation correction (AC) of the PET cardiac data in PET/CT. The ACT was obtained from a cine CT scan of over one breath cycle per couch position while the patient was free breathing. We applied this technique on four patients who underwent tumor imaging with F18-FDG in PET/CT, whose PET data showed high uptake of F18-FDG in the heart and whose CT and PET data had misregistration. All four patients did not have known myocardiac infarction or ischemia. The patients were injected with 555-740MBq of F18-FDG and scanned 1h after injection. The helical CT (HCT) data were acquired in 16s for the coverage of 100cm. The PET acquisition was 3min per bed of 15cm. The duration of cine CT acquisition per 2cm was 5.9s. We used a fast gantry rotation cycle time of 0.5s to minimize motion induced reconstruction artifacts in the cine CT images, which were averaged to become the ACT images for AC of the PET data. The radiation dose was about 5mGy for 5.9s cine duration. The selection of 5.9s was based on our analysis of the respiratory signals of 600 patients; 87% of the patients had average breath cycles of less than 6s and 90% had standard deviations of less than 1s in the period of breath cycle. In all four patient studies, registrations between the CT and the PET data were improved. An increase of average uptake in the anterior and the lateral walls up to 48% and a decrease of average uptake in the septal and the inferior walls up to 16% with ACT were observed. We also compared ACT and conventional slow scan CT (SSCT) of 4s duration in one patient study and found ACT was better than SSCT in depicting average respiratory motion and the SSCT images showed motion-induced reconstruction artifacts. In conclusion, low-dose ACT improved registration of the CT and the PET data in the heart region in our study of four patients. ACT was superior than SSCT for depicting average respiration motion in a patient study.