Abstract
1721
Objectives: Attenuation correction (AC) of PET data with average CT (ACT) has been proposed for improving the registration of PET and CT data (Pan et al, JNM 05). In this study we investigated the difference in quantification of the liver nodules in a prospective study of 48 patients who underwent a routine PET/CT scan followed by a cine CT scan of 5-15 mGy for AC of PET data with ACT. Methods: 48 patients had PET/CT examination for diagnosis or follow-up of colorectal cancer over a period of 2 months. The patients were injected with 555-740 MBq of 18F-FDG and scanned 1 h after injection. A helical CT (HCT) scan was acquired in 16 s over 100 cm coverage. It was followed by a PET scan of 3 min per bed for 6 to 7 beds, and a cine CT scan of the liver for ACT. The cine duration was 5.9 s per 2 cm for capturing at least one breath cycle of CT data for ACT. Both HCT and ACT were used for AC of the PET data. Patients were free breathing during the CT scans of HCT and ACT. We recorded the maximum standard uptake values (mSUV) of the liver nodules in these patients in both the HCT-PET (AC with HCT) and the ACT-PET (AC with ACT), and measured the difference in registration at the diaphragm level. Results: 13 out of the 48 patients showed metastasis in the liver, and 6 out of the 13 cases (46%) have at least one nodule with mSUV increases of over 20%. The changes were due to misregistration between the HCT and PET data. 9 out of the 13 patients demonstrated misalignment in the diaphragm position with the average value of 12.8 mm. ACT was effective in correcting misregistration in all 9 cases. Processing time of ACT and ACT-PET was less than 5 min and could be blended in the PET acquisition of the next patient. Conclusions: ACT was effective in removing misregistration between HCT and PET data in PET/CT for colorectal cancer metastasis in the liver. Additional processing time did not cause delay in routine clinical operation.
- Society of Nuclear Medicine, Inc.