Image quality and variability for routine diagnostic FDG-PET scans in a Japanese community hospital: current status and possibility of improvement

Purpose: In Japan, commercially delivered FDG is manufactured in three batches per day at fixed constant activity and distributed in vials. Consequently, the amount of activity administered to the patient varies depending on the timing of injection. We evaluated a method for adjusting the scan time according to the body mass index (BMI) to obtain equivalent image quality for every patient. Methods: We examined a total of 301 routine clinical oncology PET scans using commercially delivered FDG. The relation between the injected activity and the noise equivalent count per scan length (NEC_patient) was evaluated as a marker of image quality; its association with BMI was also examined. Results: The injected activity and NEC_patient exhibited large variations (230.4 ± 55.8 MBq and 19.9 ± 2.9 Mcounts/m). There was a weak correlation between the injected activity and NEC_patient (r ~ 0.3) for thin patients (BMI < 21 kg/m²), but no correlation for patients with higher BMIs. However, a significant correlation was found between BMI and NEC_patient (p < 0.0001). Conclusion: In a community hospital using commercially delivered FDG, it is possible to reduce the variability of the NEC_patient and obtain uniform image quality by changing the scan time as a function of patient BMI, even with uncontrollable injected activity.