Control of whole-body FDG-positron emission tomography image quality by adjusting the acquisition time: A new physical image quality index and patientdependent parameters for clinical imaging

Objective: This study aimed to establish a methodology for obtaining visually equivalent image quality regardless of patient size by controlling the acquisition time of positron emission tomography (PET) studies.
Methods: In Part 1, we determined the physical image quality index with the highest correlation with visual assessment in 30 patients. In Part 2, 100 patients were scanned to identify the patient-dependent parameters that were most correlated with the physical image quality index. These parameters were calculated from the combination of the administered activity of 18F-FDG and weight. We drew an approximate curve from these parameters and prepared a scatter plot of the physical image quality index. In Part 3, we checked whether the image quality was constant by controlling the acquisition time in 189 patients. The approximation formula we obtained under (2) was used to control the acquisition time. The physical image quality index was a constant value, and the patient-dependent parameter was calculated from the patient’s physique.
Results: The physical image quality index with the highest correlation with visual evaluation was the noise equivalent count weight (NECweight) (correlation coefficient: 0.90). The patient-dependent index most correlated with NECweight was activity/weight3 (A/W3) (coefficient of determination: 0.978). The verification of the acquisition time to obtain a certain image quality showed an average of 0.60 ± 0.034 Mcounts/m∙kg, and a similar image quality was obtained independent of the individual physiques.
Conclusions: Calculating NECweight and A/W3 enable the determination of the appropriate acquisition time for stable image quality before the PET study.