Room: AAPM ePoster Library
Purpose: Fluorodeoxyglucose [¹8F]FDG PET imaging is a powerful tool for diagnosis of cancer and subsequent treatment planning. State-of-the-art PET/CT scanners have the ability to generate images of superior diagnostic quality due to increased detector sensitivity and new reconstruction algorithms. These technological advancements should allow acquisition of quality images with less injected activity. However, scan duration and patient anatomy also influence image quality. Increasing activity for larger patients may be necessary to obtain comparable image quality. This project aims to determine the minimum appropriate injected activity for a 75 kg patient on a state-of-the-art PET/CT scanner, and to study the way in which activity should be scaled with patient weight.
Methods: Based on guidelines recommended by the EANM, a NEMA PET phantom was filled with uniform concentrations of 2 kBq/mL for the background and 20 kBq/mL for the spheres, simulating a 75 kg patient injected with 300 MBq. Scans were acquired on a GE Discovery MI PET/CT scanner using list mode to allow for retrospective reconstructions. Reconstructions of 19s to 600s were made for the initial scan and 4.5 minutes for scans every hour after, effectively reducing injected activity. Image quality was assessed by measuring recovery coefficients of the spheres and the coefficient of variation (COV) in the background. A threshold COV of 15% was set for the analysis.
Results: For images reconstructed with TOF OSEM (2 iterations, 34 subsets), this resulted in a minimum scan duration of 84s for the reference activity of 300 MBq, and a minimum activity of 168 MBq for the clinical 2.5 minute scan duration, a reduction of 30% compared to our current clinical protocol.
Conclusion: The minimum FDG activity to achieve acceptable image quality for a 75 kg patient was determined based on a phantom study. The optimum activity scaling regimen is under investigation.