title: Determining the Minimal Required Radioactivity of 18F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study.
abstract: In pursuit of as-low-as-reasonably-achievable (ALARA) doses, this study investigated the minimal required radioactivity and corresponding imaging time for reliable semiquantification in PET/CT imaging.
  
  
  METHODS
  Using a phantom containing spheres of various diameters (3.4, 2.1, 1.5, 1.2, and 1.0 cm) filled with a fixed (18)F-FDG concentration of 165 kBq/mL and a background concentration of 23.3 kBq/mL, we performed PET/CT at multiple time points over 20 h of radioactive decay. The images were acquired for 10 min at a single bed position for each of 10 half-lives of decay using 3-dimensional list mode and were reconstructed into 1-, 2-, 3-, 4-, 5-, and 10-min acquisitions per bed position using an ordered-subsets expectation maximum algorithm with 24 subsets and 2 iterations and a gaussian 2-mm filter. SUVmax and SUVavg were measured for each sphere.
  
  
  RESULTS
  The minimal required activity (±10%) for precise SUVmax semiquantification in the spheres was 1.8 kBq/mL for an acquisition of 10 min, 3.7 kBq/mL for 3-5 min, 7.9 kBq/mL for 2 min, and 17.4 kBq/mL for 1 min. The minimal required activity concentration-acquisition time product per bed position was 10-15 kBq/mL⋅min for reproducible SUV measurements within the spheres without overestimation. Using the total radioactivity and counting rate from the entire phantom, we found that the minimal required total activity-time product was 17 MBq⋅min and the minimal required counting rate-time product was 100 kcps⋅min.
  
  
  CONCLUSIONS
  Our phantom study determined a threshold for minimal radioactivity and acquisition time for precise semiquantification in (18)F-FDG PET imaging that can serve as a guide in pursuit of achieving ALARA doses.
authors.affiliation: Radiology and Biomedical Imaging, Yale University School of Medicine, New Haven, Connecticut.
authors.forename: Ming-Kai
authors.initials: MK
authors.lastname: Chen
authors.affiliation: Yale-New Haven Hospital, New Haven, Connecticut; and.
authors.forename: David H
authors.initials: DH
authors.lastname: Menard
authors.affiliation: Sidra Medical and Research Center, Doha, Qatar dcheng@sidra.org.
authors.forename: David W
authors.initials: DW
authors.lastname: Cheng
mesh_terms: D019788:Fluorodeoxyglucose F18; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards; D019047:Phantoms, Imaging; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods* / Q000592:standards*; D011851:Radioactivity
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: PET; acquisition time; dose reduction; dosimetry; phantom; standard uptake value