title: Quantitative imaging characteristics of zirconium-89 on Gemini Time-Of-Flight PET/CT.
abstract: OBJECTIVE
  Interest in PET imaging using zirconium-89 (Zr) (t1/2=78.41 h)-labeled tracers for the tracking and quantification of monoclonal antibodies (mAbs) is growing, mainly because of its well-matched physical half-life with the biological half-life of intact mAbs. This study aims to evaluate the imaging characteristics of Zr-PET in comparison with those obtained using fluorine-18 fluorodeoxyglucose (F-FDG) PET (gold standard tracer in PET imaging) using a Time-Of-Flight (TOF) PET/computed tomography (CT) scanner.
  
  
  METHODS
  The system's spatial resolution, sensitivity, scatter fraction (SF), image uniformity, and image quality were measured on a Gemini TOF PET/CT scanner according to the NEMA NU2-2001 protocols. The NEMA 2001 kit was used to carry out these measurements. Timing and energy resolutions were measured using Na and F-FDG point sources only.
  
  
  RESULTS
  Spatial resolution in transverse and axial planes measured at 10 mm off access were 4.7 and 4.6 mm for Zr and F-FDG, respectively. At 100 mm, radial, tangential, and axial spatial resolution values were 5.2, 5.1, and 5.2 mm for Zr and 5.1, 4.9, and 5.2 mm for F-FDG, respectively. Sensitivity measured at the center of the field of view was 14.6 and 4.16 cps/kBq for Zr and F-FDG, respectively. SF was 32.6% for Zr in comparison with 31.8% for F-FDG. Image contrast for Zr-PET images was 36.9 and 29.7% for F-FDG for the smallest (10 mm)-sized sphere, and it was 70.6 and 72.8% for Zr and F-FDG, respectively, for the largest (37 mm)-sized sphere. Background variation was 10.3% for Zr and 6.8% for F-FDG for the smallest-sized sphere and 3.4 and 3.8% for Zr and F-FDG, respectively, for the largest-sized sphere.
  
  
  CONCLUSIONS
  In this study, we measured imaging characteristics of Zr on a Gemini TOF PET/CT scanner. Our results show that Zr has lower spatial resolution and noise-equivalent count rate with increased SF and background variation; however, it offered superior sensitivity and improved image contrast in comparison with F-FDG. Zr is an ideal radiotracer for immuno-PET imaging because of its physical half-life, which is well matched with mAbs, in addition to its affinity to be trapped inside the target cell after internalization of the mAbs.
authors.affiliation: aDepartment of Physics, College of Science, Imam Muhammad bin Saud Islamic University bDepartment of Radiological Sciences, College of Applied Medical Sciences cDepartment of Physics and Astronomy, King Saud University dDepartment of Cyclotron and Radiopharmaceutical, King Faisal Specialist Hospital and Research Center eDepartment of Medical Physics, Prince Sultan Military Medical City, Riyadh, Kingdom of Saudi Arabia.
authors.forename: Sitah F
authors.initials: SF
authors.lastname: Alanazi
authors.forename: Khalid S
authors.initials: KS
authors.lastname: Alzimami
authors.forename: Magdy M
authors.initials: MM
authors.lastname: Ghannam
authors.forename: Ibrahim J
authors.initials: IJ
authors.lastname: Aljammaz
authors.forename: Faisal
authors.initials: F
authors.lastname: Alrumayan
authors.forename: Salem A
authors.initials: SA
authors.lastname: Sassi
mesh_terms: D000911:Antibodies, Monoclonal / Q000493:pharmacokinetics; D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18; D006207:Half-Life; D006801:Humans; D019047:Phantoms, Imaging; D000072078:Positron Emission Tomography Computed Tomography / Q000379:methods* / Q000706:statistics & numerical data; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D015040:Zirconium
chemical_list: D000911:Antibodies, Monoclonal; D005462:Fluorine Radioisotopes; D011868:Radioisotopes; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D015040:Zirconium