title: dAcquisition setting optimization and quantitative imaging for 124I studies with the Inveon microPET-CT system.
abstract: BACKGROUND
  Noninvasive multimodality imaging is essential for preclinical evaluation of the biodistribution and pharmacokinetics of radionuclide therapy and for monitoring tumor response. Imaging with nonstandard positron-emission tomography [PET] isotopes such as 124I is promising in that context but requires accurate activity quantification. The decay scheme of 124I implies an optimization of both acquisition settings and correction processing. The PET scanner investigated in this study was the Inveon PET/CT system dedicated to small animal imaging.
  
  
  METHODS
  The noise equivalent count rate [NECR], the scatter fraction [SF], and the gamma-prompt fraction [GF] were used to determine the best acquisition parameters for mouse- and rat-sized phantoms filled with 124I. An image-quality phantom as specified by the National Electrical Manufacturers Association NU 4-2008 protocol was acquired and reconstructed with two-dimensional filtered back projection, 2D ordered-subset expectation maximization [2DOSEM], and 3DOSEM with maximum a posteriori [3DOSEM/MAP] algorithms, with and without attenuation correction, scatter correction, and gamma-prompt correction (weighted uniform distribution subtraction).
  
  
  RESULTS
  Optimal energy windows were established for the rat phantom (390 to 550 keV) and the mouse phantom (400 to 590 keV) by combining the NECR, SF, and GF results. The coincidence time window had no significant impact regarding the NECR curve variation. Activity concentration of 124I measured in the uniform region of an image-quality phantom was underestimated by 9.9% for the 3DOSEM/MAP algorithm with attenuation and scatter corrections, and by 23% with the gamma-prompt correction. Attenuation, scatter, and gamma-prompt corrections decreased the residual signal in the cold insert.
  
  
  CONCLUSIONS
  The optimal energy windows were chosen with the NECR, SF, and GF evaluation. Nevertheless, an image quality and an activity quantification assessment were required to establish the most suitable reconstruction algorithm and corrections for 124I small animal imaging.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale (INSERM) U-892, Nantes, 44035, France. nadege.anizan@gmail.com.
authors.forename: Nadège
authors.initials: N
authors.lastname: Anizan
authors.forename: Thomas
authors.initials: T
authors.lastname: Carlier
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hindorf
authors.forename: Jacques
authors.initials: J
authors.lastname: Barbet
authors.forename: Manuel
authors.initials: M
authors.lastname: Bardiès