title: Is the image quality of I-124-PET impaired by an automatic correction of prompt gammas?
abstract: OBJECTIVE
  The aim of this study is to evaluate the quality of I-124 PET images with and without prompt gamma compensation (PGC) by comparing the recovery coefficients (RC), the signal to noise ratios (SNR) and the contrast to F-18 and Ga-68. Furthermore, the influence of the PGC on the quantification and image quality is evaluated.
  
  
  METHODS
  For measuring the image quality the NEMA NU2-2001 PET/SPECT-Phantom was used containing 6 spheres with a diameter between 10 mm and 37 mm placed in water with different levels of background activity. Each sphere was filled with the same activity concentration measured by an independently cross-calibrated dose calibrator. The "hot" sources were acquired with a full 3D PET/CT (Biograph mCT®, Siemens Medical USA). Acquisition times were 2 min for F-18 and Ga-68, and 10 min for I-124. For reconstruction an OSEM algorithm was applied. For I-124 the images were reconstructed with and without PGC. For the calculation of the RCs the activity concentrations in each sphere were determined; in addition, the influence of the background correction was studied.
  
  
  RESULTS
  The RCs of Ga-68 are the smallest (79%). I-124 reaches similar RCs (87% with PGC, 84% without PGC) as F-18 (84%). showing that the quantification of I-124 images is similar to F-18 and slightly better than Ga-68. With background activity the contrast of the I-124 PGC images is similar to Ga-68 and F-18 scans. There was lower background activity in the I-124 images without PGC, which probably originates from an overcorrection of the scatter contribution. Consequently, the contrast without PGC was much higher than with PGC. As a consequence PGC should be used for I-124.
  
  
  CONCLUSIONS
  For I-124 there is only a slight influence on the quantification depending on the use of the PGC. However, there are considerable differences with respect to I-124 image quality.
authors.affiliation: Department of Nuclear Medicine, University Würzburg, Würzburg, Germany ; Martin-Luther University Halle-Wittenberg, Halle-Wittenberg, Germany.
authors.forename: Veronika
authors.initials: V
authors.lastname: Preylowski
authors.forename: Susanne
authors.initials: S
authors.lastname: Schlögl
authors.forename: Frédéric
authors.initials: F
authors.lastname: Schoenahl
authors.forename: Gerhard
authors.initials: G
authors.lastname: Jörg
authors.forename: Samuel
authors.initials: S
authors.lastname: Samnick
authors.forename: Andreas K
authors.initials: AK
authors.lastname: Buck
authors.forename: Michael
authors.initials: M
authors.lastname: Lassmann
mesh_terms: D005462:Fluorine Radioisotopes / Q000737:chemistry; D005710:Gallium Radioisotopes / Q000737:chemistry; D007091:Image Processing, Computer-Assisted / Q000592:standards*; D007457:Iodine Radioisotopes / Q000737:chemistry; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000592:standards*; D019275:Radiopharmaceuticals / Q000737:chemistry; D012015:Reference Standards; D059629:Signal-To-Noise Ratio; D015899:Tomography, Emission-Computed, Single-Photon / Q000592:standards
chemical_list: D005462:Fluorine Radioisotopes; D005710:Gallium Radioisotopes; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals