title: Cross-calibration of the Siemens mMR: easily acquired accurate PET phantom measurements, long-term stability and reproducibility.
abstract: BACKGROUND
  We present a quick and easy method to perform quantitatively accurate PET scans of typical water-filled PET plastic shell phantoms on the Siemens Biograph mMR PET/MR system. We perform regular cross-calibrations (Xcal) of our PET systems, including the PET/MR, using a Siemens mCT water phantom.
  The mMR calibration stability was evaluated over a 3-year period where 54 cross-calibrations were acquired, showing that the mMR on average underestimated the concentration by 16 %, consistently due to the use of MR-based μ-maps. The mMR produced the narrowest calibration ratio range with the lowest standard deviation, implying it is the most stable of the six systems in the study over a 3-year period. MMR ACCURACY WITH PREDEFINED μ-MAPS: With the latest mMR software version, VB20P, it is possible to utilize predefined phantom μ-maps. We evaluated both the system-integrated, predefined μ-map of the long mMR water phantom and our own user-defined CT-based μ-map of the mCT water phantom, which is used for cross-calibration. For seven scans, which were reconstructed with correctly segmented μ-maps, the mMR produced cross-calibration ratios of 1.00-1.02, well within the acceptance range [0.95-1.05], showing high accuracy.
  
  
  CONCLUSIONS
  The mMR is the most stable PET system in this study, and the mean underestimation is no longer an issue with the easily accessible μ-map, which resulted in correct cross-calibration ratios in all seven tests. We will share the user-defined μ-map of the mCT phantom and the protocol with interested mMR users.
authors.affiliation: 3982 Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet (University of Copenhagen), Blegdamsvej 9, DK-2100, Copenhagen, Denmark. sune@pet.rh.dk.
authors.forename: Sune H
authors.initials: SH
authors.lastname: Keller
authors.affiliation: Diagnostic Imaging, Magnetic Resonance, Siemens Healthcare GmbH, Allee am Roethelheimpark 2, 91052, Erlangen, Germany.|University of Surrey, Guildford, UK.
authors.forename: Björn
authors.initials: B
authors.lastname: Jakoby
authors.affiliation: 3982 Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet (University of Copenhagen), Blegdamsvej 9, DK-2100, Copenhagen, Denmark.
authors.forename: Susanne
authors.initials: S
authors.lastname: Svalling
authors.affiliation: 3982 Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet (University of Copenhagen), Blegdamsvej 9, DK-2100, Copenhagen, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kjaer
authors.affiliation: 3982 Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet (University of Copenhagen), Blegdamsvej 9, DK-2100, Copenhagen, Denmark.
authors.forename: Liselotte
authors.initials: L
authors.lastname: Højgaard
authors.affiliation: 3982 Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet (University of Copenhagen), Blegdamsvej 9, DK-2100, Copenhagen, Denmark.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Klausen
keywords: Calibration; Cross-calibration; PET phantom; PET/MR; Quality control