title: MRI quality assurance using the ACR phantom in a multi-unit imaging center.
abstract: BACKGROUND
  Magnetic resonance imaging (MRI) instrumentation is vulnerable to technical and image quality problems, and quality assurance is essential. In the studied regional imaging center the long-term quality assurance has been based on MagNET phantom measurements. American College of Radiology (ACR) has an accreditation program including a standardized image quality measurement protocol and phantom. The ACR protocol includes recommended acceptance criteria for clinical sequences and thus provides possibility to assess the clinical relevance of quality assurance. The purpose of this study was to test the ACR MRI phantom in quality assurance of a multi-unit imaging center.
  
  
  METHODS
  The imaging center operates 11 MRI systems of three major manufacturers with field strengths of 3.0 T, 1.5 T and 1.0 T. Images of the ACR phantom were acquired using a head coil following the ACR scanning instructions. Both ACR T1- and T2-weighted sequences as well as T1- and T2-weighted brain sequences in clinical use at each site were acquired. Measurements were performed twice. The images were analyzed and the results were compared with the ACR acceptance levels.
  
  
  RESULTS
  The acquisition procedure with the ACR phantom was faster than with the MagNET phantoms. On the first and second measurement rounds 91% and 73% of the systems passed the ACR test. Measured slice thickness accuracies were not within the acceptance limits in site T2 sequences. Differences in the high contrast spatial resolution between the ACR and the site sequences were observed. In 3.0 T systems the image intensity uniformity was slightly lower than the ACR acceptance limit.
  
  
  CONCLUSIONS
  The ACR method was feasible in quality assurance of a multi-unit imaging center and the ACR protocol could replace the MagNET phantom tests. An automatic analysis of the images will further improve cost-effectiveness and objectiveness of the ACR protocol.
authors.affiliation: HUS Helsinki Medical Imaging Center, Helsinki, Finland. toni.ihalainen@hus.fi
authors.forename: Toni M
authors.initials: TM
authors.lastname: Ihalainen
authors.forename: Nadja T
authors.initials: NT
authors.lastname: Lönnroth
authors.forename: Juha I
authors.initials: JI
authors.lastname: Peltonen
authors.forename: Jouni K
authors.initials: JK
authors.lastname: Uusi-Simola
authors.forename: Marjut H
authors.initials: MH
authors.lastname: Timonen
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Kuusela
authors.forename: Sauli E
authors.initials: SE
authors.lastname: Savolainen
authors.forename: Outi E
authors.initials: OE
authors.lastname: Sipilä
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D011786:Quality Control; D011859:Radiography