title: Pediatric brain tumor consortium multisite assessment of apparent diffusion coefficient z-axis variation assessed with an ice-water phantom.
abstract: OBJECTIVE
  Magnetic resonance diffusion imaging can characterize physiologic characteristics of pediatric brain tumors used to assess therapy response. The purpose of this study was to assess the variability of the apparent diffusion coefficient (ADC) along z-axis of scanners in the multicenter Pediatric Brain Tumor Consortium (PBTC).
  
  
  METHODS
  Ice-water diffusion phantoms for each PBTC site were distributed with a specific diffusion imaging protocol. The phantom was scanned four successive times to 1) confirm water in the tube reached thermal equilibrium and 2) allow for assessment of intra-examination ADC repeatability. ADC profiles across slice positions for each vendor and institution combination were characterized using linear regression modeling with a quadratic fit.
  
  
  RESULTS
  Eleven sites collected data with a high degree of compliance to the diffusion protocol for each scanner. The mean ADC value at slice position zero for vendor A was 1.123 × 10(-3) mm(2)/s, vendor B was 1.0964 × 10(-3) mm(2)/s, and vendor C was 1.110 × 10(-3) mm(2)/s. The percentage coefficient of variation across all sites was 0.309% (standard deviation = 0.322). The ADC values conformed well to a second-order polynomial along the z-axis, (ie, following a linear model pattern with quadratic fit) for vendor-institution combinations and across vendor-institution combinations as shown in the longitudinal model.
  
  
  CONCLUSIONS
  Assessment of the variability of diffusion metrics is essential for establishing the validity of using these quantitative metrics in multicenter trials. The low variability in ADC values across vendors and institutions and validates the use of ADC as a quantitative tumor marker in pediatric multicenter trials.
authors.affiliation: Department of Radiology, Harvard Medical School, Boston, Massachusetts; Department of Radiology, Boston Children's Hospital, Boston, Massachusetts.
authors.forename: Robert V
authors.initials: RV
authors.lastname: Mulkern
authors.affiliation: Department of Radiology, Boston Children's Hospital, Boston, Massachusetts.
authors.forename: Kelsey I
authors.initials: KI
authors.lastname: Ricci
authors.affiliation: Department of Radiology, Harvard Medical School, Boston, Massachusetts; Department of Radiology, Boston Children's Hospital, Boston, Massachusetts.
authors.forename: Sridhar
authors.initials: S
authors.lastname: Vajapeyam
authors.affiliation: Department of Radiology, University of Michigan Health System, Ann Arbor, Michigan; Department of Radiology, University of Michigan Medical Center, Ann Arbor, Michigan.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Chenevert
authors.affiliation: Department of Radiology, University of Michigan Medical Center, Ann Arbor, Michigan.
authors.forename: Dariya I
authors.initials: DI
authors.lastname: Malyarenko
authors.affiliation: Division of Biostatistics and Epidemiology, University of Tennessee Health Science Center, Memphis, Tennessee; Department of Preventive Medicine, University of Tennessee Health Science Center, Memphis, Tennessee; Pediatric Brain Tumor Consortium, St Jude Children's Research Hospital, Memphis, Tennessee.
authors.forename: Mehmet
authors.initials: M
authors.lastname: Kocak
authors.affiliation: Department of Radiology, Harvard Medical School, Boston, Massachusetts; Pediatric Brain Tumor Consortium Neuroimaging Center, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115. Electronic address: tinayoung.poussaint@childrens.harvard.edu.
authors.forename: Tina Young
authors.initials: TY
authors.lastname: Poussaint
mesh_terms: D001932:Brain Neoplasms / Q000175:diagnosis*; D002648:Child; D006801:Humans; D007053:Ice; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D014867:Water
chemical_list: D007053:Ice; D014867:Water
keywords: Diffusion phantom; MRI; pediatric brain tumors; quality assurance