title: Multi-site study of diffusion metric variability: effects of site, vendor, field strength, and echo time on regions-of-interest and histogram-bin analyses.
abstract: It is now common for magnetic-resonance-imaging (MRI) based multi-site trials to include diffusion-weighted imaging (DWI) as part of the protocol. It is also common for these sites to possess MR scanners of different manufacturers, different software and hardware, and different software licenses. These differences mean that scanners may not be able to acquire data with the same number of gradient amplitude values and number of available gradient directions. Variability can also occur in achievable b-values and minimum echo times. The challenge of a multi-site study then, is to create a common protocol by understanding and then minimizing the effects of scanner variability and identifying reliable and accurate diffusion metrics. This study describes the effect of site, scanner vendor, field strength, and TE on two diffusion metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA) using two common analyses (region-of-interest and mean-bin value of whole brain histograms). The goal of the study was to identify sources of variability in diffusion-sensitized imaging and their influence on commonly reported metrics. The results demonstrate that the site, vendor, field strength, and echo time all contribute to variability in FA and MD, though to different extent. We conclude that characterization of the variability of DTI metrics due to site, vendor, field strength, and echo time is a worthwhile step in the construction of multi-center trials.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA; Department of Radiology, Massachusetts General Hospital, Boston, MA; Harvard Medical School, Boston, MA.
authors.forename: K G
authors.initials: KG
authors.lastname: Helmer
authors.affiliation: Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: M-C
authors.initials: MC
authors.lastname: Chou
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA.
authors.forename: R I
authors.initials: RI
authors.lastname: Preciado
authors.affiliation: Geisel School of Medicine at Dartmouth, Hanover, NH.
authors.forename: B
authors.initials: B
authors.lastname: Gimi
authors.affiliation: Univ. of Texas, Southwestern Medical Center at Dallas, Radiology, Dallas TX.
authors.forename: N K
authors.initials: NK
authors.lastname: Rollins
authors.affiliation: Brain Imaging and Analysis Center, Duke University School of Medicine, Durham, NC.
authors.forename: A
authors.initials: A
authors.lastname: Song
authors.affiliation: MIND Research Network, Albuquerque, NM.
authors.forename: J
authors.initials: J
authors.lastname: Turner
authors.affiliation: Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: S
authors.initials: S
authors.lastname: Mori
keywords: MRI; calibration; diffusion; multi-site study