title: Effect of scanner in asymmetry studies using diffusion tensor imaging.
abstract: The purpose of this study was to evaluate the effects of longitudinal drift in scanner hardware, inter-scanner variability (bias) and scanner upgrade on asymmetries of diffusion properties using longitudinal data obtained on two scanners of the exact same model at one institution. A total of 224 normal subjects (63 females and 161 males) were included in this study. Each subject was scanned twice, at an interval of about 1 year (mean interval=1.0±0.11 years, range=0.6-1.3 years), using two 3.0-T scanners of the exact same model. Both scanners were simultaneously upgraded during the study period (159 subjects underwent a follow-up scan before upgrade, and the remaining 65 subjects underwent a follow-up scan after upgrade). The subjects were divided into 4 groups according to the combination of scanners used. With the use of tract-based spatial statistics (TBSS), we investigated the effects of scanner drift and inter-scanner variability (bias) on asymmetries of fractional anisotropy (FA) and mean diffusivity (MD). We also investigated the effect of scanner upgrade on FA and MD asymmetries. The voxel-wise analyses revealed a number of regions with significant longitudinal changes in FA and MD asymmetries in the groups where baseline and follow-up images were obtained on different scanners. Even with scanners of the exact same model, inter-scanner variability (bias) significantly affected FA and MD asymmetries, which were relatively stable within the same scanner. Scanner upgrade had a small effect on FA and MD asymmetries. The results indicate that the use of multiple scanners increases variability of DTI asymmetry measurements, and can affect the results of cross-sectional and especially longitudinal DTI asymmetry studies.
authors.affiliation: Department of Radiology, Graduate School of Medicine, University of Tokyo, Tokyo, Japan. takaoh-tky@umin.ac.jp
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Takao
authors.forename: Naoto
authors.initials: N
authors.lastname: Hayashi
authors.forename: Kuni
authors.initials: K
authors.lastname: Ohtomo
mesh_terms: D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results