title: Comparison of phantom and registration scaling corrections using the ADNI cohort.
abstract: Rates of brain atrophy derived from serial magnetic resonance (MR) studies may be used to assess therapies for Alzheimer's disease (AD). These measures may be confounded by changes in scanner voxel sizes. For this reason, the Alzheimer's Disease Neuroimaging Initiative (ADNI) included the imaging of a geometric phantom with every scan. This study compares voxel scaling correction using a phantom with correction using a 9 degrees of freedom (9DOF) registration algorithm. We took 129 pairs of baseline and 1-year repeat scans, and calculated the volume scaling correction, previously measured using the phantom. We used the registration algorithm to quantify any residual scaling errors, and found the algorithm to be unbiased, with no significant (p=0.97) difference between control (n=79) and AD subjects (n=50), but with a mean (SD) absolute volume change of 0.20 (0.20) % due to linear scalings. 9DOF registration was shown to be comparable to geometric phantom correction in terms of the effect on atrophy measurement and unbiased with respect to disease status. These results suggest that the additional expense and logistic effort of scanning a phantom with every patient scan can be avoided by registration-based scaling correction. Furthermore, based upon the atrophy rates in the AD subjects in this study, sample size requirements would be approximately 10-12% lower with (either) correction for voxel scaling than if no correction was used.
authors.affiliation: Dementia Research Centre, University College London, Institute of Neurology, London, UK. m.clarkson@ucl.ac.uk
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Clarkson
authors.forename: Sébastien
authors.initials: S
authors.lastname: Ourselin
authors.forename: Casper
authors.initials: C
authors.lastname: Nielsen
authors.forename: Kelvin K
authors.initials: KK
authors.lastname: Leung
authors.forename: Josephine
authors.initials: J
authors.lastname: Barnes
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Whitwell
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Gunter
authors.forename: Derek L G
authors.initials: DL
authors.lastname: Hill
authors.forename: Michael W
authors.initials: MW
authors.lastname: Weiner
authors.forename: Clifford R
authors.initials: CR
authors.lastname: Jack
authors.forename: Nick C
authors.initials: NC
authors.lastname: Fox
mesh_terms: D000465:Algorithms; D000544:Alzheimer Disease / Q000175:diagnosis*; D016477:Artifacts; D015331:Cohort Studies; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique