While the potential for small amounts of motion in functional magnetic resonance imaging
(fMRI) scans to bias the results of functional neuroimaging studies is well appreciated,
the impact of in-scanner motion on morphological analysis of structural MRI is relatively
under-studied. Even among "good quality" structural scans, there may be systematic
effects of motion on measures of brain morphometry. In the present study, the subjects'
tendency to move during fMRI scans, acquired in the same scanning sessions as their
structural scans, yielded a reliable, continuous estimate of in-scanner motion. Using
this approach within a sample of 127 children, adolescents, and young adults, significant
relationships were found between this measure and estimates of cortical gray matter
volume and mean curvature, as well as trend-level relationships with cortical thickness.
Specifically, cortical volume and thickness decreased with greater motion, and mean
curvature increased. These effects of subtle motion were anatomically heterogeneous,
were present across different automated imaging pipelines, showed convergent validity
with effects of frank motion assessed in a separate sample of 274 scans, and could
be demonstrated in both pediatric and adult populations. Thus, using different motion
assays in two large non-overlapping sets of structural MRI scans, convergent evidence
showed that in-scanner motion-even at levels which do not manifest in visible motion
artifact-can lead to systematic and regionally specific biases in anatomical estimation.
These findings have special relevance to structural neuroimaging in developmental
and clinical datasets, and inform ongoing efforts to optimize neuroanatomical analysis
of existing and future structural MRI datasets in non-sedated humans. Hum Brain Mapp
37:2385-2397, 2016. © 2016 Wiley Periodicals, Inc.