Abstract
Longitudinal imaging studies are crucial for advancing the understanding of brain development over the lifespan. Thus, more and more studies acquire imaging data at multiple time points or with long follow-up intervals. In these studies changes to magnetic resonance imaging (MRI) scanners often become inevitable which may decrease the reliability of the MRI assessments and introduce biases. We therefore investigated the difference between MRI scanners with subsequent versions (3 Tesla Siemens Verio vs. Skyra) on the cortical and subcortical measures of grey matter in 116 healthy, young adults using the well-established longitudinal FreeSurfer stream for T1-weighted brain images. We found excellent between-scanner reliability for cortical and subcortical measures of grey matter structure (intra-class correlation coefficient > 0.8). Yet, paired t-tests revealed statistically significant differences in at least 67% of the regions, with percent differences around 2 to 4%, depending on the outcome measure. Offline correction for gradient distortions only slightly reduced these biases. Further, T1-imaging based quality measures reflecting gray-white matter contrast systematically differed between scanners. We conclude that scanner upgrades during a longitudinal study introduce bias in measures of cortical and subcortical grey matter structure. Therefore, before upgrading a MRI scanner during an ongoing study, researchers should prepare to implement an appropriate correction method for these effects.
Highlights
Many longitudinal neuroimaging studies of aging and development investigate changes in local grey matter volume (GMV) over time to identify biomarkers relevant to health and disease
The most pronounced bias was found for cortical thickness (CT), with lower CT in Verio compared to Skyra in medial frontal and central regions, and higher values in Verio compared to Skyra in lateral occipital and inferior temporal regions
We found a medial-frontal to lateral-occipital gradient, with medial-frontal CT as well as subcortical volumes biased towards higher CT and GM volume in Skyra compared to Verio, while lateral-occipital CT was higher in Verio
Summary
Many longitudinal neuroimaging studies of aging and development investigate changes in local grey matter volume (GMV) over time to identify biomarkers relevant to health and disease. In the past decade many large-scale studies have implemented longitudinal designs in the general population Scanner upgrade and grey matter structure code are available on github (https://github.com/ fBeyer89/life_upgrade). The authors may provide access to the wholebrain MRI data
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