title: Impact of time-of-day on brain morphometric measures derived from T1-weighted magnetic resonance imaging.
abstract: Measures of brain morphometry derived from T1-weighted (T1W) magnetic resonance imaging (MRI) are widely used to elucidate the relation between brain structure and function. However, the computation of T1W morphometric measures can be confounded by subject-related factors such as head motion and level of hydration. A recent study reported subtle yet significant changes in brain volume from morning to evening in a large group of patient populations as well as in healthy elderly individuals. In addition, there is a growing recognition that factors such as circadian rhythm can impact MRI measures of brain function and structure. Here, we provide a comprehensive assessment of the impact of time-of-day (TOD) on widely used measures of brain morphometry in a group of 19 healthy young adults. Our results show that (a) even in a small group of healthy adult volunteers, a highly significant reduction in apparent brain volume, from morning to evening, could be detected; (b) the apparent volume of all three major tissue compartments - gray matter, white matter, and cerebrospinal fluid - were influenced by TOD, and the magnitude of the TOD effect varied across the tissue compartments; (c) measures of cortical thickness, cortical surface area, and gray matter density computed with widely used neuroimaging software suites (i.e., FreeSurfer, FSL-VBM) were all affected by TOD, while other measures, such as curvature indices and sulcal depth, were not; and (d) the effect of TOD appeared to have a greater impact on morphometric measures of the frontal and temporal lobe than on other major lobes of the brain. Our results suggest that the TOD effect is a physiological phenomenon and that controlling for the effect of TOD is crucial for proper interpretation of apparent structural differences measured with T1W morphometry.
authors.affiliation: Section on Learning and Plasticity, National Institute of Mental Health, United States.
authors.forename: Aaron
authors.initials: A
authors.lastname: Trefler
authors.affiliation: Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, United States.
authors.forename: Neda
authors.initials: N
authors.lastname: Sadeghi
authors.affiliation: Section on Functional Imaging Methods, National Institute of Mental Health, United States.
authors.forename: Adam G
authors.initials: AG
authors.lastname: Thomas
authors.affiliation: Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, United States.
authors.forename: Carlo
authors.initials: C
authors.lastname: Pierpaoli
authors.affiliation: Section on Learning and Plasticity, National Institute of Mental Health, United States.
authors.forename: Chris I
authors.initials: CI
authors.lastname: Baker
authors.affiliation: Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, United States; Center for Neuroscience and Regenerative Medicine, Uniformed Services University of the Health Sciences, United States. Electronic address: cibu.thomas@nih.gov.
authors.forename: Cibu
authors.initials: C
authors.lastname: Thomas
mesh_terms: D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D000071218:Ultradian Rhythm / Q000502:physiology*; D055815:Young Adult