Abstract
Longitudinal MRI is used in clinical research studies to examine illness progression, neurodevelopment, and the effect of medical interventions. Such studies typically report changes in brain volume of less than 5%. However, there is a concern that these findings could be obscured or confounded by small changes in brain volume estimates caused by physiological factors such as, dehydration, blood pressure, caffeine levels, and circadian rhythm. In this study, MRI scans using the ADNI-III protocol were acquired from 20 participants (11 female) at two time points (mean interval = 20.3 days). Hydration, systolic and diastolic blood pressure, caffeine intake, and time of day were recorded at both visits. Images were processed using FreeSurfer. Three a priori hypothesised brain regions (hippocampus, lateral ventricles, and total brain) were selected, and an exploratory analysis was conducted on FreeSurfer's auto-segmented brain regions. There was no significant effect of the physiological factors on changes in the hypothesised brain regions. We provide estimates for the maximum percentage change in regional brain volumes that could be expected to occur from normal variation in each of the physiological measures. In this study, normal variations in physiological parameters did not have a detectable effect on longitudinal changes in brain volume.
Highlights
Longitudinal structural MRI studies are increasingly used to examine neurodevelopment, illness progression and the effect of medical interventions
We have previously published intra-class correlation coefficients (ICC) on the current dataset (Hedges et al, 2022), and we provide these values in the current study for the hippocampus, lateral ventricles, and total brain volume
3.5 Range of percentage change in hypothesised brain regions from physiological variables findings in the present study indicate that physiological variables did not have a substantial effect on brain volume, we have estimated the maximum percentage change in brain volumes that could be expected to occur from normal variation of such physiological variables
Summary
Longitudinal structural MRI studies are increasingly used to examine neurodevelopment, illness progression and the effect of medical interventions These studies may focus on neurological illnesses or mental health disorders, such as illness progression in Alzheimer’s disease (Márquez & Yassa, 2019) and schizophrenia (Dietsche et al, 2017), as well as looking at healthy aging and neurodevelopment (Ecker et al, 2015; Resnick et al, 2003). If there are common physiological variables that affect brain volume, these could obscure the effects of disease, development or interventions that are being measured. It is important to measure and understand the effects of physiological variables on changes in brain volume so they can be controlled for in clinical studies.
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