Commonly, examining MRI (magnetic resonance imaging) employs volumetric measurements of CSF (cerebral spinal fluid), GM (grey matter), WM (white matter) and CT (cortical thickness). A recent study investigated the effect time-of-day (TOD) had on volume of the whole brain and regional areas. Using a linear mixed effect model, the results indicated a statistically significant correlation between changes in TOD and changes in brain volume. For example, there was a decreasing trend in volume effected by TOD in the CSF, GM and WM, respectively. This implies that the time-of-day an MRI scan is acquired can affect the volume of these common measurements. Importantly, volumetric changes attributed to TOD are not consistent throughout the brain. The cortical areas of the frontal and temporal lobes showed greater effect from TOD while parietal and occipital lobes showed an opposing trend. This highlights a necessity to “factor in” the time-of-day for MRI scan acquisition in order to minimise potential error and account for bias in further statistical analysis.