The normalizing properties of intracranial volume across race and sex

Abstract

In volumetric analysis of the human brain with MRI, intracranial volume is an important covariate as it has a strong correlation with the volume of regions of interest in the brain. Therefore, accurate adjustment for intracranial volume (e.g. by division) is essential to mitigate the impact of head size on brain measurements. In this study, we assess the effects of intracranial volume normalization on differences across sex and racial groups, using a diverse cohort with 5977 subjects from three different (self-reported) races. We show that (i) differences in intracranial volume across sex are consistent across race and vice versa; and (ii) intracranial volume normalization almost completely accounts for differences by race and sex. These results suggest that subjects of different sexes and races can be safely aggregated in volumetric studies by normalizing the volume of regions of interest to intracranial volume.