# The normalizing properties of intracranial volume across race and sex

## TL;DR

This study shows that adjusting brain measurements for intracranial volume can eliminate differences between sexes and races, allowing for fair comparisons in MRI-based brain research.

## Contribution

The study demonstrates that intracranial volume normalization effectively accounts for sex and race differences in brain volume measurements.

## Key findings

- Intracranial volume differences are consistent across sex and race.
- Normalizing brain volumes by intracranial volume removes sex and race differences in MRI studies.
- This normalization allows aggregation of diverse groups in brain volumetric analyses.

## 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.

Liu et al. report that intracranial volume strongly correlates with brain region volumes in MRI studies. Using a diverse cohort, they show that intracranial volume normalization effectively removes sex and race differences, enabling safe aggregation of subjects across groups in volumetric analyses.

Graphical Abstract