Widely Used Calculations of Intracranial Volume Provide Inaccurate Estimates in Developmental Cohorts: Evidence and Recommendations for the Neuroimaging Community

Intracranial volume (ICV) is estimated as part of automated neuroimaging processing pipelines and commonly used to account for and characterize cranial size. FreeSurfer’s estimated intracranial volume (eTIV) produces unreliable estimates in developmental samples when using versions prior to FreeSurfer 8, which longitudinal cohorts reveal to be biologically implausible. Across two different adolescent datasets, we document eTIV changes of up to 39% between 1.5 - 2 year sessions for FreeSurfer 7, with errors more pronounced on Siemens scanners and in female participants. The errors are derived from failures of an early registration step, which was upgraded to a deep learning registration algorithm in FreeSurfer 8, where these errors are markedly reduced and produce eTIV estimates comparable to an independent estimation method, AssemblyNet. However, the widespread use of FreeSurfer 7 raises concern about developmental neuroimaging studies that utilize eTIV without quality control. Recommendations for future research and considerations for past research in the field are discussed.