Validation of Intracranial Area as a Surrogate Measure of Intracranial Volume When Using Clinical MRI

BACKGROUND AND PURPOSE: We sought to determine whether mid-sagittal intracranial area (ICA) is a valid surrogate of intracranial volume (ICV) when using retrospective data with relatively thick (6-7 mm) sagittal slices. METHODS: Data were retrospectively analyzed from 47 subjects who had two MRI scans taken at least nine months apart. Twenty-three subjects had manual segmentation of ICV on the T2-weighted sequence for comparison. RESULTS: Intraclass correlation coefficient (ICC) for intraobserver, interobserver, and intraobserver scan-rescan comparisons were 0.96, 0.97 and 0.95. Pearson correlation coefficients between ICV and ICA, averaging the cumulative 1, 2, 3, and 4 most midline slices, were 0.89, 0.94, 0.93, and 0.95. There was a significant marginal increase in explained variance of ICV by measuring two, rather than one, slices (P= 0.001). CONCLUSIONS: These data suggest that ICA, even measured without high-resolution imaging, is a reasonable substitute for ICV.