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.