Measuring the thickness of the human cerebral cortex from magnetic resonance images

Abstract

Accurate and automated methods for measuring the thickness of human cerebral cortex could provide powerful tools for diagnosing and studying a variety of neurodegenerative and psychiatric disorders. Manual methods for estimating cortical thickness from neuroimaging data are labor intensive, requiring several days of effort by a trained anatomist. Furthermore, the highly folded nature of the cortex is problematic for manual techniques, frequently resulting in measurement errors in regions in which the cortical surface is not perpendicular to any of the cardinal axes. As a consequence, it has been impractical to obtain accurate thickness estimates for the entire cortex in individual subjects, or group statistics for patient or control populations. Here, we present an automated method for accurately measuring the thickness of the cerebral cortex across the entire brain and for generating cross-subject statistics in a coordinate system based on cortical anatomy. The intersubject standard deviation of the thickness measures is shown to be less than 0.5 mm, implying the ability to detect focal atrophy in small populations or even individual subjects. The reliability and accuracy of this new method are assessed by within-subject test-retest studies, as well as by comparison of cross-subject regional thickness measures with published values.

Figure 1

Coronal (Left) and horizontal (Right) slices of the left hemisphere with gray/white (yellow) and pial (red) surfaces overlaid. The green crosses indicate a point at which using the coronal view only would result in a dramatic overestimation of the thickness of the cortex.

Figure 2

Lateral views of the gray/white (Left), pial (Center), and inflated (Right) surface representations with cortical thickness measurements overlaid in a red/green color scale.

Figure 3

Histogram of thickness values in cortical regions of the subject shown in Fig. 2. More than 99% of the surface is between 1- and 4.5-mm thick.

Figure 4

Average cortical thickness across 30 subjects, with primary auditory (A1), somatosensory (S1), and visual (V1) cortices indicated by the white arrows.

Figure 5

Map of the standard deviations of the thickness measurements across 30 subjects. Noncortical regions have been excluded on the medial aspect of the surface.

Figure 6

Average thickness of posterior (area 3b/1) and anterior (area 4/3a) banks of the central sulcus together with a comparison of manually measured published values [Meyer et al. (20)].