The Effect of Skull Volume and Density on Differentiating Gray and White Matter on Routine Computed Tomography Scans of the Head

Abstract

Increased volume and density of the skull makes computed tomography differentiation of gray and white matter (GM and WM, respectively) more difficult. The purpose of this investigation was to study the effects of skull volume and bone density on GM and WM differentiation. A total of 21 patients with thick skulls and 22 controls were included in this study. Three consecutive slices from the computed tomography scan were analyzed. The basal ganglia had to be visualized on at least 1 slice. Calvarial volume measurement, mean pixel value in each slice, and Hounsfield unit difference between WM and GM, were compared between the thick-skulled and control groups. The mean bone volume of each slice in the thick-skulled group was 55.7, 54.3, and 56 mL, whereas the mean volume of each slice in the normal group was 39.3, 38.5, and 39.9 mL (P < 0.001). In our series, patients with thick skulls had 41% more bone volume than the normal group. The mean skull pixel value in each slice was 935.9 in patients with thick skulls and 987 in patients in the normal group. There was no difference between right and left sides of the same group of patients. Patients with larger volumes of skull have significant decrease in the Hounsfield unit of the GM and WM compared with the control group. As a result, diagnosing any low-contrast brain abnormality including early/subtle infarction in subjects with a thicker calvarium may be more difficult.

Brain Segmentation From Computed Tomography of Healthy Aging and Geriatric Concussion at Variable Spatial Resolutions

“…The ability to segment soft brain tissues from CT is largely dependent upon image contrast-to-noise ratio (CNR). In CT, the CNR itself depends on tube settings, iterative reconstruction method, radiation dosage and other factors; at standard dosages, the average radio-densities of GM and WM have been reported as 38.7 ± 2.2 Hounsfield units (HU) and 31.8 ± 2.3 HU, respectively (Craddock et al, 2006), resulting in an average X-ray attenuation of ~5 HU. Bier et al (2016) similarly report radio-densities of 40.2 ± 3.3 HU (GM) and 28.48 ± 3.6 HU (WM) in their CT images, with the GM-WM radio-intensity difference being significantly different ( p < 0.0001).…”

Head CT: Toward Making Full Use of the Information the X-Rays Give

“…Since the initial development of head CT imaging, it has been noted that the high attenuation of the skull creates a significant beam-hardening artifact, which greatly limits image quality. 37,38 This artifact is greater for thicker skulls, and can impact image interpretation. 6,39 Modifications in machine design have enabled prehardening of the beam, reducing the effects of beam-hardening on the images; 40,41 however, the effects can still be seen on many current acquisitions (Fig 5 and Cauley et al 6 ).…”