Bone specimens were collected from the frontal and parietal bones of 4 adult, human skulls. The microstructure was characterized using micro-tomography (CT) at about 6-μm resolution to map the change of porosity as a function of the depth, P(d), from the inner surface nearest to the brain to the outer surface nearest to the skin. A quantifiable method was developed using the measured P(d) to objectively distinguish between the 3 layers of the skull: the outer table, diploë, and inner table. The thickness and average porosity of each of the layers were then calculated from the measured porosity distributions. A Gaussian function was used to represent the P(d) curves. The Gaussian parameters were identified through least squares, and the values indicated the peak porosity and the relative thickness of the diploë. The results for total thickness, the thickness and average porosity of each of the layers, and the Gaussian parameters were compared between the 2 bone types (frontal and parietal), while accounting for skull-to-skull variability. The primary differences were that parietal bones generally had a larger diploë accompanied by a thinner inner table. The arrangement of the porous vesicular structure within the outer table was also obtained with micro-CT scans with longer scan times, using enhanced parameters for higher resolution and lower noise in the images. From these scans, the porous structure of the bone appeared to be randomly arranged in the transverse plane, compared to the porous structure of the human femur, which is aligned in the loading direction.
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