Researchers have used CT scan technology to study the geometric characteristics of living human skulls and, in so doing, have confirmed that women’s are thicker than men’s and that the skulls of both shrink slowly during adulthood. The results of the study could help in the design of improved devices for protecting the head in vehicle collisions and other accidents. Previous studies have suggested that head size and shape play a significant role during impact, but reliable data on the characteristics of the skull are needed. CT scans were used to investigate the geometric characteristics of the skulls of living male and female adults. Part of the process involved image segmentation, where an input image (right) is transformed into an output binary (black and white) skull image (left). Reprinted with permission of the International Journal of Vehicle Safety.In their study, Jesse Ruan of the Ford Motor Co., in Dearborn, Mich., and colleagues at Tianjin University of Science and Technology in China analyzed the CT scans of 1500 male and 1500 female patients who had received head scans for diagnostic purposes. The average age of the males and females was 48 and 52, respectively.For each individual, there were 10 to 15 scan images (1 cm apart), which were taken from the top to the base of the head. Using the images, the scientists analyzed and measured the skull anterior-posterior length, the breadth and the skull thicknesses in the frontal, parietal and occipital bones.To characterize the skull’s geometric features, they needed to segment the cranial bone portion of the CT image precisely. With the thresholding method, the skull was singled out from the jpeg format image and transformed into a binary image data array. Image noise was filtered, and image deviation was corrected as much as possible. The image analysis and measurement process included the methods of edge detection, boundary tracing and reference point fixing. Animal skulls were used to validate the measurement method. The results showed that, for the male, the average thicknesses of the frontal, parietal and occipital bones were 6.58, 5.37 and 7.56 mm, respectively, and, for the female, 7.48, 5.58 and 8.17 mm, respectively. They demonstrated that, for the male, the anterior-posterior length and the breadth of the skull were 175.81 and 145.35 mm, respectively, and for the female, 170.61 and 140.11 mm, respectively.The next step in the study will be to determine how these measurement differences affect the head impact response. The design of gender-appropriate head protection could be a long-range result.International Journal of Vehicle Safety, Vol. 2, No. 4, 2007, pp. 345-367.