Age-related changes of the cranial bone mineral: a quantitative study with computed tomography.

Age-related changes of the cranial bone mineral in 495 subjects were assessed by computed tomography (CT) in terms of the Hounsfield number. By means of computer programs available in the CT system, the histograms for the bone were obtained. The peak of this histogram for males increased gradually and reached a plateau beyond 20 years of age, while that for females rose rather steeply from age 0 to age 20 and formed a plateau in the 20s and 30s, then declined precipitously from a value of 1164 +/- 143 to a value of 629 +/- 119 in the 70s and older. In the 20s and 30s, the peak for females was greater than that for males. The total pixel number of this histogram was constant after the 20s. The pixel number of the peak for males made a plateau after the 10s, but that for females showed a similar pattern until the 40s, then increased steeply after the 50s. The peak may reflect calcium concentration of the cranial bone, and therefore the skull of the female may store more calcium than that of the male in the 20s and 30s.