The peak CT number of profiles perpendicular to the vertebral cortical shell may be a useful indicator of the integrity of the cortical shell

Limited spatial resolution affects the ability of clinical CT systems to directly measure the thickness and density of the vertebral cortical shell. In such cases the peak CT number (CTp) of a profile through the cortical shell is approximately proportional to the product of thickness and density and hence an average of several of these values (CTp) may be useful as an indicator of the integrity of the cortical shell. Values of CTp were determined around the anterior two-thirds of the cortical shell of the L3 and L4 lumbar vertebrae of 96 Kuwaiti women (mean age±SD=50.0±8.5). There was no significant difference between the two vertebrae in terms of CTp and trabecular BMD values. There was a significant correlation between CTp and trabecular BMD for each vertebra (r=0.597, p<0.0001), and between CTp and patient age (r=0.624, p<0.001), suggesting that both cortical and trabecular bone may be subject to similar thinning mechanisms during ageing and osteoporosis. The variation of CTp around the cortical shell, represented by the standard deviation of nine CTp measurements, was significantly correlated with the mean value (r=0.503, p<0.0001) and may be useful as a descriptor of cortical structure.