Tomographic imaging of bone composition using coherently scattered x rays

Bone tissue consists primarily of calcium hydroxyapatite crystals (bone mineral) and collagen fibrils. Bone mineral density (BMD) is commonly used as an indicator of bone health. Techniques available at present for assessing bone health provide a measure of BMD, but do not provide information about the degree of mineralization of the bone tissue. This may be adequate for assessing diseases in which the collagen-mineral ratio remains constant, as assumed in osteoporosis, but is insufficient when the mineralization state is known to change, as in osteomalacia. No tool exists for the in situ examination of collagen and hydroxyapatite density distributions independently. Coherent-scatter computed tomography (CSCT) is a technique we are developing that produces images of the low-angle scatter properties of tissue. These depend on the molecular structure of the scatterer making it possible to produce material-specific maps of each component in a conglomerate. After corrections to compensate for exposure fluctuations, self-attenuation of scatter and the temporal response of the image intensifier, material-specific images of mineral, collagen, fat and water distributions are obtained. The grey-level in these images provides the volumetric density of each component independently.