The images of in vitro vertebrae acquired by this experimental system show a great improvement compared to the images acquired by a conventional medical scanner.

At present, in the frame of a project partly supported by the french local authorities, we are studying, in collaboration with medical research staffs, the fine cancellous bone structure. This project entitled "Cellular and in tissue mechanisms of the rarefaction of bone during aging" includes especially a morphological approach, using quantitative histological methods and high resolution X-ray computed tomography. In the same way, a current biomechanical study should allow to define essential parameters to build up a biomechanical bone model fit for aging effects.

The comparison between tomography and histomorphometry is an essential step, histomorphometry being considered as a reference. The comparison is made by means of parameters like the trabecular bone volume, trabeculae length, nodes number. These parameters are characteristic of the bone structure, and the measures are executed on segmented tomographic slices. The segmentation consists in separating trabeculae and cortex from the rest of the image. At present, tomographic slices are segmented by several methods, particularly a watershed method and an edges enhancement method. The objective is to get accurate images of the real internal bone structure, allowing a correct correlation with histological results.

The results we obtained allow to derive coherent relationships between histomorphometry and tomography. We are investigating to get a resolution of about 50 - 70µm in order to improve correlations with histomorphometry. Three methods are considered to obtain a higher resolution: an over sampling method; using of a microfocus X-ray generator; removing the linear detector by a higher resolution CCD camera.