Local x-ray tomography for in vivo bone structure examinations

Precise information about the microarchitecture of cancellous bone would be helpful to further fracture risk prediction in individual patients. Recent ly 3D-QCT of the distal radius has been introduced to this end. The validit y of this new procedure is limited by the spatial resolution of the CT imag es, which in turn is limited by the x-ray dose. Local tomography, where onl y the region of interest has to be scanned with x rays, might provide a way out of this dilemma. In this work the feasibility of local tomography for in vivo trabecular bone structure assessment is studied. In a first part th e accuracy of structural indices obtainable with local tomography is compar ed with the accuracy of results from global (traditional) tomographic measu rements. The results show that local tomography generates no substantial de gradation in the structural indices. In a second part, the reduction in the radiation dose of local tomography is quantified with Monte Carlo simulati ons of the x-ray scanning procedure. The results show that skin dose at the lower forearm can be reduced by a factor of 4-6, if the CT measurements ar e restricted to the distal radius. We conclude that with the help of local tomography in vivo 3D-QCT examinations of the trabecular bone microarchitec ture are feasible with a skin dose of 0.1 mGy at 165(3) mu m(3) resolution, or with a skin dose of 1 mGy at a resolution of 100(3) mu m(3). The increa sed resolution is expected to further improve the accuracy and precision of current in vivo bone structure examinations, allowing a detailed analysis of the processes of bone changes due to aging, disease, and treatment. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01403-0 ].