OPTIMAL CT SCANNING PLAN FOR LONG-BONE 3-D RECONSTRUCTION

Digital computed tomographic (CT) data are widely used in three-dimens ional (3-D) reconstruction of bone geometry and density features for 3 -D modeling purposes, During in vivo CT data acquisition the number of scans must be limited in order to protect patients from the risks rel ated to X-ray absorption. Aim of this work is to automatically define, given a finite number of CT slices, the scanning plan which returns t he optimal 3-D reconstruction of a bone segment from in vivo acquired CT images. An optimization algorithm based on a Discard-Insert-Exchang e technique has been developed, In the proposed method the optimal sca nning sequence is searched by minimizing the overall reconstruction er ror of a two-dimensional (2-D) prescanning image: an anterior-posterio r (AP) X-ray projection of the bone segment, This approach has been va lidated ill vitro on three different femurs. The 3-D reconstruction er rors obtained through the optimization of the scanning plan on the 2-D prescanning images and on the corresponding 3-D data sets have been c ompared. Two-dimensional and 3-D data sets have been reconstructed by linear interpolation along the longitudinal axis. Results show that di rect 3-D optimization yields root mean square reconstruction errors wh ich are only 4%-7% lower than the 2-D-optimized plan, thus proving tha t 2-D-optimization provides a good suboptimal scanning plan for 3-D re construction. Further on, 3-D reconstruction errors given by the optim ized scanning plan and a standard radiological protocol for long bones have been compared. Results show that the optimized plan yields 20%-5 0% lower 3-D reconstruction errors.