Accelerated-scan X-ray microtomography for assessing bone mineral content

X-ray tomography is a reliable tool for determining density and three-dimensional (3D) structure of bone tissue. However, traditional reconstruction methods such as FDK require dense angular sampling in data acquisition phase leading to long measurement times. Especially in X-ray micro-tomography acquisition times between 6 and 12 hours are typical in high-resolution scans. Acquiring less data using greater angular steps is an obvious way for speeding up the process. However, computing 3D reconstruction from such a sparsely sampled dataset is very sensitive to measurement noise and modelling errors. An automatic regularization method is proposed for robust reconstruction, based on enforcing sparsity in the three-dimensional shearlet transform domain. The inputs of the algorithm are the projection data and a priori known expected degree of sparsity, denoted 0 < Cpr \leq 1. The number Cpr can be calibrated from a few dense-angle reconstructions and fixed. The morphology of the bone is then analyzed using standard metrics. The proposed method is shown to outperform the baseline algorithm (FDK) in the case of sparsely collected data. The number of X-ray projections can be reduced to 10\% of the currently used amount while retaining quality of morphology analysis.