Figure 4.

Study #1: Simulation study involving a water cylinder with a variety of metal spheres and rods. (a) Coarse attenuation map μ_c computed from 2 scout views. The central axial (x, y) plane is shown, recognizing that the coarse attenuation map is computed over the full 3D volume. (b) Segmentation b_seg computed by the U-Net. (c) Metric map q_poly (θ, ϕ) computed over a realistic range of rotation (θ) and tilt (ϕ) angles. Optimal tilted semi-circular orbits are marked by dashed green lines labeled ➁ and ➃, which avoid projection views with high spectral shift. (d) Objective function Q_poly (ϕ) computed from equation (5). (e) Axial and sagittal slices from FBP image reconstructions of data acquired at various tilt angles. (f) The RMSE analyzed as a function of tilt angle ϕ is seen to follow a similar trend as the objective function in (d), confirming the basic notion that minimization of variation in spectral shift (from q_poly (θ, ϕ)) minimizes metal artifacts in 3D image reconstructions.