Fig 7. Pseudocode for PCD only reconstruction with the split Bregman method.

As a control experiment for the proposed hybrid spectral CT reconstruction algorithm (Fig 1), which uses both EID (w) and PCD (Y) projection data, we performed a second iterative reconstruction using only the PCD projection data. This PCD only reconstruction algorithm is largely analogous to the hybrid reconstruction algorithm, with two main exceptions. First, the PCD data is reconstructed directly (X) rather than indirectly as a function of the EID reconstruction (X_L) and the spectral contrast provided by the PCD data (X_S). Second, during initialization, the dictionary is trained using a variance (${\mathrm{\sigma }}_e^2$) weighted average of the initialized reconstruction results (avg_e(X), step 7) rather than using a FBP reconstruction of the EID data (Fig 1, step 11).