1. An apparatus, comprising: processing circuitry configured to obtain projection data representing an intensity of radiation detected at a plurality of detectors, the radiation having been transmitted through an object space, wherein the projection data includes a plurality of datasets, and each dataset corresponds to a respective detector configuration of a plurality of detector configurations; and reconstruct a combined image using the plurality of datasets, wherein the combined image is reconstructed using at least one modified-dual variable and using a splitting-based subproblem method.