1. A method for performing image reconstruction, comprising: deriving background projection data for an area outside a targeted field of view and an area inside a scan field of view of a tomographic image; reconstructing the tomographic image of the targeted field of view, said reconstructing comprising: obtaining an image estimate of the scan field of view; forward projecting the image estimate of the scan field of view; comparing the targeted projection data with the forward projected image estimate to obtain a correction ratio; back projecting the correction ratio to obtain correction image data; applying the correction image data to the image estimate to obtain an updated image estimate, and wherein the background projection data is used in the reconstruction.