Modified ordered subsets scheme for attenuation weighted reconstruction

Methods of selecting subsets for attenuation weighed algorithms were investigated in order to reduce observed artifacts. Artifacts are observed primarily in the transaxial view of the images using the typically used subset selection scheme. By changing the subset selection scheme, the artifacts were determined to originate from the attenuation weighting of the data across the angular range of the data. By clustering subset projections, the measured data used in an image update are similarly attenuated for any given image point. Such subset selection improves the image quality in objects with high activity regions that are located toward the edges of the object. Preliminary results show that the new subset scheme produces less distorted images with fewer artifacts.