Efficient correction for CT image artifacts caused by objects extending outside the scan field of view

The purpose of this paper is to develop a method of eliminating CT image ar tifacts generated by objects extending outside the scan field of view, such as obese or inadequately positioned patients. CT projection data are measu red only within the scan field of view and thus are abruptly discontinuous at the projection boundaries if the scanned object extends outside the scan held of view. This data discontinuity causes an artifact that consists of a bright peripheral band that obscures objects near the boundary of the sca n held of view. An adaptive mathematical extrapolation scheme with low comp utational expense was applied to reduce the data discontinuity prior to con volution in a filtered backprojection reconstruction. Despite extended proj ection length, the convolution length was not increased and thus the recons truction time was not affected. Raw projection data from ten patients whose bodies extended beyond the scan field of view were reconstructed using a c onventional method and our extended reconstruction method. Limitations of t he algorithm are investigated and extensions for further improvement are di scussed. The images reconstructed by conventional filtered backprojection d emonstrated peripheral bright-band artifacts near the boundary of the scan field of view. Images reconstructed with our technique were free of such ar tifacts and clearly shoveled the anatomy at the periphery of the scan field of view with correct attenuation values. We conclude that blight-band arti facts generated by obese patients whose bodies extend beyond the scan field of View were eliminated with our reconstruction method, which reduces boun dary data discontinuity. The algorithm can be generalized to objects with i nhomogeneous peripheral density and to true "Region of Interest Reconstruct ion" from truncated projections. (C) 2000 American Institute of Physics.