Evaluation of a preprocessing algorithm for truncated CT projections.

A preprocessing algorithm for completing truncated computed tomography (CT) projection data (so that reconstruction methods suitable for complete projection data can be applied) is experimentally investigated. The study is motivated primarily by the problem of patients who are too obese to fit into the fan beam of a rotate-only (third generation) scanner, and secondarily by dose reduction considerations. Four sets of patient data collected by a rotate-only scanner are used, and the reconstructions from the complete and truncated projection data are compared. It is illustrated that the preprocessing algorithm leads to qualitatively good images, since local variations are nearly identical in the reconstruction from the complete and from the truncated data. Quantitatively, the results are less encouraging; the exact values of CT numbers differ in the two reconstructions by a significant (although slowly varying) amount across the two reconstructed images.