Abstract: A method of reducing artifacts in images acquired with fan beam, helical scanning, tomographic imaging systems, applies a weighting function to the tomographic projection set. The weighting function reduces the contribution to the final image of projection data with large helical offset. Other redundant data within the projection set is increased in weight by the weighting function to prevent image artifacts from the weighting. In one embodiment, the projection set is centered on the slice plane to avoid discontinuities in the projection data caused by the weighting functions.

Abstract: An apparatus for reducing image artifacts caused by over-ranging or clipping of the data collected in a tomographic scan fits a geometric model to the in-range data of each projection. The geometric model is sized to the in-range data by summing all of the data of the projection to obtain a value of the total slice volume. This geometric model is used to compute the slope of the over-range data from the last point of in-range data and this extrapolated data is substituted for the over-range data. The correction process is implemented in pipeline form by convolving an over-range mask indicating which data is in-range and which data is over-range with a box car convolution kernel which produces a trapezoidal correction mask. This correction mask, multiplied by the uncorrected projection data provides the appropriate slope to its clipped portions.

Abstract: A CT apparatus reduces errors in projection data acquired in helical scanning. The imaged object moves concurrently along a translation axis and the x-ray beam is periodically translated with the imaged object so as to subtend a single predetermined volume element during the acquisition of one projection set of data for a first slice. The x-ray beam then returns to its starting position and tracks a second predetermined volume element within a next slice. The x-ray beam may be translated by moving the focal point or a collimator or a combination of both.

Abstract: An x-ray CT system acquires attenuation data over a field of view which is larger than the field of view of the reconstructed image. The data used to reconstruct the image is compensated for the shading effects otherwise caused by objects outside the image, but within the x-ray path. This compensation is accomplished with minimal impact on computation time by using a first order estimation of the convolution of the acquired attenuation data outside the image field of view.

Abstract: A correction method and apparatus for Computed Tomography (CT) removes ring and streak artifacts from images by correcting for data contamination by crosstalk errors. Crosstalk coupling between all adjacent detectors can be measured using an off-center phantom to provide X-ray flux having a changing gradient profile from view to view across the detector array of the CT apparatus. Correction factors are found that will remove crosstalk contamination from subsequently measured imaging data.