Correction of some time-dependent deformations in parallel-beam computed tomography

In computed tomography on interventional X-ray systems, image quality is frequently degraded by uncontrolled patient motion such as breath-hold failures, intestinal contractions, or nervous shaking. To overcome this problem, an iterative workflow is proposed to estimate a dynamic displacement field representing the time-varying position of image elements. An elastic signal registration algorithm computes the displacement in projection space from the difference between measured projections and reference projections, sampled from the image reconstructed in previous iterations. Considering the sampled image as a motionless reference, the motion estimation is exact for a certain class of deformations, including shifting, expansion, and compression. From a new estimate of the displacement field, a better image can be reconstructed by introducing motion compensation in the backprojection step of filtered-backprojection methods. The result of the first iteration is equivalent to a standard reconstruction without motion correction and further iterations progressively sharpen the image.