One important consideration for reconstructing an image using computed tomography (CT) is that the axis of rotation must pivot at the same point on the reconstruction plane as the X-ray source and that the CT detector assembly rotates around the imaged object. This pivot point is used as a reference point for backprojecting pixel values to their proper coordinates. Therefore, reconstructing an image with a nonstationary axis of rotation would backproject pixel values to incorrect coordinate points, since the reference point is nonstationary for every projection angle. A convolution filtered backprojection algorithm has been derived for correcting images that were acquired with a nonstationary axis of rotation using the fan beam geometry with a col linear (flat) detector. Fan beam reconstruction algorithms which filter and backproject projection data without correcting for this misalignment would produce structured artifacts and sharp degradation of the resulting image. The correction method described in this paper accounts for the vertical displacements of the axis of rotation as the CT scanner rotates around the imaged object, as may be the case when sagging occurs. Software simulations are performed to show how the algorithm corrects for the shift in the axis of rotation.
All Science Journal Classification (ASJC) codes
- Radiological and Ultrasound Technology
- Computer Science Applications
- Electrical and Electronic Engineering