Showing papers by "Jean-Baptiste Thibault published in 2004"

A novel reconstruction algorithm to extend the CT scan field-of-view.

Abstract: For various reasons, a projection dataset acquired on a computed tomography (CT) scanner can be truncated. That is, a portion of the scanned object is positioned outside the scan field-of-view (SFOV) and the line integrals corresponding to those regions are not measured. A projection truncation problem causes imaging artifacts that lead to suboptimal image quality. In this paper, we propose a reconstruction algorithm that enables an adequate estimation of the projection outside the SFOV. We make use of the fact that the total attenuation of each ideal projection in a parallel sampling geometry remains constant over views. We use the magnitudes and slopes of the projection samples at the location of truncation to estimate water cylinders that can best fit to the projection data outside the SFOV. To improve the robustness of the algorithm, continuity constraints are placed on the fitting parameters. Extensive phantom and patient experiments were conducted to test the robustness and accuracy of the proposed algorithm.

Methods, apparatus, and software to facilitate iterative reconstruction of images

Abstract: A method of reconstructing an image includes performing an iterative CT X-ray image reconstruction using a model including a point spread function (PSF) to reconstruct an image.

Methods, apparatus, and software to facilitate computing the elements of a forward projection matrix

Abstract: A method for calculating an element of a projection includes calculating an element A i,j of a projection matrix using at least two different rays through a voxel.

Algorithm to extend reconstruction field-of-view

Abstract: Images obtained from CT scanners are often used to estimate the radiation dose delivered to a target organ in oncology applications. Since a patient needs to be positioned in a similar manner as in a therapy machine, a portion of the patient is often positioned outside the scan field-of-view (SFOV). Projection truncation problem also occurs frequently in conventional CT scans and causes imaging artifacts that lead to suboptimal image quality. In this paper, we propose a reconstruction algorithm that enables an adequate estimation of the object outside the SFOV. We make use of the fact that the total attenuation of each ideal projection in a parallel sampling geometry remains constant over views. We use the magnitudes and slopes of the projection samples at the location of truncation to estimate water cylinders that can best fit to the projection data outside the SFOV. To improve the robustness of the algorithm, continuity constraints are placed on the fitting parameters. Extensive phantom and patient experiments were conducted to test the robustness and accuracy of the proposed algorithm.

Method, system and storage medium for reference normalization for blocked reference channels

Abstract: A method for performing reference normalization for an image created by an imaging system. The imaging system includes a radiation detector array with a right and left edge. The method includes receiving a projection dataset created by the imaging system in response to a varying x-ray tube current. The projection dataset includes a view and predicted fluxes are calculated for the set of reference channels within the view. A right set of reference channels are located proximate at the right edge of the detector array and a left set of reference channels are located proximate to the left edge of the detector array. The method also includes calculating average actual fluxes for the sets of reference channels. Based on the predicted reference fluxes and the average fluxes, a reference correction value for the view is determined. The correction value is applied for the reference correction of the view.

Methods, apparatus, and software to compensate for failed or degraded components

Abstract: A method for improving images of an imaging system including a plurality of detector cells includes assigning a quality factor for each detector cell.