Correction for Resolution Nonuniformities Caused by Anode Angulation in Computed Tomography
| Autor: | Phillip Vargas, P.J. La Riviere |
|---|---|
| Rok vydání: | 2008 |
| Předmět: |
Iterative reconstruction
Sensitivity and Specificity Article Line Focus Principle Optics Focal Spot Size Electrical and Electronic Engineering Electrodes Image resolution Physics Radiological and Ultrasound Technology business.industry Detector Reproducibility of Results Equipment Design Computer Science Applications Anode Equipment Failure Analysis Radiographic Image Enhancement Heat generation Radiographic Image Interpretation Computer-Assisted Tomography Artifacts Tomography X-Ray Computed business Algorithms Software |
| Zdroj: | IEEE Transactions on Medical Imaging. 27:1333-1341 |
| ISSN: | 1558-254X 0278-0062 |
| Popis: | Most X-ray tubes comprise a rotating anode that is bombarded with electrons to produce X-rays. A substantial amount of heat is generated, and to increase the area of the anode exposed to the electrons, without increasing the apparent size of the focal spot, the focal track of the anode is generally beveled with a very shallow angle (typically 5 degrees-7 degrees in a computed tomography (CT) tube). Due to the line focus principle, this allows a fairly large area of the focal track to be exposed to electrons while retaining a fairly small effective projected focal spot. One side effect of anode angulation is that the focal spot appears different from different positions in the detector array; the effective focal spot size at a constant distance from the tube will be larger for a peripheral detector channel than for a central one. These differences in the effective size of the focal spot across the field-of-view lead to worse resolution in the periphery than in the center of reconstructed images. In this work we describe a method for achieving more uniform resolution in fanbeam CT images by correcting for these focal spot angulation effects. We do so by modeling the effects as a series of local blurrings in the space of transmitted CT intensities and determining the effective coefficients of the corresponding discrete convolutions. The effect of these blurrings can then be compensated for in the sinogram domain through the use of a penalized-likelihood sinogram restoration model we have recently developed. |
| Databáze: | OpenAIRE |
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