Document Detail


The exponential edge-gradient effect in x-ray computed tomography.
MedLine Citation:
PMID:  7243880     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The exponential edge-gradient effect must arise in any x-ray transmission CT scanner whenever long sharp edges of high contrast are encountered. The effect is non-linear and is due to the interaction of the exponential law of x-ray attenuation and the finite width of the scanning beam in the x-y plane. The error induced in the projection values is proved to be always negative. While the most common effect is lucent streaks emerging from single straight edges, it is demonstrated that dense streaks from pairs of edges are possible. It is shown that an exact correction of the error is possible only under very special (and rather unrealistic) circumstances in which an infinite number of samples per beam width are available and all thin rays making up the beam can be considered parallel. As a practical matter, nevertheless, increased sample density is highly desirable in making good approximate corrections; this is demonstrated with simulated scans. Two classes of approximate correction algorithms are described and their effectiveness evaluated on simulated CT phantom scans. One such algorithm is also shown to work well with a real scan of a physical phantom on a machine that provides approximately four samples per beam width.
Authors:
P M Joseph; R D Spital
Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Physics in medicine and biology     Volume:  26     ISSN:  0031-9155     ISO Abbreviation:  Phys Med Biol     Publication Date:  1981 May 
Date Detail:
Created Date:  1981-08-10     Completed Date:  1981-08-10     Revised Date:  2004-11-17    
Medline Journal Info:
Nlm Unique ID:  0401220     Medline TA:  Phys Med Biol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  473-87     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Humans
Models, Structural
Technology, Radiologic*
Tomography, X-Ray Computed*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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