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Overranging at multisection CT: an underestimated source of excess radiation exposure.

Authors
Type
Published Article
Journal
Radiographics : a review publication of the Radiological Society of North America, Inc
Publication Date
Volume
30
Issue
4
Pages
1057–1067
Identifiers
DOI: 10.1148/rg.304095167
PMID: 20631368
Source
Medline
License
Unknown

Abstract

To reconstruct the first and last sections of a helical computed tomographic (CT) scan, the scan length is automatically extended beyond the planned image boundaries, a phenomenon known as overranging. With common 16-section CT scanning protocols, the overrange length is between 3 and 6 cm. For scanners with 64 or more sections, this length will be much greater, since overranging increases as pitch or detector collimation increases. Manufacturers have equipped the latest generation of CT scanners (128 sections or more) with overrange dose-reducing innovations that reduce overranging by typically up to 50%, which in the best cases reduces overranging to that of the previous scanner models (64 sections). To reduce the impact of overranging on radiosensitive organs just outside the planned scan region, it is best to use an axial protocol rather than a helical protocol. If this is not an option, lowering the pitch or the detector collimation will significantly reduce overranging. Finally, CT examinations should be planned in such a way that radiosensitive organs are as far as possible from the imaged volume.

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