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. 2011 Jan-Feb;35(1):50-6.
doi: 10.1097/RCT.0b013e3181f5a652.

Extra Z-axis coverage at CT imaging resulting in excess radiation dose: frequency, degree, and contributory factors

Eric A Liao  1 , Leslie E Quint, Mitchell M Goodsitt, Isaac R Francis, Shokoufeh Khalatbari, James D Myles
Affiliations

Extra Z-axis coverage at CT imaging resulting in excess radiation dose: frequency, degree, and contributory factors

Eric A Liao et al. J Comput Assist Tomogr. 2011 Jan-Feb.

Abstract

Objective: To assess the degree of extra scanning beyond the prescribed anatomic boundaries for thoracic and body computed tomographic (CT) scans and to identify associated factors.

Methods: For 442 consecutive chest, abdomen, and/or pelvis CT examinations, the length of extra scanning beyond the prescribed anatomic boundaries was determined. Examinations were grouped according to the locations/types of the prescribed boundaries and compared with regard to length of extra scanning.

Results: Of 442 CT examinations, 438 (99%) included extraneous imaging, showing a mean excess scanning length of 43.2 mm per examination (range, 0-180 mm). Significantly more extraneous imaging was performed when soft tissue or vascular structures defined anatomic boundaries compared to when osseous (P < 0.001) or air/soft tissue interfaces (P < 0.0001) defined the boundaries. The average percent of total scan dose attributable to extra imaging was 8.64% to 10.38%.

Conclusions: Computed tomographic scanning beyond the prescribed anatomic boundaries occurs commonly, resulting in moderate extra radiation dose.

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Figures

Figure 1
Figure 1
Box and whisker plot showing length of extraneous scanning according to top boundary location group. The celiac artery boundary group demonstrated the greatest length of extraneous scanning, while the iliac crest boundary group demonstrated the least amount of extraneous scanning.
Figure 2
Figure 2
Box and whisker plot showing length of extraneous scanning according to bottom boundary location group. The aortic bifurcation boundary group demonstrated the greatest length of extraneous scanning, while the iliac crest boundary group demonstrated the least amount of extraneous scanning.
Figure 3
Figure 3
Box and whisker plot showing length of extraneous scanning according to top boundary type group. The soft tissue/vascular boundary type group demonstrated the greatest length of extraneous scanning, while the osseous boundary type group demonstrated the least amount of extraneous scanning.
Figure 4
Figure 4
Box and whisker plot showing length of extraneous scanning according to bottom boundary type group. The soft tissue/vascular boundary type group demonstrated the greatest length of extraneous scanning, while the osseous boundary type group demonstrated the least amount of extraneous scanning.
See this image and copyright information in PMC

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