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Extra Z-Axis Coverage at CT Imaging Resulting in Excess Radiation Dose: Frequency, Degree, and Contributory Factors

Liao, Eric A. MD*; Quint, Leslie E. MD*; Goodsitt, Mitchell M. PhD*; Francis, Isaac R. MD*; Khalatbari, Shokoufeh MS; Myles, James D. PhD

Journal of Computer Assisted Tomography: January-February 2011 - Volume 35 - Issue 1 - p 50-56
doi: 10.1097/RCT.0b013e3181f5a652
Original Articles

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.

From the *Department of Radiology, University of Michigan Health System; and †Michigan Institute for Clinical Health Research, University of Michigan, Ann Arbor, MI.

Received for publication July 8, 2010; accepted August 3, 2010.

Reprints: Leslie E. Quint, MD, Department of Radiology, University of Michigan Health System, 1500 E Medical Center Dr, Ann Arbor, MI 48109-5030 (e-mail:

This work was supported by NIH Grant No. UL1RR024986.

© 2011 Lippincott Williams & Wilkins, Inc.