Extra Z-axis coverage at CT imaging resulting in excess radiation dose: frequency, degree, and contributory factors.
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.
Department of Radiology, University of Michigan Health System, Ann Arbor, MI 48109-5030, USA.
Eric A
EA
Liao
Leslie E
LE
Quint
Mitchell M
MM
Goodsitt
Isaac R
IR
Francis
Shokoufeh
S
Khalatbari
James D
JD
Myles
D000704:Analysis of Variance; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012307:Risk Factors; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
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