Prevalence and Severity of Off-centering During Diagnostic CT: Observations from 57,621 CT scans of the Chest, Abdomen, and/or Pelvis

Publication date: Available online 23 February 2018
Source:Current Problems in Diagnostic Radiology
Author(s): Oladunni O. Akin-Akintayo, Lauren F. Alexander, Rebecca Neill, Elizabeth A. Krupinksi, Xiangyang Tang, Pardeep K. Mittal, William C. Small, Courtney C. Moreno
Off-centering in the computed tomography (CT) gantry impacts radiation dose due to 1) magnification effects in the topogram with use of topogram-based tube current and tube voltage modulation software and 2) malalignment with the x-ray beam shape with use of a bow-tie filter. We retrospectively determined the distances between patient centroid and gantry isocenter during CT imaging of the chest, abdomen, and/or pelvis, and examined differences based on patient gender, scan region, patient position, and gantry aperture. A water phantom and an anthropomorphic phantom were imaged in the centered position in the CT gantry and at several off-centered positions. Additionally, data from 57,621 adult chest, abdomen, and/or pelvic CT acquisitions were evaluated. Data were analyzed with an analysis of variance using the centroid-to-isocenter data as the dependent variable and the other parameters as independent variables. The majority of patient acquisitions (83.7% (48271/57621)) were performed with the patient′s centroid positioned below isocenter (mean 1.7cm below isocenter (SD 1.8cm); range 12.1cm below to 7.8cm above isocenter). Off-centering in the x-axis was less severe (mean 0.01cm left of isocenter (SD 1.6cm)). Distance between centroid and isocenter in the y-axis did not differ as a function of gender but did differ based on scan region, patient position, and gantry aperture.



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