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Precise and Automatic Patient Positioning in Computed Tomography

Avatar Modeling of the Patient Surface Using a 3-Dimensional Camera

Saltybaeva, Natalia, PhD*; Schmidt, Bernhard, PhD; Wimmer, Andreas, MSc; Flohr, Thomas, PhD; Alkadhi, Hatem, MD, MPH, EBCR*

doi: 10.1097/RLI.0000000000000482
Original Articles

Objectives The aim of this study was to evaluate the accuracy of a 3-dimensional (3D) camera algorithm for automatic and individualized patient positioning based on body surface detection and to compare the results of the 3D camera with manual positioning performed by technologists in routinely obtained chest and abdomen computed tomography (CT) examinations.

Materials and Methods This study included data of 120 patients undergoing clinically indicated chest (n = 68) and abdomen (n = 52) CT. Fifty-two of the patients were scanned with CT using a table height manually selected by technologists; 68 patients were automatically positioned with the 3D camera, which is based on patient-specific body surface and contour detection. The ground truth table height (TGT) was defined as the table height that aligns the axial center of the patient’s body region in the CT scanner isocenter. Off-centering was defined as the difference between the ground truth table height (TGT) and the actual table position used in all CT examinations. The t test was performed to determine significant differences in the vertical offset between automatic and manual positioning. The χ2 test was used to check whether there was a relationship between patient size and the magnitude of off-centering.

Results We found a significant improvement in patient centering (offset 5 ± 3 mm) when using the automatic positioning algorithm with the 3D camera compared with manual positioning (offset 19 ± 10 mm) performed by technologists (P < 0.005). Automatic patient positioning based on the 3D camera reduced the average offset in vertical table position from 19 mm to 7 mm for chest and from 18 mm to 4 mm for abdomen CT. The absolute maximal offset was 39 mm and 43 mm for chest and abdomen CT, respectively, when patients were positioned manually, whereas with automatic positioning using the 3D camera the offset never exceeded 15 mm. In chest CT performed with manual patient positioning, we found a significant correlation between vertical offset greater than 20 mm and patient size (body mass index, >26 kg/m2, P < 0.001). In contrast, no such relationship was found for abdomen CT (P = 0.38).

Conclusions Automatic individualized patient positioning using a 3D camera allows for accurate patient centering as compared with manual positioning, which improves radiation dose utilization.

From the *Institute for Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland; and

Computed Tomography Division, Siemens Healthineers, Forchheim, Germany.

Received for publication March 5, 2018; and accepted for publication, after revision, April 3, 2018.

Correspondence to: Hatem Alkadhi, MD, MPH, EBCR, Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Raemistrasse 100, 8091 Zurich, Switzerland. E-mail:

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