The effect of vertical centering and scout direction on automatic tube voltage selection in chest CT: a preliminary phantom study on two different CT.

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Presentation transcript:

The effect of vertical centering and scout direction on automatic tube voltage selection in chest CT: a preliminary phantom study on two different CT equipments Touko Kaasalainen, Teemu Mäkelä, Mika Kortesniemi European Journal of Radiology Open Volume 6, Pages 24-32 (January 2019) DOI: 10.1016/j.ejro.2018.12.001 Copyright © 2018 The Authors Terms and Conditions

Fig. 1 A 0.6 mm thick axial CT image (left) and a photograph (right) of the chest phantom. The phantom represented an average human torso in proportion, density, and two dimensional structures, and was constructed of three specific epoxy materials simulating lung, soft, and bone tissues. Black crosses on the left indicate the scan isocenter locations at the five studied vertical levels. These (from the bottom to the top) are referred in the article as: +6 cm (i.e. phantom is positioned too high), +3 cm, 0 cm, -3 cm, and -6 cm (i.e. phantom is positioned too low). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 2 Region-of-interest (ROI) placement. The ROIs were defined to represent homogeneous soft-tissue areas in the relevant antero-posterior range in the phantom, and inside and around the stronger attenuation of the spine region. The ROI areas were: 700 mm2 for ROI 1, 900 mm2 for ROIs 2–3, and 2100 mm2 for ROIs.4–6. European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 3 The apparent phantom widths measured from the scout images at different table heights. The effect of vertical positioning on the projected image magnification and minification was pronounced in the AP and PA scout directions (true phantom right-to-left length was 30 cm), whereas only a minimal effect was seen using the lateral scout (true length in AP direction was 20 cm). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 4 Relative CTDIvol values as a function of phantom’s vertical position in chest CT scans for pulmonary embolism using ATVS (A) and routine chest CT scans with the fixed 120 kVp tube voltage (B). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 5 Average image noise values (±1 SD) over ten slices in different phantom regions using pulmonary embolism protocols with ATVS. The upper and lower images show the corresponding values for GE and Siemens systems, respectively. Noise values are calculated for six regions-of-interest (ROI 1 is spine, ROIs 2–6 are in soft tissue, see Fig. 2) using three scout directions (AP, LAT, PA) and at five vertical table positions (phantom center -6 to +6 cm from the CT scanner isocenter). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 6 Average image noise values (±1 SD) over ten slices in different phantom regions using chest CT protocol with fixed 120 kVp tube voltage. The upper and lower images show the corresponding values for GE and Siemens systems, respectively. Noise values are calculated for six regions-of-interest (ROI 1 is spine, ROIs 2–6 are in soft tissue, see Fig. 2) using three scout directions (AP, LAT, PA) and at five vertical table positions (phantom center -6 to +6 cm from the CT scanner isocenter). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 7 Axial image data from the GE chest CT scan with a fixed 120 kVp tube voltage after an AP scout. The reference axial CT image with mean CT numbers (A) and corresponding 1SD noise map (B) were calculated from ten slices comprising a total z-direction volume coverage of 10 cm. Absolute CT number differences (C) and relative noise difference maps (D) at table heights +6, +3, -3, and -6 cm were calculated relative to the reference centering (0 cm). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

Fig. 8 Axial image data from the Siemens chest CT scan with a fixed 120 kVp tube voltage after an AP scout. The reference axial CT image with mean CT numbers (A) and corresponding 1SD noise map (B) were calculated from ten slices comprising a total z-direction volume coverage of 10 cm. Absolute CT number differences (C) and relative noise difference maps (D) at table heights +6, +3, -3, and -6 cm were calculated relative to the reference centering (0 cm). European Journal of Radiology Open 2019 6, 24-32DOI: (10.1016/j.ejro.2018.12.001) Copyright © 2018 The Authors Terms and Conditions

European Journal of Radiology Open 2019 6, 24-32DOI: (10. 1016/j. ejro Copyright © 2018 The Authors Terms and Conditions

European Journal of Radiology Open 2019 6, 24-32DOI: (10. 1016/j. ejro Copyright © 2018 The Authors Terms and Conditions