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Vertical Off-Centering in Reduced Dose Chest-CT: Impact on Effective Dose and Image Noise Values

Published on Jul 1, 2019in Academic Radiology2.267
· DOI :10.1016/j.acra.2019.07.004
Matthias Eberhard4
Estimated H-index: 4
(UZH: University of Zurich),
Christian Blüthgen2
Estimated H-index: 2
(UZH: University of Zurich)
+ 3 AuthorsKatharina Martini7
Estimated H-index: 7
(UZH: University of Zurich)
Abstract
Objectives To assess the effect of vertical off-centering in tube current modulation (TCM) on effective-dose and image-noise in reduced-dose (RD) chest-CT. Methods One-hundred consecutive patients (36 female; mean age 56 years) were scanned on a 192-slice CT scanner with a standard-dose (ND) and a RD chest-CT protocol using tube current modulation. Image-noise was evaluated by placing circular regions of interest in the apical, middle, and lower lung regions. Two independent readers evaluated image quality. Study population was stratified according to patient position in the gantry: positioned in the gantry isocenter (i), higher than the gantry isocenter (ii), and lower than the gantry isocenter, (iii). Pearson correlation was used to determine the correlation between effective radiation dose and vertical off-centering. Student's t test was used to evaluate for differences in image-noise between groups (i-iii). Results Mean vertical off-centering was of 10.6 mm below the gantry-isocenter (range −45.0–27.9 mm). Effective radiation dose varied in a linear trend, with the highest doses noted below gantry isocenter, and the lowest doses noted above gantry isocenter (ND: r = −0.296; p = 0.003 – RD: r = −0.258; p = 0.010). Lowest image-noise was observed where patients were positioned below the gantry isocenter, and highest in patients positioned above (ND: 79.35 HU vs. 94.86 HU – RD: 143.44 HU vs. 160.13 HU). Subjective image quality was not significantly affected by patient-position (p > 0.05). Overall, there was no over-proportional noise-increase from the ND to the RD protocol in patients which were positioned off-center. Conclusion Vertical off-centering influences effective radiation dose and image-noise on ND and RD protocols. Advances in Knowledge There is no over-proportional noise increase in RD compared to ND protocols when patients are positioned off-center.
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References24
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#1Hongbing Shen (Nanjing Medical University)H-Index: 54
Lung cancer is among the most frequently diagnosed cancers worldwide and the leading cause of cancer death in both males and females. Screening for lung cancer coupled with earlier intervention has long been studied as an approach to mortality reduction. However, minimal progress was achieved until recently, when lowdose spiral computed tomography (LDCT) screening demonstrated a 20% reduction in mortality from lung cancer in a randomized controlled trial (RCT), the National Lung Screening Trial,...
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#1Natalia Saltybaeva (UZH: University of Zurich)H-Index: 6
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OBJECTIVE. The purpose of this study is to assess the image quality and radiation dose reduction of ultra-low-dose CT using sinogram-affirmed iterative reconstruction (SAFIRE). SUBJECTS AND METHODS. This prospective study enrolled 25 patients who underwent three consecutive unenhanced CT scans including low-dose CT (120 kVp and 30 mAs) and two ultra-low-dose CT protocols (protocol A, 100 kVp and 20 mAs; protocol B, 80 kVp and 30 mAs) with image reconstruction using SAFIRE. The image quality and ...
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OBJECTIVE. The objective of our study was to evaluate the effect of vertical centering on dose and image noise in chest MDCT of different-sized patients using anthropomorphic phantoms and retrospectively studying examinations of clinical patients. MATERIALS AND METHODS. Three different anthropomorphic phantoms were scanned using different vertical centering (offset ± 6 cm) and were assessed with radiation dose–monitoring software. The effect of vertical positioning on the radiation dose was stud...
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