Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Switzerland.
Acad Radiol. 2020 Apr;27(4):508-517. doi: 10.1016/j.acra.2019.07.004. Epub 2019 Jul 27.
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.
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).
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.
Vertical off-centering influences effective radiation dose and image-noise on ND and RD protocols.
There is no over-proportional noise increase in RD compared to ND protocols when patients are positioned off-center.
评估管电流调制（TCM）中垂直偏心对降低剂量（RD）胸部 CT 的有效剂量和图像噪声的影响。
对 100 例连续患者（36 例女性；平均年龄 56 岁）使用标准剂量（ND）和 RD 胸部 CT 协议在 192 层 CT 扫描仪上进行扫描。通过在肺尖、中部和下部放置圆形感兴趣区来评估图像噪声。两名独立的读者评估图像质量。根据患者在机架中的位置将研究人群分层：位于机架等中心（i）、高于机架等中心（ii）和低于机架等中心（iii）。使用 Pearson 相关系数确定有效辐射剂量与垂直偏心之间的相关性。使用 Student's t 检验评估组间（i-iii）图像噪声的差异。
平均垂直偏心距机架等中心下方 10.6mm（范围-45.0-27.9mm）。有效辐射剂量呈线性变化，机架等中心下方剂量最高，机架等中心上方剂量最低（ND：r=-0.296；p=0.003-RD：r=-0.258；p=0.010）。患者位于机架等中心下方时，图像噪声最低，位于机架等中心上方时噪声最高（ND：79.35HU 与 94.86HU-RD：143.44HU 与 160.13HU）。患者位置对主观图像质量没有显著影响（p>0.05）。总体而言，在偏心患者中，与 ND 相比，RD 方案并没有不成比例的噪声增加。
垂直偏心会影响 ND 和 RD 方案的有效辐射剂量和图像噪声。
当患者位置偏心时，RD 方案与 ND 方案相比，噪声没有不成比例的增加。
