CT Systems Engineering W-1140, GE Healthcare, General Electric Company, 3000 N. Grandview Boulevard, Waukesha, Wisconsin 53201-0414, USA.
Med Phys. 2007 Jul;34(7):3093-101. doi: 10.1118/1.2748113.
Although x-ray intensity shaping filters (bowtie filters) have been used since the introduction of some of the earliest CT scanner models, the clinical implications on dose and noise are not well understood. To achieve the intended dose and noise advantage requires the patient to be centered in the scan field of view. In this study we explore the implications of patient centering in clinical practice. We scanned various size and shape phantoms on a GE LightSpeed VCT scanner using each available source filter with the phantom centers positioned at 0, 3, and 6 cm below the center of rotation (isocenter). Surface doses were measured along with image noise over a large image region. Regression models of surface dose and noise were generated as a function of phantom size and centering error. Methods were also developed to determine the amount of miscentering using a scout scan projection radiograph (SPR). These models were then used to retrospectively evaluate 273 adult body patients for clinical implications. When miscentered by 3 and 6 cm, the surface dose on a 32 cm CTDI phantom increased by 18% and 41% while image noise also increased by 6% and 22%. The retrospective analysis of adult body scout SPR scans shows that 46% of patients were miscentered in elevation by 20-60 mm with a mean position 23 mm below the center of rotation (isocenter). The analysis indicated a surface dose penalty of up to 140% with a mean dose penalty of 33% assuming that tube current is increased to compensate for the increased noise due to miscentering. Clinical image quality and dose efficiency can be improved on scanners with bowtie filters if care is exercised when positioning patients. Automatically providing patient specific centering and scan parameter selection information can help the technologist improve workflow, achieve more consistent image quality and reduce patient dose.
虽然 X 射线强度成型滤波器（蝴蝶结滤波器）自一些最早的 CT 扫描仪模型问世以来就已被使用，但它们对剂量和噪声的临床影响尚未得到很好的理解。要实现预期的剂量和噪声优势，需要将患者置于扫描视场的中心。在这项研究中，我们探讨了在临床实践中患者居中的意义。我们使用每个可用的源滤波器对 GE LightSpeed VCT 扫描仪上的各种大小和形状的体模进行了扫描，将体模中心置于旋转中心（等中心）下方 0、3 和 6cm 处。在较大的图像区域上测量了表面剂量和图像噪声。生成了表面剂量和噪声的回归模型，作为体模大小和中心误差的函数。还开发了使用透视扫描投影射线照片（SPR）确定偏心量的方法。然后，使用这些模型对 273 名成人身体患者进行了回顾性评估，以评估其临床意义。当偏心 3cm 和 6cm 时，32cm CTDI 体模的表面剂量增加了 18%和 41%，而图像噪声也增加了 6%和 22%。对成人身体透视 SPR 扫描的回顾性分析表明，46%的患者在 20-60mm 的高度上偏心，平均位置在旋转中心（等中心）下方 23mm。分析表明，由于偏心导致的噪声增加，假定管电流增加以补偿噪声增加，则表面剂量的惩罚高达 140%，平均剂量的惩罚为 33%。如果在定位患者时小心谨慎，带有蝴蝶结滤波器的扫描仪可以提高临床图像质量和剂量效率。自动提供患者特定的中心位置和扫描参数选择信息可以帮助技术人员改善工作流程，实现更一致的图像质量并降低患者剂量。
