Dose Reduction in Helical CT: Dynamically Adjustable z-Axis X-Ray Beam Collimation
Dose Reduction in Helical CT: Dynamically Adjustable z-Axis X-Ray Beam Collimation
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DOI：
10.2214/ajr.09.2878
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发表时间：
2010-01-01
影响因子：
5
通讯作者：
McCollough, Cynthia H.
中科院分区：
文献类型：
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作者：
Christner, Jodie A.;Zavaletta, Vanessa A.;McCollough, Cynthia H.
OBJECTIVE.本研究的目的是测量动态可调z轴准直实现的剂量减少。材料和方法。使用商业CT系统采集具有和不具有动态z轴准直的CT扫描。剂量减少作为螺距、扫描长度和等中心点处空气中总入射辐射的位置、扫描体积中心的累积剂量以及距固定长度扫描体积不同距离处的点的累积剂量的函数进行测量。在扫描开始和中心测量图像噪声。结果。对于20 mm和500 mm的扫描长度，等中心处空气中总入射辐射的减少分别为27%和3%（间距，0.5）以及46%和8%（间距，1.5）。对于20 mm扫描，间距为0.5和1.5时，扫描中心的累积剂量减少分别为15%和29%。对于大于300 mm的扫描长度，所有节距的剂量节省均小于3%。剂量减少80毫米或更远的100毫米扫描范围分别为15%和40%的间距为0.5和1.5。在动态z轴准直的情况下，螺旋扫描的极端处的噪声相对于中心处的噪声不变。在螺距为0.2和3.4时，估计头部有效剂量减少16%（0.4 mSv），胸部和肝脏有效剂量减少10%（0.8和1.4 mSv），腹部和骨盆有效剂量减少6%（0.8 mSv），冠状动脉CT血管造影有效剂量减少4%（0.4 mSv）和55%（1.0 mSv）。动态z轴准直的使用通过最小化过度扫描来降低螺旋CT中的剂量。扫描长度越短，间距值越大，剂量减少百分比越大。
OBJECTIVE. The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation.MATERIALS AND METHODS. A commercial CT system was used to acquire CT scans with and without dynamic z-axis collimation. Dose reduction was measured as a function of pitch, scan length, and position for total incident radiation in air at isocenter, accumulated dose to the center of the scan volume, and accumulated dose to a point at varying distances from a scan volume of fixed length. Image noise was measured at the beginning and center of the scan.RESULTS. The reduction in total incident radiation in air at isocenter varied between 27% and 3% (pitch, 0.5) and 46% and 8% (pitch, 1.5) for scan lengths of 20 and 500 mm, respectively. Reductions in accumulated dose to the center of the scan were 15% and 29% for pitches of 0.5 and 1.5 for 20-mm scans. For scan lengths greater than 300 mm, dose savings were less than 3% for all pitches. Dose reductions 80 mm or farther from a 100-mm scan range were 15% and 40% for pitches of 0.5 and 1.5. With dynamic z-axis collimation, noise at the extremes of a helical scan was unchanged relative to noise at the center. Estimated reductions in effective dose were 16% (0.4 mSv) for the head, 10% (0.8 and 1.4 mSv) for the chest and liver, 6% (0.8 mSv) for the abdomen and pelvis, and 4% (0.4 mSv) and 55% (1.0 mSv) for coronary CT angiography at pitches of 0.2 and 3.4.CONCLUSION. Use of dynamic z-axis collimation reduces dose in helical CT by minimizing overscanning. Percentage dose reductions are larger for shorter scan lengths and greater pitch values.