Department of Radiology, Mayo Clinic Rochester, 200 First St. SW, East-2 Mayo Bldg., Rochester, MN 55905, USA.
AJR Am J Roentgenol. 2010 Jan;194(1):W49-55. doi: 10.2214/AJR.09.2878.
The purpose of this study was to measure the dose reduction achieved with dynamically adjustable z-axis collimation.
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.
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.
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.
本研究旨在测量动态可调 z 轴准直实现的剂量降低。
使用商业 CT 系统采集带和不带动态 z 轴准直的 CT 扫描。剂量减少作为螺距、扫描长度和在等中心的空气中总入射辐射、扫描体积中心的累积剂量以及从固定长度扫描体积的不同距离处的一个点的累积剂量的函数进行测量。在扫描的开始和中心测量图像噪声。
在等中心的空气中，总入射辐射分别减少了 27%和 3%（螺距为 0.5）和 46%和 8%（螺距为 1.5），扫描长度分别为 20 和 500mm。对于 20mm 的扫描，0.5 和 1.5 的螺距的扫描中心累积剂量的减少分别为 15%和 29%。对于大于 300mm 的扫描长度，所有螺距的剂量节省都小于 3%。距 100mm 扫描范围 80mm 或更远的剂量减少分别为 0.5 和 1.5 的 15%和 40%。使用动态 z 轴准直，与中心噪声相比，螺旋扫描的极端噪声保持不变。有效剂量的估计减少分别为 0.4mSv（头部）、0.8mSv 和 1.4mSv（胸部和肝脏）、0.8mSv（腹部和骨盆）以及 0.4mSv 和 55%（1.0mSv）对于螺距为 0.2 和 3.4 的冠状动脉 CT 血管造影。
使用动态 z 轴准直通过最小化过度扫描来降低螺旋 CT 的剂量。对于较短的扫描长度和较大的螺距值，剂量减少的百分比更大。
