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最近Deak等采用剂量测量与蒙特卡罗(MC）剂量模拟法评价了适当准直器宽度对降低CTz-向重叠扫描剂量的作用。
对不用和采用适当准直器宽度按照心脏与胸部螺旋CT扫描参数对Alderson-Rando模型扫描，采用CT剂量指数模型，热释光剂量计测量X线剂量并与MC模型剂量进行对照研究。另外采用电离室对扫描范围5－50cm、螺距为0.5－1.5的扫描剂量进行测量。结果显示：测量剂量与模拟剂量一致性在3％之内。使用准直器宽度对心脏与胸部进行CT扫描，空气内自由测量剂量明显降低，降低幅度达到10％；而模型测量平均下降了7％。扫描范围小于12cm时，电离室测量与模拟剂量下降达38％。因此适当准直器宽度可显著降低螺旋CT Z向重叠扫描中不必要的曝光。该技术可与其他降低剂量的方法协同应用（如扫描方案优化和自动曝光控制）。
Effects of adaptive section collimation on patient radiation dose in multisection spiral CT.
PURPOSE: To evaluate the potential effectiveness of adaptive collimation in reducing computed tomographic (CT) radiation dose owing to z-overscanning by using dose measurements and Monte Carlo (MC) dose simulations.
MATERIALS AND METHODS: Institutional review board approval was not necessary. Dose profiles were measured with thermoluminescent dosimeters in CT dose index phantoms and in an Alderson-Rando phantom without and with adaptive section collimation for spiral cardiac and chest CT protocols and were compared with the MC simulated dose profiles. Additional dose measurements were performed with an ionization chamber for scan ranges of 5-50 cm and pitch factors of 0.5-1.5.
RESULTS: The measured and simulated dose profiles agreed to within 3%. By using adaptive section collimation, a substantial dose reduction of up to 10% was achieved for cardiac and chest CT when measurements were performed free in air and of 7% on average when measurements were performed in phantoms. For scan ranges smaller than 12 cm, ionization chamber measurements and simulations indicated a dose reduction of up to 38%.
CONCLUSION: Adaptive section collimation allows substantial reduction of unnecessary exposure owing to z-overscanning in spiral CT. It can be combined in synergy with other means of dose reduction, such as spectral optimization and automatic exposure control. (c) RSNA, 2009.
英文原文来源Deak PD, Langner O, Lell M, Kalender WA.Radiology. 2009 Jul;252(1):140-7.
文章来自：影像园
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