长杆电离室中心与CT机光束之距对CTDIw测量影响

目的:多排CT在轴扫条件下长杆电离室中心偏离X线束平面的距离对CTDIw测量精度的影响。方法:用满足IEC标准的头部体模(T6M164)和长杆电离室测量PhilipBrillianceiCT256在轴扫条件下不同偏移距离时测CTDIw,并分析对CTDIw偏差的因素。结果:在偏离距离在±1cm处,CTDIw的相对偏差在±5%以内;偏移距离在±3cm,相对偏差在-5%～15%之间;当偏移距离在±5cm时,CTDIw的测量偏差在40%～70%之间。结论:对CTDIw测量偏差影响较大的因素是偏移距离,而毫安秒和管电压对CTDIw测量偏差之间相关性低;毫安秒和管电压可能影响某个偏移距离处CTDIw测量偏差的区间范围;剂量在z轴上分布具有不对称性。

The Influence of Offset Distance between Penciled Ionization Chamber and CT X-ray Beam to CTDIw Measurement

Objective:d ionization chamber and X-ray beam plane on relevant deviation(RD),on behalf of the accuracy of CTDIw measurement,while The influence of offset distance(OD)between the center of pencile conducting axial scanning with multi-detector CT.Method:A head phantom(in compliance with ICE standard) and penciled ionization chamber are utilized to measure the CTDIw at variant OD with Philip Brilliance iCT256 using axial scanning,meanwhile,impact factors on RD were analyzed.Result:when offset distance(OD)equal to ±1 cm,the relevant deviation(RD)within the range of±5%;when OD equal to±3 cm,RD within the range of -5%~15%,and when OD equal to±5 cm,RD within the range of 40%~70%.Conclusion:OD is considered as a main impact factor to RD,while the milliampere time second(mAs)and tube voltage have little relevance on RD. However,mAs and tube voltage might affect the value range of RD at a certain OD.More importantly,dose distribution along Z axial exhibits asymmetry.