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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。
OBJECTIVE: The influence of the distance from the plane of X-ray beam on the centerline of long pole ionization chamber under multi-row CT scanning under axial scanning conditions on the measurement accuracy of CTDIw. Methods: The CTDIw was measured with a head phantom (T6M164) meeting the IEC standard and a Philip Barilli CT 256 under the long shaft ionization chamber at different offset distances under axial sweeping conditions. The factors affecting the CTDIw deviation were analyzed. Results: The relative deviation of CTDIw was within ± 5% at a deviation of ± 1 cm, the offset distance was ± 3 cm and the relative deviation was between -5% and 15%. When the offset distance was ± 5 cm, CTDIw Measurement deviation between 40% to 70%. CONCLUSIONS: The major contributor to the CTDIw measurement bias is the offset distance, and the milliampere seconds and tube voltage have a low correlation with the CTDIw measurement bias; milliampere seconds and tube voltage may affect the CTDIw measurement bias at an offset distance Of the interval range; dose distribution in the z-axis asymmetry.