Finney Laura
Health Physics, Ground Floor, West House, Gartnavel Royal Hospital, Glasgow, UK G12OXH.
Health Phys. 2004 May;86(5 Suppl):S88-9.
The total filtration of a fluoroscopy x-ray tube assembly may be deduced from the half value layer (HVL) of the x-ray beam at a specified tube voltage using published data tables. The HVL is usually measured by placing increasing thicknesses of Al plates between the focus and a dosimeter, and measuring the output while keeping the kV constant. However, on many of the newer fluoroscopy units, it is not possible to set the tube potential manually. This can create difficulties when measuring the HVL since the increasing thicknesses of aluminum trigger the automatic brightness control to adjust the kV and mA automatically, thus altering the tube output and HVL. This communication describes a simple but effective method to measure the amount of filtration on such units, which has the advantage of not requiring any extra equipment.
利用已发表的数据表，可根据在特定管电压下X射线束的半值层（HVL）推导出荧光透视X射线管组件的总过滤量。通常通过在焦点和剂量计之间放置厚度不断增加的铝板，并在保持千伏值恒定的同时测量输出，来测量半值层。然而，在许多新型荧光透视设备上，无法手动设置管电位。在测量半值层时，这可能会带来困难，因为铝板厚度的增加会触发自动亮度控制，从而自动调整千伏值和毫安值，进而改变管输出和半值层。本文介绍了一种简单而有效的方法来测量此类设备上的过滤量，其优点是不需要任何额外设备。
