Chan Charles Tai Po, Fung Karl Ka Lok
Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong.
Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hong Kong.
J Med Imaging Radiat Sci. 2014 Sep;45(3):223-229. doi: 10.1016/j.jmir.2014.04.006. Epub 2014 Sep 13.
This study aimed at investigating the air kerma distribution of the radiation output in two and three dimensions of three general radiographic units by physical measurements.
A 6-cm ionization chamber was placed at 5-cm intervals of 225 locations in a 70 × 70 cm x-ray beam field. The chamber was placed at a level of 30 cm above the x-ray table to measure the air kerma intensity of the x-ray output across the whole area. Three different brands of radiographic units with different anode target angles and at different tube aging stages were studied. The same exposure parameters were used for each location, and measurements were made for three different tube potentials at 60, 85, and 110 kilovoltage peaks (kV[p]).
At the tube potential of 85 kV(p), the relative maximum percentage differences on the average air kerma measured along the central anode-cathode axis (x-axis) of the x-ray tube were found to be 31.5%, 15.5%, and 43.1% more at the cathode ends than those at the anode ends of the three radiographic units. Results of a paired samples t test (confidence intervals at 95%, two-tailed) on three of the four fixed pair-wise sampling points along the x-axis were found to be statistically significant in their relative percentage differences in air kerma intensity with respect to the central point (labeled as 35 cm) with a P value ≤.03. However, those measured at four fixed pair-wise points at 90° across the anode-cathode direction were all found to be statistically nonsignificant (P ≥ .29). Similar trends were observed for the other two tube potentials tested. From the three-dimensional displays of radiation output intensity, a similar unique pyramidal shape pattern with a skewed peak toward the cathode end was observed for all three diagnostic x-ray tubes tested.
The anode heel effect was found to be enhanced in the x-ray tube with a smaller anode target angle, more aging, and higher tube potentials. Three-dimensional air kerma distribution maps of the three x-ray units tested were found to be similar in pattern, and this was displayed in detail regarding the extent of the anode heel effect.
本研究旨在通过物理测量来调查三种普通X射线摄影设备在二维和三维空间中辐射输出的空气比释动能分布情况。
将一个6厘米的电离室放置在70×70厘米X射线束场中225个位置处，间隔5厘米。电离室放置在X射线检查台上方30厘米的高度，以测量整个区域内X射线输出的空气比释动能强度。研究了三种不同品牌、具有不同阳极靶角且处于不同管老化阶段的X射线摄影设备。每个位置使用相同的曝光参数，并在60、85和110千伏峰值（kV[p]）的三种不同管电压下进行测量。
在85 kV(p)的管电压下，发现沿X射线管中心阳极 - 阴极轴（x轴）测量的平均空气比释动能，在三种X射线摄影设备的阴极端比阳极端分别高出31.5%、15.5%和43.1%。在沿x轴的四个固定成对采样点中的三个点上进行的配对样本t检验（95%置信区间，双侧）结果显示，相对于中心点（标记为35厘米），其空气比释动能强度的相对百分比差异具有统计学意义，P值≤0.03。然而，在与阳极 - 阴极方向成90°的四个固定成对点处测量的结果均无统计学意义（P≥0.29）。在测试的其他两种管电压下也观察到了类似趋势。从辐射输出强度的三维显示中可以看出，对于所有测试的三种诊断X射线管，都观察到了类似的独特金字塔形状模式，其峰值向阴极端倾斜。
发现阳极靶角较小、老化程度较高和管电压较高的X射线管中，阳极足跟效应增强。测试的三种X射线设备的三维空气比释动能分布图在模式上相似，并且详细显示了阳极足跟效应的程度。
