Regional Cooperation Research Center of Life and Material Sciences, University of Szeged, Dugonics tér 13, 6720 Szeged, Hungary.
Med Phys. 2010 Nov;37(11):5737-45. doi: 10.1118/1.3495541.
Spectral and angular distribution of the x-ray beam generated by medical x-ray tubes as a function of anode surface roughness was analyzed.
Different sets of profiles such as ideal flat, regular profiles, and measured profiles adopted from the literature were analyzed by means of MCNPX Monte Carlo simulator. The geometry used was simplified to separate different physical effects. A sphere centered on the origin of the coordinate system was divided into two hemispheres filled with tungsten and a vacuum, respectively. The studied anode surfaces were placed at the center of the plane of the hemisphere. The profiles were realized by means of the general lattice structure of the MCNPX. The energy and angular distributions of the excited photons were recorded with energy and angular resolutions of 0.5 keV and 1 degrees, respectively, by means of point detectors. The range of the studied anode surface roughness was 0-550 micro Ra. The emission angle dependencies of the following quantities were analyzed: Half value layer (HVL) value, intensity, and spectral photon flux.
The analysis of the HVL of the x-ray beam showed that around an emission angle of 5 degrees, the hardness of the beam was practically independent of the surface roughness. The value of this emission angle depends on the filtration. Below this critical angle, the HVL value decreases, while at a higher emission angle, the beam becomes harder with increasing surface roughness. The intensity degradation saturates with increasing roughness. The position of the maximum spectral photon flux shifts to higher emission angles as the anode surface roughness increases. The surface roughness (Ra) was found to be an inadequate quantity to describe the effect of anode surface roughness on x-ray spectra since no definite connection was found between the values of the intensity degradation and surface roughness. At 120 kVp tube voltage and at a 3.84 microm Ra roughness value, the effect of anode surface roughness introduces a 5% and 12% intensity degradation at a 5 degrees and 12 degrees emission angle, respectively. However, it has a higher impact at low tube voltages (<60 keV), e.g., in mammography systems where the intensity degradation could even be 25% at the "newly" polished anode surface.
The effects of anode surface roughness on x-ray spectra were successfully simulated by a Monte Carlo method. It was proved that the effect of the anode surface roughness could not be modeled by simple filters made from the anode material. The surface roughness (Ra) was found to be an inadequate quantity to describe the effect of anode surface roughness on x-ray spectra.
分析了作为阳极表面粗糙度函数的医用 X 射线管产生的 X 射线束的光谱和角度分布。
通过 MCNPX 蒙特卡罗模拟器分析了不同的轮廓集，如理想平面、规则轮廓和文献中采用的测量轮廓。使用的几何形状被简化以分离不同的物理效应。一个以坐标系原点为中心的球体被分为两个半球，分别填充钨和真空。研究的阳极表面放置在半球平面的中心。通过 MCNPX 的通用晶格结构来实现轮廓。通过点探测器以 0.5keV 和 1 度的能量和角度分辨率记录激发光子的能量和角度分布。研究的阳极表面粗糙度范围为 0-550 微米 Ra。分析了以下量的发射角依赖性：半值层（HVL）值、强度和光谱光子通量。
X 射线束的 HVL 分析表明，在发射角约为 5 度时，光束的硬度实际上与表面粗糙度无关。该发射角的值取决于过滤。低于这个临界角，HVL 值减小，而在更高的发射角，随着表面粗糙度的增加，光束变得更硬。随着粗糙度的增加，强度衰减趋于饱和。随着阳极表面粗糙度的增加，最大光谱光子通量的位置向更高的发射角移动。表面粗糙度（Ra）被发现是描述阳极表面粗糙度对 X 射线光谱影响的不充分数量，因为在强度衰减值和表面粗糙度值之间没有发现明确的联系。在 120kVp 管电压和 3.84μm Ra 粗糙度值下，阳极表面粗糙度的影响在 5 度和 12 度发射角下分别引入 5%和 12%的强度衰减。然而，在低管电压（<60keV）下，它的影响更大，例如在乳腺摄影系统中，阳极表面新抛光后的强度衰减甚至可能达到 25%。
通过蒙特卡罗方法成功模拟了阳极表面粗糙度对 X 射线光谱的影响。证明了阳极表面粗糙度的影响不能用阳极材料制成的简单滤波器来建模。表面粗糙度（Ra）被发现是描述阳极表面粗糙度对 X 射线光谱影响的不充分数量。
