Nishiki Masayuki, Yanagita Satoshi, Nishikawa Noriko, Sugimura Hitomi
International University of Health and Welfare, Department of Radiological Sciences, Ohtawara, Japan.
Tsukuba International University, Department of Radiological Technology, Tsuchiura, Japan.
J Med Imaging (Bellingham). 2020 Mar;7(2):023502. doi: 10.1117/1.JMI.7.2.023502. Epub 2020 Mar 23.
For the focal spot measurement of x-ray tubes, we propose a practical method in which only a metal edge and a digital detector are used, together with a process of removing detector blur inherently associated. The evaluation was made through the optical transfer function (OTF) measurements using the edge response of a 1-mm-thick tungsten plate. First, we made the acquisition of a geometrically magnified edge response, which consists of focal spot penumbra and detector blur, followed by the acquisition of nonmagnified edge response, which includes only detector blur. Then the detector blur was removed by taking the ratio of the two OTFs. Finally, the focal spot profile was obtained by the inverse Fourier transform of this ratio. Resultant full widths at the half-maximum of a small focus profile were for the proposed method and for the conventional slit method with film, indicating excellent agreement between both methods. Comparing between results obtained using two flat panel detectors with different pixel pitches (0.143 and 0.175 mm) confirmed no differences with these variations. Through the whole study, the accuracy and the practicality of the proposed method were demonstrated, indicating a possibility of the method to be widely used to evaluate the effective focal spot size and profile of x-ray systems.
对于X射线管的焦点测量，我们提出了一种实用方法，该方法仅使用金属边缘和数字探测器，并结合去除固有相关探测器模糊的过程。通过使用1毫米厚钨板的边缘响应进行光学传递函数（OTF）测量来进行评估。首先，采集由焦点半影和探测器模糊组成的几何放大边缘响应，然后采集仅包括探测器模糊的非放大边缘响应。然后通过取两个OTF的比值去除探测器模糊。最后，通过该比值的逆傅里叶变换获得焦点轮廓。所提出方法得到的小焦点轮廓的半高全宽为 ，传统胶片狭缝法得到的半高全宽为 ，表明两种方法之间具有极好的一致性。比较使用不同像素间距（0.143和0.175毫米）的两个平板探测器获得的结果，证实这些变化没有差异。通过整个研究，证明了所提出方法的准确性和实用性，表明该方法有可能广泛用于评估X射线系统的有效焦点尺寸和轮廓。
