Müller Mark, Yaroshenko Andre, Velroyen Astrid, Bech Martin, Tapfer Arne, Pauwels Bart, Bruyndonckx Peter, Sasov Alexander, Pfeiffer Franz
Lehrstuhl für Biomedizinische Physik, Physik-Department & Institut für Medizintechnik, Technische Universität München, 85748 Garching, Germany.
Medical Radiation Physics, Lund University, Barngatan 2:1, 221 85 Lund, Sweden.
Rev Sci Instrum. 2015 Dec;86(12):123705. doi: 10.1063/1.4938163.
In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed.
在生物医学X射线成像领域，诸如相衬成像和暗场成像等新技术有潜力提高对比度，并提供有关样本的补充结构信息。本文对基于塔尔博特-劳干涉仪的临床前X射线相衬CT扫描仪的首个原型进行了表征。我们对用该原型扫描仪获取的衰减图像和相衬图像的对比度噪声比进行了研究。所示结果基于一系列投影图像以及用不同采集设置记录的塑料模型的相衬和衰减对比度断层数据集。随后，确定了模型中不同区域的信号和噪声分布。我们提出了一种基于模型圆柱几何形状来估计投影图像对比度噪声比的新方法。将表示圆形物体在相衬和衰减对比度下预期信号的解析函数拟合到投影数据的各个线轮廓上。拟合函数的自由参数用于估计对比度，并通过确定拟合优度来评估相应信号中的噪声。结果描述了对比度噪声比对所施加源电压、相移例程的步数以及单个步长的曝光时间的依赖性。此外，还研究了投影角度数量对CT切片图像质量的影响。最后，讨论了该扫描仪对未来成像目的的意义。
