Department of Physics, PO Box 64, FI-00014 University of Helsinki, Finland.
Measurements and Environmental Monitoring, Radiation and Nuclear Safety Authority (STUK), Jokiniemenkuja 1, FI-01370 Vantaa, Finland.
Biomed Phys Eng Express. 2024 Jun 13;10(4). doi: 10.1088/2057-1976/ad5206.
X-ray phase-contrast imaging has become a valuable tool for biomedical research due to its improved contrast abilities over regular attenuation-based imaging. The recently emerged Talbot-Lau interferometer can provide quantitative attenuation, phase-contrast and dark-field image data, even with low-brilliance x-ray tube sources. Thus, it has become a valid option for clinical environments. In this study, we analyze the effects of x-ray tube voltage and total number of images on the contrast-to-noise ratio (CNR) and dose-weighted CNR (CNRD) calculated from tomographic transmission and phase-contrast data of a phantom sample. Constant counting statistics regardless of the voltage was ensured by adjusting the image exposure time for each voltage setting. The results indicate that the x-ray tube voltage has a clear effect on both image contrast and noise. This effect is amplified in the case of phase-contrast images, which is explained by the polychromatic x-ray spectrum and the dependence of interferometer visibility on the spectrum. CNRD is additionally affected by the total imaging time. While submerging the sample into a water container effectively reduces image artefacts and improves the CNR, the additional attenuation of the water must be compensated with a longer exposure time. This reduces dose efficiency. Both the CNR and CNRD are higher in the phase-contrast images compared to transmission images. For transmission images, and phase-contrast images without the water container, CNRD can be increased by using higher tube voltages (in combination with a lower exposure time). For phase-contrast images with the water container, CNRD is increased with lower tube voltages. In general, the CNRD does not strongly depend on the number of tomographic angles or phase steps used.
X 射线相衬成像是一种有价值的生物医学研究工具，因为它比基于常规衰减的成像具有更好的对比度增强能力。最近出现的泰伯-劳厄干涉仪可以提供定量衰减、相衬和暗场图像数据，即使使用低亮度的 X 射线管源也是如此。因此，它已成为临床环境的有效选择。在这项研究中，我们分析了 X 射线管电压和总图像数量对来自幻影样本的断层透射和相衬数据计算的对比噪声比（CNR）和剂量加权 CNR（CNRD）的影响。通过调整每个电压设置的图像曝光时间，确保了恒定的计数统计数据，而与电压无关。结果表明，X 射线管电压对图像对比度和噪声都有明显的影响。这种影响在相衬图像中放大，这可以用多色 X 射线光谱和干涉仪可见度对光谱的依赖性来解释。CNRD 还受到总成像时间的影响。虽然将样品浸入水容器中可以有效地减少图像伪影并提高 CNR，但必须用更长的曝光时间来补偿水的额外衰减。这降低了剂量效率。与透射图像相比，相衬图像的 CNR 和 CNRD 都更高。对于透射图像和没有水容器的相衬图像，可以通过使用更高的管电压（与更低的曝光时间相结合）来提高 CNRD。对于具有水容器的相衬图像，CNRD 随着管电压的降低而增加。总的来说，CNRD 不强烈依赖于使用的断层角度或相阶的数量。
