Hagen Charlotte Klara, Roche I Morgó Oriol, Olivo Alessandro
Department of Medical Physics and Biomedical Engineering, University College London, Malet Place, Gower Street, London, WC1E 6BT, UK.
Med Phys. 2020 Sep;47(9):4439-4449. doi: 10.1002/mp.14366. Epub 2020 Jul 19.
To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each other. The second objective is to compare the hybrid images with attenuation-only images based on their respective signal-to-noise ratio (SNR).
Noise is propagated from the raw images into the retrieved hybrid images, yielding analytic expressions for the variances and noise power spectra of the latter. An expression for the relative SNR between hybrid and attenuation images is derived. A comparison with simulated data is performed. Experimental data are also shown and discussed in the context of the theory.
The noise transfer into the retrieved hybrid images is strongly related to the setup and acquisition parameters, as well as the imaged sample itself. Consequently, the relative merit between hybrid and attenuation images also depends on these criteria. Generally, the hybrid approach tends to perform worse for highly attenuating samples, as the availability of phase contrast is outweighed by the loss of photons that is necessarily encountered in hybrid acquisitions. On the contrary, the hybrid approach can lead to a much better SNR for weakly attenuating samples, as here phase effects lead to much stronger contrast, outweighing the reduction in photon numbers.
The analytic expressions inform the design of edge illumination setups that lead to minimum noise transfer into the retrieved hybrid images. We also anticipate our theory to guide the decision as to which imaging mode (hybrid or attenuation) to use in order to maximize SNR for a specific sample.
分析在应用“单次”相位恢复时基于边缘照明相位的X射线成像技术的噪声性能。后者包括对原始数据应用特定于样品的低通滤波器，从而产生“混合”图像，其中相位和衰减对比度相互融合。第二个目标是根据混合图像和仅基于衰减的图像各自的信噪比（SNR）对它们进行比较。
噪声从原始图像传播到恢复的混合图像中，得出后者的方差和噪声功率谱的解析表达式。推导了混合图像与衰减图像之间相对信噪比的表达式。与模拟数据进行了比较。还展示了实验数据并在理论背景下进行了讨论。
噪声向恢复的混合图像中的传递与设置和采集参数以及成像样品本身密切相关。因此，混合图像和衰减图像之间的相对优劣也取决于这些标准。一般来说，对于高衰减样品，混合方法往往表现较差，因为在混合采集中必然会遇到光子损失，这使得相位对比度的可用性相形见绌。相反，对于弱衰减样品，混合方法可以导致更好的信噪比，因为在这里相位效应会导致更强的对比度，超过光子数量的减少。
解析表达式为边缘照明设置提供了指导，这些设置可使噪声向恢复的混合图像中的传递最小化。我们还期望我们的理论能够指导关于使用哪种成像模式（混合或衰减）的决策，以便为特定样品最大化信噪比。
