School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia. School of Mathematics and Statistics, College of Engineering, University of Canterbury, Ilam, Christchurch, 8041, New Zealand.
Phys Med Biol. 2020 Sep 18;65(18):185014. doi: 10.1088/1361-6560/ab9558.
This paper expands the linear iterative near-field phase retrieval (LIPR) formalism to achieve quantitative material thickness decomposition. Propagation-based phase contrast x-ray imaging with subsequent phase retrieval has been shown to improve the signal-to-noise ratio (SNR) by factors of up to hundreds compared to conventional x-ray imaging. This is a key step in biomedical imaging, where radiation exposure must be kept low without compromising the SNR. However, for a satisfactory phase retrieval from a single measurement, assumptions must be made about the object investigated. To avoid such assumptions, we use two measurements collected at the same propagation distance but at different x-ray energies. Phase retrieval is then performed by incorporating the Alvarez-Macovski (AM) model, which models the x-ray interactions as being comprised of distinct photoelectric and Compton scattering components. We present the first application of dual-energy phase retrieval with the AM model to monochromatic experimental x-ray projections at two different energies for obtaining split x-ray interactions. Our phase retrieval method allows us to separate the object investigated into the projected thicknesses of two known materials. Our phase retrieval output leads to no visible loss in spatial resolution while the SNR improves by factors of 2 to 10. This corresponds to a possible x-ray dose reduction by a factor of 4 to 100, under the Poisson noise assumption.
本文将线性迭代近场相位恢复（LIPR）公式扩展到实现定量材料厚度分解。基于传播的相衬 X 射线成像与后续的相位恢复已被证明可以将信号噪声比（SNR）提高数百倍，与传统的 X 射线成像相比。这是生物医学成像中的关键步骤，其中必须在不影响 SNR 的情况下将辐射暴露保持在低水平。然而，为了从单次测量中获得令人满意的相位恢复，必须对所研究的物体做出假设。为了避免这种假设，我们使用在相同传播距离但不同 X 射线能量下收集的两个测量值。然后通过包含 Alvarez-Macovski（AM）模型来执行相位恢复，该模型将 X 射线相互作用建模为由明显的光电和康普顿散射分量组成。我们首次将双能相位恢复与 AM 模型应用于两种不同能量的单色实验 X 射线投影，以获得分裂的 X 射线相互作用。我们的相位恢复方法允许我们将所研究的物体分解为两个已知材料的投影厚度。我们的相位恢复输出不会导致空间分辨率明显下降，而 SNR 则提高了 2 到 10 倍。在泊松噪声假设下，这对应于 X 射线剂量可能降低 4 到 100 倍。
