Department of Medical Physics and Bioengineering, University College London, Torrington Place, London WC1E 6BT, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Aug 28;109(35):13922-7. doi: 10.1073/pnas.1205396109. Epub 2012 Aug 13.
X-ray phase contrast imaging has overcome the limitations of X-ray absorption imaging in many fields. Particular effort has been directed towards developing phase retrieval methods: These reveal quantitative information about a sample, which is a requirement for performing X-ray phase tomography, allows material identification and better distinction between tissue types, etc. Phase retrieval seems impossible with conventional X-ray sources due to their low spatial coherence. In the only previous example where conventional sources have been used, collimators were employed to produce spatially coherent secondary sources. We present a truly incoherent phase retrieval method, which removes the spatial coherence constraints and employs a conventional source without aperturing, collimation, or filtering. This is possible because our technique, based on the pixel edge illumination principle, is neither interferometric nor crystal based. Beams created by an X-ray mask to image the sample are smeared due to the incoherence of the source, yet we show that their displacements can still be measured accurately, obtaining strong phase contrast. Quantitative information is extracted from only two images rather than a sequence as required by several coherent methods. Our technique makes quantitative phase imaging and phase tomography possible in applications where exposure time and radiation dose are critical. The technique employs masks which are currently commercially available with linear dimensions in the tens of centimeters thus allowing for a large field of view. The technique works at high photon energy and thus promises to deliver much safer quantitative phase imaging and phase tomography in the future.
X 射线相衬成像在许多领域克服了 X 射线吸收成像的局限性。人们特别致力于开发相位恢复方法：这些方法揭示了样品的定量信息，这是进行 X 射线相层析成像的要求，允许进行材料识别并更好地区分组织类型等。由于传统 X 射线源的空间相干性低，相位恢复似乎是不可能的。在仅有的以前使用传统源的示例中，使用准直器产生空间相干的次级源。我们提出了一种真正的非相干相位恢复方法，该方法消除了空间相干性约束，并使用常规源而无需孔径、准直或滤波。这是可能的，因为我们的技术基于像素边缘照明原理，既不是干涉的也不是基于晶体的。由于源的非相干性，用于对样品成像的 X 射线掩模产生的光束会模糊，但我们表明仍然可以准确测量它们的位移，从而获得强的相位对比度。与几种相干方法要求的序列相比，仅从两个图像中提取定量信息。我们的技术使得在曝光时间和辐射剂量至关重要的应用中进行定量相位成像和相位层析成像成为可能。该技术使用的掩模目前在商业上可用，线性尺寸为几十厘米，从而允许大的视场。该技术在高光子能量下工作，因此有望在未来提供更安全的定量相位成像和相位层析成像。
