Department of Medical Physics and Bioengineering, University College London, London, WC1E 6BT, UK.
Med Phys. 2017 May;44(5):1876-1885. doi: 10.1002/mp.12179. Epub 2017 Apr 3.
This article is aimed at comparing edge illumination (EI) x-ray phase contrast computed tomography (PCT) and conventional (attenuation-based) computed tomography (CT), based on their respective contrast and noise transfer.
The noise in raw projections obtained with EI PCT is propagated through every step of the data processing, including phase retrieval and tomographic reconstruction, leading to a description of the noise in the reconstructed phase tomograms. This is compared to the noise in corresponding attenuation tomograms obtained with CT. Specifically, a formula is derived that allows evaluating the relative performance of both modalities on the basis of their contrast-to-noise ratio (CNR), for a variety of experimental parameters.
The noise power spectra of phase tomograms are shifted towards lower spatial frequencies, leading to a fundamentally different noise texture. The relative performance of EI PCT and CT, in terms of their CNR, is linked to spatial resolution: the CNR in phase tomograms is generally superior to that in attenuation tomograms for higher spatial resolutions (tens to hundreds of μm), but inferior for lower spatial resolutions (hundreds of μm to mm).
These results imply that EI PCT could outperform CT in applications for which high spatial resolutions are key, e.g., small animal or specimen imaging.
本文旨在比较边缘照明（EI）X 射线相衬计算机断层扫描（PCT）和传统（基于衰减的）计算机断层扫描（CT），基于它们各自的对比度和噪声传递。
EI PCT 获得的原始投影中的噪声通过数据处理的每一步进行传播，包括相位恢复和层析重建，从而描述重建的相层析图像中的噪声。这与 CT 获得的相应衰减层析图像中的噪声进行了比较。具体而言，推导出了一个公式，该公式允许根据对比度噪声比（CNR）评估两种模态的相对性能，针对各种实验参数。
相层析图像的噪声功率谱向较低的空间频率移动，导致根本不同的噪声纹理。EI PCT 和 CT 的相对性能，以 CNR 为单位，与空间分辨率有关：对于较高的空间分辨率（数十至数百微米），相层析图像中的 CNR 通常优于衰减层析图像中的 CNR，但对于较低的空间分辨率（数百微米至毫米）则较差。
这些结果表明，在需要高空间分辨率的应用中，EI PCT 可能优于 CT，例如小动物或标本成像。
