Pahn Gregor, Skornitzke Stephan, Schlemmer Hans-Peter, Kauczor Hans-Ulrich, Stiller Wolfram
Clinic of Diagnostic and Interventional Radiology (DIR), University Hospital Heidelberg, Heidelberg, Germany.
Department of Radiology (E010), German Cancer Research Center (DKFZ), Heidelberg, Germany.
Phys Med. 2016 Jan;32(1):104-15. doi: 10.1016/j.ejmp.2015.09.017. Epub 2015 Oct 28.
Based on the guidelines from "Report 87: Radiation Dose and Image-quality Assessment in Computed Tomography" of the International Commission on Radiation Units and Measurements (ICRU), a software framework for automated quantitative image quality analysis was developed and its usability for a variety of scientific questions demonstrated.
The extendable framework currently implements the calculation of the recommended Fourier image quality (IQ) metrics modulation transfer function (MTF) and noise-power spectrum (NPS), and additional IQ quantities such as noise magnitude, CT number accuracy, uniformity across the field-of-view, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of simulated lesions for a commercially available cone-beam phantom. Sample image data were acquired with different scan and reconstruction settings on CT systems from different manufacturers.
Spatial resolution is analyzed in terms of edge-spread function, line-spread-function, and MTF. 3D NPS is calculated according to ICRU Report 87, and condensed to 2D and radially averaged 1D representations. Noise magnitude, CT numbers, and uniformity of these quantities are assessed on large samples of ROIs. Low-contrast resolution (CNR, SNR) is quantitatively evaluated as a function of lesion contrast and diameter. Simultaneous automated processing of several image datasets allows for straightforward comparative assessment.
The presented framework enables systematic, reproducible, automated and time-efficient quantitative IQ analysis. Consistent application of the ICRU guidelines facilitates standardization of quantitative assessment not only for routine quality assurance, but for a number of research questions, e.g. the comparison of different scanner models or acquisition protocols, and the evaluation of new technology or reconstruction methods.
根据国际辐射单位与测量委员会（ICRU）“第87号报告：计算机断层扫描中的辐射剂量与图像质量评估”的指南，开发了一个用于自动定量图像质量分析的软件框架，并展示了其对各种科学问题的适用性。
这个可扩展框架目前实现了推荐的傅里叶图像质量（IQ）指标调制传递函数（MTF）和噪声功率谱（NPS）的计算，以及其他IQ量，如噪声幅度、CT值准确性、视野内的均匀性、针对商用锥束体模的模拟病变的对比噪声比（CNR）和信噪比（SNR）。使用来自不同制造商的CT系统，在不同的扫描和重建设置下采集样本图像数据。
从边缘扩展函数、线扩展函数和MTF方面分析空间分辨率。根据ICRU第87号报告计算三维NPS，并将其浓缩为二维和径向平均一维表示形式。在大量感兴趣区域（ROI）样本上评估这些量的噪声幅度、CT值和均匀性。低对比度分辨率（CNR、SNR）作为病变对比度和直径的函数进行定量评估。对多个图像数据集的同时自动处理允许进行直接的比较评估。
所提出的框架实现了系统、可重复、自动化且高效的定量IQ分析。一致应用ICRU指南不仅有助于常规质量保证的定量评估标准化，而且有助于许多研究问题的标准化，例如不同扫描仪型号或采集协议的比较，以及新技术或重建方法的评估。
