Medical Physics Department, University General Hospital of Heraklion, Stavrakia 71110, Crete, Greece.
Medical Physics Department, University General Hospital of Heraklion, Stavrakia 71110, Crete, Greece.
Phys Med. 2021 Jun;86:75-81. doi: 10.1016/j.ejmp.2021.05.025. Epub 2021 May 29.
To assess the task-based performance of images obtained under different focal spot size and acquisition mode on a dual-energy CT scanner.
Axial CT image series of the Catphan phantom were obtained using a tube focus at different sizes. Acquisitions were performed in standard single-energy, high resolution (HR) and dual-energy modes. Images were reconstructed using conventional and high definition (HD) kernels. Task-based transfer function at the 50% level (TTF) for teflon, delrin, low density polyethylene (LDPE) and acrylic, as well as image noise and noise texture, were assessed across all focal spots and acquisition modes using Noise Power Spectrum (NPS) analysis. A non-prewhitening mathematical observer model was used to calculate detectability index (d).
TTF degraded with increasing focal spot size. TTF ranged from 0.67 mm for teflon to 0.25 mm for acrylic. For standard kernel, image noise and NPS-determined average spatial frequency were 8.3 HU and 0.29 mm, respectively in single-energy, 12.0 HU and 0.37 mm in HR, and 7.9 HU and 0.26 mm in dual-energy mode. For standard kernel, d was 61 in single-energy and HR mode and reduced to 56 in dual-energy mode.
The task-based image quality assessment metrics have shown that spatial resolution is higher for higher image contrast materials and detectability is higher in the standard single-energy mode compared to HR and dual-energy mode. The results of the current study provide CT operators the required knowledge to characterize their CT system towards the optimization of its clinical performance.
评估在双能 CT 扫描仪上使用不同焦点大小和采集模式获得的图像的基于任务的性能。
使用不同大小的管焦点对 Catphan 体模的轴向 CT 图像系列进行采集。在标准单能量、高分辨率（HR）和双能量模式下进行采集。使用常规和高清晰度（HD）内核进行图像重建。使用噪声功率谱（NPS）分析评估所有焦点和采集模式下特氟隆、聚缩醛、低密度聚乙烯（LDPE）和丙烯酸的 50% 水平的转移函数（TTF）以及图像噪声和噪声纹理。使用非预白化的数学观察者模型计算可检测性指数（d）。
TTF 随焦点尺寸的增加而降低。TTF 范围从特氟隆的 0.67mm 到丙烯酸的 0.25mm。对于标准内核，图像噪声和 NPS 确定的平均空间频率分别为单能量模式下的 8.3HU 和 0.29mm，HR 模式下的 12.0HU 和 0.37mm，双能量模式下的 7.9HU 和 0.26mm。对于标准内核，d 在单能量和 HR 模式下为 61，在双能量模式下降至 56。
基于任务的图像质量评估指标表明，空间分辨率对于更高的图像对比度材料更高，并且在标准单能量模式下的检测能力高于 HR 和双能量模式。当前研究的结果为 CT 操作人员提供了表征其 CT 系统的必要知识，以优化其临床性能。
