Department of Medical Imaging, CHU Nimes, Univ Montpellier, Medical Imaging Group Nimes, EA 2415, Nîmes, France.
Department of Medical Imaging, CHU Nimes, Univ Montpellier, Medical Imaging Group Nimes, EA 2415, Nîmes, France.
Phys Med. 2020 Sep;77:36-42. doi: 10.1016/j.ejmp.2020.07.024. Epub 2020 Aug 6.
To assess the impact of iterative reconstructions on image quality and detectability of focal liver lesions in low-energy monochromatic images from a Fast kV-Switching Dual Energy CT (KVSCT) platform.
Acquisitions on an image-quality phantom were performed using a KVSCT for three dose levels (CTDI:12.72/10.76/8.79 mGy). Raw data were reconstructed for five energy levels (40/50/60/70/80 keV) using Filtered Back Projection (FBP) and four levels of ASIR (ASIR30/ASIR50/ASIR70/ASIR100). Noise power spectrum (NPS) and task-based transfer function (TTF) were measured before computing a Detectability index (d') to model the detection task of liver metastasis (LM) and hepatocellular carcinoma (HCC) as function of keV.
From 40 to 70 keV, noise-magnitude was reduced on average by -68% ± 1% with FBP; -61% ± 3% with ASIR50 and -52% ± 6% with ASIR100. The mean spatial frequency of the NPS decreased when the energy level decreased and the iterative level increased. TTF values at 50% decreased as the energy level increased and as the percentage of ASIR increased. The detectability of both lesions increased with increasing dose level and percentage of ASIR. For the LM, d' peaked at 70 keV for all reconstruction types, except for ASIR70 at 12.72 mGy and ASIR100, where d' peaked at 50 keV. For HCC, d' peaked at 60 keV for FBP and ASIR30 but peaked at 50 keV for ASIR50, ASIR70 and ASIR100.
Using percentage of ASIR above 50% at low-energy monochromatic images could limit the increase of noise-magnitude, benefit from spatial resolution improvement and hence enhance detectability of subtle low contrast focal liver lesions such as HCC.
评估迭代重建对 Fast kV-Switching 双能 CT（KVSCT）平台低能单色图像的图像质量和局灶性肝病变检测能力的影响。
使用 KVSCT 在三个剂量水平（CTDI：12.72/10.76/8.79 mGy）对图像质量体模进行采集。使用滤波反投影（FBP）和四个 ASIR 水平（ASIR30/ASIR50/ASIR70/ASIR100）对五种能量水平（40/50/60/70/80 keV）重建原始数据。在计算检测肝脏转移（LM）和肝细胞癌（HCC）的检测能力（d'）之前，测量噪声功率谱（NPS）和基于任务的传递函数（TTF），以作为 keV 的函数来模拟 LM 和 HCC 的检测任务。
从 40 到 70 keV，FBP 平均降低噪声幅度为-68%±1%；ASIR50 为-61%±3%；ASIR100 为-52%±6%。随着能量水平降低和迭代水平增加，NPS 的平均空间频率降低。当能量水平增加和 ASIR 百分比增加时，50%的 TTF 值降低。两种病变的检测能力都随着剂量水平和 ASIR 百分比的增加而增加。对于 LM，除了 12.72 mGy 时 ASIR70 和 ASIR100 的情况下，所有重建类型的 d'在 70 keV 时达到峰值，而在 HCC 中，FBP 和 ASIR30 的 d'在 60 keV 时达到峰值，而 ASIR50、ASIR70 和 ASIR100 的 d'在 50 keV 时达到峰值。
在低能单色图像中使用超过 50%的 ASIR 百分比可以限制噪声幅度的增加，从空间分辨率的提高中受益，并提高 HCC 等细微低对比度局灶性肝病变的检测能力。
