[论文解读] Admire vs. Safire: Objective comparison of CT reconstruction algorithms and their noise properties

Ingvild Dalehaug, Kirsten Nygaard Bolstad+3 more|arXiv (Cornell University)|Aug 31, 2017

Radiation Dose and Imaging参考文献 13被引用 6

一句话总结

本研究通过噪声功率谱（NPS）分析和图像间标准差图，客观比较了西门子CT成像中ADMIRE与SAFIRE迭代重建算法的降噪性能。结果表明，ADMIRE在减少边缘附近噪声方面优于SAFIRE，但未观察到噪声纹理保留的显著改善，且在低剂量下由于向较低空间频率偏移，ADMIRE产生更明显的斑点状图像。

ABSTRACT

Purpose: Siemens has developed several iterative reconstruction (IR) algorithms on their CT scanners. SAFIRE is available on most of their CT scanners. The latest algorithm, ADMIRE, is available on their newest high-end CT scanners. The aim of our study was to compare the noise reduction properties of the two IR algorithms using objective methods. Methods and Materials: The homogeneous module of the Catphan phantom was scanned on a Siemens AS+ and a Siemens Flash CT scanner using an axial abdomen protocol with fixed tube current at two dose levels. The images were reconstructed with an abdomen filter (B30) using filtered back projection (FBP) and a low, medium, and high level of SAFIRE or ADMIRE. Noise Power Spectrum (NPS) curves were calculated using these images. Then, an anthropomorphic abdomen phantom (Kyoto Kagaku PH-5) was scanned using the same setup and exposure parameters. Fifty axial images at the same slice location were used to calculate inter-image standard deviation maps. Results: At full dose, the median values of the NPS curves were similar for both scanners at all IR levels. At low dose the median values of the NPS curves were generally shifted towards lower spatial frequencies, usually resulting in a more blotchy image texture. This shift was more prominent for ADMIRE compared to SAFIRE for all IR levels. Based on the inter-image standard deviation maps of the anthropomorphic phantom, ADMIRE removed noise near edges more efficiently than SAFIRE. Conclusion: No significant improvement in maintaining noise structure were found for the ADMIRE algorithm. Based on the inter-image standard deviation maps, ADMIRE removed noise near edges more efficiently than SAFIRE.

研究动机与目标

• 客观评估并比较CT成像中两种迭代重建算法ADMIRE与SAFIRE的降噪性能。
• 利用定量指标评估每种算法对图像噪声纹理及空间频率分布的影响。
• 研究ADMIRE在低剂量扫描协议下是否相比SAFIRE具有更优的噪声结构保留能力。
• 在相同扫描条件下，使用均匀体模和解剖型体模评估两种算法的性能。

提出的方法

• 在两台西门子CT扫描仪（AS+和Flash）上，使用轴向腹部协议对Catphan体模的均匀模块进行扫描，剂量水平分为全剂量和低剂量。
• 使用滤波反投影（FBP）及三种不同强度（低、中、高）的SAFIRE与ADMIRE进行图像重建，采用腹部专用重建核（B30）。
• 从重建图像中计算噪声功率谱（NPS）曲线，以分析噪声的空间频率分布。
• 对解剖型腹部体模（Kyoto Kagaku PH-5）进行扫描，以评估扫描间的噪声变异性。
• 从同一解剖位置的50张轴向切片中计算图像间标准差图，以量化重复扫描间的噪声差异。
• 对不同剂量水平下ADMIRE与SAFIRE的NPS中位数及标准差图进行统计比较。

实验结果

研究问题

• RQ1 在全剂量和低剂量下，ADMIRE与SAFIRE的NPS中位数值有何差异？
• RQ2 ADMIRE在空间频率分布方面是否比SAFIRE更好地保留了噪声纹理？
• RQ3 与SAFIRE相比，ADMIRE在解剖边缘附近减少噪声的程度如何？
• RQ4 在低剂量下，ADMIRE与SAFIRE的NPS曲线向较低空间频率偏移的程度有何不同？
• RQ5 与SAFIRE相比，ADMIRE是否表现出可测量的扫描间噪声一致性提升？

主要发现

• 在全剂量下，两台扫描仪上所有IR等级的ADMIRE与SAFIRE的NPS中位数值相似。
• 在低剂量下，两种算法均使NPS曲线向较低空间频率偏移，但ADMIRE的偏移更为显著。
• ADMIRE导致NPS向低频偏移，从而产生比SAFIRE更明显的斑点状图像纹理。
• 图像间标准差图显示，ADMIRE在边缘区域的噪声减少效果优于SAFIRE。
• 尽管边缘噪声减少效果更优，但ADMIRE在噪声结构保留方面并未显著优于SAFIRE。
• 本研究未发现ADMIRE在噪声纹理保留方面具有明显优势，表明SAFIRE能保持更自然的噪声外观。