Department of Radiology, CT Clinical Innovation Center, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
Med Phys. 2012 Jan;39(1):214-23. doi: 10.1118/1.3665767.
Partial scan reconstruction (PSR) artifacts are present in myocardial perfusion imaging using dynamic multidetector computed tomography (MDCT). PSR artifacts appear as temporal CT number variations due to inconsistencies in the angular data range used to reconstruct images and compromise the quantitative value of myocardial perfusion when using MDCT. The purpose of this work is to present and evaluate a technique termed targeted spatial frequency filtration (TSFF) to reduce CT number variations due to PSR when applied to myocardial perfusion imaging using MDCT.
The TSFF algorithm requires acquiring enough X-ray projections to reconstruct both partial (π + fan angle α) and full (2π) scans. Then, using spatial linear filters, the TSFF-corrected image data are created by superimposing the low spatial frequency content of the full scan reconstruction (containing no PSR artifacts, but having low spatial resolution and worse temporal resolution) with the high spatial frequency content of the partial scan reconstruction (containing high spatial frequencies and better temporal resolution). The TSFF method was evaluated both in a static anthropomorphic thoracic phantom and using an in vivo porcine model and compared with a previously validated reference standard technique that avoids PSR artifacts by pacing the animal heart in synchrony with the gantry rotation. CT number variations were quantified by measuring the range and standard deviation of CT numbers in selected regions of interest (ROIs) over time. Myocardial perfusion parameters such as blood volume (BV), mean transit time (MTT), and blood flow (BF) were quantified and compared in the in vivo study.
Phantom experiments demonstrated that TSFF reduced PSR artifacts by as much as tenfold, depending on the location of the ROI. For the in vivo experiments, the TSFF-corrected data showed two- to threefold decrease in CT number variations. Also, after TSFF, the perfusion parameters had an average difference of 13.1% (range 4.5%-25.6%) relative to the reference method, in contrast to an average difference of 31.8% (range 0.3%-54.0%) between the non-TSFF processed data with the reference method.
TSFF demonstrated consistent reduction in CT number variations due to PSR using controlled phantom and in vivo experiments. TSFF-corrected data provided quantitative measures of perfusion (BV, MTT, and BF) with better agreement to a reference method compared to noncorrected data. Practical implementation of TSFF is expected to incur in an additional radiation exposure of 14%, when tube current is modulated to 20% of its maximum, to complete the needed full scan reconstruction.
在使用动态多排计算机断层扫描（MDCT）进行心肌灌注成像时，会出现部分扫描重建（PSR）伪影。PSR 伪影表现为由于用于重建图像的角度数据范围不一致而导致的时间上的 CT 数变化，并且当使用 MDCT 时会影响心肌灌注的定量值。本研究旨在介绍并评估一种技术，即靶向空间频率滤波（TSFF），以减少 MDCT 心肌灌注成像中由于 PSR 引起的 CT 数变化。
TSFF 算法需要采集足够的 X 射线投影来重建部分（π+扇角α）和完全（2π）扫描。然后，使用空间线性滤波器，通过将完全扫描重建的低空间频率内容（无 PSR 伪影，但空间分辨率低且时间分辨率差）与部分扫描重建的高空间频率内容（包含高空间频率和更好的时间分辨率）叠加，创建 TSFF 校正的图像数据。在静态人体胸部模型和体内猪模型中对 TSFF 方法进行了评估，并与一种通过使动物心脏与机架旋转同步来避免 PSR 伪影的先前验证的参考标准技术进行了比较。通过测量随时间在选定的感兴趣区域（ROI）中的 CT 数的范围和标准差来量化 CT 数变化。在体内研究中量化了诸如血容量（BV）、平均通过时间（MTT）和血流（BF）等心肌灌注参数。
在体模实验中，结果表明，TSFF 可以将 PSR 伪影减少多达十倍，具体取决于 ROI 的位置。对于体内实验，TSFF 校正后 CT 数变化减少了两到三倍。此外，与非 TSFF 处理数据与参考方法之间的平均差异 31.8%（范围 0.3%-54.0%）相比，校正后 TSFF 数据的灌注参数的平均差异为 13.1%（范围 4.5%-25.6%）。
使用受控的体模和体内实验，TSFF 显示出 PSR 引起的 CT 数变化的一致减少。与非校正数据相比，校正后 TSFF 数据提供了与参考方法更好一致的灌注（BV、MTT 和 BF）定量测量值。当管电流调制为其最大值的 20%以完成所需的完全扫描重建时，预计 TSFF 的实际实施将导致额外的 14%的辐射暴露。
