Division of Medical Imaging Physics, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, USA.
Cardiac Arrhythmia Service, Johns Hopkins University School of Medicine, Baltimore, MD, 21287, USA.
Med Phys. 2017 Sep;44(9):4677-4686. doi: 10.1002/mp.12425. Epub 2017 Aug 1.
This work concerns computed tomography (CT)-based cardiac functional analysis (CFA) with a reduced radiation dose. As CT-CFA requires images over the entire heartbeat, the scans are often performed at 10-20% of the tube current settings that are typically used for coronary CT angiography. A large image noise then degrades the accuracy of motion estimation. Moreover, even if the scan was performed during the sinus rhythm, the cardiac motion observed in CT images may not be cyclic with patients with atrial fibrillation. In this study, we propose to use two CT scan data, one for CT angiography at a quiescent phase at a standard dose and the other for CFA over the entire heart beat at a lower dose.
We have made the following four modifications to an image-based cardiac motion estimation method we have previously developed for a full-dose retrospectively gated coronary CT angiography: (a) a full-dose prospectively gated coronary CT angiography image acquired at the least motion phase was used as the reference image; (b) a three-dimensional median filter was applied to lower-dose retrospectively gated cardiac images acquired at 20 phases over one heartbeat in order to reduce image noise; (c) the strength of the temporal regularization term was made adaptive; and (d) a one-dimensional temporal filter was applied to the estimated motion vector field in order to decrease jaggy motion patterns. We describe the conventional method iME1 and the proposed method iME2 in this article. Five observers assessed the accuracy of the estimated motion vector field of iME2 and iME1 using a 4-point scale. The observers repeated the assessment with data presented in a new random order 1 week after the first assessment session.
The study confirmed that the proposed iME2 was robust against the mismatch of noise levels, contrast enhancement levels, and shapes of the chambers. There was a statistically significant difference between iME2 and iME1 (accuracy score, 2.08 ± 0.81 versus 2.77 ± 0.98, P < 0.01) and the improvement by the score of + 0.69 seemed clinically relevant. Inter-observer concordance was good: The inter-class correlation coefficient was 0.63 and Kendall's rank correlation coefficients were in the range of 0.41-0.67 (P < 0.01), respectively. Intra-observer reproducibility between sessions was good with the inter-class correlation coefficient of 0.76.
We have proposed iME2 method for CT-CFA with two CT scans. The observer study verified the robustness and accuracy of iME2 method and its improved performance over iME1 method.
本研究旨在探讨基于计算机断层扫描（CT）的心脏功能分析（CFA）的辐射剂量降低问题。由于 CT-CFA 需要对整个心跳过程进行成像，因此通常以冠状动脉 CT 血管造影术（CCTA）中常用的管电流设置的 10%-20%进行扫描。较大的图像噪声会降低运动估计的准确性。此外，即使扫描是在窦性心律期间进行的，在 CT 图像中观察到的心脏运动也可能与心房颤动患者的心脏运动不同步。在这项研究中，我们建议使用两种 CT 扫描数据，一种用于标准剂量下的静息期 CT 血管造影，另一种用于低剂量下的整个心脏搏动。
我们对我们之前开发的用于全剂量回顾性门控冠状动脉 CT 血管造影的基于图像的心脏运动估计方法进行了以下四项修改：（a）使用最少运动相位采集的全剂量前瞻性门控冠状动脉 CT 血管造影图像作为参考图像；（b）对在一个心动周期内采集的 20 个相位的低剂量回顾性门控心脏图像应用三维中值滤波器以降低图像噪声；（c）自适应调整时间正则化项的强度；（d）应用一维时间滤波器对估计的运动矢量场进行平滑处理，以减少运动伪影。本文中我们描述了常规方法 iME1 和改进方法 iME2。五位观察者使用 4 分制评估了 iME2 和 iME1 的估计运动矢量场的准确性。观察者在第一次评估后一周以新的随机顺序重复评估。
研究证实，所提出的 iME2 对噪声水平、对比增强水平和心室形状的不匹配具有鲁棒性。与 iME1 相比，iME2 具有统计学意义上的差异（准确性评分 2.08±0.81 与 2.77±0.98，P<0.01），且评分提高了+0.69 分，这似乎具有临床意义。观察者间的一致性较好：组间相关系数为 0.63，肯德尔等级相关系数在 0.41-0.67 之间（P<0.01）。两次评估之间的观察者内可重复性较好，组内相关系数为 0.76。
我们提出了一种用于两次 CT 扫描的 CT-CFA 的 iME2 方法。观察者研究验证了 iME2 方法的稳健性和准确性，以及与 iME1 方法相比的性能提高。
