Institute of Technical Medicine, University of Twente, 7500 AE, Enschede, The Netherlands.
Med Phys. 2009 Oct;36(10):4616-24. doi: 10.1118/1.3213530.
ECG-gated CT enables the visualization of motions caused by the beating of the heart. Although ECG gating is frequently used in cardiac CT imaging, this technique is also very promising for evaluating vessel wall motion of the aortic artery and the motions of (stent grafts inside) abdominal aortic aneurysms (AAA). Late stent graft failure is a serious complication in endovascular repair of aortic aneurysms. Better understanding of the motion characteristics of stent grafts will be beneficial for designing future devices. In addition, these data can be valuable in predicting stent graft failure in patients. To be able to reliably quantify the motion, however, it is of importance to know the performance and limitations of ECG gating, especially when the motions are small, as is the case in AAA. Since the details of the reconstruction algorithms are proprietary information on the CT manufacturers and not in the public domain, empirical experiments are required. The goal of this study is to investigate as to what extent the motions in AAA can be measured using ECG-gated CT. The authors quantitatively investigate four aspects of motion in ECG-gated CT: The detectability of the motion of objects at different amplitudes and different periodic motions, the temporal resolution, and the volume gaps that occur as a function of heart rate.
They designed an experiment on a standard static phantom to empirically determine temporal resolution. To investigate motion amplitude and frequency, as well as patient heart rate, they designed dynamic experiments in which a home-made phantom driven by a motion unit moves in a predetermined pattern.
The duration of each ECG-gated phase was found to be 185 ms, which corresponds to half of the rotation time and is thus in accordance with half scan reconstruction applied by the scanner. By using subpixel localization, motions become detectable from amplitudes of as small as 0.4 mm in the x direction and 0.7 mm in the z direction. With the rotation time used in this study, motions up to 2.7 Hz can be reliably detected. The reconstruction algorithm fills volume gaps with noisy data using interpolation, but objects within these gaps remain hidden.
This study gives insight into the possibilities and limitations for measuring small motions using ECG-gated CT. Application of the experimental method is not restricted to the CT scanner of a single manufacturer. From the results, they conclude that ECG-gated CTA is a suitable technique for studying the expected motions of the stent graft and vessel wall in AAA.
心电图门控 CT 能够可视化心脏跳动引起的运动。虽然心电图门控在心脏 CT 成像中经常使用，但该技术对于评估主动脉血管壁运动和腹主动脉瘤（AAA）内（支架移植物）的运动也非常有前景。支架移植物晚期失效是主动脉瘤血管内修复的严重并发症。更好地了解支架移植物的运动特征将有助于设计未来的设备。此外，这些数据对于预测患者支架移植物失败具有重要价值。为了能够可靠地量化运动，了解心电图门控的性能和局限性非常重要，尤其是在 AAA 中运动较小的情况下。由于重建算法的细节是 CT 制造商的专有信息，不在公共领域，因此需要进行经验实验。本研究的目的是调查使用心电图门控 CT 可以在多大程度上测量 AAA 中的运动。作者定量研究了心电图门控 CT 中运动的四个方面：不同幅度和不同周期性运动的物体运动的可检测性、时间分辨率以及作为心率函数的体积间隙。
他们在标准静态体模上设计了一个实验，以经验确定时间分辨率。为了研究运动幅度和频率以及患者的心率，他们设计了动态实验，其中由运动单元驱动的自制体模以预定模式移动。
每个心电图门控阶段的持续时间发现为 185ms，这对应于旋转时间的一半，因此与扫描仪应用的半扫描重建一致。通过使用亚像素定位，运动的幅度可小至 x 方向的 0.4mm 和 z 方向的 0.7mm 即可检测到。使用本研究中使用的旋转时间，可以可靠地检测到高达 2.7Hz 的运动。重建算法使用插值用噪声数据填充体积间隙，但这些间隙内的物体仍然隐藏。
本研究深入了解了使用心电图门控 CT 测量小运动的可能性和局限性。实验方法的应用不限于单一制造商的 CT 扫描仪。根据结果，他们得出结论，心电图门控 CTA 是研究 AAA 中支架移植物和血管壁预期运动的合适技术。
