Department of Medical Biophysics, University of Toronto, Toronto, Ontario M4N 3M5, Canada.
Med Phys. 2012 Jun;39(6):3009-18. doi: 10.1118/1.4711757.
Currently, the use of cine magnetic resonance imaging (MRI) to identify cardiac quiescent periods relative to the electrocardiogram (ECG) signal is insufficient for producing submillimeter-resolution coronary MR angiography (MRA) images. In this work, the authors perform a time series comparison between tissue Doppler echocardiograms of the interventricular septum (IVS) and concurrent biplane x-ray angiograms. Our results indicate very close agreement between the diastasis gating windows identified by both the IVS and x-ray techniques.
Seven cath lab patients undergoing diagnostic angiograms were simultaneously scanned during a breath hold by ultrasound and biplane x-ray for six to eight heartbeats. The heart rate of each patient was stable. Dye was injected into either the left or right-coronary vasculature. The IVS was imaged using color tissue Doppler in an apical four-chamber view. Diastasis was estimated on the IVS velocity curve. On the biplane angiograms, proximal, mid, and distal regions were identified on the coronary artery (CA). Frame by frame correlation was used to derive displacement, and then velocity, for each region. The quiescent periods for a CA and its subsegments were estimated based on velocity. Using Pearson's correlation coefficient and Bland-Altman analysis, the authors compared the start and end times of the diastasis windows as estimated from the IVS and CA velocities. The authors also estimated the vessel blur across the diastasis windows of multiple sequential heartbeats of each patient.
In total, 17 heartbeats were analyzed. The range of heart rate observed across patients was 47-79 beats per minute (bpm) with a mean of 57 bpm. Significant correlations (R > 0.99; p < 0.01) were observed between the IVS and x-ray techniques for the identification of the start and end times of diastasis windows. The mean difference in the starting times between IVS and CA quiescent windows was -12.0 ms. The mean difference in end times between IVS and CA quiescent windows was -3.5 ms. In contrast, the correlation between RR interval and both the start and duration of the x-ray gating windows were relatively weaker: R = 0.63 (p = 0.13) and R = 0.86 (p = 0.01). For IVS gating windows, the average estimated vessel blurs during single and multiple heartbeats were 0.5 and 0.66 mm, respectively. For x-ray gating windows, the corresponding values were 0.26 and 0.44 mm, respectively.
In this study, the authors showed that IVS velocity can be used to identify periods of diastasis for coronary arteries. Despite variability in mid-diastolic rest positions over multiple steady rate heartbeats, vessel blurring of 0.5-1 mm was found to be achievable using the IVS gating technique. The authors envision this leading to a new cardiac gating system that, compared with conventional ECG gating, provides better resolution and shorter scan times for coronary MRA.
目前，利用电影磁共振成像（MRI）相对于心电图（ECG）信号来识别心脏静止期，对于产生亚毫米分辨率的冠状动脉磁共振血管造影（MRA）图像来说还不够。在这项工作中，作者对室间隔（IVS）的组织多普勒超声心动图和同时进行的双平面 X 射线血管造影进行了时间序列比较。我们的结果表明，IVS 和 X 射线技术确定的舒张期门控窗口之间非常吻合。
7 名在诊断性血管造影过程中接受检查的患者在进行超声和双平面 X 射线扫描时，在呼吸暂停期间同时进行六到八次心跳扫描。每位患者的心率均保持稳定。将染料注入左或右冠状动脉。使用心尖四腔视图中的彩色组织多普勒成像来对 IVS 进行成像。在 IVS 速度曲线上估计舒张期。在双平面血管造影中，确定冠状动脉（CA）的近端、中段和远端区域。逐帧相关用于获得每个区域的位移，然后是速度。根据速度，估计 CA 和其亚段的静止期。使用 Pearson 相关系数和 Bland-Altman 分析，作者比较了从 IVS 和 CA 速度估计的舒张期窗口的开始和结束时间。作者还估计了每个患者多个连续心跳的舒张期窗口的血管模糊程度。
总共分析了 17 次心跳。观察到的患者心率范围为 47-79 次/分钟（bpm），平均为 57 bpm。IVS 和 X 射线技术在确定舒张期窗口的开始和结束时间方面存在显著相关性（R > 0.99；p < 0.01）。IVS 和 CA 静止期窗口开始时间的平均差异为-12.0 ms。IVS 和 CA 静止期窗口结束时间的平均差异为-3.5 ms。相比之下，RR 间隔与 X 射线门控窗口的开始和持续时间之间的相关性较弱：R = 0.63（p = 0.13）和 R = 0.86（p = 0.01）。对于 IVS 门控窗口，单次和多次心跳期间估计的血管模糊度分别为 0.5 和 0.66 毫米。对于 X 射线门控窗口，相应的值分别为 0.26 和 0.44 毫米。
在这项研究中，作者表明 IVS 速度可用于识别冠状动脉的舒张期。尽管在多个稳定心率的心跳中，舒张中期休息位置存在变异性，但使用 IVS 门控技术可实现 0.5-1 毫米的血管模糊度。作者设想这将产生一种新的心脏门控系统，与传统的 ECG 门控相比，它为冠状动脉 MRA 提供了更好的分辨率和更短的扫描时间。
