Meloni Antonella, Zymeski Heather, Pepe Alessia, Lombardi Massimo, Wood John C
CMR Unit, Fondazione G. Monasterio CNR-Regione Toscana and Institute of Clinical Physiology, Pisa, Italy; Department of Pediatrics, Division of Cardiology, Children's Hospital Los Angeles, Los Angeles, California, USA.
J Magn Reson Imaging. 2014 Mar;39(3):550-8. doi: 10.1002/jmri.24207. Epub 2013 Oct 7.
To evaluate the efficiency of a novel transit time (Δt) estimation method from cardiovascular magnetic resonance flow curves.
Flow curves were estimated from phase contrast images of 30 patients. Our method (TT-GD: transit time group delay) operates in the frequency domain and models the ascending aortic waveform as an input passing through a discrete-component "filter," producing the observed descending aortic waveform. The GD of the filter represents the average time delay (Δt) across individual frequency bands of the input. This method was compared with two previously described time-domain methods: TT-point using the half-maximum of the curves and TT-wave using cross-correlation. High temporal resolution flow images were studied at multiple downsampling rates to study the impact of differences in temporal resolution.
Mean Δts obtained with the three methods were comparable. The TT-GD method was the most robust to reduced temporal resolution. While the TT-GD and the TT-wave produced comparable results for velocity and flow waveforms, the TT-point resulted in significant shorter Δts when calculated from velocity waveforms (difference: 1.8±2.7 msec; coefficient of variability: 8.7%). The TT-GD method was the most reproducible, with an intraobserver variability of 3.4% and an interobserver variability of 3.7%.
Compared to the traditional TT-point and TT-wave methods, the TT-GD approach was more robust to the choice of temporal resolution, waveform type, and observer.
评估一种从心血管磁共振血流曲线估计新型渡越时间（Δt）方法的效率。
从30例患者的相位对比图像估计血流曲线。我们的方法（TT-GD：渡越时间群延迟）在频域中运行，并将升主动脉波形建模为通过离散分量“滤波器”的输入，产生观察到的降主动脉波形。滤波器的群延迟表示输入各个频带的平均时间延迟（Δt）。将该方法与之前描述的两种时域方法进行比较：使用曲线半最大值的TT点法和使用互相关的TT波法。在多个下采样率下研究高时间分辨率血流图像，以研究时间分辨率差异的影响。
三种方法获得的平均Δt具有可比性。TT-GD方法对降低的时间分辨率最稳健。虽然TT-GD和TT波在速度和血流波形方面产生了可比的结果，但从速度波形计算时，TT点法得到的Δt明显更短（差异：1.8±2.7毫秒；变异系数：8.7%）。TT-GD方法的可重复性最高，观察者内变异为3.4%，观察者间变异为3.7%。
与传统的TT点法和TT波法相比，TT-GD方法对时间分辨率、波形类型和观察者的选择更稳健。
