Bindschadler Michael, Modgil Dimple, Branch Kelley R, La Riviere Patrick J, Alessio Adam M
Department of Bioengineering University of Washington, Seattle, WA 98195, US. Department of Radiology, University of Washington, Seattle, WA 98195, US.
Phys Med Biol. 2014 Apr 7;59(7):1533-56. doi: 10.1088/0031-9155/59/7/1533. Epub 2014 Mar 10.
Myocardial blood flow (MBF) can be estimated from dynamic contrast enhanced (DCE) cardiac CT acquisitions, leading to quantitative assessment of regional perfusion. The need for low radiation dose and the lack of consensus on MBF estimation methods motivates this study to refine the selection of acquisition protocols and models for CT-derived MBF. DCE cardiac CT acquisitions were simulated for a range of flow states (MBF = 0.5, 1, 2, 3 ml (min g)(-1), cardiac output = 3, 5, 8 L min(-1)). Patient kinetics were generated by a mathematical model of iodine exchange incorporating numerous physiological features including heterogenenous microvascular flow, permeability and capillary contrast gradients. CT acquisitions were simulated for multiple realizations of realistic x-ray flux levels. CT acquisitions that reduce radiation exposure were implemented by varying both temporal sampling (1, 2, and 3 s sampling intervals) and tube currents (140, 70, and 25 mAs). For all acquisitions, we compared three quantitative MBF estimation methods (two-compartment model, an axially-distributed model, and the adiabatic approximation to the tissue homogeneous model) and a qualitative slope-based method. In total, over 11 000 time attenuation curves were used to evaluate MBF estimation in multiple patient and imaging scenarios. After iodine-based beam hardening correction, the slope method consistently underestimated flow by on average 47.5% and the quantitative models provided estimates with less than 6.5% average bias and increasing variance with increasing dose reductions. The three quantitative models performed equally well, offering estimates with essentially identical root mean squared error (RMSE) for matched acquisitions. MBF estimates using the qualitative slope method were inferior in terms of bias and RMSE compared to the quantitative methods. MBF estimate error was equal at matched dose reductions for all quantitative methods and range of techniques evaluated. This suggests that there is no particular advantage between quantitative estimation methods nor to performing dose reduction via tube current reduction compared to temporal sampling reduction. These data are important for optimizing implementation of cardiac dynamic CT in clinical practice and in prospective CT MBF trials.
心肌血流量（MBF）可通过动态对比增强（DCE）心脏CT采集进行估算，从而实现对局部灌注的定量评估。由于需要低辐射剂量以及在MBF估算方法上缺乏共识，促使本研究优化CT衍生MBF的采集方案和模型选择。针对一系列血流状态（MBF = 0.5、1、2、3 ml·(min·g)⁻¹，心输出量 = 3、5、8 L·min⁻¹）模拟了DCE心脏CT采集。通过包含众多生理特征（包括异质性微血管血流、通透性和毛细血管对比梯度）的碘交换数学模型生成患者动力学。针对多种实际X射线通量水平的情况模拟了CT采集。通过改变时间采样（1、2和3秒采样间隔）和管电流（140、70和25 mAs）来实现降低辐射暴露的CT采集。对于所有采集，我们比较了三种定量MBF估算方法（双室模型、轴向分布模型以及组织均匀模型的绝热近似）和一种基于斜率的定性方法。总共使用了超过11000条时间衰减曲线来评估多种患者和成像场景下的MBF估算。在基于碘的束硬化校正后，斜率法平均持续低估血流量47.5%，而定量模型提供的估算平均偏差小于6.5%，并且随着剂量降低方差增加。三种定量模型表现同样良好，对于匹配的采集提供的估算具有基本相同的均方根误差（RMSE）。与定量方法相比，使用定性斜率法的MBF估算在偏差和RMSE方面较差。对于所有评估的定量方法和技术范围，在匹配的剂量降低情况下MBF估算误差相等。这表明在定量估算方法之间没有特别优势，并且与通过减少时间采样来降低剂量相比，通过降低管电流来降低剂量也没有特别优势。这些数据对于在临床实践和前瞻性CT MBF试验中优化心脏动态CT的实施非常重要。
