Beier Susann, Ormiston John, Webster Mark, Cater John, Norris Stuart, Medrano-Gracia Pau, Young Alistair, Gilbert Kathleen, Cowan Brett
Annu Int Conf IEEE Eng Med Biol Soc. 2016 Aug;2016:1220-1223. doi: 10.1109/EMBC.2016.7590925.
The majority of patients with angina or heart failure have coronary artery disease. Left main bifurcations are particularly susceptible to pathological narrowing. Flow is a major factor of atheroma development, but limitations in imaging technology such as spatio-temporal resolution, signal-to-noise ratio (SNRv), and imaging artefacts prevent in vivo investigations. Computational fluid dynamics (CFD) modelling is a common numerical approach to study flow, but it requires a cautious and rigorous application for meaningful results. Left main bifurcation angles of 40°, 80° and 110° were found to represent the spread of an atlas based 100 computed tomography angiograms. Three left mains with these bifurcation angles were reconstructed with 1) idealized, 2) stented, and 3) patient-specific geometry. These were then approximately 7× scaled-up and 3D printing as large phantoms. Their flow was reproduced using a blood-analogous, dynamically scaled steady flow circuit, enabling in vitro phase-contrast magnetic resonance (PC-MRI) measurements. After threshold segmentation the image data was registered to true-scale CFD of the same coronary geometry using a coherent point drift algorithm, yielding a small covariance error (σ <;5.8×10). Natural-neighbour interpolation of the CFD data onto the PC-MRI grid enabled direct flow field comparison, showing very good agreement in magnitude (error 2-12%) and directional changes (r 0.87-0.91), and stent induced flow alternations were measureable for the first time. PC-MRI over-estimated velocities close to the wall, possibly due to partial voluming. Bifurcation shape determined the development of slow flow regions, which created lower SNRv regions and increased discrepancies. These can likely be minimised in future by testing different similarity parameters to reduce acquisition error and improve correlation further. It was demonstrated that in vitro large phantom acquisition correlates to true-scale coronary flow simulations when dynamically scaled, and thus can overcome current PC-MRI's spatio-temporal limitations. This novel method enables experimental assessment of stent induced flow alternations, and in future may elevate CFD coronary flow simulations by providing sophisticated boundary conditions, and enable investigations of stenosis phantoms.
大多数心绞痛或心力衰竭患者患有冠状动脉疾病。左主干分叉尤其容易发生病理性狭窄。血流是动脉粥样硬化发展的主要因素，但诸如时空分辨率、信噪比（SNRv）和成像伪影等成像技术的局限性阻碍了体内研究。计算流体动力学（CFD）建模是研究血流的常用数值方法，但为了获得有意义的结果，需要谨慎且严格地应用。基于100例计算机断层血管造影构建的图谱显示，左主干分叉角度为40°、80°和110°。对具有这些分叉角度的三根左主干进行了如下重建：1）理想化几何形状，2）置入支架后的几何形状，3）患者特异性几何形状。然后将这些模型按比例放大约7倍并3D打印成大型模型。使用血液模拟的动态缩放稳态血流回路再现其血流，从而能够进行体外相位对比磁共振（PC-MRI）测量。经过阈值分割后，使用相干点漂移算法将图像数据配准到相同冠状动脉几何形状的真实比例CFD上，产生较小的协方差误差（σ<5.8×10）。将CFD数据通过自然邻域插值到PC-MRI网格上，实现了直接的流场比较，结果表明在大小（误差2%-12%）和方向变化（r=0.87-0.91）方面具有很好的一致性，并且首次测量到了支架引起的血流变化。PC-MRI高估了靠近血管壁处的速度，这可能是由于部分容积效应所致。分叉形状决定了缓慢血流区域的形成，这些区域会产生较低的SNRv区域并增加差异。未来通过测试不同的相似性参数以减少采集误差并进一步提高相关性，这些差异可能会降至最低。结果表明，体外大型模型采集在动态缩放时与真实比例的冠状动脉血流模拟相关，因此可以克服当前PC-MRI的时空限制。这种新方法能够对支架引起的血流变化进行实验评估，并且未来可能通过提供复杂的边界条件提升CFD冠状动脉血流模拟，并能够对狭窄模型进行研究。
