Liu Haofei, Canton Gador, Yuan Chun, Yang Chun, Billiar Kristen, Teng Zhongzhao, Hoffman Allen H, Tang Dalin
Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609, USA.
J Biomech Eng. 2012 Jan;134(1):011008. doi: 10.1115/1.4005685.
In vivo magnetic resonance image (MRI)-based computational models have been introduced to calculate atherosclerotic plaque stress and strain conditions for possible rupture predictions. However, patient-specific vessel material properties are lacking in those models, which affects the accuracy of their stress/strain predictions. A noninvasive approach of combining in vivo Cine MRI, multicontrast 3D MRI, and computational modeling was introduced to quantify patient-specific carotid artery material properties and the circumferential shrinkage rate between vessel in vivo and zero-pressure geometries. In vivo Cine and 3D multicontrast MRI carotid plaque data were acquired from 12 patients after informed consent. For each patient, one nearly-circular slice and an iterative procedure were used to quantify parameter values in the modified Mooney-Rivlin model for the vessel and the vessel circumferential shrinkage rate. A sample artery slice with and without a lipid core and three material parameter sets representing stiff, median, and soft materials from our patient data were used to demonstrate the effect of material stiffness and circumferential shrinkage process on stress/strain predictions. Parameter values of the Mooney-Rivlin models for the 12 patients were quantified. The effective Young's modulus (YM, unit: kPa) values varied from 137 (soft), 431 (median), to 1435 (stiff), and corresponding circumferential shrinkages were 32%, 12.6%, and 6%, respectively. Using the sample slice without the lipid core, the maximum plaque stress values (unit: kPa) from the soft and median materials were 153.3 and 96.2, which are 67.7% and 5% higher than that (91.4) from the stiff material, while the maximum plaque strain values from the soft and median materials were 0.71 and 0.293, which are about 700% and 230% higher than that (0.089) from the stiff material, respectively. Without circumferential shrinkages, the maximum plaque stress values (unit: kPa) from the soft, median, and stiff models were inflated to 330.7, 159.2, and 103.6, which were 116%, 65%, and 13% higher than those from models with proper shrinkage. The effective Young's modulus from the 12 human carotid arteries studied varied from 137 kPa to 1435 kPa. The vessel circumferential shrinkage to the zero-pressure condition varied from 6% to 32%. The inclusion of proper shrinkage in models based on in vivo geometry is necessary to avoid over-estimating the stresses and strains by up 100%. Material stiffness had a greater impact on strain (up to 700%) than on stress (up to 70%) predictions. Accurate patient-specific material properties and circumferential shrinkage could considerably improve the accuracy of in vivo MRI-based computational stress/strain predictions.
基于体内磁共振成像（MRI）的计算模型已被引入，用于计算动脉粥样硬化斑块的应力和应变情况，以预测其可能的破裂。然而，这些模型缺乏患者特异性的血管材料属性，这影响了其应力/应变预测的准确性。本文介绍了一种将体内电影MRI、多对比度3D MRI和计算建模相结合的非侵入性方法，以量化患者特异性的颈动脉材料属性以及体内血管与零压力几何形状之间的周向收缩率。在获得知情同意后，从12名患者身上采集了体内电影和3D多对比度MRI颈动脉斑块数据。对于每位患者，使用一个近似圆形的切片和一个迭代程序来量化修正的Mooney-Rivlin模型中血管的参数值以及血管周向收缩率。使用一个有和没有脂质核心的动脉样本切片以及来自我们患者数据的三个代表硬、中、软材料的材料参数集，来展示材料刚度和周向收缩过程对应力/应变预测的影响。对12名患者的Mooney-Rivlin模型的参数值进行了量化。有效杨氏模量（YM，单位：kPa）值从137（软）、431（中）到1435（硬）不等，相应的周向收缩率分别为32%、12.6%和6%。使用没有脂质核心的样本切片，软材料和中材料的最大斑块应力值（单位：kPa）分别为153.3和96.2，比硬材料的（91.4）分别高67.7%和5%，而软材料和中材料的最大斑块应变值分别为0.71和0.293，分别比硬材料的（0.089）高约700%和230%。如果没有周向收缩，软、中、硬模型的最大斑块应力值（单位：kPa）分别膨胀到330.7、159.2和103.6，比有适当收缩的模型分别高116%、65%和13%。所研究的12条人类颈动脉的有效杨氏模量从137 kPa到1435 kPa不等。血管到零压力状态的周向收缩率从6%到32%不等。在基于体内几何形状的模型中纳入适当的收缩对于避免将应力和应变高估多达100%是必要的。材料刚度对应变（高达700%）的影响比对应力（高达70%）预测的影响更大。准确的患者特异性材料属性和周向收缩可以显著提高基于体内MRI的计算应力/应变预测的准确性。
