Using In Vivo Cine and 3D Multi-Contrast MRI to Determine Human Atherosclerotic Carotid Artery Material Properties and Circumferential Shrinkage Rate and Their Impact on Stress/Strain Predictions

Abstract

Background 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 affect the accuracy of their stress/strain predictions. A non-invasive approach of combining in vivo Cine MRI, multi-contrast 3D MRI and computational modeling was introduced to quantify patient-specific carotid artery material properties and circumferential shrinkage rate between vessel in vivo and zero-pressure geometries. Method 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. Results Parameter values of the Mooney-Rivlin models for the 12 patients were quantified. 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% to 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, 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, 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. Conclusion Effective Young's Modulus from the 12 human carotid arteries studied varied from 137 kPa to 1435 kPa. Vessel circumferential shrinkage to zero-pressure condition varied from 6% to 32%. 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 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.

Image-based modeling for better understanding and assessment of atherosclerotic plaque progression and vulnerability: Data, modeling, validation, uncertainty and predictions

“…The shrinking rate in the axial direction and shrinkage rates of lumen and outer wall (which have to be different) were determined so that (1) mass conservation is satisfied; and (2) the contours of the plaque and its components after pressurization and axial stretch achieve the best match with the in vivo geometry from MRI. A circular artery segment under in vivo condition goes through three stages to get its open-up zero-stress state: axial shrinkage (up to 30–50%; could be smaller for atherosclerotic plaques), circumferential shrinkage (5–20% based on our data, Huang et al, 2009; Liu et al, 2012b), and final opening-up with an opening angle (63.5°, n = 5) (Kural et al, 2012). Omitting any of the three stages would lead to stress/strain prediction errors on the order of 50–100% or even more (Liu et al, 2012b; Huang et al, 2009; Ohayon et al, 2007).…”

“…A circular artery segment under in vivo condition goes through three stages to get its open-up zero-stress state: axial shrinkage (up to 30–50%; could be smaller for atherosclerotic plaques), circumferential shrinkage (5–20% based on our data, Huang et al, 2009; Liu et al, 2012b), and final opening-up with an opening angle (63.5°, n = 5) (Kural et al, 2012). Omitting any of the three stages would lead to stress/strain prediction errors on the order of 50–100% or even more (Liu et al, 2012b; Huang et al, 2009; Ohayon et al, 2007). Ohayon et al (2007) investigated the influence of residual stress/strain related to opening angle on the biomechanical stability of vulnerable coronary plaques and their potential impact for evaluating the risk of plaque rupture.…”

“…Speelman et al (2011) introduced an inverse method to address the initial stress in biomechanical models of atherosclerotic plaques. The inverse method was more sophisticated compared to the direct trial-and-error iterative shrinkage identification process used in our papers (Huang et al, 2009; Liu et al, 2012b). Actually, even including all the three stages for computational models would still not be able to account for plaque local plaque material and morphology variations.…”

“…The method was tested using both ex vivo and in vivo human coronary plaque samples (Baldewsing, et al, 2008). Liu et al introduced a method based on human CINE MRI carotid data and computational modeling to determined plaque material parameters (Liu et al, 2012b). Data from 12 patients were used.…”

Quantify patient-specific coronary material property and its impact on stress/strain calculations using in vivo IVUS data and 3D FSI models: a pilot study

“…The mean opening angles for coronary and carotid samples were 120° and 63.5°, respectively. Liu et al (2012) introduced a finite element approach based on in vivo MRI Cine data to determine human carotid material properties. Their results from 12 patients showed that material stiffness measured by the effective Young’s modulus (YM) varied from 137 (soft), 431 (median), to 1435 kPa (stiff), respectively.…”