Can we obtain in vivo transmural mean hoop stress of the aortic wall without knowing patient-specific material properties and residual deformations?

AbstractIt is well known that residual deformations/stresses alter the mechanical behavior of arteries, e.g. the pressure-diameter curves. In an effort to enable personalized analysis of the aortic wall stress, approaches have been developed to incorporate experimentally-derived residual deformations into in vivo loaded geometries in finite element simulations using thick-walled models. Solid elements are typically used to account for “bending-like” residual deformations. Yet, the difficulty in obtaining patient-specific residual deformations and material properties has become one of the biggest challenges of these thick-walled models. In thin-walled models, fortunately, static determinacy offers an appealing prospect that allows for the calculation of the thin-walled membrane stress without patient-specific material properties. The membrane stress can be computed using forward analysis by enforcing an extremely stiff material property as penalty treatment, which is referred to as the forward penalty approach. However, thin-walled membrane elements, which have zero bending stiffness, are incompatible with the residual deformations, and therefore, it is often stated as a limitation of thin-walled models. In this paper, by comparing the predicted stresses from thin-walled models and thick-walled models, we demonstrate that the transmural mean hoop stress is the same for the two models and can be readily obtained from in vivo clinical images without knowing the patient-specific material properties and residual deformations. Computation of patient-specific mean hoop stress can be greatly simplified by using membrane model and the forward penalty approach, which may be clinically valuable.

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Abstract 562: Human Carotid Atherosclerosis Plaque Progression and Vessel Material Stiffness at Follow Up Had Positive Correlation: An in vivo Vessel Stiffness MRI Follow Up Study

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.37.suppl_1.562 ◽

2017 ◽

Vol 37 (suppl_1) ◽

Author(s):

Qingyu Wang ◽

Dalin Tang ◽

Gador Canton ◽

Jian Guo ◽

Xiaoya Guo ◽

...

Keyword(s):

Negative Correlation ◽

Material Properties ◽

Stretch Ratio ◽

Patient Specific ◽

Plaque Progression ◽

Material Stiffness ◽

Variation Rate ◽

Vessel Material

It is hypothesized that artery stiffness may be associated with plaque progression. However, in vivo vessel material stiffness follow-up data is lacking in the literature. In vivo 3D multi-contrast and Cine magnetic resonance imaging (MRI) carotid plaque data were acquired from 8 patients with follow-up (18 months) with written informed consent obtained. Cine MRI and 3D thin-layer models were used to determine parameter values of the Mooney-Rivlin models for the 81slices from 16 plaques (2 scans/patient) using our established iterative procedures. Effective Young’s Modulus (YM) values for stretch ratio [1.0,1.3] were calculated for each slice for analysis. Stress-stretch ratio curves from Mooney-Rivlin models for the 16 plaques and 81 slices are given in Fig. 1. Average YM value of the 81 slices was 411kPa. Slice YM values varied from 70 kPa (softest) to 1284 kPa (stiffest), a 1734% difference. Average slice YM values by vessel varied from 109 kPa (softest) to 922 kPa (stiffest), a 746% difference. Location-wise, the maximum slice YM variation rate within a vessel was 306% (139 kPa vs. 564 kPa). Average slice YM variation rate within a vessel for the 16 vessels was 134%. Average variation of YM values from baseline (T1) to follow up (T2) for all patients was 61.0%. The range of the variation of YM values was [-28.4%, 215%]. For progression study, YM increase (YMI=YM T2 -TM T1 ) showed negative correlation with plaque progression measured by wall thickness increase (WTI), (r= -0.6802, p=0.0634). YM T2 showed strong negative correlation with WTI (r= -0.7764, p=0.0235). Correlation between YM T1 and WTI was not significant (r= -0.4353, p= 0.2811). Conclusion In vivo carotid vessel material properties have large variations from patient to patient, along the vessel segment within a patient, and from baseline to follow up. Use of patient-specific, location specific and time-specific material properties could potentially improve the accuracy of model stress/strain calculations.

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In Vivo Quantification of Regional Circumferential Green Strain in the Thoracic and Abdominal Aorta by Two-Dimensional Spiral Cine DENSE MRI

Journal of Biomechanical Engineering ◽

10.1115/1.4040910 ◽

2019 ◽

Vol 141 (6) ◽

Cited By ~ 1

Author(s):

John S. Wilson ◽

Xiaodong Zhong ◽

Jackson Hair ◽

W. Robert Taylor ◽

John N. Oshinski

Keyword(s):

Abdominal Aorta ◽

Aortic Wall ◽

Patient Specific ◽

Peak Strain ◽

Ssfp Cine ◽

Green Strain ◽

The Mean ◽

Thoracic And Abdominal ◽

Cine Dense

Regional tissue mechanics play a fundamental role in the patient-specific function and remodeling of the cardiovascular system. Nevertheless, regional in vivo assessments of aortic kinematics remain lacking due to the challenge of imaging the thin aortic wall. Herein, we present a novel application of displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify the regional displacement and circumferential Green strain of the thoracic and abdominal aorta. Two-dimensional (2D) spiral cine DENSE and steady-state free procession (SSFP) cine images were acquired at 3T at either the infrarenal abdominal aorta (IAA), descending thoracic aorta (DTA), or distal aortic arch (DAA) in a pilot study of six healthy volunteers (22–59 y.o., 4 females). DENSE data were processed with multiple custom noise reduction techniques including time-smoothing, displacement vector smoothing, sectorized spatial smoothing, and reference point averaging to calculate circumferential Green strain across 16 equispaced sectors around the aorta. Each volunteer was scanned twice to evaluate interstudy repeatability. Circumferential Green strain was heterogeneously distributed in all volunteers and locations. The mean spatial heterogeneity index (standard deviation of all sector values divided by the mean strain) was 0.37 in the IAA, 0.28 in the DTA, and 0.59 in the DAA. Mean (homogenized) peak strain by DENSE for each cross section was consistent with the homogenized linearized strain estimated from SSFP cine. The mean difference in peak strain across all sectors following repeat imaging was −0.1±2.3%, with a mean absolute difference of 1.7%. Aortic cine DENSE MRI is a viable noninvasive technique for quantifying heterogeneous regional aortic wall strain and has significant potential to improve patient-specific clinical assessments of numerous aortopathies, as well as to provide the lacking spatiotemporal data required to refine patient-specific computational models of aortic growth and remodeling.

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Predictive Models with Patient Specific Material Properties for the Biomechanical Behavior of Ascending Thoracic Aneurysms

Annals of Biomedical Engineering ◽

10.1007/s10439-015-1374-8 ◽

2015 ◽

Vol 44 (1) ◽

pp. 84-98 ◽

Cited By ~ 18

Author(s):

Olfa Trabelsi ◽

Ambroise Duprey ◽

Jean-Pierre Favre ◽

Stéphane Avril

Keyword(s):

Predictive Models ◽

Material Properties ◽

Patient Specific ◽

Biomechanical Behavior ◽

Specific Material ◽

Thoracic Aneurysms

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Assessing Patient-Specific Mechanical Properties of Aortic Wall and Peri-Aortic Structures From In Vivo DENSE Magnetic Resonance Imaging Using an Inverse Finite Element Method and Elastic Foundation Boundary Conditions

Journal of Biomechanical Engineering ◽

10.1115/1.4047721 ◽

2020 ◽

Vol 142 (12) ◽

Author(s):

Johane H. Bracamonte ◽

John S. Wilson ◽

Joao S. Soares

Keyword(s):

Magnetic Resonance Imaging ◽

Finite Element Method ◽

Finite Element ◽

Magnetic Resonance ◽

Aortic Wall ◽

Patient Specific ◽

Resonance Imaging ◽

Displacement Fields ◽

Inverse Finite Element Method

Abstract The establishment of in vivo, noninvasive patient-specific, and regionally resolved techniques to quantify aortic properties is key to improving clinical risk assessment and scientific understanding of vascular growth and remodeling. A promising and novel technique to reach this goal is an inverse finite element method (FEM) approach that utilizes magnetic resonance imaging (MRI)-derived displacement fields from displacement encoding with stimulated echoes (DENSE). Previous studies using DENSE MRI suggested that the infrarenal abdominal aorta (IAA) deforms heterogeneously during the cardiac cycle. We hypothesize that this heterogeneity is driven in healthy aortas by regional adventitial tethering and interaction with perivascular tissues, which can be modeled with elastic foundation boundary conditions (EFBCs) using a collection of radially oriented springs with varying stiffness with circumferential distribution. Nine healthy IAAs were modeled using previously acquired patient-specific imaging and displacement fields from steady-state free procession (SSFP) and DENSE MRI, followed by assessment of aortic wall properties and heterogeneous EFBC parameters using inverse FEM. In contrast to traction-free boundary condition, prescription of EFBC reduced the nodal displacement error by 60% and reproduced the DENSE-derived heterogeneous strain distribution. Estimated aortic wall properties were in reasonable agreement with previously reported experimental biaxial testing data. The distribution of normalized EFBC stiffness was consistent among all patients and spatially correlated to standard peri-aortic anatomical features, suggesting that EFBC could be generalized for human adults with normal anatomy. This approach is computationally inexpensive, making it ideal for clinical research and future incorporation into cardiovascular fluid–structure analyses.

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Abstract 16230: Pulmonary Autograft Wall Stresses One Year After Ross Operation

Circulation ◽

10.1161/circ.142.suppl_3.16230 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Edgardo Alonso ◽

Yue XUAN ◽

Alexander Emmott ◽

Zhongjie Wang ◽

Shalni Kumar ◽

...

Keyword(s):

Ascending Aorta ◽

Patient Specific ◽

Principal Stresses ◽

Ross Operation ◽

Children And Young Adults ◽

Specific Material ◽

One Year ◽

Patients Experience

Introduction: The Ross procedure is an excellent option for children and young adults who need aortic valve replacement as this surgery can restore patient survival to that of a normal sex and aged-matched population. However, some patients experience aneurysmal formation during autograft remodeling and require reoperation. As the underlying biomechanics of autograft remodeling are unknown, we investigated patient-specific wall stresses in pulmonary autografts one year post-operatively to better understand systemic pressure-driven early autograft wall stresses. Methods: Ross patients (n=16) who underwent intraoperative collection of pulmonary root/aortic specimen, and subsequent one-year MRI follow-up were recruited. Patient-specific material properties from their tissue were experimentally determined and incorporated into autograft ± Dacron and ascending aorta finite element models. A multiplicative approach was used to account for pre-stress geometry from in-vivo MRI. Physiologic pressure loading was simulated with LS-DYNA software. Results: At systemic systole, first principal stresses were 567kPa (25-75% IQR, 485-675kPa), 809kPa (691-1219kPa), and 382kPa (334-413kPa) at autograft sinuses, sinotubular junction (STJ), and ascending aorta, respectively. Second principal stresses were 355kPa (320-394kPa), 360kPa (310-426kPa), and 184kPa (147-222kPa) at autograft sinuses, STJ, and ascending aorta, respectively. Mean autograft diameters were 38.3±5.3mm, 29.9±2.7mm, and 26.6±4.0mm at sinuses, STJ, and annulus, respectively. Conclusions: First principal stresses were mainly located at STJ, particularly when Dacron reinforcement was applied to constrain STJ dilatation. However, at one-year after the Ross operation, autograft dilatation was not seen despite elevated autograft wall stresses compared to their internal controls, the lower wall stresses in corresponding native distal ascending aorta. In this group of patients, higher risk of dilatation is expected in the sinuses and STJ if not constrained by Dacron than the corresponding ascending aorta. Future follow-up will elucidate the biomechanics of long-term autograft remodeling to develop predictive models for autograft dilatation.

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Non-invasive, energy-based assessment of patient-specific material properties of arterial tissue

Biomechanics and Modeling in Mechanobiology ◽

10.1007/s10237-015-0653-5 ◽

2015 ◽

Vol 14 (5) ◽

pp. 1045-1056 ◽

Cited By ~ 21

Author(s):

M. Smoljkić ◽

J. Vander Sloten ◽

P. Segers ◽

N. Famaey

Keyword(s):

Material Properties ◽

Patient Specific ◽

Non Invasive ◽

Arterial Tissue ◽

Specific Material

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Impact of Patient-Specific In Vivo Vessel Material Properties on Carotid Atherosclerotic Plaque Stress/Strain Calculations

International Journal of Computational Methods ◽

10.1142/s0219876218420021 ◽

2019 ◽

Vol 16 (03) ◽

pp. 1842002 ◽

Cited By ~ 1

Author(s):

Qingyu Wang ◽

Dalin Tang ◽

Gador Canton ◽

Thomas S. Hatsukami ◽

Kristen L. Billiar ◽

...

Keyword(s):

Material Properties ◽

Carotid Plaque ◽

Computational Models ◽

Patient Specific ◽

Stress And Strain ◽

Carotid Atherosclerotic Plaque ◽

Plaque Vulnerability ◽

Material Models ◽

Vessel Material

Patient-specific vessel material properties are in general lacking in image-based computational models. Carotid plaque stress and strain conditions with in vivo material and old material models were investigated (8 patients, 16 plaques). Plaque models using patient-specific in vivo vessel material properties showed significant differences from models using old material properties from the literature on stress and strain calculations. These differences demonstrated that models using in vivo material properties could improve the accuracy of stress and strain calculations which could potentially lead to more accurate plaque vulnerability assessment.

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Identification of in vivo nonlinear anisotropic mechanical properties of ascending thoracic aortic aneurysm from patient-specific CT scans

Scientific Reports ◽

10.1038/s41598-019-49438-w ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 4

Author(s):

Minliang Liu ◽

Liang Liang ◽

Fatiesa Sulejmani ◽

Xiaoying Lou ◽

Glen Iannucci ◽

...

Keyword(s):

Mechanical Properties ◽

Aortic Aneurysm ◽

Thoracic Aortic Aneurysm ◽

Aortic Wall ◽

Inverse Methods ◽

Ct Scans ◽

Patient Specific ◽

Accurate Identification ◽

Anisotropic Mechanical Properties

Abstract Accurate identification of in vivo nonlinear, anisotropic mechanical properties of the aortic wall of individual patients remains to be one of the critical challenges in the field of cardiovascular biomechanics. Since only the physiologically loaded states of the aorta are given from in vivo clinical images, inverse approaches, which take into account of the unloaded configuration, are needed for in vivo material parameter identification. Existing inverse methods are computationally expensive, which take days to weeks to complete for a single patient, inhibiting fast feedback for clinicians. Moreover, the current inverse methods have only been evaluated using synthetic data. In this study, we improved our recently developed multi-resolution direct search (MRDS) approach and the computation time cost was reduced to 1~2 hours. Using the improved MRDS approach, we estimated in vivo aortic tissue elastic properties of two ascending thoracic aortic aneurysm (ATAA) patients from pre-operative gated CT scans. For comparison, corresponding surgically-resected aortic wall tissue samples were obtained and subjected to planar biaxial tests. Relatively close matches were achieved for the in vivo-identified and ex vivo-fitted stress-stretch responses. It is hoped that further development of this inverse approach can enable an accurate identification of the in vivo material parameters from in vivo image data.

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