Intravascular Ultrasound Elastography Research Articles

Contrast Venography Versus Intravenous Ultrasound in Hemodialysis Arteriovenous Access Dysfunction

Contrast Venography Versus Intravenous Ultrasound in Hemodialysis Arteriovenous Access Dysfunction

Plasma biomarkers and plaque strain predict long-term cardiovascular events in patients with acute coronary syndrome.

To test whether circulating and intracoronary biomarkers and coronary plaque strain have additive values to Global Registry of Acute Coronary Events (GRACE) score for predicting long-term cardiovascular events in ACS patients. One hundred ACS patients were enrolled and the GRACE score and plasma levels and intracoronary gradients of a number of biomarkers were measured. Coronary plaque burden and morphology in non-critical stenotic plaques were determined by intravascular ultrasound (IVUS) technique, and the maximal shear strain (SSmax) and maximal area strain (ASmax) were determined by intravascular ultrasound elastography (IVUSE) technique. Patients were followed for cardiovascular events and the predictive values of clinical characteristics, plasma biomarkers and plaque parameters were compared with GRACE score, and the incremental values of these measurements to the GRACE score were assessed. GRACE score, plasma biomarkers and plaque strain were independent predictors of cardiovascular events. Combination of GRACE score, plasma biomarkers and plaque strains significantly improved the predictive value of the GRACE score alone with the receiver-operating characteristic area increased from 0.457 to 0.667 (P=0.014). The combination of circulating and intracoronary biomarkers, plaque strain and GRACE score provides a better predictive tool than GRACE score alone in patients with ACS.

Development of an intravascular ultrasound elastography based on a dual-element transducer.

The ability to measure the elastic properties of plaques and vessels would be useful in clinical diagnoses, particularly for detecting a vulnerable plaque. This study demonstrates the feasibility of the combination of intravascular ultrasound (IVUS) and acoustic radiation force elasticity imaging for detecting the distribution of stiffness within atherosclerotic arteries ex vivo. A dual-frequency IVUS transducer with two elements was used to induce the propagation of the shear wave (by the 8.5 MHz pushing element) which could be simultaneously monitored by the 31 MHz imaging element. The wave-amplitude image and the wave-velocity image were reconstructed by measuring the peak displacement and wave velocity of shear wave propagation, respectively. System performance was verified using gelatin phantoms. The phantom results demonstrate that the stiffness differences of shear modulus of 1.6 kPa can be distinguished through the wave-amplitude and wave-velocity images. The stiffness distributions of the atherosclerotic aorta from a rabbit were obtained, for which the values of peak displacement and the shear wave velocity were 3.7 ± 1.2 µm and 0.38 ± 0.19 m s−1 for the lipid-rich plaques, and 1.0 ± 0.2 µm and 3.45 ± 0.45 m s−1 for the arterial walls, respectively. These results indicate that IVUS elasticity imaging can be used to distinguish the elastic properties of plaques and vessels.

Research on the relationship between area strain and eccentric index of atherosclerotic plaques by intravascular ultrasonic elastography

Objective To assess the relationships between area strain (AS) and eccentric index (EI) of atherosclerotic plaques as seen by intravascular ultrasonic elastography (IVUSE), and to reveal the effect of EI on the plaques stability. Methods Forty purebred New Zealand rabbits were fed with a high-cholesterol diet; the abdominal aorta endothelium was balloon-injured after 2 weeks; at the end of week 12, 2 plaques with moderate echo from each rabbit were chosen for in situ imaging, and 2 consecutive frames near the end-diastole images in situ were used to construct an IVUS elastogram. Results The eccentric plaques showed significantly greater area stain (AS) than the centripetal plaques [4.77(2.92, 8.01)% vs 3.27(2.15, 4.82)%, P=0.029] with smaller plaque area and plaque burden (P<0.05). The plaque AS was positively correlated with EI (r=0.392, P=0.003). The eccentric plaques showed significantly greater AS in the shoulder than in body [4.98(3.17, 8.48)% vs 4.64(2.51, 5.92)%, P=0.008]. Conclusions The EI is one of influential factors on plaque AS.Eccentric plaques may be more vulnerable than centripetal plaques, especially in the shoulder of eccentric plaques which have greater AS than their body. Key words: Intravascular ultrasound elastography; Atherosclerotic plaque; Eccentric index; Area strain

Erratum to: Intravascular ultrasound elastography analysis of the elastic mechanical properties of atherosclerotic plaque.

To assess the elastic mechanical properties of atherosclerotic plaque with different morphological properties by intravascular ultrasound elastography (IVUSE). 30 purebred New Zealand rabbits were fed a high-cholesterol diet; the abdominal aorta endothelium was balloon-injured after 2 weeks; at week 12, 2 plaques with moderate echo from each rabbit were chosen for in situ imaging, and 2 consecutive frames near the end-diastole images in situ were used to construct an IVUS elastogram. Shear strain (SS) and area strain (AS) were greater for eccentric than centripetal plaque (SS: 2.65(2.45)% vs. 1.79 ± 0.97%, p < 0.05; AS: 4.81(4.99)% vs. 3.23 ± 1.75%, p < 0.05) but were lower with low than high plaque burden (SS: 2.14 ± 0.37% vs. 3.40 ± 0.34%, p < 0.05; AS: 3.88 ± 0.60% vs. 5.81 ± 0.54%, p < 0.05). SS and AS were significantly greater for plaque with negative than no remodeling (SS: 3.98 ± 1.53% vs. 1.82(1.40)%, p < 0.017; AS: 6.94 ± 2.24% vs. 2.59(2.87)%, p < 0.017) and were found correlated with eccentric index and plaque burden (R2 = 0.365 and R2 = 0.359, both p < 0.05). Plaques associated with eccentricity, high plaque burden and negative remodeling showed greater strain than those with centripetalism, low plaque burden and positive remodeling. Eccentric index and plaque burden may be useful to predict the elastic stability of plaque.

Intravascular ultrasound elastography analysis of the elastic mechanical properties of atherosclerotic plaque.

To assess the elastic mechanical properties of atherosclerotic plaque with different morphological properties by intravascular ultrasound elastography (IVUSE). 30 purebred New Zealand rabbits were fed a high-cholesterol diet; the abdominal aorta endothelium was balloon-injured after 2 weeks; at week 12, 2 plaques with moderate echo from each rabbit were chosen for in situ imaging, and 2 consecutive frames near the end-diastole images in situ were used to construct an IVUS elastogram. Shear strain (SS) and area strain (AS) were greater for eccentric than centripetal plaque (SS: 2.65(2.45)% vs. 1.79 ± 0.97%, p < 0.05; AS: 4.81(4.99)% vs. 3.23 ± 1.75%, p < 0.05) but were lower with low than high plaque burden (SS: 2.14 ± 0.37% vs. 3.40 ± 0.34%, p < 0.05; AS: 3.88 ± 0.60% vs. 5.81 ± 0.54%, p < 0.05). SS and AS were significantly greater for plaque with negative than no remodeling (SS: 3.98 ± 1.53% vs. 1.82(1.40)%, p < 0.017; AS: 6.94 ± 2.24% vs. 2.59(2.87)%, p < 0.017) and were found correlated with eccentric index and plaque burden (R2 = 0.365 and R2 = 0.359, both p < 0.05). Plaques associated with eccentricity, high plaque burden and negative remodeling showed greater strain than those with centripetalism, low plaque burden and positive remodeling. Eccentric index and plaque burden may be useful to predict the elastic stability of plaque.

Effect of rosuvastatin on atherosclerotic plaque stability: An intravascular ultrasound elastography study

ObjectivesThe present study aimed to investigate the effect of potent rosuvastatin therapy on plaque mechanical stabilization as seen on IVUSE. Methods14 purebred New Zealand rabbits were fed a high-cholesterol diet; the abdominal aorta endothelium was balloon-injured after 2 weeks; at week 13, 7 rabbits received rosuvastatin (1.5 mg/kg/day), and the other 7 received an equal volume of saline. IVUS images of abdominal aortas were acquired, and 2 consecutive frames near the end-diastole images in situ were used to construct an IVUS elastogram. ResultsControl rabbits showed a significant increase in shear strain (SS) and area strain (AS) in total plaques. The rosuvastatin group showed no change in SS and AS, but serum TG and LDL-C levels were reduced, with less lipid deposition, macrophage infiltration, production of proinflammatory cytokines and apoptosis in plaques. The changes in SS and AS from baseline between groups significantly differed (SS: 1.15 (1.96) % vs. −0.99 ± 2.83%, p = 0.013; AS: 1.25 (2.29) % vs. −1.67 ± 5.05%, p = 0.022). At follow-up, for controls, strain values were increased in the shoulder of eccentric plaques (SS: 2.66 ± 1.31% vs. 4.86 ± 1.93%, p = 0.016; AS: 4.45 ± 2.33% vs. 7.91 ± 2.74%, p = 0.009) but not the plaque body. Changes in SS and AS in the plaque shoulder differed between the control and rosuvastatin groups (SS: 2.20 ± 2.17% vs. −0.87 ± 3.31%, p = 0.028; AS: 2.10 (4.61) % vs. −2.75 ± 5.97%, p = 0.009). ConclusionRosuvastatin therapy in rabbits with atherosclerotic plaques led to less vulnerable plaque features. IVUSE is a very sensitive technique for detecting pharmacologically-induced mechanical changes in rabbit atherosclerotic plaques.

Contrast-Enhanced Quantitative Intravascular Elastography: The Impact of Microvasculature on Model-Based Elastography

Model-based intravascular ultrasound elastography visualizes the stress distribution within vascular tissue—information that clinicians could use to predict the propensity of atherosclerotic plaque rupture. However, there are concerns that clusters of microvessels may reduce the accuracy of the estimated stress distribution. Consequently, we have developed a contrast-enhanced intravascular ultrasound system to investigate how plaque microvasculature affects the performance of model-based elastography. In simulations, diameters of 200, 400 and 800 μm were used, where the latter diameter represented a cluster of microvessels. In phantoms, we used a microvessel with a diameter of 750 μm. Peak stress errors of 3% and 38% were incurred in the fibrous cap when stress recovery was performed with and without a priori information about microvessel geometry. The results indicate that incorporating geometric information about plaque microvasculature obtained with contrast-enhanced ultrasound imaging improves the accuracy of estimates of the stress distribution within the fibrous cap precisely.

Visualizing the Stress Distribution Within Vascular Tissues Using Intravascular Ultrasound Elastography: A Preliminary Investigation

A methodology for computing the stress distribution of vascular tissue using finite element-based, intravascular ultrasound (IVUS) reconstruction elastography is described. This information could help cardiologists detect life-threatening atherosclerotic plaques and predict their propensity to rupture. The calculation of vessel stresses requires the measurement of strain from the ultrasound images, a calibrating pressure measurement and additional model assumptions. In this work, we conducted simulation studies to investigate the effect of varying the model assumptions, specifically Poisson's ratio and the outer boundary conditions, on the resulting stress fields. In both simulation and phantom studies, we created vessel geometries with two fibrous cap thicknesses to determine if we could detect a difference in peak stress (spatially) between the two. The results revealed that (i) Poisson's ratios had negligible impact on the accuracy of stress elastograms, (ii) the outer boundary condition assumption had the greatest effect on the resulting modulus and stress distributions and (iii) in simulation and in phantom experiments, our stress imaging technique was able to detect an increased peak stress for the vessel geometry with the smaller cap thickness. This work is a first step toward understanding and creating a robust stress measurement technique for evaluating atherosclerotic plaques using IVUS elastography.

Non-Rigid Image Registration Based Strain Estimator for Intravascular Ultrasound Elastography

Intravascular ultrasound elastography (IVUSe) could improve the diagnosis of cardiovascular disease by revealing vulnerable plaques through their mechanical tissue properties. To improve the performance of IVUSe, we developed and implemented a non-rigid image-registration method to visualize the radial and circumferential component of strain within vascular tissues. We evaluated the algorithm's performance with four initialization schemes using simulated and experimentally acquired ultrasound images. Applying the registration method to radio-frequency (RF) echo frames improved the accuracy of displacements compared to when B-mode images were employed. However, strain elastograms measured from RF echo frames produce erroneous results when both the zero-initialization method and the mesh-refinement scheme were employed. For most strain levels, the cross-correlation-initialization method produced the best performance. The simulation study predicted that elastograms obtained from vessels with average strains in the range of 3%–5% should have high elastographic signal-to-noise ratio (SNRe)–on the order of 4.5 and 7.5 for the radial and circumferential components of strain, respectively. The preliminary in vivo validation study (phantom and an atherosclerotic rabbit) demonstrated that the non-rigid registration method could produce useful radial and circumferential strain elastograms under realistic physiologic conditions. The results of this investigation were sufficiently encouraging to warrant a more comprehensive in vivo validation.

Intravascular Ultrasound Area Strain Imaging Used to Characterize Tissue Components and Assess Vulnerability of Atherosclerotic Plaques in a Rabbit Model

The purpose of this study was to investigate the association of area strain and tissue components and vulnerability of atherosclerotic plaques in a rabbit model. Forty purebred New Zealand rabbits underwent balloon-induced abdominal aorta endothelium injury, then a high-cholesterol diet for 24 weeks. Intravascular ultrasound (IVUS) images of abdominal aortas were acquired in situ and two consecutive frames near the end-diastole were used to construct an IVUS elastogram. Histologic slices matched with corresponding IVUS images were stained for fatty and collagen components, smooth muscle cells (SMCs) and macrophages. Regions-of-interest (ROIs) in plaques were classified as fibrous, fibro-fatty or fatty according to histologic study. Vulnerability indexes of ROIs were calculated as (fat + macrophage)/(collagen + SMCs). The area strain of these ROIs was calculated by use of an in-house–designed software system with a block-matching–based algorithm. Area strain was significantly higher in fatty ROIs (0.056 ± 0.003) than in fibrous (0.019 ± 0.002, p < 0.001) or fibro-fatty ROIs (0.033 ± 0.003, p < 0.001). The sensitivity and specificity of area strain for fatty ROIs characterization was 75.0% and 80.2% (area under the curve [AUC] 0.858, 95% confidence interval [CI] = 0.800–0.916, p < 0.001) and 75.0% and 75.3% (AUC 0.859, 95% CI = 0.801–0.917, p < 0.001) for fibrous ROIs, as demonstrated by receiver operating characteristic curve analysis. Area strain was positively correlated with vulnerability index (r 2 = 0.495, p < 0.001), fatty components (r 2 = 0.332, p < 0.001) and macrophage infiltration (r 2 = 0.406, p < 0.001); and negatively correlated with collagen and SMC composition (r 2 = 0.115 and r 2 = 0.169, p < 0.001, respectively). Area strain calculation with IVUS elastography based on digital B-mode analysis is feasible and can be useful for tissue characterization and plaque vulnerability assessment.

Vascular ultrasound for atherosclerosis imaging.

Cardiovascular disease is a leading cause of death in the Western world. Therefore, detection and quantification of atherosclerotic disease is of paramount importance to monitor treatment and possible prevention of acute events. Vascular ultrasound is an excellent technique to assess the geometry of vessel walls and plaques. The high temporal as well as spatial resolution allows quantification of luminal area and plaque size and volume. While carotid arteries can be imaged non-invasively, scanning of coronary arteries requires invasive intravascular catheters. Both techniques have already demonstrated their clinical applicability. Using linear array technology, detection of disease as well as monitoring of pharmaceutical treatment in carotid arteries are feasible. Data acquired with intravascular ultrasound catheters have proved to be especially beneficial in understanding the development of atherosclerotic disease in coronary arteries. With the introduction of vascular elastography not only the geometry of plaques but also the risk for rupture of plaques might be identified. These so-called vulnerable plaques are frequently not flow-limiting and rupture of these plaques is responsible for the majority of cerebral and cardiac ischaemic events. Intravascular ultrasound elastography studies have demonstrated a high correlation between high strain and vulnerable plaque features, both ex vivo and in vivo. Additionally, pharmaceutical intervention could be monitored using this technique. Non-invasive vascular elastography has recently been developed for carotid applications by using compound scanning. Validation and initial clinical evaluation is currently being performed. Since abundance of vasa vasorum (VV) is correlated with vulnerable plaque development, quantification of VV might be a unique tool to even prevent this from happening. Using ultrasound contrast agents, it has been demonstrated that VV can be identified and quantified. Although far from routine clinical application, non-invasive and intravascular ultrasound VV imaging might pave the road to prevent atherosclerotic disease in an early phase. This paper reviews the conventional vascular ultrasound techniques as well as vascular ultrasound strain and vascular ultrasound VV imaging.

Measurement of the 3D arterial wall strain tensor using intravascular B-mode ultrasound images: a feasibility study

Intravascular ultrasound (IVUS) elastography is a promising tool for studying atherosclerotic plaque composition and assessing plaque vulnerability. Current IVUS elastography techniques can measure the 1D or 2D strain of the vessel wall using various motion tracking algorithms. Since biological soft tissue tends to deform non-uniformly in 3D, measurement of the complete 3D strain tensor is desirable for more rigorous analysis of arterial wall mechanics. In this paper, we extend our previously developed method of 2D arterial wall strain measurement based on non-rigid image registration into 3D strain measurement. The new technique registers two image volumes acquired from the same vessel segment under different levels of luminal pressure and longitudinal stress. The 3D displacement field obtained from the image registration is used to calculate the local 3D strain tensor. From the 3D strain tensor, radial, circumferential and longitudinal strain distributions can be obtained and displayed. This strain tensor measurement method is validated and evaluated using IVUS images of healthy porcine carotid arteries subjected to a luminal pressure increase and longitudinal stretch. The ability of the algorithm to overcome systematic noise was tested, as well as the consistency of the results under different longitudinal frame resolutions.

Atherosclerotic plaque components characterization and macrophage infiltration identification by intravascular ultrasound elastography based on b-mode analysis: validation in vivo

Intravascular ultrasound elastography (IVUSE) is a promising imaging technique for early investigation of vulnerable plaques. Compared to radiofrequency signal processing, digital B-mode analysis is simple and of higher portability. However, rare studies have been reported validating the latter technique in vivo. In this study, we developed an IVUSE computer software system involving semi-automatic border delineation and block-matching algorithm and validated the system in vivo. Seven minipigs were fed with atherogenic diet for 40weeks. For each pig, the endothelium of one side of the renal arteries was denuded at the fifth week. With cross-correlation analysis, Lagrangian strain was calculated from two intravascular ultrasound images acquired in situ. Sixty regions of interests were selected from 35 elastograms matched well with the corresponding histological slices. Plaque types within these regions were classified as fibrous, fibro-fatty or fatty on Masson's trichrome and Oil-red O staining. Macrophage infiltration was also evaluated with immunohistology. Comparison between the mean strain value of the region of interest and the histological results revealed significant differences in strain values among different plaque types and non-diseased artery walls. The extent of macrophage infiltration was found to be correlated positively with strain values. For identification of fibro-fatty and fibrous plaques and macrophage infiltration, the system showed high sensitivity (93, 96 and 92%, respectively) and specificity (89, 76 and 66%, respectively), as revealed by receiver operating characteristic analysis. Our IVUSE system based on B-mode analysis is capable of characterizing fibrous and fibro-fatty plaques and macrophage intensity, thus holds potential for identifying vulnerable plaque.

Visualization of atherosclerotic plaque mechanical properties using model based intravascular ultrasound elastography.

Cardiovascular disease related deaths occur primarily from fatty plaques inside an artery that rupture and cause clots that disrupt blood flow. The study of arterial plaque mechanics is essential to the monitoring of atherosclerosis and the detection of vulnerable plaques or the likelihood of their rupture. The aim of this work is to measure and image the mechanical behavior of plaques using a clinically available intravascular ultrasound system (IVUS). To test the methods, radial displacements were measured from simulated images and phantom data within two dimensional IVUS rf images using standard elastography techniques. Simulations and phantom experiments were designed to mimic arterial geometries and deformations, which include plaque regions of varying stiffnesses. In addition, an optimization inversion algorithm was used to infer the elastic modulus of the underlying material. This algorithm utilizes a finite element based model and assumes that the deformation is quasi-static, plane strain and that the material is incompressible and linear elastic. The full spatially reconstructed modulus images, with no geometric constraints, are presented and compared to radial strain images. The phantom results are compared to the known modulus contrasts, and the simulated images are compared to contrasts and distributions.

Molecular mechanisms and therapeutic strategies of vulnerable atherosclerotic plaques

Vulnerable atherosclerotic plaque rupture leading to thrombosis is the major cause of acute coronary syndrome (ACS). Studies on the pathophysiologic mechanism of both ACS and plaque stabilizing treatment are driving the development of animal models of vulnerable plaque. In our laboratory, we established animal models of plaque rupture and thrombosis in rabbits and mice that are similar to human plaque rupture. Potential mechanisms involved in plaque vulnerability were studied from the inflammation-immunity, proliferation-apoptosis, oxidative stress and biomechanics aspects. Imaging markers and biomarkers were used to detect vulnerable plaques, including high frequency duplex ultrasound, intravascular ultrasound (IVUS), intravascular ultrasound elastography, magnetic resonance imaging (MRI) and inflammatory markers. Effective gene and drug strategies to treat vulnerable plaques were explored.

Estimation of the Transverse Strain Tensor in the Arterial Wall Using IVUS Image Registration

Intravascular ultrasound (IVUS) elastography is an imaging technique that obtains the local mechanical properties of the artery wall and atherosclerotic plaques through strain measurements using IVUS. Knowledge of these mechanical properties may provide crucial information that can help in estimating plaque composition and its vulnerability. Here, we present a new method to estimate the transverse strain tensor of the arterial wall based on nonrigid image registration using IVUS images. This method registers a pair of images acquired at a vessel site under different levels of luminal pressure. The 2-D displacement field in the vessel cross-section is estimated from image registration; then the displacement field is used to calculate the 2-D local strain tensor. From the strain tensor, the strain in any direction in the cross-section can be obtained; here, the radial and circumferential strain distributions are presented. This strain estimation method has been validated with synthetic motion IVUS images and evaluated using the IVUS images of a polyvinyl alcohol cryogel phantom. The accuracy of the estimated strain and the ability of the method to overcome IVUS system noise are demonstrated. (E-mail: mhfriedm@duke.edu)

An Inverse Method for Imaging the Local Elasticity of Atherosclerotic Coronary Plaques

The rupture of thin-cap fibroatheroma (TCFA) plaques is a major cause of acute coronary events. A TCFA has a trombogenic soft lipid core, shielded from the blood stream by a thin, possibly inflamed, stiff cap. The majority of atherosclerotic plaques resemble a TCFA in terms of overall structural composition, but have a more complex, heterogeneous morphology. An assessment of the material distribution is vital for quantifying the plaque's mechanical stability and for determining the effect of plaque-stabilizing pharmaceutical agents. We describe a new automated inverse elasticity method, intravascular ultrasound (IVUS) modulography, which is capable of reconstructing a heterogeneous Young's modulus distribution. The elastogram (i.e., spatial strain distribution) of the plaque is the input for the method, and is measured using the clinically available technique, IVUS elastography. Our method incorporates a novel divide-and-conquer strategy, allowing the reconstruction of TCFAs as well as heterogeneous plaques with localized regions of soft, weakened tissue. The method was applied to ex vivo elastograms, which were simulated from the cross sections of postmortem human coronary plaques. To demonstrate the clinical feasibility of the method, measured elastograms from human atherosclerotic coronary arteries were analyzed. One elastogram was measured in vitro; the other, in vivo. The method approximated the true Young's modulus distribution of all simulated plaques, while the in vitro reconstruction was in agreement with histology. In conclusion, the IVUS modulography in combination with the IVUS elastography has strong potential to become an all-encompassing modality for detecting plaques, for assessing the information related to their rupture-proneness, and for imaging their heterogeneous elastic material composition.

Characterization of Atherosclerotic Plaques and Mural Thrombi With Intravascular Ultrasound Elastography: A Potential Method Evaluated in an Aortic Rabbit Model and a Human Coronary Artery

Plaque rupture is correlated with the plaque morphology, composition, mechanical properties, and with the blood pressure. Whereas the geometry can accurately be assessed with intravascular ultrasound (IVUS) imaging, intravascular elastography (IVE) is capable of extracting information on the plaque local mechanical properties and composition. This paper reports additional IVE validation data regarding reproducibility and potential to characterize atherosclerotic plaques and mural thrombi. In a first investigation, radio frequency (RF) data were acquired from the abdominal aorta of an atherosclerotic rabbit model. In a second investigation, IVUS RF data were recorded from the left coronary artery of a patient referred for angioplasty. In both cases, Galaxy IVUS scanners (Boston Scientific, Freemont, CA), equipped with 40 MHz Atlantis catheters, were used. Elastograms were computed using two methods, the Lagrangian speckle model estimator (LSME) and the scaling factor estimator (SFE). Corroborated with histology, the LSME and the SFE both clearly detected a soft thrombus attached to the vascular wall. Moreover, shear elastograms, only available with the LSME, confirmed the presence of the thrombus. Additionally, IVE was found reproducible with consistent elastograms between cardiac cycles (CCs). Regarding the human dataset, only the LSME was capable of identifying a plaque that presumably sheltered a lipid core. Whereas such an assumption could not be certified with histology, radial shear and tangential strain LSME elastograms enabled the same conclusion. It is worth emphasizing that this paper reports the first ever in vivo tangential strain elastogram with regards to vascular imaging, due to the LSME. It is concluded that the IVE was reproducible exhibiting consistent strain patterns between CCs. The IVE might provide a unique tool to assess coronary wall lesions.

Robustness of reconstructing the Young’s modulus distribution of vulnerable atherosclerotic plaques using a parametric plaque model

Assessment of atherosclerotic plaque composition is crucial for quantitative monitoring of atherosclerosis and for quantifying the effect of pharmaceutical plaque-stabilizing treatments during clinical trials. We assessed this composition by applying a geometrically constrained, iterative inverse solution method to reconstruct a modulus elastogram ( i.e., Young’s modulus image) from a plaque strain elastogram ( i.e., radial strain image) that is measured using intravascular ultrasound strain elastography. This reconstruction method is especially suited for thin-cap fibroatheromas (TCFAs) ( i.e., plaques with a thin fibrous cap overlaying a lipid pool). Because a strain elastogram of a plaque depends upon the plaque material composition, catheter position within the vessel and measurement noise, this paper investigates how robust the reconstruction is when these parameters are varied. To this end, a standard plaque was defined as the modulus elastogram that was reconstructed from an in vivo measured strain elastogram of a human coronary plaque. This standard plaque was used to computer-simulate different strain elastograms, by varying the 1. geometry and material properties of its plaque components, 2. catheter position and 3. level of added strain noise. Robustness was evaluated by quantifying the correctly reconstructed size, shape and Young’s modulus of each plaque component region and minimal cap thickness. The simulations showed that TCFAs can be adequately reconstructed; the thinner and stiffer the cap or the softer and larger the lipid pool, the better is the reconstruction of these components and minimal cap thickness. Furthermore, reconstructions were 1. independent of catheter position and 2. independent of strain noise. As such, this method has potential to monitor robustly and quantitatively atherosclerosis in vivo. (E-mail: r.baldewsing@erasmusmc.nl)