Yun Liang

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.

Measurement of the transverse strain tensor in the coronary arterial wall from clinical intravascular ultrasound images

Atherosclerotic plaque rupture is the major cause of acute coronary syndromes. Currently, there is no reliable diagnostic tool to predict plaque rupture. Knowledge of plaque mechanical properties based on local artery wall strain measurements would be useful for characterizing its composition and predicting its vulnerability. Due to cardiac motion, strain estimation in clinical intravascular ultrasound (IVUS) images is extremely challenging. A method is presented to estimate cross-sectional coronary artery wall strain in response to cardiac pulsatile pressure using clinically acquired IVUS images, which are acquired in continuous pullback mode. First, cardiac phase information is retrieved retrospectively from an IVUS image sequence using an image-based gating method, and image sub-sequences at systole and diastole are extracted. Then, images at branch sites are used as landmarks to align the two image sub-sequences. Finally, the paired images at each site are registered to measure the 2D strain tensor of the coronary artery cross-section. This method has been successfully applied to IVUS images of a left anterior descending (LAD) coronary artery acquired clinically during a standard procedure. Such complete strain information should be useful for identifying vulnerable plaque.

The correspondence between coronary arterial wall strain and histology in a porcine model of atherosclerosis.

Atherosclerotic plaque rupture is the leading cause of mortality in cardiovascular disease. Intravascular ultrasound (IVUS) imaging is a powerful clinical technique that provides real-time cross-sectional images of the arterial wall and atherosclerotic plaques. However, it does not provide sufficient information about the histological composition of plaques to characterize their vulnerability. Arterial wall strain measurements may provide insights into plaque composition and vulnerability, complementing the information directly available in the IVUS echogram. We have developed a method to measure the transverse arterial wall strain tensor in response to luminal pressure change, by registering IVUS images acquired at different pressures. This method has been validated by using IVUS images with simulated motion and IVUS images of a vessel phantom. In this study, we further evaluate the method by assessing the correspondence of the calculated strain distribution and the histological composition of atherosclerotic coronary arteries from Sinclair miniature pigs following 12 months of a high fat diet. The images were acquired in situ using a clinical IVUS system and under computer-controlled pressurization. After image acquisition, the artery segments were fixed for histology to identify plaque components. The strain distributions were aligned with the corresponding histological sections. The stiffness of various components of the lesion, inferred from the wall strain distribution, was consistent with the tissue composition seen in the histological cross-sections. These findings suggest that strain measurements from IVUS are promising for assessing plaque vulnerability.

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.

Estimation of Arterial Wall Strain Based on IVUS Image Registration

In this study, we propose a method to estimate arterial wall strain using intravascular ultrasound (IVUS) images. The method is based on a nonrigid image registration algorithm, which represents the displacement field by cubic B-splines, and incorporates smoothness and incompressibility constraints. The 2D displacement field is then used to calculate the local strain tensors. With the 2D strain tensors, both radial and circumferential strain distributions can be obtained, and color-coded for display. The algorithm has been evaluated with synthetic motion IVUS images and phantom IVUS images under two luminal pressures

ESTIMATION OF CORONARY ARTERIAL WALL STRAIN IN CLINICAL IVUS IMAGES

In this study, we propose a practical method to estimate cross-sectional wall strain distribution of coronary arteries from clinically acquired intravascular ultrasound (IVUS) images in continuous pullback mode. First, cardiac phase information is retrieved retrospectively from an IVUS image sequence using an image-based gating method, and image sub-sequences at systole and diastole are extracted. Images at branch sites are used as benchmarks to align the two image sub-sequences. Finally, the paired images at each site are registered to estimate the cross-sectional strain of the coronary artery.

Measurement of Coronary Artery Wall Strain In Situ Using IVUS

Atherosclerotic plaque rupture is the leading cause of mortality in cardiovascular diseases. Studying biomechanics of plaque provides important insights into its vulnerability, since a plaque behaves consistently with its underlying contents. Arterial wall strain in response to luminal pressure change is such a measurable quantity. Intravascular ultrasound (IVUS) imaging is a wildly available clinical technique providing real time cross-sectional images of the vessel wall and plaque morphometry. IVUS elastography has been used to measure the radial strain through correlation analysis of the IVUS radiofrequency (RF) signals. We have developed a strain estimation method based on IVUS image registration. Our method has the ability to overcome nonlinear tissue deformation and measure 2D strain.Copyright

Coronary Artery Wall Strain Estimation From Clinical IVUS Images

Atherosclerotic plaque rupture is responsible for the majority of acute coronary syndromes and myocardial infarctions. Intravascular ultrasound (IVUS) imaging is a widely available clinical technique providing real time cross-sectional images of the vessel wall and plaque morphometry. However, IVUS echo images have limited ability to predict the vulnerability of the plaque. The mechanical behavior of the plaque is consistent with its underlying components, suggesting that measurements of plaque mechanical response can be used to assess the likelihood of plaque rupture [1]. Arterial wall strain in response to luminal pressure change is such a measurable quantity. IVUS elastography has been developed to measure the radial strain through correlation analysis of the IVUS radiofrequency (RF) signal [2]. Due to the movements of IVUS catheter caused by cardiac motion and the nonlinearity of tissue deformation, reliable strain is obtained by elastography only when the tissue motion is aligned with the RF direction and the RF traces correspond to the same axial location. This is difficult to achieve in vivo. We have developed a strain estimation method based on IVUS image registration. This 2D processing method has the ability to overcome in-plane catheter movement and heterogeneous tissue deformation, thereby increasing its accuracy. Using retrospectively retrieved cardiac phase information, we propose a practical method to estimate cross-sectional coronary arterial wall strain distribution from clinically acquired images during a conventional IVUS procedure.Copyright