Validation of Noninvasive In Vivo Compound Ultrasound Strain Imaging Using Histologic Plaque Vulnerability Features

Abstract

A therosclerotic carotid plaque rupture is a major cause of cerebrovascular mortality and morbidity. The proneness of a plaque to rupture is mainly related to its composition and geometry.1,2 Rupture-prone plaques typically contain a medium to large necrotic/lipid-rich core, which is separated from the lumen by a thin fibrous cap, whereas stable plaques have a thicker cap and often no necrotic/lipid-rich core. 1,2 Furthermore, vulnerable plaques frequently present with intraplaque hemorrhage, a high concentration of macrophages, and a decreased number of smooth muscle cells (SMCs). 2,3 Local features of plaque vulnerability are correlated with an increased risk of future cerebrovascular events (CVE). 4,5 This explains why local detection of these features is important. Detection of local features might also serve as a surrogate marker for plaque progression and subsequent CVE in other vascular beds. For instance, catheter-based techniques such as virtual histology or near-infrared spectroscopy have demonstrated that detection of lipid in the vascular tree has potential for accurate risk stratification of patients with acute coronary syndromes. 6 However, because plaques are often asymptomatic before the first CVE, a patient-friendly noninvasive technique is required. Ultrasound is nonionizing, fast, and relatively inexpensive, and, therefore, has many advantages for assessment of plaque characteristics. Unfortunately, conventional ultrasound does not allow an accurate determination of the ratio of lipids and fibrous tissue throughout the plaque.A relatively new technique is ultrasound strain imaging, also referred to as elastography or palpography. 3,[7][8][9][10][11][12][13] Background and Purpose-Carotid plaque rupture is a major cause of stroke. Key issue for risk stratification is early identification of rupture-prone plaques. A noninvasive technique, compound ultrasound strain imaging, was developed providing high-resolution radial deformation/strain images of atherosclerotic plaques. This study aims at in vivo validation of compound ultrasound strain imaging in patients by relating the measured strains to typical features of vulnerable plaques derived from histology after carotid endarterectomy. Materials and Methods-Strains were measured in 34 severely stenotic (>70%) carotid arteries at the culprit lesion site within 48 hours before carotid endarterectomy. In all cases, the lumen-wall boundary was identifiable on B-mode ultrasound, and the imaged cross-section did not move out of the imaging plane from systole to diastole. After endarterectomy, the plaques were processed using a validated histology analysis technique. Results-Locally elevated strain values were observed in regions containing predominantly components related to plaque vulnerability, whereas lower values were observed in fibrous, collagen-rich plaques. The median strain of the inner plaque layer (1 mm thickness) was significantly higher (P<0.01) for (fibro)atheromatous (n=20, strain=0.27%) than that for fibrous plaques (n=14, strain=...

Feasibility and relevance of compound strain imaging in non-stenotic arteries: comparison between individuals with cardiovascular diseases and healthy controls

“…Strain parameters (RS and CS) were calculated from the radiofrequency data using custom made software written in Matlab R2014 (The MathWorks Inc., USA) [10, 19]. First ultrasonic frames were identified that corresponded to the systolic and diastolic phases (maximum and minimum lumen diameter, respectively) in an M-mode view of the image line that crossed the vessel lumen center.…”

“…Recently, several RF-based strain techniques specifically designed to evaluate arterial wall strain have been developed [10–15]. Some of these techniques have already been validated against post-endarterectomy histology and/or magnetic resonance imaging derived plaque composition [16–19]. In all of these validation studies patients with severe amounts of stenosis (>50%) were included.…”

A PSF-Shape-Based Beamforming Strategy for Robust 2D Motion Estimation in Ultrafast Data

“…Tissue motion and deformation can provide information about the structure, composition and functioning of the tissue and changes in the dynamic behavior of tissue can be used as indicator of disease. For example, stiff regions in breasts are often related to cancers [11,12], the assessment of local arterial deformation provides information about the atherosclerotic progression and vulnerability of lesions [13][14][15][16], increased blood velocities indicate the presence of a stenosis in the vessel [17][18][19], and infarcted myocardial tissue shows changed deformation patterns as compared to healthy tissue [20].…”

Multi-Plane Ultrafast Compound 3D Strain Imaging: Experimental Validation in a Carotid Bifurcation Phantom

“…One of them is functional assessment of the carotid vessel wall. Strain imaging holds the ability to quantify the mechanical deformation of the arterial wall induced by the pulsating blood and provides insight into the composition and morphology of the vessel wall, which is unavailable from ultrasonic imaging alone [2][3][4][5]. Therefore, strain imaging could reveal ongoing, frequently asymptomatic, pathological processes like plaque development.…”

“…With these techniques, it has been shown that arterial strain distribution correlates with histological composition of plaques in pigs [16] and in humans [2,17]. For intravascular imaging and non-invasive imaging in longitudinal planes, the US beam is aligned with the principal direction of deformation of the artery (radial for a concentric homogeneous artery), which implies a direct and accurate estimation of the strains in the principal direction using algorithms that only estimate the (axial) displacement component along the beam.…”