Combined Use of Multiple Intravascular Imaging Techniques in Acute Coronary Syndrome

A Multicenter Feasibility and Safety Study of a Novel Hybrid IVUS-OCT Imaging System

Currently, precise stent manipulation and placement in percutaneous coronary intervention remain compromised. Intravascular imaging techniques are often limited by either spatial resolution or depth of penetration. A hybrid intravascular ultrasound (IVUS)-optical coherence tomography (OCT) system would be a better choice for interventional cardiologists. To validate the image quality and safety of the novel IVUS-OCT system for guiding coronary intervention in Chinese patients, a total of 114 cases were included. The proportion of clear imaging length was 96.21% ± 10.16%. Device success rate was 99.1%, technical success rate was 98.2%, and excellent image rate was 96.5%. No catheter-related adverse events occurred, and the incidence of device defects was 0.9%. This study preliminarily verified the image quality and safety of the novel Hybrid IVUS and OCT imaging system. (The StUdy to Evaluate the Performance and safEty of the Novasight HybRid System Using Objective PeRformance Criteria [SUPERIOR]; NCT04617899).

NIRS-IVUS Assessment of OCT-Derived Healed Coronary Plaques

AIMS

Healed plaque (HP) is associated with rapid plaque growth and luminal narrowing. Thin-cap fibroatheroma (TCFA) is recognized as a precursor lesion to plaque rupture. The aim of the present study was to compare the lipid size among optical coherence tomography (OCT)-derived HP, TCFA, and thick-cap fibroatheroma (ThCFA) using near-infrared spectroscopy-intravascular ultrasound (NIRS-IVUS).

METHODS

The present study included 173 patients with acute myocardial infarction (AMI) who underwent percutaneous coronary intervention. Non-culprit lesions with angiographically intermediate stenosis were assessed by both OCT and NIRS-IVUS.

RESULTS

The frequency of TCFA, HP, and ThCFA was 35 (20%), 53 (30%), and 85 (49%), respectively. Minimum lumen area was not significantly different between TCFA and HP, but was smaller in TCFA and HP than in ThCFA (4.6 [interquartile range {IQR}: 3.5-6.4] mm2 vs. 4.3 [3.4-5.3] mm2 vs. 6.5 [4.8-8.6] mm2, P＜0.001). Plaque burden was not significantly different between TCFA and HP, but was larger in TCFA and HP than in ThCFA (72 [IQR: 66-80] % vs. 75 [67-80] % vs. 62 [54-69] %, P＜0.001). Maximum lipid core burden index in 4mm (maxLCBI4mm) was largest in TCFA, followed by HP and ThCFA (493 [IQR: 443-606] vs. 446 [347-520] vs. 231 [161-302], P＜0.001). The frequency of lipid rich plaque with maxLCBI4mm ＞400 was highest in TCFA, followed by HP and ThCFA (89% vs. 60% vs. 7%, P＜0.001).

CONCLUSIONS

Based on NIRS-IVUS findings, non-culprit coronary HP in AMI was associated with vulnerable plaque characteristics, but not as much as TCFA.

The microenvironment of the atheroma expresses phenotypes of plaque instability

Data from histopathology studies of human atherosclerotic tissue specimens and from vascular imaging studies support the concept that the local arterial microenvironment of a stable atheroma promotes destabilizing conditions that result in the transition to an unstable atheroma. Destabilization is characterized by several different plaque phenotypes that cause major clinical events such as acute coronary syndrome and cerebrovascular strokes. There are several rupture-associated phenotypes causing thrombotic vascular occlusion including simple fibrous cap rupture of an atheroma, fibrous cap rupture at site of previous rupture-and-repair of an atheroma, and nodular calcification with rupture. Endothelial erosion without rupture has more recently been shown to be a common phenotype to promote thrombosis as well. Microenvironment features that are linked to these phenotypes of plaque instability are neovascularization arising from the vasa vasorum network leading to necrotic core expansion, intraplaque hemorrhage, and cap rupture; activation of adventitial and perivascular adipose tissue cells leading to secretion of cytokines, growth factors, adipokines in the outer artery wall that destabilize plaque structure; and vascular smooth muscle cell phenotypic switching through transdifferentiation and stem/progenitor cell activation resulting in the promotion of inflammation, calcification, and secretion of extracellular matrix, altering fibrous cap structure, and necrotic core growth. As the technology evolves, studies using noninvasive vascular imaging will be able to investigate the transition of stable to unstable atheromas in real time. A limitation in the field, however, is that reliable and predictable experimental models of spontaneous plaque rupture and/or erosion are not currently available to study the cell and molecular mechanisms that regulate the conversion of the stable atheroma to an unstable plaque.

QOCT-Net: A Physics-Informed Neural Network for Intravascular Optical Coherence Tomography Attenuation Imaging

Intravascular optical coherence tomography (IVOCT) provides high-resolution, depth-resolved images of coronary arterial microstructure by acquiring backscattered light. Quantitative attenuation imaging is important for accurate characterization of tissue components and identification of vulnerable plaques. In this work, we proposed a deep learning method for IVOCT attenuation imaging based on the multiple scattering model of light transport. A physics-informed deep network named Quantitative OCT Network (QOCT-Net) was designed to recover pixel-level optical attenuation coefficients directly from standard IVOCT B-scan images. The network was trained and tested on simulation and in vivo datasets. Results showed superior attenuation coefficient estimates both visually and based on quantitative image metrics. The structural similarity, energy error depth and peak signal-to-noise ratio are improved by at least 7%, 5% and 12.4%, respectively, compared with the state-of-the-art non-learning methods. This method potentially enables high-precision quantitative imaging for tissue characterization and vulnerable plaque identification.

Optical Coherence Tomography in Vulnerable Plaque and Acute Coronary Syndrome

Optical coherence tomography (OCT) is an intravascular imaging technique that uses near-infrared light. OCT provides high-resolution cross-sectional images of coronary arteries and enables tissue characterization of atherosclerotic plaques. OCT can identify plaque rupture, plaque erosion, and calcified nodule in culprit lesions of acute coronary syndrome. OCT can also detect important morphologic features of vulnerable plaques such as thin fibrous caps, large lipid cores, macrophages accumulation, intraplaque microvasculature, cholesterol crystals, healed plaques, and intraplaque hemorrhage.

Diagnostic Performance of 60 MHz High-Definition Intravascular Ultrasound versus Fourier Domain Optical Coherence Tomography for Identifying Plaque Rupture, Plaque Erosion, and Thrombosis in a Rabbit Model

Background

Most acute coronary syndromes occur due to coronary thrombosis caused by plaque rupture (PR) and plaque erosion (PE). Precise in vivo differentiation between PR and PE is challenging for intravascular imaging. This study is the first to determine the diagnostic performance of the novel 60 MHz high-definition intravascular ultrasound (HD-IVUS) for differentiating atherosclerotic plaque morphology influenced by local hemodynamic flow in rabbits. This study evaluated the diagnostic performance of 60 MHz HD-IVUS in identifying thrombosis in rabbits.

Methods

We established 60 rabbit models of atherosclerosis with left common carotid artery (LCCA) stenosis and 30 FeCl 3 -induced LCCA thrombosis. Intravascular imaging was assessed with 60 MHz HD-IVUS and fourier-domain optical coherence tomography (FD-OCT). The present study investigated the diagnostic accuracy of 60 MHz HD-IVUS for PR and PE, as well as thrombosis, using OCT-diagnosis as a standard reference.

Results

60 MHz HD-IVUS for identifying atherosclerotic plaque morphology using plaque cavity and minor intimal irregularities showed high sensitivity and specificity; 92.0 and 90.0% for identifying OCT-defined PR, and 80.0 and 70.0% for OCT-defined PE, respectively. In a rabbit thrombus model, 60 MHz HD-IVUS showed high sensitivity (88.0%) and specificity (80.0%) in identifying OCT-defined thrombosis.

Conclusions

60 MHz HD-IVUS can accurately identify PR and thrombosis. Further studies should confirm the clinical value of this novel technique in PE diagnosis.

Medical Image-Based Computational Fluid Dynamics and Fluid-Structure Interaction Analysis in Vascular Diseases

Hemodynamic factors, induced by pulsatile blood flow, play a crucial role in vascular health and diseases, such as the initiation and progression of atherosclerosis. Computational fluid dynamics, finite element analysis, and fluid-structure interaction simulations have been widely used to quantify detailed hemodynamic forces based on vascular images commonly obtained from computed tomography angiography, magnetic resonance imaging, ultrasound, and optical coherence tomography. In this review, we focus on methods for obtaining accurate hemodynamic factors that regulate the structure and function of vascular endothelial and smooth muscle cells. We describe the multiple steps and recent advances in a typical patient-specific simulation pipeline, including medical imaging, image processing, spatial discretization to generate computational mesh, setting up boundary conditions and solver parameters, visualization and extraction of hemodynamic factors, and statistical analysis. These steps have not been standardized and thus have unavoidable uncertainties that should be thoroughly evaluated. We also discuss the recent development of combining patient-specific models with machine-learning methods to obtain hemodynamic factors faster and cheaper than conventional methods. These critical advances widen the use of biomechanical simulation tools in the research and potential personalized care of vascular diseases.