Intravascular ultrasound: novel pathophysiological insights and current clinical applications

Innovations in cardiac computed tomography: Imaging in coronary artery disease

Coronary computed tomography angiography (CCTA) has emerged as a pivotal tool in the non-invasive evaluation of coronary artery disease (CAD). Recent advancements in imaging techniques, quantitative plaque assessment methods, assessment of coronary physiology, and perivascular coronary inflammation have propelled CCTA to the forefront of CAD management, enabling precise risk stratification, disease monitoring, and evaluation of treatment response. However, challenges persist, including the need for cardiovascular outcomes data for therapy modifications based on CCTA findings and the lack of standardized quantitative plaque assessment techniques to establish universal guidelines for treatment strategies. This review explores the current utilization of CCTA in clinical practice, highlighting its clinical impact and discussing challenges and opportunities for future development. By addressing these nuances, CCTA holds promise for revolutionizing coronary imaging and improving CAD management in the years to come. Ultimately, the goal is to provide precise risk stratification, optimize medical therapy, and improve cardiovascular outcomes while ensuring cost-effectiveness for healthcare systems.

Emerging applications of single-cell profiling in precision medicine of atherosclerosis

Atherosclerosis is a chronic, progressive, inflammatory disease that occurs in the arterial wall. Despite recent advancements in treatment aimed at improving efficacy and prolonging survival, atherosclerosis remains largely incurable. In this review, we discuss emerging single-cell sequencing techniques and their novel insights into atherosclerosis. We provide examples of single-cell profiling studies that reveal phenotypic characteristics of atherosclerosis plaques, blood, liver, and the intestinal tract. Additionally, we highlight the potential clinical applications of single-cell analysis and propose that combining this approach with other techniques can facilitate early diagnosis and treatment, leading to more accurate medical interventions.

Atherosclerotic plaque stabilization and regression: a review of clinical evidence

Atherosclerotic plaque results from a complex interplay between lipid deposition, inflammatory changes, cell migration and arterial wall injury. Over the past two decades, clinical trials utilizing invasive arterial imaging modalities, such as intravascular ultrasonography, have shown that reducing levels of atherogenic lipoproteins, mainly serum LDL-cholesterol (LDL-C), to very low levels can safely reduce overall atherosclerotic plaque burden and favourably modify plaque composition. Classically, this outcome has been achieved with intensive statin therapy. Since 2016, newer and potent lipid-lowering strategies, such as proprotein convertase subtilisin-kexin type 9 inhibition, have shown incremental effects on plaque regression and risk of clinical events. Despite maximal reduction in plasma LDL-C levels, considerable residual cardiovascular risk remains in some patients. Therefore, there is a need to study therapeutic approaches that address residual risk beyond LDL-C reduction to promote plaque stabilization or regression. Contemporary imaging modalities, such as coronary computed tomography angiography, enable non-invasive assessment of the overall atherosclerotic plaque burden as well as of certain local plaque characteristics. This technology could allow further study of plaque stabilization and regression using novel therapeutic approaches. Non-invasive plaque assessment might also offer the potential to guide personalized management strategies if validated for this purpose.

Evaluation of the thickness of coronary calcium by 60-MHz intravascular ultrasound: head-to-head comparison with optical frequency domain imaging

The region behind the coronary calcium could not be visualized by intravascular ultrasound (IVUS) because of acoustic shadow. However, some pathological studies have shown that IVUS delineated the vessel border behind thin coronary calcium sheets. This study aimed to reveal whether recent IVUS can visualize the region behind thin coronary calcium sheets. Using 534 cross-sectional optical frequency domain images (OFDI), including severe calcified coronary lesions, calcium sheet thickness was measured by every 1°. Accordingly, the visibility of the vessel border behind the coronary calcium sheet was evaluated using 60-MHz IVUS images, which were longitudinally linked with OFDI ones. After carefully coordinating with the axial position, the association between the IVUS-derived permeability of the coronary calcium sheet and calcium thickness was evaluated. The maximum and mean calcium thickness by OFDI was 0.88 ± 0.39 and 0.62 ± 0.30 mm, respectively. By 60-MHz IVUS, 12.1% of the coronary calcium sheets had permeable segments. Comparing between OFDI and IVUS images, 48.6% of the coronary calcium sheets with maximum thickness ≤ 0.3 mm were sometimes permeable by 60-MHz IVUS, whereas most > 0.5 mm thick calcium sheets were impermeable. In the receiver operating characteristic curve analysis, the best cutoff values for the maximum and mean thickness of permeable calcium were 0.48 and 0.31 mm, respectively. Thus, 60-MHz IVUS can occasionally visualize the region behind a thin coronary calcium sheet. When using 60-MHz IVUS, this finding may be a predictive marker of calcium sheet with a thickness of < 0.5 mm.

Comparison of deep learning-based image segmentation methods for intravascular ultrasound on retrospective and large image cohort study

OBJECTIVES

The aim of this study was to investigate the generalization performance of deep learning segmentation models on a large cohort intravascular ultrasound (IVUS) image dataset over the lumen and external elastic membrane (EEM), and to assess the consistency and accuracy of automated IVUS quantitative measurement parameters.

METHODS

A total of 11,070 IVUS images from 113 patients and pullbacks were collected and annotated by cardiologists to train and test deep learning segmentation models. A comparison of five state of the art medical image segmentation models was performed by evaluating the segmentation of the lumen and EEM. Dice similarity coefficient (DSC), intersection over union (IoU) and Hausdorff distance (HD) were calculated for the overall and for subsets of different IVUS image categories. Further, the agreement between the IVUS quantitative measurement parameters calculated by automatic segmentation and those calculated by manual segmentation was evaluated. Finally, the segmentation performance of our model was also compared with previous studies.

RESULTS

CENet achieved the best performance in DSC (0.958 for lumen, 0.921 for EEM) and IoU (0.975 for lumen, 0.951 for EEM) among all models, while Res-UNet was the best performer in HD (0.219 for lumen, 0.178 for EEM). The mean intraclass correlation coefficient (ICC) and Bland-Altman plot demonstrated the extremely strong agreement (0.855, 95% CI 0.822-0.887) between model's automatic prediction and manual measurements.

CONCLUSIONS

Deep learning models based on large cohort image datasets were capable of achieving state of the art (SOTA) results in lumen and EEM segmentation. It can be used for IVUS clinical evaluation and achieve excellent agreement with clinicians on quantitative parameter measurements.

Physics-Inspired Regularized Pulse-Echo Quantitative Ultrasound: Efficient Optimization With ADMM

Pulse-echo quantitative ultrasound (PEQUS), which estimates the quantitative properties of tissue microstructure, entails estimating the average attenuation and the backscatter coefficient (BSC). Growing recent research has focused on the regularized estimation of these parameters. Herein, we make two contributions to this field: first, we consider the physics of the average attenuation and backscattering to devise regularization terms accordingly. More specifically, since the average attenuation gradually alters in different parts of the tissue, while BSC can vary markedly from tissue to tissue, we apply L2 and L1 norms for the average attenuation and the BSC, respectively. Second, we multiply different frequencies and depths of the power spectra with different weights according to their noise levels. Our rationale is that the high-frequency contents of the power spectra at deep regions have a low signal-to-noise ratio (SNR). We exploit the alternating direction method of multipliers (ADMM) for optimizing the cost function. The qualitative and quantitative evaluations of bias and variance exhibit that our proposed algorithm improves the estimations of the average attenuation and the BSC up to about 100%.

State-of-art review: intravascular imaging in percutaneous coronary interventions

The history of intravascular ultrasound (IVUS) and optical coherence tomography (OCT) reflects the relentless pursuit of innovation in interventional cardiology. These intravascular imaging technologies have played a pivotal role in our understanding of coronary atherosclerosis, vascular pathology, and the interaction of coronary stents with the vessel wall. Two decades of clinical investigations demonstrating the clinical efficacy and safety of intravascular imaging modalities have established these technologies as staples in the contemporary cardiac catheterization lab's toolbox and earning their place in revascularization clinical practice guidelines. In this comprehensive review, we will delve into the historical evolution, mechanisms, and technical aspects of IVUS and OCT. We will discuss the expanding evidence supporting their use in complex percutaneous coronary interventions, emphasizing their crucial roles in optimizing patient outcomes and ensuring procedural success. Furthermore, we will explore the substantial advances that have propelled these imaging modalities to the forefront of contemporary interventional cardiology. Finally, we will survey the latest developments in the field and explore the promising future directions that have the potential to further revolutionize coronary interventions.

Early stent fractures in superficial femoral artery resulting multiple pseudoaneurysm formation within one year: a case report

BACKGROUND

Though fracture is known complication of stenting, pseudoaneurysm asscoiated with stent fracture is an extremely rare complication. This has previoulsy been described to occur at least one or more years following initial stent placement. Here we present a case of multi-site stent fracture leading to two separate SFA pseudoaneurysms within one year of placement, successfully treated with covered stents.

CASE PRESENTATION

A 72-year-old male presented with severe claudication of his left lower extremity (Rutherford 3), found to have long segment SFA chronic total occlusion (CTO). Patient successfully underwent endovascular revascularization. Follow-up duplex ultrasound (US) at one year demonstrated a focus of severe in-stent restenosis (ISR). During repeat angiogram for treatment of the stenosis, stent fracture and pseudoaneurysm was seen in the distal SFA, which was treated successfully with a self-expanding covered stent. Additional stent fractures and pseudoanerusyms were subseuqently identified on follow-up, necessitating a third angiogram, and these were successfully repaired using overlapping covered stents, without further recurrence.

CONCLUSIONS

Superficial femoral artery stent fractures leading to pseudoaneurysms are extremely rare, particularly within first year of stent placement. Endovascular repair with covered stents has proven to be an effective treatment option with decreased procedural morbidity compared to surgical repair.

Intravascular Imaging versus Physiological Assessment versus Biomechanics-Which Is a Better Guide for Coronary Revascularization

Today, coronary artery disease (CAD) continues to be a prominent cause of death worldwide. A reliable assessment of coronary stenosis represents a prerequisite for the appropriate management of CAD. Nevertheless, there are still major challenges pertaining to some limitations of current imaging and functional diagnostic modalities. The present review summarizes the current data on invasive functional and intracoronary imaging assessment using optical coherence tomography (OCT), and intravascular ultrasound (IVUS). Amongst the functional parameters-on top of fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR)-we point to novel angiography-based measures such as quantitative flow ratio (QFR), vessel fractional flow reserve (vFFR), angiography-derived fractional flow reserve (FFRangio), and computed tomography-derived flow fractional reserve (FFR-CT), as well as hybrid approaches focusing on optical flow ratio (OFR), computational fluid dynamics and attempts to quantify the forces exaggerated by blood on the coronary plaque and vessel wall.

Ultrawide-bandwidth high-resolution all-optical intravascular ultrasound using miniaturized photoacoustic transducer

Conventional intravascular ultrasound (IVUS) uses piezoelectric transducers to electrically generate and receive ultrasound. However, it remains a challenge to achieve large bandwidth for high resolution without compromising imaging depth. We report an all-optical IVUS (AO-IVUS) imaging system using picosecond laser pulse-pumped carbon composite for ultrasound excitation and π-phase-shifted fiber Bragg gratings for ultrasound detection. Using this all-optical technique, we achieved ultrawide-bandwidth (147%) and high-resolution (18.6 micrometers) IVUS imaging, which is unattainable by conventional technique. Imaging performance has been characterized in phantoms, presenting 18.6-micrometer axial resolution, 124-micrometer lateral resolution, and 7-millimeter imaging depth. Rotational pullback imaging scans are performed in rabbit iliac artery, porcine coronary artery, and rabbit arteries with drug-eluting metal stents, in parallel with commercial intravenous ultrasound scans as reference. Results demonstrated the advantages of high-resolution AO-IVUS in delineating details in vascular structures, showing great potential in clinical applications.

High-resolution silicon photonics focused ultrasound transducer with a sub-millimeter aperture

We present an all-optical focused ultrasound transducer with a sub-millimeter aperture and demonstrate its capability for high-resolution imaging of tissue ex vivo. The transducer is composed of a wideband silicon photonics ultrasound detector and a miniature acoustic lens coated with a thin optically absorbing metallic layer used to produce laser-generated ultrasound. The demonstrated device achieves axial resolution and lateral resolutions of 12 μm and 60 μm, respectively, well below typical values achieved by conventional piezoelectric intravascular ultrasound. The size and resolution of the developed transducer may enable its use for intravascular imaging of thin fibrous cap atheroma.

Imaging of intracoronary thrombus

The identification of intracoronary thrombus and atherothrombosis is central to the diagnosis of acute myocardial infarction, with the differentiation between type 1 and type 2 myocardial infarction being crucial for immediate patient management. Invasive coronary angiography has remained the principal imaging modality used in the investigation of patients with myocardial infarction. More recently developed invasive intravascular imaging approaches, such as angioscopy, intravascular ultrasound and optical coherence tomography, can be used as adjunctive imaging modalities to provide more direct visualisation of coronary atheroma and the causes of myocardial infarction as well as to improve the sensitivity of thrombus detection. However, these invasive approaches have practical and logistic constraints that limit their widespread and routine application. Non-invasive angiographic techniques, such as CT and MRI, have become more widely available and have improved the non-invasive visualisation of coronary artery disease. Although they also have a limited ability to reliably identify intracoronary thrombus, this can be overcome by combining their anatomical and structural characterisation of coronary anatomy with positron emission tomography. Specific radiotracers which bind with high specificity and sensitivity to components of thrombus, such as activated platelets, fibrin and factor XIIIa, hold promise for the non-invasive detection of intracoronary thrombus. The development of these novel non-invasive approaches has the potential to inform clinical decision making and patient management as well as to provide a non-invasive technique to assess the efficacy of novel antithrombotic therapies or interventional strategies. However, these have yet to be realised in routine clinical practice.

A Method for High-Frequency Mechanical Scanning Ultrasonic Flow Imaging with Motion Compensation

Mechanical scanning with a single transducer is an alternative method for high-frequency ultrasound imaging, which is simple in structure, convenient to implement, and low in cost. However, traditional mechanical scanning ultrasonic imaging introduces additional Doppler shift due to the movement of the transducer, which brings a challenge for blood velocity measurement. An improved mechanical scanning system for high-frequency ultrasonic color Doppler flow imaging is developed in this paper. The mechanical scanning system has a scanning stroke range of 15 mm, a maximum scanning speed of 168 mm/s, and an imaging depth of 20 mm. Since the mechanical scanning of the system is not in uniform motion, motion compensation was applied to achieve high-precision imaging both in B-mode and Doppler mode. The experiment results show that the system imaging resolution can reach about 140 μm in B-mode imaging, the relative velocity error is less than 5% in color Doppler flow imaging at different flow rates, and the CNR of power Doppler flow imaging of this system is greater than 15 dB. The proposed mechanical scanning imaging system can achieve high-resolution structure imaging and color flow imaging, which can provide more diagnostic information for the practical diagnosis and broaden the application range of mechanical scanning ultrasound imaging.

In vivo endoscopic ultrasound imaging with a rotational-scanning, all-optical ultrasound probe

All-optical ultrasound manipulates ultrasound waves based on laser and photonics technologies, providing an alternative approach for pulse-echo ultrasound imaging. However, its endoscopic imaging capability is limited ex vivo by the multifiber connection between the endoscopic probe and the console. Here, we report on all-optical ultrasound for in vivo endoscopic imaging using a rotational-scanning probe that relies on a small laser sensor to detect echo ultrasound waves. The acoustically induced lasing frequency change is measured via heterodyne detection by beating the two orthogonally polarized laser modes, enabling a stable output of ultrasonic responses and immunity to low-frequency thermal and mechanical disturbances. We miniaturize its optical driving and signal interrogation unit and synchronously rotate it with the imaging probe. This specialized design leaves a single-fiber connection to the proximal end and allows fast rotational scanning of the probe. As a result, we used a flexible, miniature all-optical ultrasound probe for in vivo rectal imaging with a B-scan rate of 1 Hz and a pullback range of ∼7 cm. This can visualize the gastrointestinal and extraluminal structures of a small animal. This imaging modality offers an imaging depth of 2 cm at a central frequency of ∼20 MHz, showing promise for high-frequency ultrasound imaging applications in gastroenterology and cardiology.

Advances in Intravascular Ultrasound

Since its inception, intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have played a significant role in evaluating the pathophysiology of coronary artery disease (CAD) guiding the interventional and medical management of CAD improving outcomes in patients. Although the benefits of each of these modalities have been proven, due to some limitations, no single intravascular imaging technique has been proven to provide a detailed and complete evaluation of all CAD lesions. The use of different intravascular imaging modalities sequentially may lead to complications, which are cumbersome, consume time, and add financial burden to the patient. Recently, hybrid imaging catheters that combine OCT and IVUS benefits have been developed to limit these problems. Intravascular imaging techniques we are using currently have some drawbacks that hinder accurate assessment of plaque morphology and pathobiology as demonstrated in many histological studies, causing difficulty in identifying high-risk plaques. To overcome these limitations, great efforts have been put into developing hybrid, dual-probe catheters by combining imaging modalities to get an accurate analysis of plaque characteristics, and high-risk lesions. At present, many dual-probe catheters are available including combined IVUS-OCT, near-infrared spectroscopy-IVUS that is available commercially, the OCT-near infrared fluorescence (NIRF) molecular imaging, IVUS-NIRF, and combined fluorescence lifetime-IVUS imaging. Application of this combined multimodal imaging in clinical practice overcomes the limitations of standalone imaging and helps in providing a comprehensive and accurate visualization of plaque characteristics, composition, and plaque biology. The present article summarizes the advances in hybrid intravascular imaging, analyses the technical hindrances that should be known to have a use in the different clinical circumstances, and the till date shreds of evidence available from their first clinical application aiming to bring these modalities into the limelight and their potential role in the study of CAD.

Intravascular Imaging of Atherosclerosis by Using Engineered Nanoparticles

Atherosclerosis is a leading cause of morbidity and mortality, and high-risk atherosclerotic plaques can result in myocardial infarction, stroke, and/or sudden death. Various imaging and sensing techniques (e.g., ultrasound, optical coherence tomography, fluorescence, photoacoustic) have been developed for scanning inside blood vessels to provide accurate detection of high-risk atherosclerotic plaques. Nanoparticles have been utilized in intravascular imaging to enable targeted detection of high-risk plaques, to enhance image contrast, and in some applications to also provide therapeutic functions of atherosclerosis. In this paper, we review the recent progress on developing nanoparticles for intravascular imaging of atherosclerosis. We discuss the basic nanoparticle design principles, imaging modalities and instrumentations, and common targets for atherosclerosis. The review is concluded and highlighted with discussions on challenges and opportunities for bringing nanoparticles into in vivo (pre)clinical intravascular applications.

Intravascular ultrasound provides additional insights in the hypertensive patients with focal renal artery fibromuscular dysplasia

To date, few study has defined the exact role or utility of intravascular ultrasound (IVUS) in the diagnosis and treatment of renal artery fibromuscular dysplasia (FMD). We investigated whether using an IVUS would provide additional insights in the hypertensive patients with focal renal artery FMD. A prospective, observational study, including all patients with focal renal artery FMD admitted to the Ruijin hospital during 6 consecutive years (2015-2021). Based on IVUS imaging, focal FMD patients were classified as two subtypes: intima-media thickening (IMT) and negative remodeling (NR) of the whole vessel. A total of 36 consecutive patients (24 ± 7, 13-39 years) with focal renal artery FMD were enrolled. Angiographic unifocal type was present in 22 (61.1%) patients and tubular type was present in 14 (38.9%) patients. Among 22 patients with unifocal, IVUS showed that 18 (81.8%) had IMT and 4 (18.2%) had NR. 14 patients with tubular, IVUS showed 3 (21.4%) had IMT and 11 (78.6%) had NR. No difference in age of onset, gender, BMI, initial BP levels were found between IMT and NR subtypes. However, hypertension cure rates of short-term (48 h after angioplasty) (76.2% vs. 26.7%, p = 0.004) and long-term (1-6years) (90.5% vs. 20.0%, p < 0.001) were higher in patients with IMT than in those with NR subtype. In present study, we described a new classification of focal renal artery FMD into IMT or NR subtype based on IVUS. Renal FMD Patients with IMT subtype were more likely to achieve cure of hypertension. We investigated whether using an IVUS would provide additional insights in the hypertensive patients with focal renal artery FMD. A new classification of focal renal artery FMD into IMT or NR subtype based on IVUS was described. Renal FMD Patients with IMT subtype were more likely to achieve cure of hypertension.

Fibrous Cap Thickness Predicts Stable Coronary Plaque Progression: Early Clinical Validation of a Semiautomated OCT Technology

BACKGROUND

Imaging-based characteristics associated with the progression of stable coronary atherosclerotic lesions are poorly defined. Utilizing a combination of optical coherence tomography (OCT) and intravascular ultrasound (IVUS) imaging, we aimed to characterize the lesions prone to progression through clinical validation of a semiautomated OCT computational program.

METHODS

Patients with stable coronary artery disease underwent nonculprit vessel imaging with IVUS and OCT at baseline and IVUS at the 12-month follow-up. After coregistration of baseline and follow-up IVUS images, paired 5-mm segments from each patient were identified, demonstrating the greatest plaque progression and regression as measured by the change in plaque burden. Experienced readers identified plaque features on corresponding baseline OCT segments, and predictors of plaque progression were assessed by multivariable analysis. Each segment then underwent volumetric assessment of the fibrous cap (FC) using proprietary software.

RESULTS

Among 23 patients (70% men; median age, 67 years), experienced-reader analysis demonstrated that for every 100 μm increase in mean FC thickness, plaques were 87% less likely to progress (P = .01), which persisted on multivariable analysis controlling for baseline plaque burden (P = .05). Automated FC analysis (n = 17 paired segments) confirmed this finding (P = .01) and found thinner minimal FC thickness (P = .01) and larger FC surface area of <65 μm (P = .02) and <100 μm (P = .04) in progressing segments than in regressing segments. No additional imaging features predicted plaque progression.

CONCLUSIONS

A semiautomated FC analysis tool confirmed the significant association between thinner FC and stable coronary plaque progression along entire vessel segments, illustrating the diffuse nature of FC thinning and suggesting a future clinical role in predicting the progression of stable coronary artery disease.

Contemporary Evidence-Based Diagnosis and Management of Severe Coronary Artery Calcification

Percutaneous treatment of heavily calcified coronary lesions remains a challenge for interventional cardiologists with increased risk of incomplete lesion preparation, suboptimal stent deployment, procedural complications, and a higher rate of acute and late stent failure. Adequate lesion preparation through calcium modification is crucial in optimising procedural outcomes. Several calcium modification devices and techniques exist, with rotational atherectomy the predominant treatment for severely calcified lesions. Novel technologies such as intravascular lithotripsy are now available and show promise as a less technical and highly effective approach for calcium modification. Emerging evidence also emphasises the value of detailed characterisation of calcification severity and distribution especially with intracoronary imaging for appropriate device selection and individualised treatment strategy. This review aims to provide an overview of the non-invasive and invasive evaluation of coronary calcification, discuss calcium modification techniques and propose an algorithm for the management of calcified coronary lesions.

Achieving coronary plaque regression: a decades-long battle against coronary artery disease

INTRODUCTION

Traditionally atherosclerosis was thought to be progressive and medical treatment solely focused on delaying the progression of atherosclerosis rather than treating the disease itself. Multiple recent studies, however, have demonstrated a significant decrease in cardiovascular mortality with the use of additional anti-atherosclerotic therapies beyond statins. Consistent with these observations, mechanistic studies indicate that these additional anti-atherosclerotic therapies have a positive effect on both halting and reversing the course of atherosclerosis.

AREAS COVERED

We examine the progression of atherosclerosis and the efficacy of various anti-atherosclerotic treatment classes in this review utilizing multimodality imaging techniques. Searches were conducted in electronic databases: PubMed and EMBASE for all peer reviewed publications that examined coronary plaque progression, regression and stabilization using different imaging modalities and antiatherosclerosis therapies. The keywords coronary plaque, coronary angiography, IVUS, intravascular OCT, CCTA in conjunction with the various therapies included in this review were searched in different combinations. All relevant published articles on this topic were identified and their reference lists were screened for relevance.

EXPERT COMMENTARY

Though lipoprotein levels have traditionally been the target for antiatherosclerosis medication, several newer strategies have emerged creating novel targets in the treatment of coronary atherosclerosis. Using a combination of antiatherosclerosis therapies in conjunction with noninvasive imaging modalities like CCTA to directly visualize the plaque, is currently the focus of the future, with the aim of preventing and reversing atherosclerosis.

Intravascular Ultrasound for the Evaluation and Management of Retroperitoneal, Genitourinary Malignancies

PURPOSE OF REVIEW

Herein we provide a review of intravascular ultrasound (IVUS) and its ability to assist in the evaluation and surgical management of advanced retroperitoneal, genitourinary tumors.

RECENT FINDINGS

Advanced retroperitoneal tumors such as advanced renal cell carcinoma, bulky retroperitoneal lymphadenopathy associated with advanced testicular carcinoma, large adrenal tumors, and retroperitoneal sarcomas can invade, compress, or distort vascular anatomy making surgical resection challenging and high risk. Intravascular ultrasonography is commonly used by vascular and cardiothoracic surgery to provide a real time assessment of vascular invasion, compression, and aberrant anatomy to assist with pre-operative and/or intraoperative decision-making. However, the application of this technology to assist with cancer surgery has been limited. The use of intravascular ultrasound prior to radical, extirpative, retroperitoneal surgery involving large vessels can aid in the planning and execution of such challenging operations.

Advances in Endoscopic Photoacoustic Imaging

Photoacoustic (PA) imaging is able to provide extremely high molecular contrast while maintaining the superior imaging depth of ultrasound (US) imaging. Conventional microscopic PA imaging has limited access to deeper tissue due to strong light scattering and attenuation. Endoscopic PA technology enables direct delivery of excitation light into the interior of a hollow organ or cavity of the body for functional and molecular PA imaging of target tissue. Various endoscopic PA probes have been developed for different applications, including the intravascular imaging of lipids in atherosclerotic plaque and endoscopic imaging of colon cancer. In this paper, the authors review representative probe configurations and corresponding preclinical applications. In addition, the potential challenges and future directions of endoscopic PA imaging are discussed.

Intravascular ultrasound for endovascular precision in pediatrics

Intravascular ultrasound (IVUS) is used as a diagnostic adjunct to angiography and has become a valuable diagnostic and interventional tool with a well-documented safety profile. The American College of Cardiology and the European Society of Cardiology have published guidelines regarding the use of IVUS in the setting of percutaneous coronary intervention. IVUS has gained popularity in the interventional radiology (IR) community in recent years; however, there are no consensus guidelines for utilization. Furthermore, IVUS remains an infrequently used modality in pediatric IR, likely because of unfamiliarity with the equipment and techniques, as well as concerns over the compatibility of these instruments with pediatric anatomy. IVUS can be safely used as a helpful and sometimes necessary tool for pediatric interventions in appropriately selected patients. The utility of IVUS for reducing both fluoroscopy time and contrast agent volume makes it particularly valuable in pediatric practice. This article presents an overview of both the rotational and phased-array IVUS types and an in-depth discussion on the most common applications of these techniques in the pediatric setting across multiple procedure categories.

Use of Intravascular Ultrasound During First-Time Femoropopliteal Peripheral Vascular Interventions Among Medicare Beneficiaries

BACKGROUND

Intravascular ultrasound (IVUS) may be a useful adjunct to lower extremity peripheral vascular interventions (PVI) in certain clinical scenarios. We aimed to identify patient- and physician-level characteristics associated with the use of IVUS during first-time femoropopliteal PVI.

METHODS

We included all Medicare beneficiaries undergoing elective femoropopliteal PVI for claudication or chronic limb-threatening ischemia between 01/01/2019 and 12/31/2019. We excluded patients with prior open or endovascular femoropopliteal intervention and all physicians performing ≤10 PVI during the study period. We calculated the proportion of patients who had IVUS performed as part of their index PVI for each physician. Hierarchical logistic regression was used to evaluate patient- and physician-level factors associated with use of IVUS.

RESULTS

We identified 58,552 patients who underwent index femoropopliteal PVI, of whom 11,394 (19%) received IVUS. A total of 1,628 physicians performed >10 procedures during the study period, with IVUS utilization ranging from 0-100%. After hierarchical regression, claudication (versus chronic limb-threatening ischemia: OR 1.23, 95% CI 1.11-1.36), stenting (versus angioplasty alone: OR 1.57, 1.33-1.86) and atherectomy (versus angioplasty alone: OR 2.09, 1.83-2.39) were associated with higher odds of IVUS utilization. Higher-volume providers (tertile 3 vs. tertile 1: OR 3.78, 2.43-5.90) and those with high rates of service provided in an office-based laboratory (tertile 3 vs. tertile 1: OR 10.72, 6.78-19.93) were more likely to utilize IVUS. Radiologists (OR 11.23, 5.96-21.17) and cardiologists (OR 1.97, 1.32-2.93) used IVUS more frequently than vascular surgeons.

CONCLUSIONS

Wide variability exists in the use of IVUS for first-time femoropopliteal PVI. The association of IVUS with claudication, atherectomy, and office-based laboratories raises concern about its potential overuse by some physicians.

Detection of Vulnerable Coronary Plaques Using Invasive and Non-Invasive Imaging Modalities

Acute coronary syndrome (ACS) mostly arises from so-called vulnerable coronary plaques, particularly prone for rupture. Vulnerable plaques comprise a specific type of plaque, called the thin-cap fibroatheroma (TFCA). A TCFA is characterized by a large lipid-rich necrotic core, a thin fibrous cap, inflammation, neovascularization, intraplaque hemorrhage, microcalcifications or spotty calcifications, and positive remodeling. Vulnerable plaques are often not visible during coronary angiography. However, different plaque features can be visualized with the use of intracoronary imaging techniques, such as intravascular ultrasound (IVUS), potentially with the addition of near-infrared spectroscopy (NIRS), or optical coherence tomography (OCT). Non-invasive imaging techniques, such as computed tomography coronary angiography (CTCA), cardiovascular magnetic resonance (CMR) imaging, and nuclear imaging, can be used as an alternative for these invasive imaging techniques. These invasive and non-invasive imaging modalities can be implemented for screening to guide primary or secondary prevention therapies, leading to a more patient-tailored diagnostic and treatment strategy. Systemic pharmaceutical treatment with lipid-lowering or anti-inflammatory medication leads to plaque stabilization and reduction of cardiovascular events. Additionally, ongoing studies are investigating whether modification of vulnerable plaque features with local invasive treatment options leads to plaque stabilization and subsequent cardiovascular risk reduction.

Impact of intravascular ultrasound and final kissing balloon dilatation on long-term clinical outcome in percutaneous revascularization with 1-stent strategy for left main coronary artery stenosis in drug-eluting stent era

BACKGROUND

It remains uncertain whether intravascular ultrasound (IVUS) use and final kissing balloon (FKB) dilatation would be standard care of percutaneous coronary intervention (PCI) with a simple 1-stent technique in unprotected left main coronary artery (LMCA) stenosis. This study sought to investigate the impact of IVUS use and FKB dilatation on long-term major adverse cardiac events (MACEs) in PCI with a simple 1-stent technique for unprotected LMCA stenosis.

METHODS

Between June 2006 and December 2012, 255 patients who underwent PCI with 1 drug-eluting stent for LMCA stenosis were analyzed. Mean follow-up duration was 1663 ± 946 days. Long-term MACEs were defined as death, nonfatal myocardial infarction (MI) and repeat revascularizations.

RESULTS

During the follow-up, 72 (28.2%) MACEs occurred including 38 (14.9%) deaths, 21 (8.2%) nonfatal MIs and 13 (5.1%) revascularizations. The IVUS examination and FKB dilatation were done in 158 (62.0%) and 119 (46.7%), respectively. IVUS use (20.3 versus 41.2%; log-rank P < 0.001), not FKB dilatation (30.3 versus 26.5%; log-rank P = 0.614), significantly reduced MACEs. In multivariate analysis, IVUS use was a negative predictor of MACEs [hazards ratio 0.51; 95% confidence interval (CI) 0.29-0.88; P = 0.017], whereas FKB dilatation (hazard ratio 1.68; 95% CI, 1.01-2.80; P = 0.047) was a positive predictor of MACEs. In bifurcation LMCA stenosis, IVUS use (18.7 versus 48.0%; log-rank P < 0.001) significantly reduced MACEs. In nonbifurcation LMCA stenosis, FKB dilatation showed a trend of increased MACEs (P = 0.076).

CONCLUSION

IVUS examination is helpful in reducing clinical events in PCI for LMCA bifurcation lesions, whereas mandatory FKB dilatation after the 1-stent technique might be harmful in nonbifurcation LMCA stenosis.

A Novel Distal Micromotor-Based Side-Looking Intravascular Ultrasound Transducer

Cardiovascular disease has become one of the leading causes of death in China, accounting for 45.5% of all deaths in rural areas and 43.16% in urban areas. Hence, its early diagnosis is important. With the development of intravascular imaging technology, the intravascular ultrasound (IVUS) is widely used. The available commercial mechanical rotary side-looking IVUS (SL-IVUS) transducers are driven by external motors that use long flexible shafts to transmit the rotation. However, when the transducer passes through a long-curved blood vessel, it easily causes the nonuniform rotation distortion (NURD) of the image. A catheter which contains a distal motor and sodium chloride (NaCl) solution is presented in this study as an attempt to solve such issues. The NaCl solution is used to connect the transducer and micromotor so that the motor can directly drive the transducer to rotate and acquire the information of the blood vessel. The results showed that the center frequency and -6-dB fraction bandwidth of the single element were 47 MHz and 98%, respectively. The SL-IVUS catheter consists of a distal motor, with speed stability and high resolution, and has the potential to diagnose cardiovascular disease. This novel structure can decrease the dimension at the top of the catheter and reduce the risks of clinical diagnosis.

Fully automated lumen and vessel contour segmentation in intravascular ultrasound datasets

Segmentation of lumen and vessel contours in intravascular ultrasound (IVUS) pullbacks is an arduous and time-consuming task, which demands adequately trained human resources. In the present study, we propose a machine learning approach to automatically extract lumen and vessel boundaries from IVUS datasets. The proposed approach relies on the concatenation of a deep neural network to deliver a preliminary segmentation, followed by a Gaussian process (GP) regressor to construct the final lumen and vessel contours. A multi-frame convolutional neural network (MFCNN) exploits adjacency information present in longitudinally neighboring IVUS frames, while the GP regression method filters high-dimensional noise, delivering a consistent representation of the contours. Overall, 160 IVUS pullbacks (63 patients) from the IBIS-4 study (Integrated Biomarkers and Imaging Study-4, Trial NCT00962416), were used in the present work. The MFCNN algorithm was trained with 100 IVUS pullbacks (8427 manually segmented frames), was validated with 30 IVUS pullbacks (2583 manually segmented frames) and was blindly tested with 30 IVUS pullbacks (2425 manually segmented frames). Image and contour metrics were used to characterize model performance by comparing ground truth (GT) and machine learning (ML) contours. Median values (interquartile range, IQR) of the Jaccard index for lumen and vessel were 0.913, [0.882,0.935] and 0.940, [0.917,0.957], respectively. Median values (IQR) of the Hausdorff distance for lumen and vessel were 0.196mm, [0.146,0.275]mm and 0.163mm, [0.122,0.234]mm, respectively. Also, the mean value of lumen area predictions, and limits of agreement were -0.19mm², [1.1,-1.5]mm², while the mean value and limits of agreement of plaque burden were 0.0022, [0.082,-0.078]. The results obtained with the model developed in this work allow us to conclude that the proposed machine learning approach delivers accurate segmentations in terms of image metrics, contour metrics and clinically relevant variables, enabling its use in clinical routine by mitigating the costs involved in the manual management of IVUS datasets.

Anti-Apo B-100 Autoantibody is a Marker of Unstable Coronary Plaque

AIMS

Cardiovascular diseases (CVD) are a global leading cause of mortality. However, few biomarkers are available to predict future coronary plaque rupture. We have recently demonstrated that low levels of anti-apolipoprotein B-100 autoantibody (anti-apo B-100 Ab) correlated with an increased CVD risk in Japanese patients with diabetes. In the present study, we examined the relationship between serum anti-apo B-100 Ab levels and coronary plaque characteristics in patients undergoing elective percutaneous coronary intervention (PCI).

METHODS

We conducted iMAP^®-intravascular ultrasound (IVUS) in 88 Japanese male patients undergoing elective PCI, and the five consecutive slices of IVUS images at the center of the most stenotic culprit lesion were used for identifying the plaque characteristics. The serum levels of anti-apo B-100 Ab against synthetic peptides (p45 or p210) were measured using a homemade enzyme-linked immunosorbent assay.

RESULTS

Serum IgG levels of anti-apo B-100 Ab against both native p45 and p210 (IgG _N-p45 and IgG_N-p210) and malondialdehyde (MDA)-modified p45 and p210 (IgG_MDA-p45 or IgG_MDA-p210) showed a negative correlation with plaque burden in total male patients undergoing elective PCI. Additionally, both IgG_N-p45 and IgG_N-p210, but neither IgG_MDA-p45 nor IgG_MDA-p210, correlated negatively with necrotic and positively with fibrotic components of iMAP^®-IVUS plaque characteristics in the patients with ＜1 month statin treatment before elective PCI ("statin-untreated" group). There was no significant correlation between anti-apo B-100 Ab and any plaque characteristics in the patients with statin treatment for 1 month or more before elective PCI ("statin-treated" group).

CONCLUSION

Measuring serum levels of anti-apo B-100 Ab might be helpful in the evaluation of unstable coronary plaque in male CVD patients without statin treatment.

Understanding the predictive value and methods of risk assessment based on coronary computed tomographic angiography in populations with coronary artery disease: a review

Risk assessment in coronary artery disease plays an essential role in the early identification of high-risk patients. However, conventional invasive imaging procedures all require long intraprocedural times and high costs. The rapid development of coronary computed tomographic angiography (CCTA) and related image processing technology has facilitated the formulation of noninvasive approaches to perform comprehensive evaluations. Evidence has shown that CCTA has outstanding performance in identifying the degree of stenosis, plaque features, and functional reserve. Moreover, advancements in radiomics and machine learning allow more comprehensive interpretations of CCTA images. This paper reviews conventional as well as novel diagnostic and risk assessment tools based on CCTA.

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

Thrombosis in the context of atherosclerosis typically results in life-threatening consequences, including acute coronary events and ischemic stroke. As such, early detection and treatment of thrombosis in atherosclerosis patients is essential. Clinical diagnosis of thrombosis in these patients is typically based upon a combination of imaging approaches. However, conventional imaging modalities primarily focus on assessing the anatomical structure and physiological function, severely constraining their ability to detect early thrombus formation or the processes underlying such pathology. Recently, however, novel molecular and non-molecular imaging strategies have been developed to assess thrombus composition and activity at the molecular and cellular levels more accurately. These approaches have been successfully used to markedly reduce rates of atherothrombotic events in patients suffering from acute coronary syndrome (ACS) by facilitating simultaneous diagnosis and personalized treatment of thrombosis. Moreover, these modalities allow monitoring of plaque condition for preventing plaque rupture and associated adverse cardiovascular events in such patients. Sustained developments in molecular and non-molecular imaging technologies have enabled the increasingly specific and sensitive diagnosis of atherothrombosis in animal studies and clinical settings, making these technologies invaluable to patients' health in the future. In the present review, we discuss current progress regarding the non-molecular and molecular imaging of thrombosis in different animal studies and atherosclerotic patients.

Clinical significance of microvessels detected by in vivo optical coherence tomography within human atherosclerotic coronary arterial intima: a study with multimodality intravascular imagings

The significance of microvessels within atherosclerotic plaques is not yet fully clarified. Associated with plaque vulnerability. The aim of this study is to examine tissue characteristics of plaque with microvessels detected by optical coherence tomography (OCT) by use of a commercially available color-coded intravascular ultrasound (IVUS) and coronary angioscopy (CAS). The subjects examined comprised of 44 patients with stable angina pectoris who underwent percutaneous coronary intervention. Microvessels were defined as a tiny tubule with a diameter of 50-300 µm detected over three or more frames in OCT. We compared the total volume of microvessels with tissue component such as fibrotic, lipidic, necrotic, and calcified volume and the number of yellow plaque. In IVUS analysis, % necrotic volume and % lipidic volume were significantly correlated and % fibrotic volume was inversely significantly correlated with the total volume of microvessel (r = 0.485, p = 0.0009; r = 0.401, p = 0.007; r = - 0.432, p = 0.003, respectively). The number of plaque with an angioscopic yellow grade of two or more was significantly correlated with the total volume of microvessel (r = 0.461, p = 0.002). The greater the luminal volume of microvessels, the more the percent content of necrotic/lipidic tissue volume within plaque and the more the number of yellow plaques. These data suggested that microvessels within coronary plaque might be related to plaque vulnerability.

Recent Advances in Transducers for Intravascular Ultrasound (IVUS) Imaging

As a well-known medical imaging methodology, intravascular ultrasound (IVUS) imaging plays a critical role in diagnosis, treatment guidance and post-treatment assessment of coronary artery diseases. By cannulating a miniature ultrasound transducer mounted catheter into an artery, the vessel lumen opening, vessel wall morphology and other associated blood and vessel properties can be precisely assessed in IVUS imaging. Ultrasound transducer, as the key component of an IVUS system, is critical in determining the IVUS imaging performance. In recent years, a wide range of achievements in ultrasound transducers have been reported for IVUS imaging applications. Herein, a comprehensive review is given on recent advances in ultrasound transducers for IVUS imaging. Firstly, a fundamental understanding of IVUS imaging principle, evaluation parameters and IVUS catheter are summarized. Secondly, three different types of ultrasound transducers (piezoelectric ultrasound transducer, piezoelectric micromachined ultrasound transducer and capacitive micromachined ultrasound transducer) for IVUS imaging are presented. Particularly, the recent advances in piezoelectric ultrasound transducer for IVUS imaging are extensively examined according to their different working mechanisms, configurations and materials adopted. Thirdly, IVUS-based multimodality intravascular imaging of atherosclerotic plaque is discussed. Finally, summary and perspectives on the future studies are highlighted for IVUS imaging applications.

Automatic Detection of Atherosclerotic Plaque and Calcification From Intravascular Ultrasound Images by Using Deep Convolutional Neural Networks

Atherosclerosis is the major cause of cardiovascular diseases (CVDs). Intravascular ultrasound (IVUS) is a common imaging modality for diagnosing CVDs. However, an efficient analyzer for IVUS image segmentation is required for assisting cardiologists. In this study, an end-to-end deep-learning convolutional neural network was developed for automatically detecting media-adventitia borders, luminal regions, and calcified plaque in IVUS images. A total of 713 grayscale IVUS images from 18 patients were used as training data for the proposed deep-learning model. The model is constructed using the three modified U-Nets and combined with the concept of cascaded networks to prevent errors in the detection of calcification owing to the interference of pixels outside the plaque regions. Three loss functions (Dice, Tversky, and focal loss) with various characteristics were tested to determine the best setting for the proposed model. The efficacy of the deep-learning model was evaluated by analyzing precision-recall curve. The average precision (AP), Dice score coefficient, precision, sensitivity, and specificity of the predicted and ground truth results were then compared. All training processes were validated using leave-one-subject-out cross-validation. The experimental results showed that the proposed deep-learning model exhibits high performance in segmenting the media-adventitia layers and luminal regions for all loss functions, with all tested metrics being higher than 0.90. For locating calcified tissues, the best result was obtained when the focal loss function was applied to the proposed model, with an AP of 0.73; however, the prediction efficacy was affected by the proportion of calcified tissues within the plaque region when the focal loss function was employed. Compared with commercial software, the proposed method exhibited high accuracy in segmenting IVUS images in some special cases, such as when shadow artifacts or side vessels surrounded the target vessel.

Ultrasound Methods in the Evaluation of Atherosclerosis: From Pathophysiology to Clinic

Atherosclerosis is a key pathological process that causes a plethora of pathologies, including coronary artery disease, peripheral artery disease, and ischemic stroke. The silent progression of the atherosclerotic disease prompts for new surveillance tools that can visualize, characterize, and provide a risk evaluation of the atherosclerotic plaque. Conventional ultrasound methods—bright (B)-mode US plus Doppler mode—provide a rapid, cost-efficient way to visualize an established plaque and give a rapid risk stratification of the patient through the Gray–Weale standardization—echolucent plaques with ≥50% stenosis have a significantly greater risk of ipsilateral stroke. Although rather disputed, the measurement of carotid intima-media thickness (C-IMT) may prove useful in identifying subclinical atherosclerosis. In addition, contrast-enhanced ultrasonography (CEUS) allows for a better image resolution and the visualization and quantification of plaque neovascularization, which has been correlated with future cardiovascular events. Newly emerging elastography techniques such as strain elastography and shear-wave elastography add a new dimension to this evaluation—the biomechanics of the arterial wall, which is altered in atherosclerosis. The invasive counterpart, intravascular ultrasound (IVUS), enables an individualized assessment of the anti-atherosclerotic therapies, as well as a direct risk assessment of these lesions through virtual histology IVUS.

Cavitation Emissions Nucleated by Definity Infused through an EkoSonic Catheter in a Flow Phantom

The EkoSonic endovascular system has been cleared by the U.S. Food and Drug Administration for the controlled and selective infusion of physician specified fluids, including thrombolytics, into the peripheral vasculature and the pulmonary arteries. The objective of this study was to explore whether this catheter technology could sustain cavitation nucleated by infused Definity, to support subsequent studies of ultrasound-mediated drug delivery to diseased arteries. The concentration and attenuation spectroscopy of Definity were assayed before and after infusion at 0.3, 2.0 and 4.0 mL/min through the EkoSonic catheter. PCI was used to map and quantify stable and inertial cavitation as a function of Definity concentration in a flow phantom mimicking the porcine femoral artery. The 2.0 mL/min infusion rate yielded the highest surviving Definity concentration and acoustic attenuation. Cavitation was sustained throughout each 15 ms ultrasound pulse, as well as throughout the 3 min infusion. These results demonstrate a potential pathway to use cavitation nucleation to promote drug delivery with the EkoSonic endovascular system.

Case Report: The Role of Intravascular Ultrasonography in Patients Underwent Percutaneous Coronary Intervention

Intravascular ultrasonography (IVUS) has an important role as a complimentary diagnostic tool in percutaneous coronary intervention procedure. IVUS provides valuable information regarding coronary vessel lumen and dimension and also plaque burden and its characteristic. The main use of IVUS in PCI is to guide the choose of interventional strategies to optimize stent deployment. Since drug eluting stent (DES) has promised to decrease the incidence in stent restenosis and stent thrombosis than bare metal stent, but neither the suboptimal results nor the complication after stenting with DES is still high. Thus, optimization of stent deployment under IVUS guidance is important in cases to decrease stent failure after PCI procedure, as well as to decrease complication rate after stenting in order to decrease mortality rate caused by coronary artery disease. We present here the use of IVUS guidance in a 43 and 46 year-old man underwent PCI.

Correlation between calcium, water contents and ultrasonographic appearance of atherosclerotic lesions of carotid artery lesions

Background

We tested the hypothesis whether there is a correlation between the echogenicity and calcium and water contents of carotid plaques.

Patients and methods

Ninety carotid befurcations from 45 deceased patients were removed during autopsy. Thirty-four plaques were categorized as homogenous echolucent (HEL), homogenous echogenic (HEG) and heterogenous (HE) plaques based on premortem B-mode image. Water content was expressed in % of wet weight. Ca was determined by proton-induced X-ray emission and expressed in ppm. Relative optical density of the B-mode images was analyzed offline using a computer program.

Results

HEL plaques had lower Ca content (medians and IQRs: 6,145 [4,465–6,536 ppm]) compared to HEG (74,100 [15,300–1,44,500−ppm]), P ≤ 0.001). HE plaques showed an intermediate calcium content (7,310 [4,840–9,920 ppm]) that was statistically not different from echolucent plaques. Water content of HEG plaques was statistically not different from HEL and HE (HEG:53.5 [35.5–64%], HEL: 73.5 [69.7–78.5%], HE: 70.6 [67.4–73.9%]). HEG plaques had the highest relative optical densities (196 [188–217%]). HEL and HE had similar relative optical densities (HEL: 176 [164–187%], HE: 164 [144–188%], respectively). A significant positive correlation was found between the Ca content and relative optical density of plaques.

Conclusions

Echogenicity of carotid plaques increases along with their calcium content. Water content may be an important factor in differentiation of different plaques.

Intravascular Ultrasound in the Endovascular Treatment of Patients With Peripheral Arterial Disease: Current Role and Future Perspectives

Over the last decade, intravascular ultrasound (IVUS) has emerged as a useful adjunctive tool to angiography in an increasing number of catheter-based procedures for peripheral arterial disease (PAD). IVUS catheters offer accurate cross-sectional imaging of arterial vessels with high dimensional accuracy and provide accurate information about lesion morphology. IVUS enables assessment of the plaque morphology, vessel diameter, and the presence of arterial dissections. Furthermore, IVUS is able to properly guide the best choice of appropriate percutaneous transluminal angioplasty (PTA) technique, guide the delivery of different devices, and assess the immediate result of any endovascular intervention. In the present review, the role of IVUS for PAD will be discussed, specifically the applications of IVUS technology during interventional procedures including PTA, stent sizing, crossing total occlusion, assessing residual narrowing and stent apposition and expansion, and atherectomy. Future perspectives of IVUS-guided treatments and cost-effectiveness of the systematic use of IVUS during endovascular interventions will be also discussed.

Influence of donor-transmitted coronary artery disease on long-term outcomes after heart transplantation - a retrospective study

BACKGROUND

Cardiac allograft vasculopathy (CAV) is an important cause of late mortality after heart transplantation, which may be influenced by preexisting coronary disease (CAD) in the donor heart.

METHODS

The aim of this study was to verify whether CAD in the donor heart had any influence on survival, cardiac-related adverse events (CRAEs), and coronary disease progression after transplantation. Donor coronary angiography performed in 289 hearts showed absence of CAD in 232 (no-CAD group) and moderate (≤50%) stenoses (CAD group) in 57. The 2 groups were compared for survival, freedom from CRAEs, and development of grade ≥ 2 CAV after transplantation.

RESULTS

Of 30-day mortality and postoperative complication rate was similar as mean follow-up (76 ± 56 and 75 ± 55 months) for no-CAD and CAD (P = 0.8). Ten-year actuarial survival was 58 ± 4% and 62 ± 7% for no-CAD and CAD (P = 0.4). Ten-year freedom from grade ≥ 2 CAV and from CRAEs was 81 ± 4% and 66 ± 5% vs 75 ± 8% and 67 ± 9% in no-CAD and CAD (P = 0.9 and 0.9, respectively).

CONCLUSIONS

Donor hearts with moderate CAD did not affect survival, freedom from CRAEs and did not accelerate development of high-grade CAV after transplantation supporting the use of such grafts to expand the donor pool. Routine use of coronary angiography in donor selection appears justified.

The role of intravascular ultrasound in percutaneous coronary intervention of complex coronary lesions

Intravascular ultrasound (IVUS) is a catheter-based coronary imaging technique. It utilises the emission & subsequent detection of reflected high frequency (30-60 MHz) sound waves to create high resolution, cross-sectional images of the coronary artery. IVUS has been the cornerstone of intracoronary imaging for more than two decades. When compared to the invasive coronary angiogram which studies only the silhouette of the contrast-filled artery lumen, IVUS also crucially images the vessel wall. Because of this capability, IVUS has greatly facilitated understanding of the coronary atherosclerosis process. Such insights from IVUS reveal how commonly and extensively plain angiography underestimates the true extent of coronary plaque, the characteristics of plaques prone to rupture and cause acute coronary syndromes (lipid rich, thin cap atheroma), and a realisation of the widespread occurrence of vessel remodelling in response to atherosclerosis. Similarly, IVUS has historically provided salutary mechanistic insights that have guided many of the incremental advances in the techniques of percutaneous coronary intervention (PCI). Examples include mechanisms of in-stent restenosis, and the importance of high-pressure post-dilatation of stents to ensure adequate stent apposition and thereby reduce the occurrence of stent thrombosis. IVUS also greatly facilitates the choice of correct diameter and length of stent to implant. Overall, a compelling body of evidence indicates that use of intravascular ultrasound in PCI helps to achieve optimal technical results and to mitigate the risk of adverse cardiac events. In this review, the role of intravascular ultrasound as an adjunct to PCI in complex coronary lesions is explored. The complex coronary situations discussed are the left main stem, ostial stenoses, bifurcation stenoses, thrombotic lesions, the chronically occluded coronary artery, and calcified coronary artery disease. By thorough review of the available evidence, we establish that the advantages of IVUS guidance are particularly evident in each of these complex CAD subsets. In particular, some consider the use of IVUS to be almost mandatory in left main PCI. A comparison with other intracoronary imaging techniques is also explored.

Intravascular Ultrasound Transducer by Using Polarization Inversion Technique for Tissue Harmonic Imaging: Modeling and Experiments

Intravascular ultrasound (IVUS) tissue harmonic imaging (THI) is a useful vessel imaging technique that can provide deep penetration depth as well as high spatial and contrast resolution. Typically, a high-frequency IVUS transducer for THI requires a broad bandwidth or dual-frequency bandwidth. However, it is very difficult to make an IVUS transducer with a frequency bandwidth covering from the fundamental frequency to the second harmonic or a dual-peak at the desired frequency. To solve this problem, in this study, we applied the polarization inversion technique (PIT) to the IVUS transducer for THI. The PIT makes it relatively easy to design IVUS transducers with suitable frequency characteristics for THI depending on the inversion ratio of the piezoelectric layer and specifications of the passive materials. In this study, two types of IVUS transducers based on the PIT were developed for THI. One is a front-side inversion layer (FSIL) transducer with a broad bandwidth, and the other is a back-side inversion layer (BSIL) transducer with a dual-frequency bandwidth. These transducers were designed using finite element analysis (FEA)-based simulation, and the prototype transducers were fabricated. Subsequently, the performance was evaluated by not only electrical impedance and pulse-echo response tests but also B-mode imaging tests with a 25 μm tungsten wire and tissue-mimicking gelatin phantoms. The FEA simulation and experimental results show that the proposed scheme can successfully implement the tissue harmonic IVUS image, and thus it can be one of the promising techniques for developing IVUS transducers for THI.

A Hidden Threat: Anomalous Aortic Origins of the Coronary Arteries in Athletes

Purpose of Review

Anomalous aortic origins of the coronary arteries (AAOCA) are a primary cause of sudden cardiac death in athletes. This review will detail the epidemiology, pathophysiology, and risk stratification of AAOCA, while also highlighting return-to-play considerations for athletes.

Recent Findings

Sport pre-participation cardiovascular screening methods lack sensitivity and specificity in the identification of AAOCA. For the symptomatic athlete, clinicians must maintain a heightened clinical suspicion for AAOCA in order to proceed with appropriate cardiac imaging and functional assessments. Anomalous origin of the left coronary artery with an interarterial course is considered high-risk and requires sport restriction until surgical correction. In contrast, risks associated with anomalous origin of the right coronary artery are controversial, thus management and sports eligibility decisions may incorporate principles of shared-decision making.

Summary

Management options for athletes with AAOCA are complex, requiring a comprehensive clinical evaluation. While advances in multimodality cardiovascular imaging and physiologic functional assessments have improved AAOCA risk stratification, best practice treatment strategies for some AAOCA subtypes remain uncertain. As such, clinical management and sport eligibility decisions require an individualized approach. Future prospective data will guide optimization of treatment strategies for athletes with AAOCA.

Current status of hybrid intravascular ultrasound and optical coherence tomography catheter for coronary imaging and percutaneous coronary intervention

Both intravascular ultrasound (IVUS) and optical coherence tomography (OCT) play a crucial role in elucidating the pathophysiology of coronary artery disease (CAD) with the goal to improve patient outcomes of medical and/or interventional CAD management. However, no single intravascular imaging technique has been proven to provide complete and detailed evaluation of all CAD lesions due to some limitations. Although sequential use of multiple modalities may sometimes be performed, there may be issues related to risk, time, and cost. To overcome these problems, several hybrids involving dual-probe combined IVUS-OCT catheters have been developed. The aim of this review article is to demonstrate some limitations of stand-alone imaging devices for evaluation of CAD, summarize the advances in hybrid IVUS-OCT imaging devices, discuss the technical challenges, and present the potential value in the clinical setting, especially in patients receiving medical or interventional CAD management.

Fundamentals and role of intravascular ultrasound in percutaneous coronary intervention

Intravascular ultrasound (IVUS) is a catheter-based invasive imaging modality that has become an essential adjunctive tool to percutaneous coronary intervention (PCI) over the past 20 years. Clinical applications of IVUS in PCI include assessment of lesion severity, characterizing plaque morphology, optimization of acute stent results and clarification of mechanisms of stent failure. Numerous meta-analyses of large observational and randomized studies support the role of IVUS-guided PCI in reducing short and long-term adverse outcomes, including mortality and stent failure, particularly in patients receiving drug-eluting stents (DESs) and in complex lesion subsets. The current review provides a summary of the fundamental aspects and current clinical roles of IVUS in coronary intervention.

Capacitive micromachined ultrasound transducers for intravascular ultrasound imaging

Intravascular ultrasound (IVUS) is a burgeoning imaging technology that provides vital information for the diagnosis of coronary arterial diseases. A significant constituent that enables the IVUS system to attain high-resolution images is the ultrasound transducer, which acts as both a transmitter that sends acoustic waves and a detector that receives the returning signals. Being the most mature form of ultrasound transducer available in the market, piezoelectric transducers have dominated the field of biomedical imaging. However, there are some drawbacks associated with using the traditional piezoelectric ultrasound transducers such as difficulties in the fabrication of high-density arrays, which would aid in the acceleration of the imaging speed and alleviate motion artifact. The advent of microelectromechanical system (MEMS) technology has brought about the development of micromachined ultrasound transducers that would help to address this issue. Apart from the advantage of being able to be fabricated into arrays with lesser complications, the image quality of IVUS can be further enhanced with the easy integration of micromachined ultrasound transducers with complementary metal-oxide-semiconductor (CMOS). This would aid in the mitigation of parasitic capacitance, thereby improving the signal-to-noise. Currently, there are two commonly investigated micromachined ultrasound transducers, piezoelectric micromachined ultrasound transducers (PMUTs) and capacitive micromachined ultrasound transducers (CMUTs). Currently, PMUTs face a significant challenge where the fabricated PMUTs do not function as per their design. Thus, CMUTs with different array configurations have been developed for IVUS. In this paper, the different ultrasound transducers, including conventional-piezoelectric transducers, PMUTs and CMUTs, are reviewed, and a summary of the recent progress of CMUTs for IVUS is presented.

Intravascular Ultrasound Imaging During Aortoiliac Stenting: No Impact on Outcomes at 1 Year

PURPOSE

To investigate the effect of intravascular ultrasound (IVUS) imaging use on clinical outcomes after aortoiliac stenting in patients with peripheral artery disease (PAD).

MATERIALS AND METHODS

Subjects for this retrospective analysis were derived from the OMOTENASHI registry database, which contained 803 symptomatic PAD patients (Rutherford categories 2-4) who were treated with self-expanding stent implantation for aortoiliac atherosclerotic lesions at 61 centers in Japan between January 2014 and April 2016. Of the 803 patients, 545 (67.9%) patients (mean age 73±9 years; 453 men) underwent IVUS-supported stent implantation and were compared with the 258 patients (mean age 73±8 years; 217 men) treated without IVUS. A propensity score analysis of 138 matched pairs was conducted to compare treatment strategies and clinical outcomes between patients having IVUS-supported endovascular therapy and those treated without IVUS.

RESULTS

Endovascular strategies and postoperative medications were not significantly different between the IVUS and no-IVUS groups. A procedure time under 1 hour was less frequent in the IVUS group, which had a longer fluoroscopy time. The 12-month restenosis rate was not significantly different between the 2 groups [10.2% (95% CI 6.9 to 14.9%) vs 10.3% (95% CI 5.4 to 18.6%), p=0.99]. There was no interaction between baseline characteristics and the association of IVUS use with restenosis risk.

CONCLUSION

Propensity score matching analysis revealed that duration and fluoroscopy time during IVUS-supported procedures were significantly longer than in cases without IVUS use, whereas the 12-month restenosis rate was not significantly different between the groups. IVUS use in aortoiliac lesions may be unnecessary.