Vascular Positron Emission Tomography and Restenosis in Symptomatic Peripheral Arterial Disease: A Prospective Clinical Study

Uncovering atherosclerotic cardiovascular disease by PET imaging

Assessing atherosclerosis severity is essential for precise patient stratification. Specifically, there is a need to identify patients with residual inflammation because these patients remain at high risk of cardiovascular events despite optimal management of cardiovascular risk factors. Molecular imaging techniques, such as PET, can have an essential role in this context. PET imaging can indicate tissue-based disease status, detect early molecular changes and provide whole-body information. Advances in molecular biology and bioinformatics continue to help to decipher the complex pathogenesis of atherosclerosis and inform the development of imaging tracers. Concomitant advances in tracer synthesis methods and PET imaging technology provide future possibilities for atherosclerosis imaging. In this Review, we summarize the latest developments in PET imaging techniques and technologies for assessment of atherosclerotic cardiovascular disease and discuss the relationship between imaging readouts and transcriptomics-based plaque phenotyping.

Applications of SPECT and PET Imaging for the Physiological Evaluation of Lower Extremity Peripheral Artery Disease

Peripheral artery disease (PAD) is classified as the narrowing or complete occlusion of the lower extremity arteries due to atherosclerosis. The risk of developing PAD increases with increased age and risk factors such as smoking, diabetes, hypertension, and hypercholesterolemia. Current treatment for PAD involves lifestyle and symptom management, statin and antiplatelet therapy, and/or surgical interventions to improve quality of life with varying efficacy. PAD affects approximately 5 to 6 percent of the global population, with this global burden continuing to increase. Despite the increase in disease prevalence, no gold standard functional diagnostic tool has been established for enabling early detection of the disease, appropriate medical management, and prediction of adverse outcomes for PAD patients. The visualization and quantification of the physiological consequences of PAD are possible by way of nuclear imaging: specifically, via scintigraphy, single-photon emission computed tomography (SPECT), and positron emission tomography (PET) imaging. These non-invasive modalities, when combined with targeted radionuclides, possess utility for detecting functional perfusion deficits and provide unique insight into muscle tissue- and vascular-level characteristics of PAD patients. This review discusses the past, present, and emerging applications of hybrid nuclear imaging modalities in the evaluation and monitoring of patients with PAD.

Severely increased albuminuria in patients with type 2 diabetes mellitus is associated with increased subclinical atherosclerosis in femoral arteries with Na [18F]F activity as a proxy - The DETERMINE study

BACKGROUND AND AIMS

Sodium [18F]fluoride (Na [18F]F) positron emission tomography imaging allows detailed visualization of early arterial micro-calcifications. This study aims to investigate atherosclerosis manifested by micro-calcification, macro-calcification, and aortic stiffness in patients with type 2 diabetes mellitus (T2DM) with and without albuminuria and severely decreased kidney function.

METHODS

A cohort was stratified in four groups (N = 10 per group), based on KDIGO categories (G1-5 A1-3). G1-2A1 non-diabetic controls (median [IQR] estimated glomerular filtration rate (eGFR) in mL/min/1.73 m2 91 [81-104]), G1-2A1 with T2DM (eGFR 87 [84-93], and albumin-creatinin-ratio (ACR) in mg/mmol 0.35 [0.25-0.75]), G1-2A3 with T2DM (eGFR 85 [60-103], and ACR 74 [62-122], and G4A3 with T2DM (eGFR 19 [13-27] and ACR 131 [59-304]).

RESULTS

Na [18F]F femoral artery grading score differed significantly in the groups with the highest Na [18F]F activity in A3 groups with T2DM (G1-2A3 with T2DM 228 [100-446] and G4A3 with T2DM 198 [113-578]) from the lowest groups of the G1-2A1 with T2DM (33 [0-93]) and in G1-2A1 non-diabetic controls (75 [0-200], p = 0.001). Aortic Na [18F]F activity and femoral artery computed tomography (CT)-assessed macro-calcification was increased in G4A3 with T2DM compared with G1-2A1 with T2DM (47.5 [33.8-73.8] vs. 17.5 [8.8-27.5] (p = 0.006) and 291 [170-511] vs. 12.2 [1.41-44.3] mg (p = 0.032), respectively). Carotid-femoral pulse wave velocity (PWV)-assessed aortic stiffness was significantly higher in both A3 groups with T2DM compared with G1-2A1 with T2DM (11.15 and 12.35 vs. 8.86 m/s, respectively (p = 0.009)).

CONCLUSIONS

This study indicates that the presence of severely increased albuminuria in patients with T2DM is cross-sectionally associated with subclinical arterial disease in terms of micro-calcification and aortic stiffness. Additional decrease in kidney function was associated with advanced macro-calcifications.

Multi-modality imaging for assessment of the microcirculation in peripheral artery disease: Bench to clinical practice

Peripheral artery disease (PAD) is a highly prevalent disorder with a high risk of mortality and amputation despite the introduction of novel medical and procedural treatments. Microvascular disease (MVD) is common among patients with PAD, and despite the established role as a predictor of amputations and mortality, MVD is not routinely assessed as part of current standard practice. Recent pre-clinical and clinical perfusion and molecular imaging studies have confirmed the important role of MVD in the pathogenesis and outcomes of PAD. The recent advancements in the imaging of the peripheral microcirculation could lead to a better understanding of the pathophysiology of PAD, and result in improved risk stratification, and our evaluation of response to therapies. In this review, we will discuss the current understanding of the anatomy and physiology of peripheral microcirculation, and the role of imaging for assessment of perfusion in PAD, and the latest advancements in molecular imaging. By highlighting the latest advancements in multi-modality imaging of the peripheral microcirculation, we aim to underscore the most promising imaging approaches and highlight potential research opportunities, with the goal of translating these approaches for improved and personalized management of PAD in the future.

Role of 18F-sodium fluoride positron emission tomography in imaging atherosclerosis

Atherosclerosis involving vascular beds across the human body remains the leading cause of death worldwide. Coronary and peripheral artery disease, which are almost universally a result of atherosclerotic plaque, can manifest clinically as myocardial infarctions, ischemic stroke, or acute lower-limb ischemia. Beyond imaging myocardial perfusion and blood-flow, nuclear imaging has the potential to depict the activity of the processes that are directly implicated in the atherosclerotic plaque progression and rupture. Out of several tested tracers to date, the literature is most advanced for 18F-sodium fluoride positron emission tomography. In this review, we present the latest data in the field of atherosclerotic 18F-sodium fluoride positron emission tomography imaging, discuss the advantages and limitation of the techniques, and highlight the aspects that require further research in the future.

Quantitative assessment of angioplasty-induced vascular inflammation with 19F cardiovascular magnetic resonance imaging

BACKGROUND

Macrophages play a pivotal role in vascular inflammation and predict cardiovascular complications. Fluorine-19 magnetic resonance imaging (19F MRI) with intravenously applied perfluorocarbon allows a background-free direct quantification of macrophage abundance in experimental vascular disease models in mice. Recently, perfluorooctyl bromide-nanoemulsion (PFOB-NE) was applied to effectively image macrophage infiltration in a pig model of myocardial infarction using clinical MRI scanners. In the present proof-of-concept approach, we aimed to non-invasively image monocyte/macrophage infiltration in response to carotid artery angioplasty in pigs using 19F MRI to assess early inflammatory response to mechanical injury.

METHODS

In eight minipigs, two different types of vascular injury were conducted: a mild injury employing balloon oversize angioplasty only (BA, n = 4) and a severe injury provoked by BA in combination with endothelial denudation (BA + ECDN, n = 4). PFOB-NE was administered intravenously three days after injury followed by 1H and 19F MRI to assess vascular inflammatory burden at day six. Vascular response to mechanical injury was validated using X-ray angiography, intravascular ultrasound and immunohistology in at least 10 segments per carotid artery.

RESULTS

Angioplasty was successfully induced in all eight pigs. Response to injury was characterized by positive remodeling with predominantly adventitial wall thickening and concomitant infiltration of monocytes/macrophages. No severe adverse reactions were observed following PFOB-NE administration. In vivo 19F signals were only detected in the four pigs following BA + ECDN with a robust signal-to-noise ratio (SNR) of 14.7 ± 4.8. Ex vivo analysis revealed a linear correlation of 19F SNR to local monocyte/macrophage cell density. Minimum detection limit of infiltrated monocytes/macrophages was estimated at approximately 410 cells/mm2.

CONCLUSIONS

In this proof-of-concept study, 19F MRI enabled quantification of monocyte/macrophage infiltration after vascular injury with sufficient sensitivity. This may provide the opportunity to non-invasively monitor vascular inflammation with MRI in patients after angioplasty or even in atherosclerotic plaques.

Status and influencing factors of frailty in patients with restenosis after percutaneous transluminal angioplasty for peripheral arterial disease: A cross-sectional study

This study aimed to investigate the frailty of patients with restenosis after percutaneous transluminal angioplasty (PTA) for peripheral arterial disease, explore the influencing factors, and determine its key factors to take targeted care measures and provide a basis for further interventional care. We recruited as many eligible subjects as possible and a total of 106 patients with restenosis after PTA for peripheral arterial disease in our hospital finished this study from January 2016 to August 2021. The Shorter 12-item version of health-related quality of life scale, Chinese Tilburg debility scale, Pittsburgh sleep quality index scale and activities of daily living score scale were used for investigation, and the independent influencing factors of patients' frailty were evaluated by multivariate logistic regression analysis. The incidence of frailty in restenosis after PTA was 72.6%. Logistic regression analysis found that high levels of C-reactive protein (odds ratios [OR] = 1.080, 95% confidence interval [CI] 1.012-1.153), diabetes (OR = 2.531, 95% CI 1.024-6.257) and advanced age (OR = 1.170, 95% CI 1.042-1.314) were risk factors for restenosis patients frailty, and higher scores of shorter 12-item version of health-related quality of life scale (OR = 0.889, 95% CI 0.813-0.973) was a protective factor for frailty in these patients. The incidence of debilitation in patients with restenosis after PTA for peripheral arterial disease is high, and high C-reactive protein levels, diabetes mellitus and advanced age are significantly associated with restenosis patients. Improving the quality of life of restenosis patients can reduce the occurrence of frailty.

Multi-Modality Imaging of Atheromatous Plaques in Peripheral Arterial Disease: Integrating Molecular and Imaging Markers

Peripheral artery disease (PAD) is a common and debilitating condition characterized by the narrowing of the limb arteries, primarily due to atherosclerosis. Non-invasive multi-modality imaging approaches using computed tomography (CT), magnetic resonance imaging (MRI), and nuclear imaging have emerged as valuable tools for assessing PAD atheromatous plaques and vessel walls. This review provides an overview of these different imaging techniques, their advantages, limitations, and recent advancements. In addition, this review highlights the importance of molecular markers, including those related to inflammation, endothelial dysfunction, and oxidative stress, in PAD pathophysiology. The potential of integrating molecular and imaging markers for an improved understanding of PAD is also discussed. Despite the promise of this integrative approach, there remain several challenges, including technical limitations in imaging modalities and the need for novel molecular marker discovery and validation. Addressing these challenges and embracing future directions in the field will be essential for maximizing the potential of molecular and imaging markers for improving PAD patient outcomes.

The Role of Positron Emission Tomography in Advancing the Understanding of the Pathogenesis of Heart and Vascular Diseases

Cardiovascular disease remains the leading cause of morbidity and mortality worldwide. For developing new therapies, a better understanding of the underlying pathology is required. Historically, such insights have been primarily derived from pathological studies. In the 21st century, thanks to the advent of cardiovascular positron emission tomography (PET), which depicts the presence and activity of pathophysiological processes, it is now feasible to assess disease activity in vivo. By targeting distinct biological pathways, PET elucidates the activity of the processes which drive disease progression, adverse outcomes or, on the contrary, those that can be considered as a healing response. Given the insights provided by PET, this non-invasive imaging technology lends itself to the development of new therapies, providing a hope for the emergence of strategies that could have a profound impact on patient outcomes. In this narrative review, we discuss recent advances in cardiovascular PET imaging which have greatly advanced our understanding of atherosclerosis, ischemia, infection, adverse myocardial remodeling and degenerative valvular heart disease.

Exploring Vessel Wall Biology In Vivo by Ultrasensitive Total-Body PET

Ultrasensitive, high-resolution, extended-field-of-view total-body (TB) PET using the first-of-its-kind 194-cm axial-field-of-view uEXPLORER may facilitate the interrogation of biologic hallmarks of hitherto difficult-to-evaluate low-signal vessel wall pathology in cardiovascular disease. Methods: Healthy volunteers were imaged serially for up to 12 h after a standard dose of 18F-FDG (n = 15) or for up to 3 h after injection of a very low dose (about 5% of a standard dose; n = 15). A cohort undergoing standard 18F-FDG PET (n = 15) on a conventional scanner with a 22-cm axial field of view served as a comparison group. Arterial wall signal, crosstalk with hematopoietic and lymphoid organs, and image quality were analyzed using standardized techniques. Results: TB PET depicted the large vessel walls with excellent quality. The arterial wall could be imaged with high contrast up to 12 h after tracer injection. Ultralow-dose TB 18F-FDG images yielded a vessel wall signal and target-to-background ratio comparable to those of conventional-dose, short-axial-field-of-view PET. Crosstalk between vessel wall and lymphoid organs was identified with better accuracy in both TB PET cohorts than in conventional PET. Conclusion: TB PET enables detailed assessment of in vivo vessel wall biology and its crosstalk with other organs over an extended time window after tracer injection or at an ultralow tracer dose. These initial observations support the feasibility of serial imaging in low-risk populations and will stimulate future mechanistic studies or therapy monitoring in atherosclerosis and other vessel wall pathologies.

18F-Sodium Fluoride PET/CT in Assessing Valvular Heart and Atherosclerotic Diseases

Aortic valve stenosis is the most common valvular disease in Western countries, while atherosclerotic cardiovascular disease is the foremost cause of death and disability worldwide. Valve degeneration and atherosclerosis are mediated by inflammation and calcification and inevitably progress over time. Computed tomography can visualise the later stages of macroscopic calcification but fails to assess the early stages of microcalcification and cannot differentiate active from burnt out disease states. Molecular imaging has the ability to provide complementary information related to disease activity, which may allow us to detect disease early, to predict disease progression and to monitor preventive or therapeutic strategies for in both aortic stenosis and atherosclerosis. PET/CT is a non-invasive imaging technique that enables visualization of ongoing molecular processes within small structures, such as the coronary arteries or heart valves. ¹⁸F-sodium fluoride (¹⁸F-NaF) binds hydroxyapatite deposits in the extracellular matrix, with preferential binding to newly developing deposits of microcalcification, which provides an assessment of calcification activity. In recent years, ¹⁸F-NaF has attracted the attention of many research groups and has been evaluated in several pathological cardiovascular processes. Histologic validation of the ¹⁸F-NaF PET signal in valvular disease and atherosclerosis has been reported in multiple independent studies. The selective high-affinity binding of ¹⁸F-NaF to microscopic calcified deposits (beyond the resolution of μCT) has been demonstrated ex vivo, as well as its ability to distinguish between areas of macro- and active microcalcification. In addition, prospective clinical studies have shown that baseline ¹⁸F-NaF uptake in patients with aortic stenosis and mitral annular calcification is correlated with subsequent calcium deposition and valvular dysfunction after a follow-up period of 2 years. In patients with surgical bioprosthetic aortic valves but without morphological criteria for prosthetic degeneration, increased ¹⁸F-NaF uptake at baseline was associated with subsequent bioprosthetic degeneration over time. Similar data were obtained in a cohort of patients with transcatheter aortic valve implantation. Furthermore, several studies have confirmed the association of coronary ¹⁸F-NaF uptake with adverse atherosclerotic plaque features, active disease and future disease progression. ¹⁸F-NaF uptake is also associated with future fatal or nonfatal myocardial infarction in patients with established coronary artery disease. The link between ¹⁸F-NaF uptake and active atherosclerotic disease has not only been demonstrated in the coronary arteries, but also in peripheral arterial disease, abdominal aortic aneurysms and carotid atherosclerosis. It can be assumed that ¹⁸F-NaF PET/CT will strengthen the diagnostic toolbox of practitioners in the coming years. Indeed, there is a strong medical need to diagnose degenerative valvular disease and to detect active atherosclerotic disease states. Finally, the use of ¹⁸F-NaF as a biomarker to monitor the efficacy of drug therapies in preventing these pathological processes is attractive. In this review, we consider the role of ¹⁸F-NaF PET/CT imaging in cardiac valvular diseases and atherosclerosis.

Advances in the Assessment of Coronary Artery Disease Activity with PET/CT and CTA

Non-invasive testing plays a pivotal role in the diagnosis, assessment of progression, response to therapy, and risk stratification of coronary artery disease. Although anatomical plaque imaging by computed tomography angiography (CTA) and ischemia detection with myocardial perfusion imaging studies are current standards of care, there is a growing body of evidence that imaging of the processes which drive atherosclerotic plaque progression and rupture has the potential to further enhance risk stratification. In particular, non-invasive imaging of coronary plaque inflammation and active calcification has shown promise in this regard. Positron emission tomography (PET) with newly-adopted radiotracers provides unique insights into atheroma activity acting as a powerful independent predictor of myocardial infarctions. Similarly, by providing a quantitative measure of coronary inflammation, the pericoronary adipose tissue density (PCAT) derived from standard coronary CTA enhances cardiac risk prediction and allows re-stratification over and above current state-of-the-art assessments. In this review, we shall discuss the recent advances in the non-invasive methods of assessment of disease activity by PET and CTA, highlighting how these methods could improve risk stratification and ultimately benefit patients with coronary artery disease.

Novel PET Applications and Radiotracers for Imaging Cardiovascular Pathophysiology

PET allows the assessment of cardiovascular pathophysiology across a wide range of cardiovascular conditions. By imaging processes directly involved in disease progression and adverse events, such as inflammation and developing calcifications (microcalcifications), PET can not only enhance our understanding of cardiovascular disease, but also, as shown for 18F-sodium fluoride, has the potential to predict hard endpoints. In this review, the recent advances in disease activity assessment with cardiovascular PET, which provide hope that this promising technology could be leveraged in the clinical setting, shall be discussed.

Vitamin K antagonists and cardiovascular calcification: A systematic review and meta-analysis

Background

Many patients treated with Vitamin K antagonists (VKA) for anticoagulation have concomitant vascular or valvular calcification. This meta-analysis aimed to evaluate a hypothesis that vascular and valvular calcification is a side-effect of VKA treatment.

Methods

We conducted a systematic literature search to identify studies that reported vascular or valvular calcification in patients treated with VKA. The associations between VKA use and calcification were analyzed with random-effects inverse variance models and reported as odds ratios (OR) and 95% confidence intervals (95% CI). In addition, univariate meta-regression analyses were utilized to identify any effect moderators.

Results

Thirty-five studies were included (45,757 patients; 6,251 VKA users). The median follow-up was 2.3 years [interquartile range (IQR) of 1.2–4.0]; age 66.2 ± 3.6 years (mean ± SD); the majority of participants were males [77% (IQR: 72–95%)]. VKA use was associated with an increased OR for coronary artery calcification [1.21 (1.08, 1.36), p = 0.001], moderated by the duration of treatment [meta-regression coefficient B of 0.08 (0.03, 0.13), p = 0.0005]. Extra-coronary calcification affecting the aorta, carotid artery, breast artery, and arteries of lower extremities, was also increased in VKA treated patients [1.86 (1.43, 2.42), p < 0.00001] and moderated by the author-reported statistical adjustments of the effect estimates [B: −0.63 (−1.19, −0.08), p = 0.016]. The effect of VKA on the aortic valve calcification was significant [3.07 (1.90, 4.96), p < 0.00001]; however, these studies suffered from a high risk of publication bias.

Conclusion

Vascular and valvular calcification are potential side effects of VKA. The clinical significance of these side effects on cardiovascular outcomes deserves further investigation.

Advances in positron emission tomography tracers related to vascular calcification

Microcalcification, a type of vascular calcification, increases the instability of plaque and easily leads to acute clinical events. Positron emission tomography (PET) is a new examination technology with significant advantages in identifying vascular calcification, especially microcalcification. The use of the ¹⁸F-NaF is undoubtedly the benchmark, and other PET tracers related to vascular calcification are also currently in development. Despite all this, a large number of studies are still needed to further clarify the specific mechanisms and characteristics. This review aimed at providing a summary of the application and progress of different PET tracers and also the future development direction.

Molecular Imaging of Lower Extremity Peripheral Arterial Disease: An Emerging Field in Nuclear Medicine

Peripheral arterial disease (PAD) is an atherosclerotic disorder of non-coronary arteries that is associated with vascular stenosis and/or occlusion. PAD affecting the lower extremities is characterized by a variety of health-related consequences, including lifestyle-limiting intermittent claudication, ulceration of the limbs and/or feet, increased risk for lower extremity amputation, and increased mortality. The diagnosis of lower extremity PAD is typically established by using non-invasive tests such as the ankle-brachial index, toe-brachial index, duplex ultrasound, and/or angiography imaging studies. While these common diagnostic tools provide hemodynamic and anatomical vascular assessments, the potential for non-invasive physiological assessment of the lower extremities has more recently emerged through the use of magnetic resonance- and nuclear medicine-based approaches, which can provide insight into the functional consequences of PAD-related limb ischemia. This perspectives article specifically highlights and discusses the emerging applications of clinical nuclear medicine techniques for molecular imaging investigations in the setting of lower extremity PAD.

Role of Extracellular Vesicles as Potential Diagnostic and/or Therapeutic Biomarkers in Chronic Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the first cause of death worldwide. In recent years, there has been great interest in the analysis of extracellular vesicles (EVs), including exosomes and microparticles, as potential mediators of biological communication between circulating cells/plasma and cells of the vasculature. Besides their activity as biological effectors, EVs have been also investigated as circulating/systemic biomarkers in different acute and chronic CVDs. In this review, the role of EVs as potential diagnostic and prognostic biomarkers in chronic cardiovascular diseases, including atherosclerosis (mainly, peripheral arterial disease, PAD), aortic stenosis (AS) and aortic aneurysms (AAs), will be described. Mechanistically, we will analyze the implication of EVs in pathological processes associated to cardiovascular remodeling, with special emphasis in their role in vascular and valvular calcification. Specifically, we will focus on the participation of EVs in calcium accumulation in the pathological vascular wall and aortic valves, involving the phenotypic change of vascular smooth muscle cells (SMCs) or valvular interstitial cells (IC) to osteoblast-like cells. The knowledge of the implication of EVs in the pathogenic mechanisms of cardiovascular remodeling is still to be completely deciphered but there are promising results supporting their potential translational application to the diagnosis and therapy of different CVDs.

Regional analysis of inflammation and contractile function in reperfused acute myocardial infarction by in vivo 19F cardiovascular magnetic resonance in pigs

Inflammatory cell infiltration is central to healing after acute myocardial infarction (AMI). The relation of regional inflammation to edema, infarct size (IS), microvascular obstruction (MVO), intramyocardial hemorrhage (IMH), and regional and global LV function is not clear. Here we noninvasively characterized regional inflammation and contractile function in reperfused AMI in pigs using fluorine (¹⁹F) cardiovascular magnetic resonance (CMR). Adult anesthetized pigs underwent left anterior descending coronary artery instrumentation with either 90 min occlusion (n = 17) or without occlusion (sham, n = 5). After 3 days, in surviving animals a perfluorooctyl bromide nanoemulsion was infused intravenously to label monocytes/macrophages. At day 6, in vivo ¹H-CMR was performed with cine, T2 and T2* weighted imaging, T2 and T1 mapping, perfusion and late gadolinium enhancement followed by ¹⁹F-CMR. Pigs were sacrificed for subsequent ex vivo scans and histology. Edema extent was 35 ± 8% and IS was 22 ± 6% of LV mass. Six of ten surviving AMI animals displayed both MVO and IMH (3.3 ± 1.6% and 1.9 ± 0.8% of LV mass). The ¹⁹F signal, reflecting the presence and density of monocytes/macrophages, was consistently smaller than edema volume or IS and not apparent in remote areas. The ¹⁹F signal-to-noise ratio (SNR) > 8 in the infarct border zone was associated with impaired remote systolic wall thickening. A whole heart value of ¹⁹F integral (¹⁹F SNR × milliliter) > 200 was related to initial LV remodeling independently of edema, IS, MVO, and IMH. Thus, ¹⁹F-CMR quantitatively characterizes regional inflammation after AMI and its relation to edema, IS, MVO, IMH and regional and global LV function and remodeling.

Bench-to-Bedside in Vascular Medicine: Optimizing the Translational Pipeline for Patients With Peripheral Artery Disease

Peripheral arterial disease is a growing worldwide problem with a wide spectrum of clinical severity and is projected to consume >$21 billion per year in the United States alone. While vascular researchers have brought several therapies to the clinic in recent years, few of these approaches have leveraged advances in high-throughput discovery screens, novel translational models, or innovative trial designs. In the following review, we discuss recent advances in unbiased genomics and broader omics technology platforms, along with preclinical vascular models designed to enhance our understanding of disease pathobiology and prioritize targets for additional investigation. Furthermore, we summarize novel approaches to clinical studies in subjects with claudication and ischemic ulceration, with an emphasis on streamlining and accelerating bench-to-bedside translation. By providing a framework designed to enhance each aspect of future clinical development programs, we hope to enrich the pipeline of therapies that may prevent loss of life and limb for those with peripheral arterial disease.

Multimodality imaging for the prevention of cardiovascular events: Coronary artery calcium and beyond

Atherosclerotic cardiovascular disease (ASCVD) has been the leading cause of death worldwide for more than a decade. Prevention is of utmost importance to reduce related mortality. The innovations in cardiovascular imaging technology, in addition to our improved understanding of coronary atherosclerosis pathogenesis, have resulted in cardiovascular imaging becoming one of the most influential tools for diagnosis and risk stratification in ASCVD. Although numerous publications have emerged on this topic, data that guide routine cardiology clinical practice currently focus on the utility of a limited number of such modalities, namely arterial ultrasonography and computed tomography. Herein, current evidence with respect to the role of multimodality cardiovascular imaging on ASCVD prevention will be reviewed.

Patient and Institutional Costs of Failure of Angioplasty of the Superficial Femoral Artery

BACKGROUND

Debate surrounds the optimal management of superficial femoral artery (SFA) disease. Randomized trial data rarely reflect real world findings, specifically the consequences to the patient of angioplasty failure. We observed the effect of a failed SFA angioplasty on the need for repeated clinic visits, hospital readmissions, imaging requirements, and reinterventions.

METHODS

We reviewed a consecutive series of 148 patients (94 men, median age 72 years) undergoing solely SFA angioplasty over a 2-year period. Patient preangioplasty demographics and 2-year post-PTA follow-up data were collated, including hospital attendances (inpatient/outpatient), further imaging (including radiation exposure) and revascularization attempts. We defined "failed angioplasty" as presence of clinical symptoms with radiological evidence of significant restenosis after an initial successful primary SFA angioplasty.

RESULTS

Fifty-four patients represented with a failed angioplasty (median time of 4 months after index PTA). In this group, failure of index angioplasty resulted in a further 185 restenosis-related clinic visits and a total of 537 bed days of inpatient stay. This group underwent a further 149 imaging events and required a further 34 endovascular revascularization procedures and 12 infrainguinal bypass procedures. These interventions and investigations corresponded to overall effective radiation dose across all patients of 190.69 mSv. Of the cohort of 99 patients who did not have a "failed angioplasty," they required 100 clinic visits, 21 further scans (total radiation dose 6.42 mSv), and 36 bed days of inpatient admission.

CONCLUSIONS

Failed angioplasty results in significant additional consequences for patients and health-care systems. Further work should focus on refining decision-making, providing the right procedure to the right patient at the right time.

Imaging Biological Pathways in Abdominal Aortic Aneurysms Using Positron Emission Tomography

[Figure: see text].

The current status of drug-coated devices in lower extremity peripheral artery disease interventions

Lower limb peripheral artery disease is a leading cause of cardiovascular disease morbidity and mortality. Endovascular revascularization is often indicated to improve walking function and to prevent limb loss but restenosis in the treated vessel segment remains a concern that limits the overall effectiveness of the treatment. The most promising technique to prevent restenosis is the use of drug-coated devices, and the most common drug used to coat lower limb balloon angioplasty balloons and stents is paclitaxel. A systematic review and meta-analysis in 2018 reported a possible increase in late mortality attributable to paclitaxel-coated devices. Since then, their use has been brought into question. Here, we present an update of data focusing on the efficacy and safety of paclitaxel-coated devices in lower limb treatment applications. While paclitaxel-coated devices appear to reduce restenosis rates it is still unclear how these surrogate marker improvements translate to direct patient benefits and uncertainty remains as to whether paclitaxel-coated devices confer an increased risk of long-term mortality. Available randomized clinical data is hampered by trial heterogeneity, insufficient power, potential attrition bias and the lack of a plausible mechanistic explanation. An important step forward is that the ongoing trials that were temporarily halted due to the Katsanos et al. report have now both commenced recruitment and may ultimately resolve this clinical dilemma by virtue of their larger sample sizes. Other possible ways forward are the ongoing investigation of alternative anti-proliferative coating agents and use of new sophisticated vascular imaging techniques to more clearly identify patients at risk of restenosis already in the preoperative setting.

Imaging Atherosclerosis by PET, With Emphasis on the Role of FDG and NaF as Potential Biomarkers for This Disorder

Molecular imaging has emerged in the past few decades as a novel means to investigate atherosclerosis. From a pathophysiological perspective, atherosclerosis is characterized by microscopic inflammation and microcalcification that precede the characteristic plaque buildup in arterial walls detected by traditional assessment methods, including anatomic imaging modalities. These processes of inflammation and microcalcification are, therefore, prime targets for molecular detection of atherosclerotic disease burden. Imaging with positron emission tomography/computed tomography (PET/CT) using 18F-fluorodeoxyglucose (FDG) and 18F-sodium fluoride (NaF) can non-invasively assess arterial inflammation and microcalcification, respectively. FDG uptake reflects glucose metabolism, which is particularly increased in atherosclerotic plaques retaining macrophages and undergoing hypoxic stress. By contrast, NaF uptake reflects the exchange of hydroxyl groups of hydroxyapatite crystals for fluoride producing fluorapatite, a key biochemical step in calcification of atherosclerotic plaque. Here we review the existing literature on FDG and NaF imaging and their respective values in investigating the progression of atherosclerotic disease. Based on the large volume of data that have been introduced to the literature and discussed in this review, it is clear that PET imaging will have a major role to play in assessing atherosclerosis in the major and coronary arteries. However, it is difficult to draw definitive conclusions on the potential role of FDG in investigating atherosclerosis given the vast number of studies with different designs, image acquisition methods, analyses, and interpretations. Our experience in this domain of research has suggested that NaF may be the tool of choice over FDG in assessing atherosclerosis, especially in the setting of coronary artery disease (CAD). Specifically, global NaF assessment appears to be superior in detecting plaques in tissues with high background FDG activity, such as the coronary arteries.

Atherosclerosis Imaging with 18F-Sodium Fluoride PET

The evidence on atherosclerosis imaging with ¹⁸F-sodium-fluoride (NaF) positron emission tomography (PET) is hotly debated because of the different patient characteristics, methodology, vascular beds, etc. in reported studies. This review is a continuation of a previous review on this topic, which covered the period 2010-2018. The purpose was to examine whether some of the most important questions that the previous review had left open had been elucidated by the most recent literature. Using principles of a systematic review, we ended analyzing 25 articles dealing with the carotids, coronary arteries, aorta, femoral, intracranial, renal, and penile arteries. The knowledge thus far can be summarized as follows: by targeting active arterial microcalcification, NaF uptake is considered a marker of early stage atherosclerosis, is age-dependent, and consistently associated with cardiovascular risk. Longitudinal studies on NaF uptake, conducted in the abdominal aorta only, showed unchanged uptake in postmenopausal women for nearly four years and varying uptake in prostate cancer patients over 1.5 years, despite constant or increasing calcium volume detected by computed tomography (CT). Thus, uncertainty remains about the transition from active arterial wall calcification marked by increased NaF uptake to less active or consolidated calcification detected by CT. The question of whether early-phase atherosclerosis and calcification can be modified remains also unanswered due to lack of intervention studies.

An Update on [18F]Fluoride PET Imaging for Atherosclerotic Disease

Atherosclerosis is the leading cause of life-threatening morbidity and mortality, as the rupture of atherosclerotic plaques leads to critical atherothrombotic events such as myocardial infarction and ischemic stroke, which are the 2 most common causes of death worldwide. Vascular calcification is a complicated pathological process involved in atherosclerosis, and microcalcifications are presumed to increase the likelihood of plaque rupture. Despite many efforts to develop novel non-invasive diagnostic modalities, diagnostic techniques are still limited, especially before symptomatic presentation. From this point of view, vulnerable plaques are a direct target of atherosclerosis imaging. Anatomic imaging modalities have the limitation of only visualizing macroscopic structural changes, which occurs in later stages of disease, while molecular imaging modalities are able to detect microscopic processes and microcalcifications, which occur early in the disease process. Na[¹⁸F]-fluoride positron emission tomography/computed tomography could allow the early detection of plaque instability, which is deemed to be a primary goal in the prevention of cardiac or brain ischemic events, by quantifying the microcalcifications within vulnerable plaques and evaluating the atherosclerotic disease burden.

Rapid reduction in plaque inflammation by sonodynamic therapy inpatients with symptomatic femoropopliteal peripheral artery disease:A randomized controlled trial

BACKGROUND

Inflammation is actively involved in the clinical manifestation of peripheral artery disease (PAD). Sonodynamic therapy (SDT), a novel non-invasive, plaque-based, macrophage-targeted anti-inflammatory regimen for atherosclerosis has the potential to improve walking performance by reducing plaque inflammation.

METHODS

This phase-2, randomized, sham-controlled, double-blind clinical trial enrolled 32 participants with symptomatic femoropopliteal PAD. The primary outcome was the 30-day change in the target-to-background ratio (TBR) within the most diseased segment (MDS) of the femoropopliteal artery assessed through positron emission tomography/computed tomography (PET/CT). The secondary outcomes were changes in walking performance, limb perfusion, lesional morphology and quality of life measurements.

RESULTS

The mean age was 64.7 years and 63% were male. Thirty-one completed follow-up. SDT significantly decreased the MDS TBR by 0.53 (95% CI, -0.70 to -0.36, P < 0.001) compared with control. Furthermore, SDT increased peak walking time by 118.6 s (95% CI, 74.3 to 163.0, P < 0.001), increased ankle-brachial index by 0.11 (95% CI, 0.07 to 0.14, P < 0.001), decreased lesional diameter and area stenosis by 7.2% (95% CI, -8.6 to -4.5, P < 0.001) and 9.6% (95% CI, -24.5 to -5.3, P = 0.005), respectively, and increased the walking speed score of the Walking Impairment Questionnaire by 16.1 (95% CI, 2.6 to 29.5, P = 0.021) and the physical functioning score of the 36-item Short-Form Health Survey by 10.0 (95% CI, 5.0 to 20.0, P = 0.003) compared with control. These improvements were maintained in the SDT group up to 6-month.

CONCLUSIONS

SDT rapidly reduced plaque inflammation and improved walking performance among patients with symptomatic PAD.

TRIAL REGISTRATION

Clinical Trials NCT03457662.

Novel Positron Emission Tomography Tracers for Imaging Vascular Inflammation

Purpose of Review

To provide a focused update on recent advances in positron emission tomography (PET) imaging in vascular inflammatory diseases and consider future directions in the field.

Recent Findings

While PET imaging with ¹⁸F-fluorodeoxyglucose (FDG) can provide a useful marker of disease activity in several vascular inflammatory diseases, including atherosclerosis and large-vessel vasculitis, this tracer lacks inflammatory cell specificity and is not a practical solution for imaging the coronary vasculature because of avid background myocardial signal. To overcome these limitations, research is ongoing to identify novel PET tracers that can more accurately track individual components of vascular immune responses. Use of these novel PET tracers could lead to a better understanding of underlying disease mechanisms and help inform the identification and stratification of patients for newly emerging immune-modulatory therapies.

Summary

Future research is needed to realise the true clinical translational value of PET imaging in vascular inflammatory diseases.

18F-Sodium Fluoride (18F-NaF) for Imaging Microcalcification Activity in the Cardiovascular System

Accumulating preclinical and clinical evidence suggests that calcification is one of the body's primary responses to injury and a key pathological feature of cardiovascular disease. Calcification activity can now be imaged using 18F-sodium fluoride (18F-NaF) positron emission tomography (PET) in combination with either computed tomography or magnetic resonance. These techniques allow visualization of calcification activity and, therefore, provide different information to the established macroscopic calcium imaged with computed tomography. Indeed, 18F-NaF PET has been used to investigate a wide range of valvular conditions, including aortic stenosis, mitral annular calcification, and bioprosthetic valve disease, as well as vascular conditions, including abdominal aortic aneurysm disease, coronary, and carotid atherosclerosis, peripheral vascular disease, and erectile dysfunction. In this brief review, we will focus on how 18F-NaF PET has improved our pathophysiological understanding of cardiovascular calcification and how it can be used as a marker of vascular calcification, providing a useful tool that can be utilized in clinical trials investigating the prediction of both disease progression and clinical events. Finally, we will discuss how 18F-NaF might be employed clinically to improve patient assessment and to guide decision-making.

Clinical imaging of cardiovascular inflammation

Cardiovascular disease due to atherosclerosis is the number one cause of morbidity and mortality worldwide. In the past twenty years, compelling preclinical and clinical data have indicated that a maladaptive inflammatory response plays a crucial role in the development of atherosclerosis initiation and progression in the vasculature, all the way to the onset of life-threatening cardiovascular events. Furthermore, inflammation is key to heart and brain damage and healing after myocardial infarction or stroke. Recent evidence indicates that this interplay between the vasculature, organs target of ischemia and the immune system is mediated by the activation of hematopoietic organs (bone marrow and spleen). In this evolving landscape, non-invasive imaging is becoming more and more essential to support either mechanistic preclinical studies to investigate the role of inflammation in cardiovascular disease (CVD), or as a translational tool to quantify inflammation in the cardiovascular system and hematopoietic organs in patients. In this review paper, we will describe the clinical applications of non-invasive imaging to quantify inflammation in the vasculature, infarcted heart and brain, and hematopoietic organs in patients with cardiovascular disease, with specific focus on [18F]FDG PET and other novel inflammation-specific radiotracers. Furthermore, we will briefly describe the most recent clinical applications of other imaging techniques such as MRI, SPECT, CT, CEUS and OCT in this arena.

Infection and Inflammation Imaging: Beyond FDG

This review discusses nuclear imaging of inflammation using molecular probes beyond fluoro-d-glucose, is structured by cellular targets, and focuses on those tracers that have been successfully applied clinically.