Metabolic and Molecular Imaging of Atherosclerosis and Venous Thromboembolism

NIR-II Imaging for Tracking the Spatiotemporal Immune Microenvironment in Atherosclerotic Plaques

The inflammatory immune microenvironment is responsible for atherosclerotic plaque erosion and rupture. Near-infrared-II (NIR-II) fluorescence imaging has the potential to continuously monitor the spatiotemporal changes in the plaque immune microenvironment. Herein, we constructed three different NIR-II probes based on benzo[1,2-c;4,5-c']bis[1,2,5]thiadiazole-4,7-bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene (denoted as BBT-2FT): VHPK/BBT-2FT NPs, where VHPK is a specific peptide targeting vascular cell adhesion molecule-1; iNOS/BBT-2FT NPs for modulating the polarization of M1 macrophages by inducible NO synthase (iNOS) antibodies; and Arg-1/BBT-2FT for counterbalancing the inflammatory responses of M1 macrophages. These tracers enable precise tracking of atherosclerotic plaques and M1 and M2 macrophages through NIR-II imaging. VHPK/BBT-2FT NPs can accurately trace atherosclerotic plaques at various stages. Arg-1/BBT-2FT NPs precisely located M2 macrophages in the early plaque microenvironment with upregulation of peroxisome proliferator-activated receptor γ (PPAR-γ), signal transducer and activator of transcription (STAT) 6, and ATP-binding cassette transporter A1 (ABCA1), indicating that M2 macrophage polarization is crucial for early plaque lipid clearance. Meanwhile, iNOS/BBT-2FT NPs accurately tracked M1 macrophages in the advanced plaque microenvironment. The results showed that M1 macrophage polarization induces the formation of an inflammatory microenvironment through anaerobic glycolytic metabolism and pyroptosis in the advanced hypoxic plaque microenvironment, as indicated by the upregulation of hypoxia-inducible factor 1 alpha (HIF-1α), STAT1, NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3), pyruvate dehydrogenase kinase 1 (PDK1), and glucose transporter 1 (GLUT-1). Combining immunological approaches with NIR-II imaging has revealed that hypoxia-induced metabolic reprogramming of macrophages is a key factor in dynamic changes in the immune microenvironment of atherosclerotic plaques. Furthermore, our strategy shows the potential for real-time diagnosis and clinical prevention of unstable plaque rupture in atherosclerosis.

A novel method for the diagnosis of atherosclerosis based on nanotechnology

Cardiovascular disease (CVD) is a global health concern, presenting significant risks to human health. Atherosclerosis is among the most prevalent CVD, impacting the medium and large arteries in the kidneys, brain, heart, and other vital organs, as well as the lower limbs. As the disease progresses, arterial obstruction can result in heart attacks and strokes. Therefore, patients with atherosclerosis should receive accurate diagnosis and timely therapeutic intervention. With the advancements in nanomedicine, researchers have proposed new research strategies and methods for atherosclerosis imaging. This paper summarizes some current research findings on the use of nanomaterials in diagnosing atherosclerosis and offers insights for optimizing the imaging applications of nanomaterials in the future.

The biological applications of near-infrared optical nanomaterials in atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis, a highly pathogenic and lethal disease, is difficult to locate accurately via conventional imaging because of its scattered and deep lesions. However, second near-infrared (NIR-II) nanomaterials show great application potential in the tracing of atherosclerotic plaques due to their excellent penetration and angiographic capabilities.

RECENT FINDINGS

With the development of nanotechnology, among many nanomaterials available for the visual diagnosis and treatment of cardiovascular diseases, optical nanomaterials provide strong support for various biomedical applications because of their advantages, such as noninvasive, nondestructive and molecular component imaging. Among optical nanomaterials of different wavelengths, NIR-II-range (900 ~ 1700 nm) nanomaterials have been gradually applied in the visual diagnosis and treatment of atherosclerosis and other vascular diseases because of their deep biological tissue penetration and limited background interference. This review explored in detail the prospects and challenges of the biological imaging and clinical application of NIR-II nanomaterials in treating atherosclerosis.

Molecular Mechanisms of Ischemic Stroke: A Review Integrating Clinical Imaging and Therapeutic Perspectives

Ischemic stroke poses a significant global health challenge, necessitating ongoing exploration of its pathophysiology and treatment strategies. This comprehensive review integrates various aspects of ischemic stroke research, emphasizing crucial mechanisms, therapeutic approaches, and the role of clinical imaging in disease management. It discusses the multifaceted role of Netrin-1, highlighting its potential in promoting neurovascular repair and mitigating post-stroke neurological decline. It also examines the impact of blood-brain barrier permeability on stroke outcomes and explores alternative therapeutic targets such as statins and sphingosine-1-phosphate signaling. Neurocardiology investigations underscore the contribution of cardiac factors to post-stroke mortality, emphasizing the importance of understanding the brain-heart axis for targeted interventions. Additionally, the review advocates for early reperfusion and neuroprotective agents to counter-time-dependent excitotoxicity and inflammation, aiming to preserve tissue viability. Advanced imaging techniques, including DWI, PI, and MR angiography, are discussed for their role in evaluating ischemic penumbra evolution and guiding therapeutic decisions. By integrating molecular insights with imaging modalities, this interdisciplinary approach enhances our understanding of ischemic stroke and offers promising avenues for future research and clinical interventions to improve patient outcomes.

Biomedical Imaging in Experimental Models of Cardiovascular Disease

Major advances in biomedical imaging have occurred over the last 2 decades and now allow many physiological, cellular, and molecular processes to be imaged noninvasively in small animal models of cardiovascular disease. Many of these techniques can be also used in humans, providing pathophysiological context and helping to define the clinical relevance of the model. Ultrasound remains the most widely used approach, and dedicated high-frequency systems can obtain extremely detailed images in mice. Likewise, dedicated small animal tomographic systems have been developed for magnetic resonance, positron emission tomography, fluorescence imaging, and computed tomography in mice. In this article, we review the use of ultrasound and positron emission tomography in small animal models, as well as emerging contrast mechanisms in magnetic resonance such as diffusion tensor imaging, hyperpolarized magnetic resonance, chemical exchange saturation transfer imaging, magnetic resonance elastography and strain, arterial spin labeling, and molecular imaging.

The complementary value of intraoperative fluorescence imaging and Raman spectroscopy for cancer surgery: combining the incompatibles

A clear margin is an important prognostic factor for most solid tumours treated by surgery. Intraoperative fluorescence imaging using exogenous tumour-specific fluorescent agents has shown particular benefit in improving complete resection of tumour tissue. However, signal processing for fluorescence imaging is complex, and fluorescence signal intensity does not always perfectly correlate with tumour location. Raman spectroscopy has the capacity to accurately differentiate between malignant and healthy tissue based on their molecular composition. In Raman spectroscopy, specificity is uniquely high, but signal intensity is weak and Raman measurements are mainly performed in a point-wise manner on microscopic tissue volumes, making whole-field assessment temporally unfeasible. In this review, we describe the state-of-the-art of both optical techniques, paying special attention to the combined intraoperative application of fluorescence imaging and Raman spectroscopy in current clinical research. We demonstrate how these techniques are complementary and address the technical challenges that have traditionally led them to be considered mutually exclusive for clinical implementation. Finally, we present a novel strategy that exploits the optimal characteristics of both modalities to facilitate resection with clear surgical margins.

Compared to conventional PET/CT scanners, silicon-photomultiplier-based PET/CT scanners show higher arterial 18F-FDG uptake in whole-body 18F-FDG-PET/CT

OBJECTIVES

To clarify differences in arterial 18F-FDG (fluorodeoxyglucose) uptake between silicon photomultiplier (SiPM)-based and conventional PET/CT scanners, and to compare clinical and phantom results.

PATIENTS AND METHODS

Twenty-six patients with lung tumours underwent serial SiPM-based and conventional PET/CT scans on the same day. We compared the target-to-background ratios [TBRsi (SiPM), TBRc (conventional)] and the percentage difference between TBRsi and TBRc (ΔTBR) in the carotid artery, aorta and peripheral arteries. The correlation between ΔTBR and vessel size was also investigated. In the carotid artery, active segment analyses were performed with the threshold (TBR ≥1.6), and we compared each scanner's ratio of active segments and TBR values. We compared the clinical results with the recovery coefficients (RCs).

RESULTS

The TBRsi was significantly higher than the TBRc in the carotid artery, aorta and peripheral arteries (1.63 ± 0.22 vs. 1.43 ± 0.22, 1.65 ± 0.19 vs. 1.53 ± 0.15 and 1.37 ± 0.31 vs. 1.11 ± 0.27, mean ± SD, P ≤ 0.0001 for all), and the peripheral arteries showed the highest ΔTBR (24.4 ± 16.8%). The small (10-15 mm) vessels (26.9 ± 15.9%) showed significantly higher ΔTBRs than the larger vessels (7.3 ± 8.5% for 15-20 mm, 8.0 ± 12.8% for ≥20 mm, P < 0.0001 for both). The carotid artery showed significantly higher ratios of active segment (54.5 vs. 20.5%, P < 0.0001) and TBR values (1.85 ± 0.25 vs. 1.76 ± 0.15, P = 0.0006) for TBRsi vs. TBRc. The differences in RCs were similar to those of ΔTBR for each vessel size.

CONCLUSIONS

SiPM-based PET/CT scanners showed higher arterial 18F-FDG uptake (especially in vessels <15 mm) than conventional scanners, and the threshold TBR ≥1.6 is not applicable for the carotid artery for SiPM-based PET/CT systems.

Effect of BMI on Central Arterial Reflected Wave Augmentation Index, Toe-Brachial Index, Brachial-Ankle Pulse Wave Velocity and Ankle-Brachial Index in Chinese Elderly Hypertensive Patients with Hemorrhagic Stroke

BACKGROUND

Hypertensive cerebral hemorrhage seriously endangers the health of the elderly. However, the relationship between obesity and arterial elasticity in hypertensive cerebral hemorrhage remains to be clarified. The purpose of our study is to explore the associations between body mass index (BMI) and central arterial reflected wave augmentation index (cAIx), toe-brachial index (TBI), brachial-ankle pulse wave velocity (baPWV), and ankle-brachial index (ABI) in the elderly hypertensive patients with hemorrhagic stroke.

MATERIALS AND METHODS

A total of 502 elderly hypertensive patients with hemorrhagic stroke and 100 healthy controls were collected. According to the BMI, patients were divided into normal BMI, overweight, obesity, and obese groups. The multivariate logistic regression model was used to establish a risk model for elderly hypertensive hemorrhagic stroke.

RESULTS

Compared with the normal BMI group, systolic blood pressure (SBP), diastolic blood pressure (DBP), cAIx, and baPWV in the abnormal BMI group were significantly increased (P < 0.05), while TBI and ABI were significantly decreased (P < 0.05). Logistic regression showed that BMI (OR = 1.031, 95%CI: 1.009-1.262), cAIx (OR = 1.214, 95%CI: 1.105-1.964), TBI (OR = 0.913, 95%CI: 0.885-0.967), baPWV (OR = 1.344, 95%CI: 1.142-2.147), and ABI (OR = 0.896, 95%CI: 0.811-0.989) are important factors for the occurrence of hemorrhagic stroke in the elderly hypertensive patients. ROC curve analysis showed that the AUC of cAIx, TBI, baPWV, ABI, and BMI were 0.914, 0.797, 0.934, 0.833, and 0.608, respectively. The final prediction model of hemorrhagic stroke elderly hypertensive patients was Y_(P)= 65.424 + 0.307(cAIx) - 13.831(TBI) + 0.012(baPWV) - 0.110(ABI) + 0.339(BMI).

CONCLUSIONS

Obesity is associated with decreased arterial elasticity. Therefore, reasonable weight management of the elderly may be of great significance for reducing the risk of hemorrhagic stroke in patients with hypertension.

Assessment of ultrasmall nanocluster for early and accurate detection of atherosclerosis using positron emission tomography/computed tomography

The development of atherosclerosis therapy is hampered by the lack of molecular imaging tools to identify the relevant biomarkers and determine the dynamic variation in vivo. Here, we show that a chemokine receptor 2 (CCR2) targeted gold nanocluster conjugated with extracellular loop 1 inverso peptide (AuNC-ECL1i) determines the initiation, progression and regression of atherosclerosis in apolipoprotein E knock-out (ApoE^-/-) mouse models. The CCR2 targeted ⁶⁴Cu-AuNC-ECL1i reveals sensitive detection of early atherosclerotic lesions and progression of plaques in ApoE^-/- mice. CCR2 targeting specificity was confirmed by the competitive receptor blocking studies. In a mouse model of aortic arch transplantation, ⁶⁴Cu-AuNC-ECL1i accurately detects the regression of plaques. Human atherosclerotic tissues show high expression of CCR2 related to the status of the disease. This study confirms CCR2 as a useful marker for atherosclerosis and points to the potential of ⁶⁴Cu-AuNC-ECL1i as a targeted molecular imaging probe for future clinical translation.

Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Imaging Predicts Vein Wall Scarring and Statin Benefit in Murine Venous Thrombosis

BACKGROUND

The postthrombotic syndrome is a common, often morbid sequela of venous thrombosis (VT) that arises from thrombus persistence and inflammatory scarring of juxtaposed vein walls and valves. Noninvasive ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging can measure neutrophil inflammation in VT. Here, we hypothesized (1) early fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) VT inflammation can predict subsequent vein wall scarring (VWS) and (2) statin therapy can reduce FDG-PET VT inflammation and subsequent VWS.

METHODS

C57BL/6J mice (n=75) underwent induction of stasis-induced VT of the inferior vena cava or jugular vein. Inferior vena cava VT mice (n=44) were randomized to daily oral rosuvastatin 5 mg/kg or saline starting at day -1. Subgroups of mice then underwent FDG-PET/CT 2 days after VT induction. On day 14, a subset of mice was euthanized, and VWS was assessed via histology. In vitro studies were further performed on bone marrow-derived neutrophils.

RESULTS

Statin therapy reduced early day 2 FDG-PET VT inflammation, thrombus neutrophil influx, and plasma IL (interleukin)-6 levels. At day 14, statin therapy reduced VWS but did not affect day 2 thrombus mass, cholesterol, or white blood counts, nor reduce day 2 glucose transporter 1 or myeloperoxidase expression in thrombus or in isolated neutrophils. In survival studies, the day 2 FDG-PET VT inflammation signal as measured by mean and maximum standardized uptake values predicted the extent of day 14 VWS (area under the receiver operating characteristic curve =0.82) with a strong correlation coefficient (r) of r=0.73 and r=0.74, respectively. Mediation analyses revealed that 40% of the statin-induced VWS reduction was mediated by reductions in VT inflammation as quantified by FDG-PET.

CONCLUSIONS

Early noninvasive FDG-PET/CT imaging of VT inflammation predicts the magnitude of subsequent VWS and may provide a new translatable approach to identify individuals at risk for postthrombotic syndrome and to assess anti-inflammatory postthrombotic syndrome therapies, such as statins.

Molecular imaging of inflammation - Current and emerging technologies for diagnosis and treatment

Inflammation is a key factor in multiple diseases including primary immune-mediated inflammatory diseases e.g. rheumatoid arthritis but also, less obviously, in many other common conditions, e.g. cardiovascular disease and diabetes. Together, chronic inflammatory diseases contribute to the majority of global morbidity and mortality. However, our understanding of the underlying processes by which the immune response is activated and sustained is limited by a lack of cellular and molecular information obtained in situ. Molecular imaging is the visualization, detection and quantification of molecules in the body. The ability to reveal information on inflammatory biomarkers, pathways and cells can improve disease diagnosis, guide and monitor therapeutic intervention and identify new targets for research. The optimum molecular imaging modality will possess high sensitivity and high resolution and be capable of non-invasive quantitative imaging of multiple disease biomarkers while maintaining an acceptable safety profile. The mainstays of current clinical imaging are computed tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and nuclear imaging such as positron emission tomography (PET). However, none of these have yet progressed to routine clinical use in the molecular imaging of inflammation, therefore new approaches are required to meet this goal. This review sets out the respective merits and limitations of both established and emerging imaging modalities as clinically useful molecular imaging tools in addition to potential theranostic applications.

Ultrasound/Optical Dual-Modality Imaging for Evaluation of Vulnerable Atherosclerotic Plaques with Osteopontin Targeted Nanoparticles

Because of the high mortality of coronary atherosclerotic heart diseases, it is necessary to develop novel early detection methods for vulnerable atherosclerotic plaques. Phenotype transformation of vascular smooth muscle cells (VSMCs) plays a vital role in progressed atherosclerotic plaques. Osteopontin (OPN) is one of the biomarkers for phenotypic conversion of VSMCs. Significant higher OPN expression is found in foam cells along with the aggravating capacity of macrophage recruitment due to its arginine-glycine-aspartate sequence and interaction with CD44. Herein, a dual-modality imaging probe, OPN targeted nanoparticles (Cy5.5-anti-OPN-PEG-PLA-PFOB, denoted as COP-NPs), is constructed to identify the molecular characteristics of high-risk atherosclerosis by ultrasound and optical imaging. Characterization, biocompatibility, good binding sensibility, and specificity are evaluated in vitro. For in vivo study, apolipoprotein E deficien (ApoE^-/- ) mice fed with high fat diet for 20-24 weeks are used as atherosclerotic model. Ultrasound and optical imaging reveal that the nanoparticles are accumulated in the vulnerable atherosclerotic plaques. OPN targeted nanoparticles are demonstrated to be a good contrast agent in molecular imaging of synthetic VSMCs and foam cells, which can be a promising tool to identify the vulnerable atherosclerotic plaques.

Molecular Imaging: a Novel Tool To Visualize Pathogenesis of Infections In Situ

Molecular imaging is an emerging technology that enables the noninvasive visualization, characterization, and quantification of molecular events within living subjects. Positron emission tomography (PET) is a clinically available molecular imaging tool with significant potential to study pathogenesis of infections in humans.

Molecular imaging is an emerging technology that enables the noninvasive visualization, characterization, and quantification of molecular events within living subjects. Positron emission tomography (PET) is a clinically available molecular imaging tool with significant potential to study pathogenesis of infections in humans. PET enables dynamic assessment of infectious processes within the same subject with high temporal and spatial resolution and obviates the need for invasive tissue sampling, which is difficult in patients and generally limited to a single time point, even in animal models. This review presents current state-of-the-art concepts on the application of molecular imaging for infectious diseases and details how PET imaging can facilitate novel insights into infectious processes, ongoing development of pathogen-specific imaging, and simultaneous in situ measurements of intralesional antimicrobial pharmacokinetics in multiple compartments, including privileged sites. Finally, the potential clinical applications of this promising technology are also discussed.

Vascular Calcification: The Evolving Relationship of Vascular Calcification to Major Acute Coronary Events

Calcification in a coronary artery is accepted as definite evidence of coronary atherosclerosis. The extent and density of calcification, as combined in the Agatston score, is associated with the risk of a patient experiencing a major acute coronary event. Atherosclerosis occurs because damaged endothelial cells allow low-density lipoprotein cholesterol (LDLc) to leak into subintimal tissue. Proteoglycans in subendothelial collagen have a high affinity for LDLc, retaining the lipoprotein cholesterol complex. As the endothelial damage is repaired, the subintimal LDLc is trapped. Retained LDLc induces an inflammatory response in the overlying endothelium, causing the endothelium to express chemotactic peptides. Chemotactic peptides attract circulating monocytes, which follow the concentration gradient, enter the tissue, and become tissue macrophages to phagocytize and digest the irritating LDLc in the atheroma. In the process of digesting LDLc, enzymes in the macrophages oxidize the LDLc complex. Oxidized LDL is toxic to macrophages; when present in sufficient quantity, it may cause death of macrophages, contributing to inflammation in the atheroma. In a necrotic inflammatory lesion, the regulatory mechanisms that control tissue concentrations of calcium and phosphorus are lost, allowing the solubility product of calcium phosphate to be exceeded, resulting in the formation of microscopic calcium-phosphate crystals. With ongoing inflammation, additional calcium-phosphate crystals are formed, which may aggregate. When these aggregated calcium phosphate crystals exceed 1 mm, the lesions become visible on clinical CT as coronary calcifications. Serial gated CT scans of the heart have demonstrated that once formed, CT-visible calcifications do not decrease significantly in size but may increase.

Emerging Technologies to Image Tissue Metabolism

Due to the implication of altered metabolism in a large spectrum of tissue function and disease, assessment of metabolic processes becomes essential in managing health. In this regard, imaging can play a critical role in allowing observation of biochemical and physiological processes. Nuclear imaging methods, in particular positron emission tomography, have been widely employed for imaging metabolism but are mainly limited by the use of ionizing radiation and the sensing of only one parameter at each scanning session. Observations in healthy individuals or longitudinal studies of disease could markedly benefit from non-ionizing, multi-parameter imaging methods. We therefore focus this review on progress with the non-ionizing radiation methods of MRI, hyperpolarized magnetic resonance and magnetic resonance spectroscopy, chemical exchange saturation transfer, and emerging optoacoustic (photoacoustic) imaging. We also briefly discuss the role of nuclear and optical imaging methods for research and clinical protocols.

Assessment of artery calcification in atherosclerosis with dynamic 18F-FDG-PET/CT imaging in elderly subjects

Glucose metabolism in atherosclerotic arteries has been shown to be an indicator of inflammation, which might be a precursor of plaque rupture. In this prospective study, we assessed the correlation between artery calcification and glucose metabolism by means of 18F-FDG PET/CT imaging in elderly subjects. Nineteen elderly subjects, with age ranging from 65 to 85 years, underwent CT and dynamic 18F-FDG-PET imaging. The artery calcification was determined with a threshold of 130 Hounsfield units. Intensity of calcification and ratio of calcification area to total artery area were classified in four sequential classes from CT images. The CT artery images were also classified as having single or multi-spot calcifications. Their respective glucose metabolism was assessed with fractional uptake rate (FUR). Factor analysis was used in this study to separate blood images from tissue to extract the blood time activity curves for FUR calculations. The artery images in PET data were corrected for partial volume effect. The total arterial segments analyzed were 1332, with 1085 without calcification (81%), 247 (19%) with calcification, and 94 segments were having multi-spot of calcifications. There was a statistically significant difference in FUR values between non-calcified to calcified segments and between subjects under medication to non-medication when comparing the subjects based on calcification area. No statistically significant differences of FUR were found between single spot as a function of intensity, while in the multi-spots, there was a statistically significant difference for all artery segments. Metabolism activity varies for non-calcified to calcified segments. Based on the metabolic activity represented by FUR, calcifications in multi-spots have different effects than in single spots.

Atherosclerosis imaging to refine cardiovascular risk assessment in diabetic patients: Computed tomography and positron emission tomography applications

The lifetime cardiovascular risk of a diabetic patient is approximately 4-5 times higher than that of an age and sex matched individual without diabetes mellitus. Despite the well-publicized cardiovascular risk equivalence of diabetes mellitus, it has become apparent that not all diabetic patients are equally at high-risk and many patients may have a level of risk similar to that of the general population. Cardiovascular imaging has been employed to address the dilemma of a more accurate risk stratification of diabetic patients. Two randomized clinical trials aiming at uncovering the presence of unknown obstructive coronary artery disease (CAD) gave disappointing results. In fact, the number of patients with inducible myocardial ischemia and/or severe obstructive disease was lower than expected and the overall outcome was not improved after having brought the existence of CAD to light. Other techniques that may help identify a diabetic patient susceptible to suffer future events have therefore being explored. In this review we discuss two imaging tools that provide anatomical and functional information on pre-clinical coronary atherosclerosis: computed tomography for calcium scoring, and plaque characterization and myocardial ischemia detection and positron emission tomography using tracers to identify functionally unstable plaques. Despite the availability of several imaging techniques there remain numerous questions as to the utility of imaging to define risk in diabetes mellitus and an optimal approach has yet to be found.