Ultrathin-strut versus thin-strut stent healing and outcomes in preclinical and clinical subjects

BACKGROUND

Compared with thin-strut durable-polymer drug-eluting stents (DP-DES), ultrathin-strut biodegradable-polymer sirolimus-eluting stents (BP-SES) improve stent-related clinical outcomes in patients undergoing percutaneous coronary intervention (PCI). Reduced stent strut thickness is hypothesised to underlie these benefits, but this conjecture remains unproven.

AIMS

We aimed to assess the impact of strut thickness on stent healing and clinical outcomes between ultrathin-strut and thin-strut BP-SES.

METHODS

First, we performed a preclinical study of 8 rabbits implanted with non-overlapping thin-strut (diameter/thickness 3.5 mm/80 μm) and ultrathin-strut (diameter/thickness 3.0 mm/60 μm) BP-SES in the infrarenal aorta. On day 7, the rabbits underwent intravascular near-infrared fluorescence optical coherence tomography (NIRF-OCT) molecular-structural imaging of fibrin deposition and stent tissue coverage, followed by histopathological analysis. Second, we conducted an individual data pooled analysis of patients enrolled in the BIOSCIENCE and BIOSTEMI randomised PCI trials treated with ultrathin-strut (n=282) or thin-strut (n=222) BP-SES. The primary endpoint was target lesion failure (TLF) at 1-year follow-up, with a landmark analysis at 30 days.

RESULTS

NIRF-OCT image analyses revealed that ultrathin-strut and thin-strut BP-SES exhibited similar stent fibrin deposition (p=0.49) and percentage of uncovered stent struts (p=0.63). Histopathological assessments corroÂborated these findings. In 504 pooled randomised trial patients, TLF rates were similar for those treated with ultrathin-strut or thin-strut BP-SES at 30-day (2.5% vs 1.8%; p=0.62) and 1-year follow-up (4.3% vs 4.7%; p=0.88).

CONCLUSIONS

Ultrathin-strut and thin-strut BP-SES demonstrate similar early arterial healing profiles and 30-day and 1-year clinical outcomes.

Soft robotics-enabled large animal model of HFpEF hemodynamics for device testing

Heart failure with preserved ejection fraction (HFpEF) is a major challenge in cardiovascular medicine, accounting for approximately 50% of all cases of heart failure. Due to the lack of effective therapies for this condition, the mortality associated with HFpEF remains higher than that of most cancers. Despite the ongoing efforts, no medical device has yet received FDA approval. This is largely due to the lack of an in vivo model of the HFpEF hemodynamics, resulting in the inability to evaluate device effectiveness in vivo prior to clinical trials. Here, we describe the development of a highly tunable porcine model of HFpEF hemodynamics using implantable soft robotic sleeves, where controlled actuation of a left ventricular and an aortic sleeve can recapitulate changes in ventricular compliance and afterload associated with a broad spectrum of HFpEF hemodynamic phenotypes. We demonstrate the feasibility of the proposed model in preclinical testing by evaluating the hemodynamic response of the model post-implantation of an interatrial shunt device, which was found to be consistent with findings from in silico studies and clinical trials. This work addresses several of the limitations associated with previous models of HFpEF, such as their limited hemodynamic fidelity, elevated costs, lengthy development time, and low throughput. By showcasing exceptional versatility and tunability, the proposed platform has the potential to revolutionize the current approach for HFpEF device development and selection, with the goal of improving the quality of life for the 32 million people affected by HFpEF worldwide.

Ketone ester supplementation suppresses cardiac inflammation and improves cardiac energetics in a swine model of acute myocardial infarction

BACKGROUND

Myocardial infarction (MI) is a major risk factor for the development of heart failure with reduce ejection fraction (HFrEF). While previous studies have focused on HFrEF, the cardiovascular effects of ketone bodies in acute MI are unclear. We examined the effects of oral ketone supplementation as a potential treatment strategy in a swine acute MI model.

METHODS

Farm pigs underwent percutaneous balloon occlusion of the LAD for 80 min followed by 72 h reperfusion period. Oral ketone ester or vehicle was administered during reperfusion and continued during the follow-up period.

RESULTS

Oral KE supplementation induced ketonemia 2-3 mmol/l within 30 min after ingestion. KE increased ketone (βHB) extraction in healthy hearts without affecting glucose and fatty acid (FA) consumption. During reperfusion, the MI hearts consumed less FA with no change in glucose consumption, whereas hearts from MI-KE-fed animals consumed more βHB and FA, as well as improved myocardial ATP production. A significant elevation of infarct T2 values indicative of inflammation was found only in untreated MI group compared to sham. Concordantly, cardiac expression of inflammatory markers, oxidative stress, and apoptosis were reduced by KE. RNA-seq analysis identified differentially expressed genes related to mitochondrial energy metabolism and inflammation.

CONCLUSIONS

Oral KE supplementation induced ketosis and enhanced myocardial βHB extraction in both healthy and infarcted hearts. Acute oral supplementation with KE favorably altered cardiac substrate uptake and utilization, improved cardiac ATP levels, and reduced cardiac inflammation following MI.

A soft robotic sleeve mimicking the haemodynamics and biomechanics of left ventricular pressure overload and aortic stenosis

Preclinical models of aortic stenosis can induce left ventricular pressure overload and coarsely control the severity of aortic constriction. However, they do not recapitulate the haemodynamics and flow patterns associated with the disease. Here we report the development of a customizable soft robotic aortic sleeve that can mimic the haemodynamics and biomechanics of aortic stenosis. By allowing for the adjustment of actuation patterns and blood-flow dynamics, the robotic sleeve recapitulates clinically relevant haemodynamics in a porcine model of aortic stenosis, as we show via in vivo echocardiography and catheterization studies, and a combination of in vitro and computational analyses. Using in vivo and in vitro magnetic resonance imaging, we also quantified the four-dimensional blood-flow velocity profiles associated with the disease and with bicommissural and unicommissural defects re-created by the robotic sleeve. The design of the sleeve, which can be adjusted on the basis of computed tomography data, allows for the design of patient-specific devices that may guide clinical decisions and improve the management and treatment of patients with aortic stenosis.

Abstract 121: Acetylsalicylic Acid Accelerates Murine Stasis Venous Thrombus Resolution, Independent Of Sex

Background: The lack of a stasis venous thrombosis (VT) model in female mice has limited investigation on sex differences of anti-VT therapies, such as acetylsalicylic acid (ASA), which appears efficacious in preventing recurrent VT. Here we (i) develop a new extended stasis VT model; and (ii) examine the effects of ASA on stasis VT resolution in female and male mice using serial intravital microscopy.

Method: To extend stasis thrombus persistence, femoral vein was ligated followed by second ligation of saphenous vein (Fig. A), after 7 days of either PBS/ASA (3mg/kg, n=5-6) pre-treatment. Following FITC-dextran injection (10 mg/kg), FITC light irradiation (475/35nm, 20x) for three minutes across three illumination fields generated stasis VT. Dylight649-GPIbβ agent was injected (100ug/kg, ex 630nm) to observe platelets. At T30’, fibrin targeting agent-FTP11-CyAm7 (150nmol/kg, ex 750 nm) was injected. Serial epifluorescence IVM images were acquired (90i, NIS Elements software, Nikon).

Results: Double ligation (DL) thrombus was significantly larger than single ligation (SL) and remained so through 24h (Fig B-G) and 48h (data not shown). Corresponding sections of thrombus showed a persistent core consisting platelets and fibrin (Fig. H-J). In DL, females developed reproducible stasis VT burden and resolution profiles as in males (Fig. K). ASA pre-treatment resulted in reduced thrombus (T0’), and accelerated resolution in both sexes (Fig. L-P). ASA inhibited platelet recruitment to thrombi within T30’, consistent with its known anti-platelet effect. Also, ASA inhibited fibrinogenesis, suggestive of an impaired platelet-fibrin interface.

Conclusion: Here we establish a new extended stasis VT model applicable to both female and male mice. This model is amenable to study vein wall fibrosis-critical aspect of post-thrombotic syndrome. Furthermore, ASA inhibits thrombus formation and accelerates thrombus resolution in a sex-independent manner.

Imaging High-Risk Atherothrombosis Using a Novel Fibrin-Binding Positron Emission Tomography Probe

BACKGROUND AND PURPOSE

High-risk atherosclerosis is an underlying cause of cardiovascular events, yet identifying the specific patient population at immediate risk is still challenging. Here, we used a rabbit model of atherosclerotic plaque rupture and human carotid endarterectomy specimens to describe the potential of molecular fibrin imaging as a tool to identify thrombotic plaques.

METHODS

Atherosclerotic plaques in rabbits were induced using a high-cholesterol diet and aortic balloon injury (N=13). Pharmacological triggering was used in a group of rabbits (n=9) to induce plaque disruption. Animals were grouped into thrombotic and nonthrombotic plaque groups based on gross pathology (gold standard). All animals were injected with a novel fibrin-specific probe ⁶⁸Ga-CM246 followed by positron emission tomography (PET)/magnetic resonance imaging 90 minutes later. ⁶⁸Ga-CM246 was quantified on the PET images using tissue-to-background (back muscle) ratios and standardized uptake value.

RESULTS

Both tissue-to-background (back muscle) ratios and standardized uptake value were significantly higher in the thrombotic versus nonthrombotic group (P<0.05). Ex vivo PET and autoradiography of the abdominal aorta correlated positively with in vivo PET measurements. Plaque disruption identified by ⁶⁸Ga-CM246 PET agreed with gross pathology assessment (85%). In ex vivo surgical specimens obtained from patients undergoing elective carotid endarterectomy (N=12), ⁶⁸Ga-CM246 showed significantly higher binding to carotid plaques compared to a D-cysteine nonbinding control probe.

CONCLUSIONS

We demonstrated that molecular fibrin PET imaging using ⁶⁸Ga-CM246 could be a useful tool to diagnose experimental and clinical atherothrombosis. Based on our initial results using human carotid plaque specimens, in vivo molecular imaging studies are warranted to test ⁶⁸Ga-CM246 PET as a tool to stratify risk in atherosclerotic patients.

Highly Selective PPARα (Peroxisome Proliferator-Activated Receptor α) Agonist Pemafibrate Inhibits Stent Inflammation and Restenosis Assessed by Multimodality Molecular-Microstructural Imaging

BACKGROUND

New pharmacological approaches are needed to prevent stent restenosis. This study tested the hypothesis that pemafibrate, a novel clinical selective PPARα (peroxisome proliferator‐activated receptor α) agonist, suppresses coronary stent‐induced arterial inflammation and neointimal hyperplasia.

METHODS AND RESULTS

Yorkshire pigs randomly received either oral pemafibrate (30 mg/day; n=6) or control vehicle (n=7) for 7 days, followed by coronary arterial implantation of 3.5 × 12 mm bare metal stents (2–4 per animal; 44 stents total). On day 7, intracoronary molecular‐structural near‐infrared fluorescence and optical coherence tomography imaging was performed to assess the arterial inflammatory response, demonstrating that pemafibrate reduced stent‐induced inflammatory protease activity (near‐infrared fluorescence target‐to‐background ratio: pemafibrate, median [25th‐75th percentile]: 2.8 [2.5–3.3] versus control, 4.1 [3.3–4.3], P=0.02). At day 28, animals underwent repeat near‐infrared fluorescence–optical coherence tomography imaging and were euthanized, and coronary stent tissue molecular and histological analyses. Day 28 optical coherence tomography imaging showed that pemafibrate significantly reduced stent neointima volume (pemafibrate, 43.1 [33.7–54.1] mm³ versus control, 54.2 [41.2–81.1] mm³; P=0.03). In addition, pemafibrate suppressed day 28 stent‐induced cellular inflammation and neointima expression of the inflammatory mediators TNF‐α (tumor necrosis factor‐α) and MMP‐9 (matrix metalloproteinase 9) and enhanced the smooth muscle differentiation markers calponin and smoothelin. In vitro assays indicated that the STAT3 (signal transducer and activator of transcription 3)–myocardin axes mediated the inhibitory effects of pemafibrate on smooth muscle cell proliferation.

CONCLUSIONS

Pemafibrate reduces preclinical coronary stent inflammation and neointimal hyperplasia following bare metal stent deployment. These results motivate further trials evaluating pemafibrate as a new strategy to prevent clinical stent restenosis.

Intravascular molecular-structural imaging with a miniaturized integrated near-infrared fluorescence and ultrasound catheter

Coronary artery disease (CAD) remains a leading cause of mortality and warrants new imaging approaches to better guide clinical care. We report on a miniaturized, hybrid intravascular catheter and imaging system for comprehensive coronary artery imaging in vivo. Our catheter exhibits a total diameter of 1.0 mm (3.0 French), equivalent to standalone clinical intravascular ultrasound (IVUS) catheters but enables simultaneous near-infrared fluorescence (NIRF) and IVUS molecular-structural imaging. We demonstrate NIRF-IVUS imaging in vitro in coronary stents using NIR fluorophores, and compare NIRF signal strengths for prism and ball lens sensor designs in both low and high scattering media. Next, in vivo intravascular imaging in pig coronary arteries demonstrates simultaneous, co-registered molecular-structural imaging of experimental CAD inflammation on IVUS and distance-corrected NIRF images. The obtained results suggest substantial potential for the NIRF-IVUS catheter to advance standalone IVUS, and enable comprehensive phenotyping of vascular disease to better assess and treat patients with CAD.

In Vivo Platelet Detection Using a Glycoprotein IIb/IIIa-Targeted Near-Infrared Fluorescence Imaging Probe

Platelets play a prominent role in multiple diseases, in particular arterial and venous thrombosis and also in atherosclerosis and cancer. To advance the in vivo study of the biological activity of this cell type from a basic experimental focus to a clinical focus, new translatable platelet-specific molecular imaging agents are required. Herein, we report the development of a near-infrared fluorescence probe based upon tirofiban, a clinically approved small-molecule glycoprotein IIb/IIIa inhibitor (GPIIb/IIIa). Through in vitro experiments with human platelets and in vivo ones in a murine model of deep-vein thrombosis, we demonstrate the avidity of the generated probe for activated platelets, with the added benefit of a short blood half-life, thereby enabling rapid in vivo visualization within the vasculature.

Paclitaxel Drug-Coated Balloon Angioplasty Suppresses Progression and Inflammation of Experimental Atherosclerosis in Rabbits

Paclitaxel drug-coated balloons (DCBs) reduce restenosis, but their overall safety has recently raised concerns. This study hypothesized that DCBs could lessen inflammation and reduce plaque progression. Using 25 rabbits with cholesterol feeding- and balloon injury-induced lesions, DCB-percutaneous transluminal angioplasty (PTA), plain PTA, or sham-PTA (balloon insertion without inflation) was investigated using serial intravascular near-infrared fluorescence-optical coherence tomography and serial intravascular ultrasound. In these experiments, DCB-PTA reduced inflammation and plaque burden in nonobstructive lesions compared with PTA or sham-PTA. These findings indicated the potential for DCBs to serve safely as regional anti-atherosclerosis therapy.

3D cellular-resolution imaging in arteries using few-mode interferometry

Cross-sectional visualisation of the cellular and subcellular structures of human atherosclerosis in vivo is significant, as this disease is fundamentally caused by abnormal processes that occur at this scale in a depth-dependent manner. However, due to the inherent resolution-depth of focus tradeoff of conventional focusing optics, today's highest-resolution intravascular imaging technique, namely, optical coherence tomography (OCT), is unable to provide cross-sectional images at this resolution through a coronary catheter. Here, we introduce an intravascular imaging system and catheter based on few-mode interferometry, which overcomes the depth of focus limitation of conventional high-numerical-aperture objectives and enables three-dimensional cellular-resolution intravascular imaging in vivo by a submillimetre diameter, flexible catheter. Images of diseased cadaver human coronary arteries and living rabbit arteries were acquired with this device, showing clearly resolved cellular and subcellular structures within the artery wall, such as individual crystals, smooth muscle cells, and inflammatory cells. The capability of this technology to enable cellular-resolution, cross-sectional intravascular imaging will make it possible to study and diagnose human coronary disease with much greater precision in the future.

Quantitative intravascular biological fluorescence-ultrasound imaging of coronary and peripheral arteries in vivo

Aims

(i) to evaluate a novel hybrid near-infrared fluorescence-intravascular ultrasound (NIRF-IVUS) system in coronary and peripheral swine arteries in vivo; (ii) to assess simultaneous quantitative biological and morphological aspects of arterial disease.

Methods and results

Two 9F/15MHz peripheral and 4.5F/40MHz coronary near-infrared fluorescence (NIRF)-IVUS catheters were engineered to enable accurate co-registrtation of biological and morphological readings simultaneously in vivo. A correction algorithm utilizing IVUS information was developed to account for the distance-related fluorescence attenuation due to through-blood imaging. Corrected NIRF (cNIRF)-IVUS was applied for in vivo imaging of angioplasty-induced vascular injury in swine peripheral arteries and experimental fibrin deposition on coronary artery stents, and of atheroma in a rabbit aorta, revealing feasibility to intravascularly assay plaque structure and inflammation. The addition of ICG-enhanced NIRF assessment improved the detection of angioplasty-induced endothelial damage compared to standalone IVUS. In addition, NIRF detection of coronary stent fibrin by in vivo cNIRF-IVUS imaging illuminated stent pathobiology that was concealed on standalone IVUS. Fluorescence reflectance imaging and microscopy of resected tissues corroborated the in vivo findings.

Conclusions

Integrated cNIRF-IVUS enables simultaneous co-registered through-blood imaging of disease related morphological and biological alterations in coronary and peripheral arteries in vivo. Clinical translation of cNIRF-IVUS may significantly enhance knowledge of arterial pathobiology, leading to improvements in clinical diagnosis and prognosis, and helps to guide the development of new therapeutic approaches for arterial diseases.

Abstract 354: Early Intentional Restoration of Blood Flow Reduces Thrombus Burden and Vein Wall Scarring Following Dvt: Implications for Preventing the Post-thrombotic Syndrome

Background: Despite anticoagulation therapy, up to 50% of deep vein thrombosis (DVT) patients still develop the post-thrombotic syndrome (PTS), a condition that arises from thrombus obstruction and vein wall damage, leading to venous hypertension. While catheter-based intervention may reduce PTS, the CaVenT and ATTRACT trials demonstrated little clinical benefit of intentional restoration of blood flow (RBF) for reducing PTS. However, these trials have not explored the time-dependence of RBF, a key factor as aging VT are associated with greater vein wall injury.

Methods: To investigate the temporal effects of intentional RBF following VT, we modified a classic complete ligation inferior vena cava (IVC) stasis VT protocol in C57BL/6 mice by de-ligating the day 0 ligature at day 2 to allow RBF. Compared to intravital microscopy, the sensitivity and specificity of noninvasive ultrasound (US) to detect RBF was 82.1% and 94.4%, respectively. Serial US was then performed on mice. Mice were classified as early RBF (RBF by day 4), late RBF (RBF after day 4), no RBF, or sham de-ligation groups. Follow day 8 sacrifice, thrombus burden (mg/cm) and vein wall scarring (VWS) were measured. Kruskal-Wallis followed by Dunn’s test was used to compare statistical significance between groups.

Results: After de-ligation, RBF through VT increased gradually over time (Fig. A). The early RBF group exhibited significant reductions in VT burden (N=9) and VWS (N=5) at day 8 ( p <0.05 vs. comparator groups, Fig B-C). In contrast, the late RBF group did not experience significant reductions in thrombus burden (N=6) nor VWS (N=4), with measures similar to mice with no RBF (N=3-4), or sham de-ligation (N=8-9).

Conclusions: Intentional early RBF reduces venous thrombus burden and VWS, factors that drive PTS. Mechanistic studies to address these findings are going. The overall results suggest that anti-PTS benefits of catheter-based intervention may be enhanced in subjects receiving early RBF.

Abstract 324: Molecular Imaging of High Risk Atherosclerotic Plaque Using Fibrin-Binding PET Probe

Objectives: There is a need for better stratification of atherosclerotic patients to identify individuals at high risk for a cardiovascular event. Two key hallmarks of plaque at high risk for rupture are intraplaque hemorrhage and evidence of prior rupture. The protein fibrin is strongly associated with both hemorrhage and rupture but it is not present in earlier stages of plaque development, suggesting that fibrin imaging would be sensitive for high risk plaque versus stable/early disease. Here, we describe imaging properties of a fibrin-specific PET probe for atherosclerotic plaque rupture in rabbits.

Methods: Rabbits were fed with high cholesterol diet (HCD) for 8 weeks followed by 2 weeks of normal diet. Two weeks after the initiation of HCD, endothelial denudation of abdominal aorta was performed using balloon catheter. At 10 weeks, rabbits were randomly divided into plaque rupture (n=8; triggered by Russell’s viper venom and histamine) and control group (n=4), injected with fibrin-binding probe [ 68 Ga]CM-246, and scanned on a PET/MRI. Then, vessels of interest were removed for ex-vivo PET, autoradiography, and histology.

Results: Rabbits with plaque rupture had >2-fold increase in [ 68 Ga]CM-246 signal in the abdominal aorta compared with the control group (A). At 105-120 min post probe injection, there was a clear PET uptake on the aorta in plaque rupture rabbit (B) compared with control rabbit (C). MR images were used to differentiate abdominal aorta (green arrows) and the inferior vena cava (blue arrows). T2-dark blood images confirmed the atherosclerotic plaques in plaque rupture (D) and control rabbits (E). ToF images were used to visualize aortic lumen in plaque rupture (F) and control rabbits (G). Ex vivo PET imaging (H) and autoradiography confirmed in vivo results.

Conclusions: We demonstrated that [ 68 Ga]CM-246 detects atherosclerotic plaque rupture in a rabbit model and can be a useful tool for the diagnosis of high-risk atherosclerotic plaque in patients.

Everolimus-eluting stents stabilize plaque inflammation in vivo: assessment by intravascular fluorescence molecular imaging

Aims

Inflammation drives atherosclerosis complications and is a promising therapeutic target for plaque stabilization. At present, it is unknown whether local stenting approaches can stabilize plaque inflammation in vivo. Here, we investigate whether everolimus-eluting stents (EES) can locally suppress plaque inflammatory protease activity in vivo using intravascular near-infrared fluorescence (NIRF) molecular imaging.

Methods and results

Balloon-injured, hyperlipidaemic rabbits with atherosclerosis received non-overlapping EES and bare metal stents (BMS) placement into the infrarenal aorta (n = 7 EES, n = 7 BMS, 3.5 mm diameter x 12 mm length). Four weeks later, rabbits received an injection of the cysteine protease-activatable NIRF imaging agent Prosense VM110. Twenty-four hours later, co-registered intravascular 2D NIRF, X-ray angiography and intravascular ultrasound imaging were performed. In vivo EES-stented plaques contained substantially reduced NIRF inflammatory protease activity compared with untreated plaques and BMS-stented plaques (P = 0.006). Ex vivo macroscopic NIRF imaging of plaque protease activity corroborated the in vivo results (P = 0.003). Histopathology analyses revealed that EES-treated plaques showed reduced neointimal and medial arterial macrophage and cathepsin B expression compared with unstented and BMS-treated plaques.

Conclusions

EES-stenting stabilizes plaque inflammation as assessed by translational intravascular NIRF molecular imaging in vivo. These data further support that EES may provide a local approach for stabilizing inflamed plaques.

Atheroma Susceptible to Thrombosis Exhibit Impaired Endothelial Permeability In Vivo as Assessed by Nanoparticle-Based Fluorescence Molecular Imaging

BACKGROUND

The role of local alterations in endothelial functional integrity in atherosclerosis remains incompletely understood. This study used nanoparticle-enhanced optical molecular imaging to probe in vivo mechanisms involving impaired endothelial barrier function in experimental atherothrombosis.

METHODS AND RESULTS

Atherosclerosis was induced in rabbits (n=31) using aortic balloon injury and high-cholesterol diet. Rabbits received ultrasmall superparamagnetic iron oxide nanoparticles (CLIO) derivatized with a near-infrared fluorophore (CyAm7) 24 hours before near-infrared fluorescence imaging. Rabbits were then either euthanized (n=9) or underwent a pharmacological triggering protocol to induce thrombosis (n=22). CLIO-CyAm7 nanoparticles accumulated in areas of atheroma (P<0.05 versus reference areas). On near-infrared fluorescence microscopy, CLIO-CyAm7 primarily deposited in the superficial intima within plaque macrophages, endothelial cells, and smooth muscle cells. Nanoparticle-positive areas further exhibited impaired endothelial barrier function as illuminated by Evans blue leakage. Deeper nanoparticle deposition occurred in areas of plaque neovascularization. In rabbits subject to pharmacological triggering, plaques that thrombosed exhibited significantly higher CLIO-CyAm7 accumulation compared with nonthrombosed plaques (P<0.05). In thrombosed plaques, nanoparticles accumulated preferentially at the plaque-thrombus interface. Intravascular 2-dimensional near-infrared fluorescence imaging detected nanoparticles in human coronary artery-sized atheroma in vivo (P<0.05 versus reference segments).

CONCLUSIONS

Plaques that exhibit impaired in vivo endothelial permeability in cell-rich areas are susceptible to subsequent thrombosis. Molecular imaging of nanoparticle deposition may help to identify biologically high-risk atheroma.

Abstract 127: Colchicine Attenuates Vein Wall Scarring in Murine Venous Thrombosis: Implications for Limiting the Post-Thrombotic Syndrome

Objective: In this study, we investigated the effects of colchicine on vein wall inflammation and scarring, and thrombus burden/VT resolution, key drivers of the PTS.

Methods: Inferior vena cava (IVC) stasis VT were created in C57BL/6 mice (n=60). Colchicine (0.2 or 0.02 mg/kg for high or low dose, respectively) was administered daily via intraperitoneal injection starting 24 hours after VT initiation. At VT timepoints of day 4, 8 and 14, mice were sacrificed and VT were resected for measurements of thrombus. Picrosirius-red staining of VT sections assessed vein wall thickness. Serial sections were processed for Carstairs fibrin staining and immunostaining. The number of vein wall fibroblasts and macrophages per 5 high-power fields (400х) were calculated.

Results: Colchicine significantly decreased venous thrombus-induced vein wall scarring at Day 8 (PBS 71.53±6.97μm, Col lo 55.11±5.48μm, Col hi 46.84±2.03μm; n=5 per group; PBS vs Col lo, P < 0.01; Col lo vs Col hi, P < 0.05) and at Day 14 (PBS 55.29±8.97μm, Col lo 45.20±2.73μm, Col hi 42.68±3.57μm; n=4-7 per group; PBS vs Col lo, P < 0.05; PBS vs Col hi, P < 0.05; Col lo vs Col hi, P > 0.05). Colchicine reduced the number of vein wall F4/80+ macrophages (PBS vs Col hi, 73.33±8.63 vs 55.87±8.07, n=5 per group, P < 0.01) and FSP1+ cells (PBS vs Col hi, 73.80±8.01 vs 41.60±8.37, n=5 per group, P < 0.01) in DVT D8. Also, colchicine reduced RNA expression of both profibrotic (collagen I, collagen III, procollagen I, procollagen III, FSP1) and proinflammatory (IL-1β, CD68) markers in DVT D8 (n=8 per group, P < 0.05). Of note, despite possessing anti-inflammatory actions, colchicine did not impair VT resolution (measured by thrombus mass) at D4 PBS vs Col hi, 27.00±5.11 vs 23.47±6.03mg/cm, n=9-12 per group, P > 0.05) nor at D8 (PBS vs Col hi, 19.05±5.23 vs 15.58±6.52mg/cm, n=12 per group, P > 0.05).

Conclusion: The FDA-approved agent colchicine reduces experimental VT-induced vein wall scarring without impairing thrombus resolution. Anti-scarring effects may be related to attenuated inflammation of fibrotic mediators in the vein wall and adherent thrombus. Colchicine may offer a clinically viable option to reduce the post-thrombotic syndrome induced by deep vein thrombosis.

Intravascular fibrin molecular imaging improves the detection of unhealed stents assessed by optical coherence tomography in vivo

AIMS

Fibrin deposition and absent endothelium characterize unhealed stents that are at heightened risk of stent thrombosis. Optical coherence tomography (OCT) is increasingly used for assessing stent tissue coverage as a measure of healed stents, but cannot precisely identify whether overlying tissue represents physiological neointima. Here we assessed and compared fibrin deposition and persistence on bare metal stent (BMS) and drug-eluting stent (DES) using near-infrared fluorescence (NIRF) molecular imaging in vivo, in combination with simultaneous OCT stent coverage.

METHODS AND RESULTS

Rabbits underwent implantation of one BMS and one DES without overlap in the infrarenal aorta (N = 20 3.5 × 12 mm). At Days 7 and/or 28, intravascular NIRF-OCT was performed following the injection of fibrin-targeted NIRF molecular imaging agent FTP11-CyAm7. Intravascular NIRF-OCT enabled high-resolution imaging of fibrin overlying stent struts in vivo, as validated by histopathology. Compared with BMS, DES showed greater fibrin deposition and fibrin persistence at Days 7 and 28 (P < 0.01 vs. BMS). Notably, for edge stent struts identified as covered by OCT on Day 7, 92.8 ± 9.5% of DES and 55.8 ± 23.6% of BMS struts were NIRF fibrin positive (P < 0.001). At Day 28, 18.6 ± 10.6% (DES) and 5.1 ± 8.7% (BMS) of OCT-covered struts remained fibrin positive (P < 0.001).

CONCLUSION

Intravascular NIRF fibrin molecular imaging improves the detection of unhealed stents, using clinically translatable technology that complements OCT. A sizeable percentage of struts deemed covered by OCT are actually covered by fibrin, particularly in DES, and therefore such stents might remain prothrombotic. These findings have implications for the specificity of standalone clinical OCT assessments of stent healing.

Myocardial Infarction Alters Adaptation of the Tethered Mitral Valve

BACKGROUND

In patients with myocardial infarction (MI), leaflet tethering by displaced papillary muscles induces mitral regurgitation (MR), which doubles mortality. Mitral valves (MVs) are larger in such patients but fibrosis sets in counterproductively. The investigators previously reported that experimental tethering alone increases mitral valve area in association with endothelial-to-mesenchymal transition.

OBJECTIVES

The aim of this study was to explore the clinically relevant situation of tethering and MI, testing the hypothesis that ischemic milieu modifies mitral valve adaptation.

METHODS

Twenty-three adult sheep were examined. Under cardiopulmonary bypass, the papillary muscle tips in 6 sheep were retracted apically to replicate tethering, short of producing MR (tethered alone). Papillary muscle retraction was combined with apical MI created by coronary ligation in another 6 sheep (tethered plus MI), and left ventricular remodeling was limited by external constraint in 5 additional sheep (left ventricular constraint). Six sham-operated sheep were control subjects. Diastolic mitral valve surface area was quantified by 3-dimensional echocardiography at baseline and after 58 ± 5 days, followed by histopathology and flow cytometry of excised leaflets.

RESULTS

Tethered plus MI leaflets were markedly thicker than tethered-alone valves and sham control subjects. Leaflet area also increased significantly. Endothelial-to-mesenchymal transition, detected as α-smooth muscle actin-positive endothelial cells, significantly exceeded that in tethered-alone and control valves. Transforming growth factor-β, matrix metalloproteinase expression, and cellular proliferation were markedly increased. Uniquely, tethering plus MI showed endothelial activation with vascular adhesion molecule expression, neovascularization, and cells positive for CD45, considered a hematopoietic cell marker. Tethered plus MI findings were comparable with external ventricular constraint.

CONCLUSIONS

MI altered leaflet adaptation, including a profibrotic increase in valvular cell activation, CD45-positive cells, and matrix turnover. Understanding cellular and molecular mechanisms underlying leaflet adaptation and fibrosis could yield new therapeutic opportunities for reducing ischemic MR.

Abstract 11: Suppression of Coronary Artery Stent Inflammation by Colchicine Decreases Stent Restenosis, as Assessed by Serial in vivo Optical Molecular-structural Imaging

Background: Restenosis of coronary stents causes substantial morbidity. Inflammation drives restenosis by activating smooth muscle cells to form obstructive neointima. Recent data suggests that colchicine, an anti-proliferative and anti-inflammatory agent, may reduce clinical stent restenosis. Here we assessed the effects of colchicine on in vivo stent-induced inflammatory protease activity and subsequent restenosis using serial intravascular molecular-structural near-infrared fluorescence (NIRF)-optical coherence tomography (OCT) imaging.

Methods: Rabbits implanted with clinical-grade bare-metal stents (3.5x12 mm) received oral colchicine 0.6 mg or placebo daily (N=5 rabbits, 15 stents per group) and were imaged at 2 and 6 weeks with intravascular NIRF-OCT 24 hours following ProSense VM110 (4 mg/kg IV; ex/em 750/780 nm) for molecular NIRF imaging of cathepsin protease inflammatory activity. Neointimal formation was measured every 400 μm by co-registered structural OCT. Stents were analyzed by ex vivo fluorescence microscopy, histology, and cathepsin mRNA expression.

Results: In controls, NIRF inflammation at 2 weeks was significantly enhanced at the stent edges (edge 32.6±7.3 vs. mid 20.1±2.6 nM; p<0.0001) and corresponded to greater stent edge ΔOCT neointimal growth between 2 and 6 weeks (edge 0.61±0.25 vs. mid 0.33±0.13 mm2; p<0.01), providing strong prediction of early NIRF inflammation for subsequent restenosis by OCT (r=0.72; p=0.001). Colchicine significantly decreased 2-week NIRF inflammation (stent TBR: control 2.42±0.10 vs. colchicine 1.69±0.11; p<0.0001), and neutralized the stent edge 6-week neointimal increase observed in controls (colchicine ΔOCT edge 0.05±0.05 vs. mid 0.02±0.03 mm2; p=0.21). Ex vivo analyses corroborated the in vivo results.

Conclusion: We demonstrate that in vivo NIRF inflammatory protease activity predicts stent locations that develop greater restenosis, and that colchicine, an FDA-approved agent, decreases stent-induced inflammation and subsequent restenosis in vivo. lntravascular NIRF-OCT is a novel translatable approach to predict site-specific coronary stent restenosis based on the local inflammatory profile and monitor the effects of anti-restenosis therapeutics.

Dual modality intravascular optical coherence tomography (OCT) and near-infrared fluorescence (NIRF) imaging: a fully automated algorithm for the distance-calibration of NIRF signal intensity for quantitative molecular imaging

Intravascular optical coherence tomography (IVOCT) is a well-established method for the high-resolution investigation of atherosclerosis in vivo. Intravascular near-infrared fluorescence (NIRF) imaging is a novel technique for the assessment of molecular processes associated with coronary artery disease. Integration of NIRF and IVOCT technology in a single catheter provides the capability to simultaneously obtain co-localized anatomical and molecular information from the artery wall. Since NIRF signal intensity attenuates as a function of imaging catheter distance to the vessel wall, the generation of quantitative NIRF data requires an accurate measurement of the vessel wall in IVOCT images. Given that dual modality, intravascular OCT-NIRF systems acquire data at a very high frame-rate (>100 frames/s), a high number of images per pullback need to be analyzed, making manual processing of OCT-NIRF data extremely time consuming. To overcome this limitation, we developed an algorithm for the automatic distance-correction of dual-modality OCT-NIRF images. We validated this method by comparing automatic to manual segmentation results in 180 in vivo images from six New Zealand White rabbit atherosclerotic after indocyanine-green injection. A high Dice similarity coefficient was found (0.97 ± 0.03) together with an average individual A-line error of 22 µm (i.e., approximately twice the axial resolution of IVOCT) and a processing time of 44 ms per image. In a similar manner, the algorithm was validated using 120 IVOCT clinical images from eight different in vivo pullbacks in human coronary arteries. The results suggest that the proposed algorithm enables fully automatic visualization of dual modality OCT-NIRF pullbacks, and provides an accurate and efficient calibration of NIRF data for quantification of the molecular agent in the atherosclerotic vessel wall.

Abstract 501: Noninvasive Photodynamic Therapy of Murine Atherosclerosis Using Macrophage-Targeted Nanoparticles

Objectives: Cerebrovascular disease leading to stroke remains a leading cause of death and disability worldwide. Photodynamic therapy (PDT) of atherosclerotic plaque macrophages may be a promising approach to stabilize rupture-prone carotid lesions, but a noninvasive PDT method for carotid atherosclerosis is lacking. Here we developed a near-infrared (NIR) absorbing macrophage-targeted photosensitizing nanoparticle to determine whether plaque macrophages can be successfully ablated using noninvasive PDT.

Methods: CLIO-CyAm7-Chlorin is a dextran-based nanoparticle that contains a NIR photosensitizer (Chlorin, abs 650nm) for PDT, and a discrete NIR fluorochrome (CyAm7, ex/em 750/767nm) for fluorescence imaging of nanoparticle distribution. Noninvasive PDT optimization was performed in vivo via a PDT ablation study of hepatic macrophages in C57BL6 mice (n=65). Varying doses, exposure times, and laser power were explored. A separate group of ApoE-/- mice (n=16, 8wk HCD) injected with CLIO-Chlorin-CyAm7 or control CLIO-CyAm7 (10mgFe/kg) received noninvasive PDT of aortic root atheroma. Mice were sacrificed 1 day post-PDT for histology. Computational simulations of noninvasive PDT for human plaques were studied at multiple PDT wavelengths and light fluence.

Results: Noninvasive PDT optimization showed that increasing doses of CLIO-CyAm7-Chlorin and laser exposure time had strong linear correlations with increasing liver injury (r2=0.88 and 0.65, respectively). Mice injected with control CLIO-CyAm7 showed no damage of the liver by tunel or H&E, independent of dose or time of PDT. In ApoE-/- mice, CLIO-CyAm7-Chlorin and CLIO-CyAm7 localized to inflamed aortic root plaques, and was confirmed to be macrophage localized on fluorescence imaging. CLIO-CyAm7-Chlorin/PDT showed a 6-fold increase in tunel (+) cells in aortic root plaques compared to control CLIO-CyAm7/PDT treated animals (p<0.01). Computational simulations revealed that further NIR-shifting of the photosensitizer would enable noninvasive PDT up to 1-2 cm deep, potentially enabling noninvasive PDT of human carotid plaques.

Conclusions: CLIO-CyAm7-Chlorin is a multifunctional NIR nanoparticle that allows noninvasive macrophage-targeted PDT of atherosclerosis.

Abstract 151: Thrombosis Prone Plaques Exhibit Inflammation Prior to Rupture: Intravascular Detection via Macrophage-targeted Optical Imaging

Introduction

Inflammation modulates atherogenesis and the destabilization of plaques. However, the role of macrophages in plaque rupture is incompletely understood. Here we investigated the in vivo spatial distribution of plaque macrophages prior to triggered plaque rupture, using intravascular molecular imaging and a near-infrared fluorescence (NIRF) macrophage targeted agent, CLIO-CyAm7. We hypothesized that CLIO-CyAm7 would illuminate macrophages in vivo and preferentially localize to plaques that are vulnerable to plaque rupture.

Methods

Atherosclerosis was induced in rabbits (n=14) using a 12-week hyperlipidemic diet with alternating 1% high cholesterol and normal chow, concomitant with aortic balloon injury at 2 weeks. Rabbits were injected with 2.5mg/kg (n=8) or 5mg/kg (n=6) of CLIO-CyAm7 at 24 or 48 hours, respectively, prior to thrombosis triggering using Russell’s Viper Venom and histamine over 48 hours. The 2.5mg/kg subgroup was imaged in vivo using NIRF imaging and intravascular ultrasound (IVUS), immediately prior to thrombosis triggering. After sacrifice, ex vivo imaging, fluorescence microscopy (FM), Carstairs and Ram-11 immunostaining were performed.

Results

FM identified significantly higher CLIO-CyAm7 signal in areas of atherosclerosis compared to normal segments of the aorta (2.5mg/kg and 5.0mg/kg, p=0.03 and p=0.03). This signal was primarily localized at the intimal-luminal border of atheroma, with some penetration in the media and adventitia. CLIO-CyAm7 colocalized with a subset of superficial macrophages. Carstairs staining identified fibrin-rich thrombi, indicating plaque rupture in 6 of 14 rabbits (43%). There was increased CLIO-CyAm7 in areas underlying thrombus and particularly at the shoulder of ruptured plaques. Plaque macrophages were detectable via in vivo intravascular NIRF imaging. Areas of atherosclerosis, determined by IVUS, showed significantly higher NIRF peak signal-to-noise ratio than normal segments of the aorta (40.2±16.9 and 5.9±1.9, p=0.02).

Conclusion

Macrophages are consistently present in plaques that undergo triggered rupture, and can be detected via CLIO-CyAm7 intravascular NIRF molecular imaging. In vivo macrophage imaging may identify thrombosis-prone plaques.

Abstract 320: Heterogeneous Coronary Stent Inflammation and Healing Revealed by in vivo Optical Molecular-Structural Imaging

Introduction

Patients with diabetes mellitus that receive coronary stents experience greater stent restenosis and thrombosis, leading to adverse clinical outcomes. Impaired stent healing is linked to elevated endovascular inflammation, but in vivo data is lacking. Here, we assessed stent inflammation and tissue healing in diabetic rabbits, using intravascular molecular-structural near-infrared fluorescence (NIRF)-optical frequency domain imaging (OFDI).

Methods

A bare-metal stent (3.5x12mm) was implanted in the infrarenal aorta of alloxan-induced diabetic rabbits (n=5). At day 28, intravascular NIRF-OFDI was performed. Prosense VM110 (5mg/kg IV 24 hrs before imaging; ex/em 750/780 nm) enabled NIRF molecular imaging of inflammatory cathepsin activity. Structural OFDI stent endothelialization (coverage) was simultaneously assessed in 0.5mm intervals. Aortas were then harvested for ex vivo fluorescence reflectance imaging (FRI), electrochemical stent dissolution, and cathepsin B immunostaining.

Results

At day 28, stent NIRF inflammatory cathepsin protease activity was enhanced compared to the non-stented aorta (50.9±2.0 vs. 26.1±0.6 nM; p<0.0001). OFDI demonstrated greater average stent edge restenosis (proximal and distal 2mm stent edge neointimal area, 1.63±0.12 vs. mid 2 mm stent 0.50±0.05 mm 2 ; p<0.0001), with less de-endothelialized struts at the stent edges (2.1±1.7% vs. 14.0±4.1% mid stent; p=0.03). Stent edge NIRF inflammation was also greater (60.8±3.4 vs. 40.8±1.4 nM mid stent; p=0.0005), and correlated with neointima formation (R=0.43; p=0.003). Conversely, NIRF inflammation negatively tracked with OFDI-uncovered stent struts (R=-0.42; p=0.004). FRI corroborated the enhanced stent-edge NIRF pattern. Matched histopathology revealed cathepsin B expression in NIRF-positive regions.

Conclusions

Intravascular NIRF-OFDI molecular-structural imaging demonstrates that NIRF inflammatory protease activity is linked to increased bare-metal stent edge neointimal formation, but inversely relates to uncovered stent struts. This translatable approach provides new insights into stent inflammation and healing, and may ultimately inform the risk of stent restenosis and thrombosis.

Improving quantification of intravascular fluorescence imaging using structural information

Intravascular near-infrared fluorescence (iNIRF) imaging can enable the in vivo visualization of biomarkers of vascular pathology, including high-risk plaques. The technique resolves the bio-distribution of systemically administered fluorescent probes with molecular specificity in the vessel wall. However, the geometrical variations that may occur in the distance between fibre-tip and vessel wall can lead to signal intensity variations and challenge quantification. Herein we examined whether the use of anatomical information of the cross-section vessel morphology, obtained from co-registered intravascular ultrasound (IVUS), can lead to quantification improvements when fibre-tip and vessel wall distance variations are present. The algorithm developed employs a photon propagation model derived from phantom experiments that is used to calculate the relative attenuation of fluorescence signals as they are collected over 360° along the vessel wall, and utilizes it to restore accurate fluorescence readings. The findings herein point to quantification improvements when employing hybrid iNIRF, with possible implications to the clinical detection of high-risk plaques or blood vessel theranostics.

Two-dimensional intravascular near-infrared fluorescence molecular imaging of inflammation in atherosclerosis and stent-induced vascular injury

OBJECTIVES

This study sought to develop a 2-dimensional (2D) intravascular near-infrared fluorescence (NIRF) imaging strategy for investigation of arterial inflammation in coronary-sized vessels.

BACKGROUND

Molecular imaging of arterial inflammation could provide new insights into the pathogenesis of acute myocardial infarction stemming from coronary atheromata and implanted stents. Presently, few high-resolution approaches can image inflammation in coronary-sized arteries in vivo.

METHODS

A new 2.9-F rotational, automated pullback 2D imaging catheter was engineered and optimized for 360° viewing intravascular NIRF imaging. In conjunction with the cysteine protease-activatable imaging reporter Prosense VM110 (VisEn Medical, Woburn, Massachusetts), intra-arterial 2D NIRF imaging was performed in rabbit aortas with atherosclerosis (n =10) or implanted coronary bare-metal stents (n = 10, 3.5-mm diameter, day 7 post-implantation). Intravascular ultrasound provided coregistered anatomical images of arteries. After sacrifice, specimens underwent ex vivo NIRF imaging, fluorescence microscopy, and histological and immunohistochemical analyses.

RESULTS

Imaging of coronary artery-scaled phantoms demonstrated 8-sector angular resolution and submillimeter axial resolution, nanomolar sensitivity to NIR fluorochromes, and modest NIRF light attenuation through blood. High-resolution NIRF images of vessel wall inflammation with signal-to-noise ratios >10 were obtained in real-time through blood, without flushing or occlusion. In atherosclerosis, 2D NIRF, intravascular ultrasound-NIRF fusion, microscopy, and immunoblotting studies provided insight into the spatial distribution of plaque protease activity. In stent-implanted vessels, real-time imaging illuminated an edge-based pattern of stent-induced arterial inflammation.

CONCLUSIONS

A new 2D intravascular NIRF imaging strategy provides high-resolution in vivo spatial mapping of arterial inflammation in coronary-sized arteries and reveals increased inflammation-regulated cysteine protease activity in atheromata and stent-induced arterial injury.

In vivo near infrared fluorescence (NIRF) intravascular molecular imaging of inflammatory plaque, a multimodal approach to imaging of atherosclerosis

The vascular response to injury is a well-orchestrated inflammatory response triggered by the accumulation of macrophages within the vessel wall leading to an accumulation of lipid-laden intra-luminal plaque, smooth muscle cell proliferation and progressive narrowing of the vessel lumen. The formation of such vulnerable plaques prone to rupture underlies the majority of cases of acute myocardial infarction. The complex molecular and cellular inflammatory cascade is orchestrated by the recruitment of T lymphocytes and macrophages and their paracrine effects on endothelial and smooth muscle cells.(1) Molecular imaging in atherosclerosis has evolved into an important clinical and research tool that allows in vivo visualization of inflammation and other biological processes. Several recent examples demonstrate the ability to detect high-risk plaques in patients, and assess the effects of pharmacotherapeutics in atherosclerosis.(4) While a number of molecular imaging approaches (in particular MRI and PET) can image biological aspects of large vessels such as the carotid arteries, scant options exist for imaging of coronary arteries.(2) The advent of high-resolution optical imaging strategies, in particular near-infrared fluorescence (NIRF), coupled with activatable fluorescent probes, have enhanced sensitivity and led to the development of new intravascular strategies to improve biological imaging of human coronary atherosclerosis. Near infrared fluorescence (NIRF) molecular imaging utilizes excitation light with a defined band width (650-900 nm) as a source of photons that, when delivered to an optical contrast agent or fluorescent probe, emits fluorescence in the NIR window that can be detected using an appropriate emission filter and a high sensitivity charge-coupled camera. As opposed to visible light, NIR light penetrates deeply into tissue, is markedly less attenuated by endogenous photon absorbers such as hemoglobin, lipid and water, and enables high target-to-background ratios due to reduced autofluorescence in the NIR window. Imaging within the NIR 'window' can substantially improve the potential for in vivo imaging.(2,5) Inflammatory cysteine proteases have been well studied using activatable NIRF probes(10), and play important roles in atherogenesis. Via degradation of the extracellular matrix, cysteine proteases contribute importantly to the progression and complications of atherosclerosis(8). In particular, the cysteine protease, cathepsin B, is highly expressed and colocalizes with macrophages in experimental murine, rabbit, and human atheromata.(3,6,7) In addition, cathepsin B activity in plaques can be sensed in vivo utilizing a previously described 1-D intravascular near-infrared fluorescence technology(6), in conjunction with an injectable nanosensor agent that consists of a poly-lysine polymer backbone derivatized with multiple NIR fluorochromes (VM110/Prosense750, ex/em 750/780nm, VisEn Medical, Woburn, MA) that results in strong intramolecular quenching at baseline.(10) Following targeted enzymatic cleavage by cysteine proteases such as cathepsin B (known to colocalize with plaque macrophages), the fluorochromes separate, resulting in substantial amplification of the NIRF signal. Intravascular detection of NIR fluorescence signal by the utilized novel 2D intravascular NIRF catheter now enables high-resolution, geometrically accurate in vivo detection of cathepsin B activity in inflamed plaque. In vivo molecular imaging of atherosclerosis using catheter-based 2D NIRF imaging, as opposed to a prior 1-D spectroscopic approach,(6) is a novel and promising tool that utilizes augmented protease activity in macrophage-rich plaque to detect vascular inflammation.(11,12) The following research protocol describes the use of an intravascular 2-dimensional NIRF catheter to image and characterize plaque structure utilizing key aspects of plaque biology. It is a translatable platform that when integrated with existing clinical imaging technologies including angiography and intravascular ultrasound (IVUS), offers a unique and novel integrated multimodal molecular imaging technique that distinguishes inflammatory atheromata, and allows detection of intravascular NIRF signals in human-sized coronary arteries.

Progress on multimodal molecular / anatomical intravascular imaging of coronary vessels combining near infrared fluorescence and ultrasound

The use of intravascular imaging modalities for the detection and assessment of atherosclerotic plaque is becoming increasingly useful. Current clinical invasive modalities assess the presence of plaque using anatomical information and include Intravascular Ultrasound (IVUS) and Optical Coherence Tomography (OCT). However, such modalities cannot take into account underlying functional biological information, which can however be revealed with the use of molecular imaging. Consequently, intravascular molecular imaging is emerging as a powerful approach. We have developed such a Near-Infrared Fluorescence (NIRF) imaging system and showcased, in both phantom and in-vivo (rabbit) experiments, its potential to successfully detect inflamed atherosclerotic plaques, using appropriate fluorescent probes. Here, we discuss some limitations of the current system and suggest the combined use of the NIRF and IVUS imaging systems as a means for more accurate assessment of atherosclerotic plaque. We include some results and models that showcase the potential power of this kind of hybrid imaging.