Perfluorocarbon Nanoparticles Research Articles

Abstract 4957: Robust Transfection of Vascular Endothelium for siRNA Knockdown of Vascular Cell Adhesion Molecule-1 Through a Novel Nanoparticle-Lipid Raft Pathway

Controlling adhesion molecule expression as an antiatherosclerotic therapy is a heretofore untested concept that could modify disease progression and/or interdict acute coronary syndromes. Methods: To design a synthetic vehicle to deliver vascular cell adhesion molecule-1 (VCAM-1) siRNA to endothelial cells, perfluorocarbon nanoparticles (PFC-NP) were loaded with the cationic lipid 1,2-Dioleoyl-3-Trimethylammonium-Propane (DOTAP) in the lipid monolayer to form transfection complexes (10 pM PFC-NP + 5 nM siRNA) with VCAM-1 specific siRNA. Mouse 2F2B endothelial cells were treated with TNF α (10 ng/ml) to induce VCAM-1 expression and after 48h, mRNA and protein levels were measured. For endocytosis colabeling studies, transfection complexes were produced with fluorescently labled siRNA (red) and incubated with endothelial cells in the presence of fluorescently labeled pathway specific markers (green, macropinocytosis: dextran, clathrin: transferrin, lipid raft: cholera toxin-B). Results: PFC-NP mediated siRNA transfection led to a significant decrease in both VCAM-1 mRNA and protein levels(A) . siRNA exhibited little intracellular colocalization with common markers of both macropinocytosis (B) and clathrin mediated endocytosis (C), while abundant membrane colocalization with lipid rafts was observed(D). Conclusion: Because endothelial cells harbor an excess of lipid rafts in their plasma membranes, the development of an effective targeted nanoparticle carrier for siRNA that utilizes lipid raft transport rather than traditional endocytotic pathways could represent a valuable strategy for controlling vascular inflammation in atherosclerosis. This research has received full or partial funding support from the American Heart Association, Midwest Affiliate (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota & Wisconsin).

Drug packaging and delivery using perfluorocarbon nanoparticles for targeted inhibition of vascular smooth muscle cells

To investigate the in vitro release profile of drugs encapsulated within perfluorocarbon (PFC) nanoparticles (NPs) and their ability to inhibit the activity of vascular smooth muscle cells (SMCs). Dexamethasone phosphate (DxP) or dexamethasone acetate (DxA) was encapsulated into PFC nanoparticles using a high-pressure homogenous method. The morphology and size of the NPs were examined using scanning electron microscopy (SEM) and a laser particle size analyzer. Drug loading and in vitro release were assessed by high-performance liquid chromatography (HPLC). The impact of NP capsules on SMC proliferation, migration and apoptosis in vitro was assessed using cell counting kit-8, transwell cell migration and flow cytometry assays. The sizes of DxP-NPs and DxA-NPs were 224+/-6 nm and 236+/-9 nm, respectively. The encapsulation efficiency (EE) of DxP-NPs was 66.4%+/-1.0%, with an initial release rate of 77.2%, whereas the EE of DxA-NPs was 95.3%+/-1.3%, with an initial release rate of 23.6%. Both of the NP-coated drugs could be released over 7 d. Human umbilical artery SMCs were harvested and cultured for four to six passages. Compared to free DxP, SMCs treated with tissue factor (TF)-directed DxP-NPs showed significant differences in the inhibition of proliferation, migration and apoptosis (P<0.05). The results collectively suggest that PFC nanoparticles will be beneficial for targeted drug delivery because of the sustained drug release and effective inhibition of SMC proliferation and migration.

Molecularly targeted nanocarriers deliver the cytolytic peptide melittin specifically to tumor cells in mice, reducing tumor growth

The in vivo application of cytolytic peptides for cancer therapeutics is hampered by toxicity, nonspecificity, and degradation. We previously developed a specific strategy to synthesize a nanoscale delivery vehicle for cytolytic peptides by incorporating the nonspecific amphipathic cytolytic peptide melittin into the outer lipid monolayer of a perfluorocarbon nanoparticle. Here, we have demonstrated that the favorable pharmacokinetics of this nanocarrier allows accumulation of melittin in murine tumors in vivo and a dramatic reduction in tumor growth without any apparent signs of toxicity. Furthermore, direct assays demonstrated that molecularly targeted nanocarriers selectively delivered melittin to multiple tumor targets, including endothelial and cancer cells, through a hemifusion mechanism. In cells, this hemifusion and transfer process did not disrupt the surface membrane but did trigger apoptosis and in animals caused regression of precancerous dysplastic lesions. Collectively, these data suggest that the ability to restrain the wide-spectrum lytic potential of a potent cytolytic peptide in a nanovehicle, combined with the flexibility of passive or active molecular targeting, represents an innovative molecular design for chemotherapy with broad-spectrum cytolytic peptides for the treatment of cancer at multiple stages.

Biocompatible Peptide‐nanoparticle Constructs for Molecular Imaging and Therapy

Our recent work on melittin delivery demonstrates that melittin tightly inserts into the perfluorocarbon (PFC) nanoparticles. Here, we hypothesize that altering the melittin sequence can convert melittin from a therapeutic agent to a cargo loading linker for PFC nanoparticles. Our results illustrate that mutated melittin, D1‐7 (Ac‐ VLTTGLPALISWIKRKRQQ‐NH2), reduces the melittin lytic activity by about 50‐fold (A). While it still insertes tightly into the PFC nanoparticles (Kd=0.4 μM) without affecting their integrity (B). We also show that the linker peptide, D1‐7, is capable of integrating cargos into PFC nanoparticles by a simple mixing step. As an example, VCAM‐1 targeted PFC nanoparticles are generated through this linker peptide. 2F2B cells, treated with the VCAM‐1 targeted PFC nanoparticles, co‐labeled with Alexa Fluor 488, manifest stronger fluorescent signals (C) than those, treated with non‐targeted ones (D). VCAM‐1 targeting dramatically increases cellular PFC nanoparticle delivery (E). Moreover, targeting efficacy is controllable by amount of peptide loading (F). We conclude that this linker peptide strategy provides extended flexibility for multiplexing targeting ligands and/or drug payloads, which can be selected from a stock of possible active agents, without the need of base nanoparticle reformulation to behoove personalized molecular imaging and therapy.

Perfluorocarbon Nanoemulsions for Quantitative Molecular Imaging and Targeted Therapeutics

A broad array of nanomaterials is available for use as contrast agents for molecular imaging and drug delivery. Due to the lack of endogenous background signal in vivo and the high NMR sensitivity of the (19)F atom, liquid perfluorocarbon nanoemulsions make ideal agents for cellular and magnetic resonance molecular imaging. The perfluorocarbon core material is surrounded by a lipid monolayer which can be functionalized with a variety of agents including targeting ligands, imaging agents and drugs either individually or in combination. Multiple copies of targeting ligands (approximately 20-40 monoclonal antibodies or 200-400 small molecule ligands) serve to enhance avidity through multivalent interactions while the composition of the particle's perfluorocarbon core results in high local concentrations of (19)F. Additionally, lipophilic drugs contained within molecularly targeted nanoemulsions can result in contact facilitated drug delivery to target cells. Ultimately, the dual use of perfluorocarbon nanoparticles for both site targeted drug delivery and molecular imaging may provide both imaging of disease states as well as conclusive evidence that drug delivery is localized to the area of interest. This review will focus on liquid perfluorocarbon nanoparticles as (19)F molecular imaging agents and for targeted drug delivery in cancer and cardiovascular disease.

Anti‐angiogenic perfluorocarbon nanoparticles for diagnosis and treatment of atherosclerosis

Complementary developments in nanotechnology, genomics, proteomics, molecular biology and imaging offer the potential for early, accurate diagnosis. Molecularly-targeted diagnostic imaging agents will allow noninvasive phenotypic characterization of pathologies and, therefore, tailored treatment close to the onset. For atherosclerosis, this includes anti-angiogenic therapy with specifically-targeted drug delivery systems to arrest the development of plaques before they impinge upon the lumen. Additionally, monitoring the application and effects of this targeted therapy in a serial fashion will be important. This review covers the specific application of alpha(nu)beta(3)-targeted anti-angiogenic perfluorocarbon nanoparticles in (1) the detection of molecular markers for atherosclerosis, (2) the immediate verification of drug delivery with image-based prediction of therapy outcomes, and (3) the serial, noninvasive observation of therapeutic efficacy.

Dual PARACEST and 19F MR molecular imaging of fibrin clots with targeted perfluorocarbon nanoparticles

Dual PARACEST and 19F MR molecular imaging of fibrin clots with targeted perfluorocarbon nanoparticles

Nanoparticle pharmacokinetic profiling in vivo using magnetic resonance imaging

Contrast agents targeted to molecular markers of disease are currently being developed with the goal of identifying disease early and evaluating treatment effectiveness using noninvasive imaging modalities such as MRI. Pharmacokinetic profiling of the binding of targeted contrast agents, while theoretically possible with MRI, has thus far only been demonstrated with more sensitive imaging techniques. Paramagnetic liquid perfluorocarbon nanoparticles were formulated to target alpha(v)beta(3)-integrins associated with early atherosclerosis in cholesterol-fed rabbits to produce a measurable signal increase on magnetic resonance images after binding. In this work, we combine quantitative information of the in vivo binding of this agent over time obtained by means of MRI with blood sampling to derive pharmacokinetic parameters using simultaneous and individual fitting of the data to a three compartment model. A doubling of tissue exposure (or area under the curve) is obtained with targeted as compared to control nanoparticles, and key parameter differences are discovered that may aid in development of models for targeted drug delivery.

Detection of targeted perfluorocarbon nanoparticle binding using 19F diffusion weighted MR spectroscopy

Real-time detection of targeted contrast agent binding is challenging due to background signal from unbound agent. (19)F diffusion weighted MR spectroscopy (DWS) could selectively detect binding of angiogenesis-targeted perfluorocarbon nanoparticles in vivo. Transgenic K14-HPV16 mice with epidermal squamous carcinomas exhibiting up-regulated neovasculature were used, with nontransgenic littermates as controls. Mice were treated with alpha(v)beta(3)-integrin targeted perfluorocarbon nanoparticles. (19)F DWS (b-values from 0 to 16,000 s/mm(2)) was performed on mouse ears in vivo at 11.74 Tesla. Progressive decay of (19)F signal with increased diffusion weighting at low b-values (< 1500 s/mm(2)) was observed in ears of both K14-HPV16 and control mice, demonstrating suppression of background (19)F signal from unbound nanoparticles in the blood. Much of the (19)F signal from ears of K14-HPV16 mice persisted at high b-values, indicating a stationary signal source, reflecting abundant nanoparticle binding to angiogenesis. (19)F signal in controls decayed completely at high b-values (> 1500 s/mm(2)), reflecting a moving signal source due to absence of angiogenesis (no binding sites). Estimated ADCs of nanoparticles in K14-HPV16 and control mice were 33.1 +/- 12.9 microm(2)/s and 19563 +/- 5858 microm(2)/s (p < 0.01). In vivo (19)F DWS can be used for specific detection of bound perfluorocarbon nanoparticles by selectively suppressing background (19)F signal from nanoparticles flowing in blood.

Gadolinium‐modulated 19F signals from perfluorocarbon nanoparticles as a new strategy for molecular imaging

Recent advances in the design of fluorinated nanoparticles for molecular magnetic resonance imaging (MRI) have enabled specific detection of (19)F nuclei, providing unique and quantifiable spectral signatures. However, a pressing need for signal enhancement exists because the total (19)F in imaging voxels is often limited. By directly incorporating a relaxation agent, gadolinium (Gd), into the lipid monolayer that surrounds the perfluorocarbon (PFC), a marked augmentation of the (19)F signal from 200-nm nanoparticles was achieved. This design increases the magnetic relaxation rate of the (19)F nuclei fourfold at 1.5 T and effects a 125% increase in signal--an effect that is maintained when they are targeted to human plasma clots. By varying the surface concentration of Gd, the relaxation effect can be quantitatively modulated to tailor particle properties. This novel strategy dramatically improves the sensitivity and range of (19)F MRI/MRS and forms the basis for designing contrast agents capable of sensing their surface chemistry.

New mechanisms for non-porative ultrasound stimulation of cargo delivery to cell cytosolwith targeted perfluorocarbon nanoparticles

The cell membrane constitutes a major barrier for non-endocytotic intracellular delivery oftherapeutic molecules from drug delivery vehicles. Existing approaches to breaching the cellmembrane include cavitational ultrasound (with microbubbles), electroporationand cell-penetrating peptides. We report the use of diagnostic ultrasound forintracellular delivery of therapeutic bulky cargo with the use of molecularly targetedliquid perfluorocarbon (PFC) nanoparticles. To demonstrate the concept, we useda lipid with a surrogate polar head group, nanogold-DPPE, incorporated intothe nanoparticle lipid monolayer. Melanoma cells were incubated with nanogoldparticles and this was followed by insonication with continuous wave ultrasound(2.25 MHz, 5 min, 0.6 MPa). Cells not exposed to ultrasound showed gold particlespartitioned only in the outer bilayer of the cell membrane with no evidence of theintracellular transit of nanogold. However, the cells exposed to ultrasound exhibitednumerous nanogold-DPPE components inside the cell that appeared polarizedinside intracellular vesicles demonstrating cellular uptake and trafficking. Further,ultrasound-exposed cells manifested no incorporation of calcein or the release of lactatedehydrogenase. These observations are consistent with a mechanism that suggests thatultrasound is capable of stimulating the intracellular delivery of therapeutic moleculesvia non-porative mechanisms. Therefore, non-cavitational adjunctive ultrasoundoffers a novel paradigm in intracellular cargo delivery from PFC nanoparticles.

Perfluorocarbon Nanoparticles for Molecular Imaging and Targeted Therapeutics

Molecular imaging is a novel tool that has allowed noninvasive diagnostic imaging to transition from gross anatomical description to identification of specific tissue epitopes and observation of biological processes at the cellular level. Until recently, this technique was confined to the field of nuclear imaging; however, advances in nanotechnology have extended this research to include magnetic resonance (MR) imaging, positron emission tomography (PET), single photon emission computed tomography (SPECT), and ultrasound (US), among others. The application of nanotechnology to MR, SPECT, and US molecular imaging has generated several candidate contrast agents. We discuss the application of one multimodality platform, a targeted perfluorocarbon nanoparticle. Our results show that it is useful for noninvasive detection with all three imaging modalities and may additionally be used for local drug delivery.

Cytolytic peptides on nanoparticle carriers induce dramatic melanoma tumor shrinkage in vivo by apoptosis

The potential application of cytolytic peptides (CP) for cancer therapeutics has met with limited success due to in vivo degradation and systemic toxicity. We now illustrate the first successful in vivo deployment of a “first‐generation” CP (melittin, a 26 amino‐acid amphipathic peptide in bee venom) for cancer therapy after incorporation onto a lipid monolayer of a perfluorocarbon (PFC) nanoparticle (NP, size ~200 nm). The hydrophobic brominated PFC core maintains the structural integrity of the NP (as shown by electron microscopy) and allows a very slow dissociation of melittin (Kd ~1.5 nM by surface plasmon resonance). In vitro, melittin‐NPs are effective against C‐32 melanoma cells (IC50 ~ 32 μM) and cause a non‐porative apoptotic cell death as revealed by annexin‐FITC/propidium iodide staining and cytochrome c/lactate dehydrogenase release assays. Although free melittin is toxic in vivo (LD50 ~ 4 mg/kg), four doses of melittin‐NPs (8 mg/kg) are effective in causing a 7.6‐fold reduction in the volume of B16 melanoma tumors in C57BL/6 mice (n=5, p = 0.004) without any associated systemic toxicity. PFC nanoparticles thus represent the first class of unique lipid‐based nanovehicles that can provide a stable and safe synthetic delivery vector for melittin (or other CPs) in vivo by preventing their degradation, reducing systemic toxicity, while simultaneously maintaining effectiveness for cancer therapeutics.

Synthetic nanoparticle vehicles deliver siRNA to vascular endothelial cells for VCAM‐1 knockdown

The therapeutic promise of siRNA relies on its ability to knock down genes with minimal side effects. Upregulation of inflammatory genes such as vascular cell adhesion molecule‐1 (VCAM‐1) in atherosclerosis suggests that targeted delivery of siRNA as an antiatherosclerotic therapy might modify disease progression. We have shown previously that liquid perfluorocarbon nanoparticle emulsions (PFC‐NP) can serve as molecularly targeted vehicles for imaging and drug delivery in vivo. In this study, we sought to utilize PFC NP as carriers of siRNA to endothelial cells. Cationic PFC‐NP emulsions were produced with 1,2‐Dioleoyl‐3‐Trimethylammonium‐Propane (DOTAP). siRNA to VCAM‐1 was complexed to the emulsions and incubated with mouse 2F‐2B endothelial cells. We observed that fluorescently labeled siRNA in cells 24 h after transfection as determined by confocal microscopy. Optimized transfection conditions (10 pM PFC‐NP with 5 nM siRNA) produce a 52% decrease in VCAM‐1 mRNA levels after 48h. Corresponding viability data measured 24 h after transfection using flow cytometry indicated 80–90% viability in 2F‐2B cells under similar transfection conditions. Accordingly, these particles offer an efficient method for siRNA delivery to endothelial cells and they can simultaneously serve as a vehicle for molecular imaging to confirm siRNA delivery. This work was supported by NIH grant #HL073646

Synthesis and Characterization of Stable Fluorocarbon Nanostructures as Drug Delivery Vehicles for Cytolytic Peptides

The therapeutic potential of cytolytic peptides is plagued by nonspecificity and enzymatic degradation. We report the first stable incorporation of melittin (a 26 amino acid amphipathic peptide) into an outer lipid monolayer of perfluorocarbon nanoparticles. Melittin binds avidly to the nanoparticles (dissociation constant approximately 3.27 nM) and retains its pore-forming activity after contact-mediated delivery to model bilayer membrane (liposomes) thereby demonstrating the effectiveness of perfluorocarbon nanoparticles as unique nanocarriers for cytolytic peptides.

Detection and quantification of angiogenesis in experimental valve disease with integrin-targeted nanoparticles and 19-fluorine MRI/MRS.

BackgroundAngiogenesis is a critical early feature of atherosclerotic plaque development and may also feature prominently in the pathogenesis of aortic valve stenosis. It has been shown that MRI can detect and quantify specific molecules of interest expressed in cardiovascular disease and cancer by measuring the unique fluorine signature of appropriately targeted perfluorocarbon (PFC) nanoparticles. In this study, we demonstrated specific binding of ανβ3 integrin targeted nanoparticles to neovasculature in a rabbit model of aortic valve disease. We also showed that fluorine MRI could be used to detect and quantify the development of neovasculature in the excised aortic valve leaflets.MethodsNew Zealand White rabbits consumed a cholesterol diet for ~180 days and developed aortic valve thickening, inflammation, and angiogenesis mimicking early human aortic valve disease. Rabbits (n = 7) were treated with ανβ3 integrin targeted PFC nanoparticles or control untargeted PFC nanoparticles (n = 6). Competitive inhibition in vivo of nanoparticle binding (n = 4) was tested by pretreatment with targeted nonfluorinated nanoparticles followed 2 hours later by targeted PFC nanoparticles. 2 hours after treatment, aortic valves were excised and 19F MRS was performed at 11.7T. Integrated 19F spectral peaks were compared using a one-way ANOVA and Hsu's MCB (multiple comparisons with the best) post hoc t test. In 3 additional rabbits treated with ανβ3 integrin targeted PFC nanoparticles, 19F spectroscopy was performed on a 3.0T clinical scanner. The presence of angiogenesis was confirmed by immunohistochemistry.ResultsValves of rabbits treated with targeted PFC nanoparticles had 220% more fluorine signal than valves of rabbits treated with untargeted PFC nanoparticles (p < 0.001). Pretreatment of rabbits with targeted oil-based nonsignaling nanoparticles reduced the fluorine signal by 42% due to competitive inhibition, to a level not significantly different from control animals. Nanoparticles were successfully detected in all samples scanned at 3.0T. PECAM endothelial staining and ανβ3 integrin staining revealed the presence of neovasculature within the valve leaflets.ConclusionIntegrin-targeted PFC nanoparticles specifically detect early angiogenesis in sclerotic aortic valves of cholesterol fed rabbits. These techniques may be useful for assessing atherosclerotic components of preclinical aortic valve disease in patients and could assist in defining efficacy of medical therapies.

Colloidal-chemical characteristics of perfluorocarbon emulsions

Colloidal-chemical properties of perfluorocarbon (PFC) emulsions, which are used as plasma substitutes when the transfer of normal blood is problematic or impossible, ere considered. Physicochemical properties of emulsions based on perfluorodecalin and perfluoromethylcyclohexylpiperidine stabilized by Proksanol 268 (Pluronic F68) at an average particle size of 50–80 nm are considered. According to the colloidal-chemical classification, PFC emulsions for biomedical applications represent direct, concentrated, highly and freely dispersed heterogeneous thermodynamically unstable colloidal systems possessing an excess of free energy and a very large gas-exchange surface, in which a dispersed phase of insoluble monodisperse PFC nanoparticles is coated with a surfactant (emulsifier) and occurs in the suspended state in a surrounding structured aqueous dispersion medium.

Fibrin-Targeted Perfluorocarbon Nanoparticles for Targeted Thrombolysis

Reperfusion of the ischemic brain is the most effective therapy for acute stroke, restoring blood flow to threatened tissues. Thrombolytics, such as recombinant tissue plasminogen activator, administered within 3 h of symptom onset can improve neurologic outcome, although the potential for adverse hemorrhagic events limits its use to less than 3% of acute ischemic stroke patients. Targeting of clot-dissolving therapeutics has the potential to decrease the frequency of complications while simultaneously increasing treatment effectiveness, by concentrating the available drug at the desired site and permitting a lower systemic dose. We aimed to develop a fibrin-specific, liquid perfluorocarbon nanoparticle that is surface modified to deliver the plasminogen activator streptokinase. We also aimed to evaluate its effectiveness for targeted thrombolysis in vitro using quantitative acoustic microscopy. Human plasma clots were formed in vitro and targeted with streptokinase-loaded nanoparticles, control nanoparticles or a mixture of both. Depending on the treatment group, clots were then exposed to either phosphate-buffered saline (PBS), PBS with plasminogen or PBS with plasminogen and free streptokinase. Spatially registered ultrasound scans were performed at 15-min intervals for 1 h to quantify changes in clot morphology and backscatter. Nanoparticles bound to the clot significantly increased the acoustic contrast of the targeted clot surface, permitting volumetric estimates. Profile plots of detected clot surfaces demonstrated that streptokinase-loaded, fibrin-targeted perfluoro-octylbromide nanoparticles in the presence of plasminogen induced rapid fibrinolysis (<60 min) without concurrent microbubble production and cavitation. Streptokinase-loaded or fibrin-targeted control nanoparticles insonified in PBS did not induce clot lysis. Morphologic changes in the treated group were accompanied by temporal and spatial changes in backscatter. Ultrasound exposure had no effect on the digestion process. Effective concentrations of targeted streptokinase were orders of magnitude lower than equivalently efficacious levels of free drug. Moreover, increasing competitive inhibition of fibrin-bound streptokinase nanoparticles reduced clot lysis in a monotonic fashion. As little as 1% surface targeting of streptokinase nanoparticles produced significant decreases in clot volumes (approximately 30%) in 1 h. This new nanoparticle-based thrombolytic agent provides specific and rapid fibrinolysis in vitro and may have a clinical role in early reperfusion during acute ischemic stroke.

Properties of an entropy-based signal receiver with an application to ultrasonic molecular imaging

Qualitative and quantitative properties of the finite part, H(f), of the Shannon entropy of a continuous waveform f(t) in the continuum limit are derived in order to illuminate its use for waveform characterization. Simple upper and lower bounds on H(f), based on features of f(t), are defined. Quantitative criteria for a priori estimation of the average-case variation of H(f) and log E(f), where E(f) is the signal energy of f(t) are also derived. These provide relative sensitivity estimates that could be used to prospectively choose optimal imaging strategies in real-time ultrasonic imaging machines, where system bandwidth is often pushed to its limits. To demonstrate the utility of these sensitivity relations for this application, a study designed to assess the feasibility of identification of angiogenic neovasculature targeted with perfluorocarbon nanoparticles that specifically bind to alpha(v)beta3-integrin expression in tumors was performed. The outcome of this study agrees with the prospective sensitivity estimates that were used for the two receivers. Moreover, these data demonstrate the ability of entropy-based signal receivers when used in conjunction with targeted nanoparticles to elucidate the presence of alpha(v)beta3 integrins in primordial neovasculature, particularly in acoustically unfavorable environments.

Fluorine Cardiovascular Magnetic Resonance Angiography In Vivo at 1.5 T with Perfluorocarbon Nanoparticle Contrast Agents

While the current gold standard for coronary imaging is X-ray angiography, evidence is accumulating that it may not be the most sensitive technique for detecting unstable plaque. Other imaging modalities, such as cardiovascular magnetic resonance (CMR), can be used for plaque characterization, but suffer from long scan and reconstruction times for determining regions of stenosis. We have developed an intravascular fluorinated contrast agent that can be used for angiography with cardiovascular magnetic resosnace at clinical field strengths (1.5 T). This liquid perfluorocarbon nanoparticle contains a high concentration of fluorine atoms that can be used to generate contrast on 19F MR images without any competing background signal from surrounding tissues. By using a perfluorocarbon with 20 equivalent fluorine molecules, custom-built RF coils, a modified clinical scanner, and an efficient steady-state free procession sequence, we demonstrate the use of this agent for angiography of small vessels in vitro, ex vivo, and in vivo. The surprisingly high signal generated with very short scan times and low doses of perfluorocarbon indicates that this technique may be useful in clinical settings when coupled with advanced imaging strategies.