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.

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.

19F magnetic resonance imaging for stem/progenitor cell tracking with multiple unique perfluorocarbon nanobeacons.

MRI has been employed to elucidate the migratory behavior of stem/progenitor cells noninvasively in vivo with traditional proton (1H) imaging of iron oxide nanoparticle-labeled cells. Alternatively, we demonstrate that fluorine (19F) MRI of cells labeled with different types of liquid perfluorocarbon (PFC) nanoparticles produces unique and sensitive cell markers distinct from any tissue background signal. To define the utility for cell tracking, mononuclear cells harvested from human umbilical cord blood were grown under proendothelial conditions and labeled with nanoparticles composed of two distinct PFC cores (perfluorooctylbromide and perfluoro-15-crown-5 ether). The sensitivity for detecting and imaging labeled cells was defined on 11.7T (research) and 1.5T (clinical) scanners. Stem/progenitor cells (CD34+ CD133+ CD31+) readily internalized PFC nanoparticles without aid of adjunctive labeling techniques, and cells remained functional in vivo. PFC-labeled cells exhibited distinct 19F signals and were readily detected after both local and intravenous injection. PFC nanoparticles provide an unequivocal and unique signature for stem/progenitor cells, enable spatial cell localization with 19F MRI, and permit quantification and detection of multiple fluorine signatures via 19F MR spectroscopy. This method should facilitate longitudinal investigation of cellular events in vivo for multiple cell types simultaneously.

Applications of nanotechnology to atherosclerosis, thrombosis, and vascular biology.

The role of nanotechnology in cardiovascular diagnosis is expanding rapidly. The goal of this brief review is to illustrate selected examples of nanosystems that have been applied to the arenas of atherosclerosis, thrombosis, and vascular biology. The technologies for producing targeted nanosystems are multifarious and reflect end uses in many cases. The results to date indicate rapid growth of interest and capability in the field. The future of cardiovascular diagnosis already is being impacted by nanosystems that can both diagnose pathology and treat it with targeted delivery systems.

Endothelial alpha(v)beta3 integrin-targeted fumagillin nanoparticles inhibit angiogenesis in atherosclerosis.

OBJECTIVE: Angiogenic expansion of the vasa vasorum is a well-known feature of progressive atherosclerosis, suggesting that antiangiogenic therapies may stabilize or regress plaques. Alpha(v)beta3 integrin-targeted paramagnetic nanoparticles were prepared for noninvasive assessment of angiogenesis in early atherosclerosis, for site-specific delivery of antiangiogenic drug, and for quantitative follow-up of response. METHODS AND RESULTS: Expression of alpha(v)beta3 integrin by vasa vasorum was imaged at 1.5 T in cholesterol-fed rabbit aortas using integrin-targeted paramagnetic nanoparticles that incorporated fumagillin at 0 microg/kg or 30 microg/kg. Both formulations produced similar MRI signal enhancement (16.7%+/-1.1%) when integrated across all aortic slices from the renal arteries to the diaphragm. Seven days after this single treatment, integrin-targeted paramagnetic nanoparticles were readministered and showed decreased MRI enhancement among fumagillin-treated rabbits (2.9%+/-1.6%) but not in untreated rabbits (18.1%+/-2.1%). In a third group of rabbits, nontargeted fumagillin nanoparticles did not alter vascular alpha(v)beta3-integrin expression (12.4%+/-0.9%; P>0.05) versus the no-drug control. In a second study focused on microscopic changes, fewer microvessels in the fumagillin-treated rabbit aorta were counted compared with control rabbits. CONCLUSIONS: This study illustrates the potential of combined molecular imaging and drug delivery with targeted nanoparticles to noninvasively define atherosclerotic burden, to deliver effective targeted drug at a fraction of previous levels, and to quantify local response to treatment.

In vitro demonstration using 19F magnetic resonance to augment molecular imaging with paramagnetic perfluorocarbon nanoparticles at 1.5 Tesla.

OBJECTIVES: This study explored the use of F spectroscopy and imaging with targeted perfluorocarbon nanoparticles for the simultaneous identification of multiple bio-signatures at 1.5 T. MATERIALS AND METHODS: Two nanoparticle emulsions with perfluoro-15-crown-5-ether (CE) or perfluorooctylbromide (PFOB) cores were targeted in vitro to fibrin clot phantoms (n=12) in 4 progressive ratios using biotin-avidin interactions. The CE nanoparticles incorporated gadolinium. Fluorine images were acquired using steady-state gradient-echo techniques; spectra using volume-selective and nonselective sampling. RESULTS: On conventional T1-weighted imaging, clots with CE nanoparticles enhanced as expected, with intensity decreasing monotonically with CE concentration. All clots were visualized using wide bandwidth fluorine imaging, while restricted bandwidth excitation permitted independent imaging of CE or PFOB nanoparticles. Furthermore, F imaging and spectroscopy allowed visual and quantitative confirmation of relative perfluorocarbon nanoparticle distributions. CONCLUSIONS: F MRI/S molecular imaging of perfluorocarbon nanoparticles in vitro suggests that noninvasive phenotypic characterization of pathologic bio-signatures is feasible at clinical field strengths.

Potential role of three-dimensional rotational angiography and C-arm CT for valvular repair and implantation.

Imaging modalities utilized in the interventional cardiology suite have seen an impressive evolution and expansion recently, particularly with regard to the recent interest in three-dimensional (3D) imaging. Despite this, the backbone of visualization in the catheterization laboratory remains two-dimensional (2D) X-ray fluoroscopy and cine-angiography. New imaging techniques under development, referred to as three-dimensional rotational angiography (RA) and C-arm CT, hold great promise for improving current device implantation and understanding of cardiovascular anatomy. This paper reviews the evolution of rotational angiography and advanced 3D X-ray imaging applications to interventional cardiology.

Clinical feasibility of a fully automated 3D reconstruction of rotational coronary X-ray angiograms.

BACKGROUND: Although fixed view x-ray angiography remains the primary technique for anatomic imaging of coronary artery disease, the known shortcomings of 2D projection imaging may limit accurate 3D vessel and lesion definition and characterization. A recently developed method to create 3D images of the coronary arteries uses x-ray projection images acquired during a 180 degrees C-arm rotation and continuous contrast injection followed by ECG-gated iterative reconstruction. This method shows promise for providing high-quality 3D reconstructions of the coronary arteries with no user interaction but requires clinical evaluation. METHODS AND RESULTS: The reconstruction strategy was evaluated by comparing the reconstructed 3D volumetric images with the 2D angiographic projection images from the same 23 patients to ascertain overall image quality, lesion visibility, and a comparison of 3D quantitative coronary analysis with 2D quantitative coronary analysis. The majority of the resulting 3D volume images were rated as having high image quality (66%) and provided the physician with additional clinical information such as complete visualization of bifurcations and unobtainable views of the coronary tree. True-positive lesion detection rates were high (90 to 100%), whereas false-positive detection rates were low (0 to 8.1%). Finally, 3D quantitative coronary analysis showed significant similarity with 2D quantitative coronary analysis in terms of lumen diameters and provided vessel segment length free from the errors of foreshortening. CONCLUSIONS: Fully automated reconstruction of rotational coronary x-ray angiograms is feasible, produces 3D volumetric images that overcome some of the limitations of standard 2D angiography, and is ready for further implementation and study in the clinical environment.

Molecular imaging and therapy of atherosclerosis with targeted nanoparticles.

Advances in bionanotechnology are poised to impact the field of cardiovascular diagnosis and therapy for decades to come. This review seeks to illustrate selected examples of newly developed diagnostic and therapeutic nanosystems that have been evaluated in experimental atherosclerosis, thrombosis, and vascular biology. We review a variety of nanotechnologies that are capable of detecting early cardiovascular pathology, as well as associated imaging approaches and conjunctive strategies for site-targeted treatment with nanoparticle delivery systems.

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.

Clinical applications of perfluorocarbon nanoparticles for molecular imaging and targeted therapeutics.

Molecular imaging is a novel tool that has allowed non-invasive diagnostic imaging to transition from gross anatomical description to identification of specific tissue epitopes and observation of biological processes at the cellular level. This technique has been confined to the field of nuclear imaging; however, recent advances in nanotechnology have extended this research to include ultrasound (US) and magnetic resonance (MR) imaging. The exploitation of nanotechnology for MR and US molecular imaging has generated several candidate contrast agents. One multimodality platform, targeted perfluorocarbon (PFC) nanoparticles, is useful for noninvasive detection with US and MR, targeted drug delivery, and quantification.

Nanomedicine opportunities for cardiovascular disease with perfluorocarbon nanoparticles.

Nanomedicine promises to enhance the ability of clinicians to address some of the serious challenges responsible for cardiovascular mortality, morbidity and numerous societal consequences. Targeted imaging and therapy applications with perfluorocarbon nanoparticles are relevant to a broad spectrum of cardiovascular diseases, ranging from asymptomatic atherosclerotic disease to acute myocardial infarction or stroke. As illustrated in this article, perfluorocarbon nanoparticles offer new tools to recognize and characterize pathology, to identify and segment high-risk patients and to treat chronic and acute disease.

1H/19F magnetic resonance molecular imaging with perfluorocarbon nanoparticles.

Developments in genomics, proteomics, and cell biology are leading a trend toward individualized segmentation and treatment of patients based on early, noninvasive recognition of unique biosignatures. Although developments in molecular imaging have been dominated by nuclear medicine agents in the past, the advent of nanotechnology in the 1990s has led to magnetic resonance (MR) molecular agents that allow detection of sparse biomarkers with a high-resolution imaging modality that can provide both physiological and functional agents. A wide variety of nanoparticulate MR contrast agents have emerged, most of which are superparamagnetic iron oxide-based constructs. However, this chapter focuses on a diagnostic and therapeutic perfluorocarbon (PFC) nanoparticulate platform that is not only effective as a T1-weighted agent, but also supports (19)F MR spectroscopy and imaging. The unique capability of (19)F permits confirmation and segmentation of MR contrast images as well as direct quantification of nanoparticle concentrations within a voxel. PFC nanoparticles have the capability to effectively deliver therapeutic agents to target sites by a novel mechanism termed "contact-facilitated drug delivery." Combined with MR spectroscopy, the concentration of drug delivered to the target site can be determined and the expected response predicted. Moreover, mixtures of nanoparticles with different perfluorocarbon cores can provide a quantitative, multispectral signal, which can be used to simultaneously distinguish the relative concentrations of several important epitopes within a region of interest. In conjunction with rapid improvements in MR imaging, the prospects for personalized medicine and early recognition and treatment of disease have never been better.