doi: 10.1161/01.RES.0000119321.18573.5A
© 2004 American Heart Association, Inc.
Reviews |
Seeing Within
Molecular Imaging of the Cardiovascular System
From the Center for Molecular Imaging Research (F.A.J., R.W.), Massachusetts General Hospital, Harvard Medical School, Charlestown, Mass; Cardiology Division (F.A.J.), Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Mass.
Correspondence to Farouc Jaffer, MD, PhD, or Ralph Weissleder, MD, PhD, MGH-CMIR, 149 13th St, Room 5406, Charlestown, MA 02129. E-mail fjaffer{at}partners.org or weissleder{at}helix.mgh.harvard.edu
This Review is part of a thematic series on Biological Imaging of the Cardiovascular System, which includes the following articles:
Noninvasive Imaging of Myocardial Viability: Current Techniques and Future Development
Seeing Within: Molecular Imaging of the Cardiovascular System
Imaging Neovascular Growth
Emerging Imaging Techniques
Elliot R. McVeigh Guest Editor
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Abstract |
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 Top Abstract IntroductionImaging TechnologiesInjectable Imaging Agents With...Agents for Different Imaging...In Vivo Molecular Imaging...ConclusionsReferences |
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Molecular imaging is a rapidly evolving discipline with the goal of developing tools to display and quantify molecular and cellular targets in vivo. The heart of this field is based on the rational design and screening of targeted and activatable imaging reporter agents to sense fundamental processes of biology. Parallel advances in small animal imaging systems and in agent synthesis have allowed molecular imaging applications to extend into the in vivo arena. These advances have permitted, for example, in vivo sensing of inflammation, apoptosis, cell trafficking, and gene expression. In this review, we first review core principles of molecular imaging with an emphasis on smart, activatable agent technology. We then discuss applications of state-of-the-art molecular probes to interrogate important aspects of cardiovascular biology, with a focus on atherosclerosis, thrombosis, and heart failure. In the ensuing years, we anticipate that fundamental aspects of cardiovascular biology will be detectable in vivo, and that promising molecular imaging agents will be translated into the clinical arena to guide diagnosis and therapy of human cardiovascular illness.
Key Words: molecular imaging • atherosclerosis • thrombosis • heart failure • contrast agents
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Introduction |
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TopAbstractIntroductionImaging TechnologiesInjectable Imaging Agents With...Agents for Different Imaging...In Vivo Molecular Imaging...ConclusionsReferences |
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Conventional imaging technologies typically rely on anatomical, physiological, or metabolic heterogeneity to provide image contrast. In comparison, the emerging field of molecular imaging uses targeted and activatable imaging agents to exploit specific molecular targets, pathways, or cellular processes to generate image contrast. The underpinning hypothesis of this newer approach to imaging is that most disease processes have a molecular basis that can be exploited to (1) detect disease earlier, (2) stratify disease subsets (eg, active versus inactive), (3) objectively monitor novel therapies by imaging molecular biomarkers, and to (4) prognosticate disease. The goal of this review is to briefly highlight advances and capabilities in molecular imaging hardware and to provide an overview of novel imaging agents. We then focus on three important aspects of cardiovascular disease, namely atherosclerosis, thrombosis, and heart failure. We will review salient molecular imaging applications in these fields and discuss how new applications could be used to further our understanding of these diseases.
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Imaging Technologies |
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TopAbstractIntroductionImaging TechnologiesInjectable Imaging Agents With...Agents for Different Imaging...In Vivo Molecular Imaging...ConclusionsReferences |
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Imaging technologies allow for visualization of the body based on different forms of energy-tissue interactions. They can be used to image 3-D cardiovascular structures, assess biophysical parameters such as ventricular function, stress, and strain, and monitor physiological events such as changes in vascular blood flow and myocardial perfusion. Although some imaging methods [magnetic resonance imaging (MRI), ultrasound (US)] rely mainly on energy/tissue interactions, others [fluorescence reflectance imaging (FRI), fluorescence mediated tomography (FMT), bioluminescence imaging (BLI), single photon emission computed tomography (SPECT), positron emission tomography (PET)] require the administration of imaging agents to generate a physical signal. Common to all of these methods is the ability to transform a detected signal into an image. For a more detailed discussion of high-resolution imaging systems useful for mouse imaging, the interested reader is referred to the online data supplement available at http://circres.ahajournals.org and several recent review articles.1–9
Proteins as Transgenic Imaging Reporters
Transgenic animal models are essential tools in understanding biological processes, and many experimental and clinical applications of molecular medicine such as gene therapy, stem cell transfer, and adoptive immunotherapy dictate the use of transgenes. Furthermore, drug discovery and testing frequently utilize transgenic murine models to better understand the biology governing drug-target interaction. Several recent articles have reviewed reporter transgenes and fusion proteins for PET and SPECT,10–12 multicolor fluorescence,13 bioluminescence,14,15 and MRI.16–20 Some transgenes are directly detectable (eg, photoproteins by optical methods, tyrosinase by MRI16), whereas others require additional injectable imaging substrates discussed later. For noninvasive detection of myocardial gene expression, PET,21 BLI,22 and potentially noninvasive imaging of green fluorescent protein are good options, although at relatively lower spatial resolutions.
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Injectable Imaging Agents With Molecular Specificity |
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Imaging agents with molecular specificity have been designed for MR, nuclear, optical, and ultrasound imaging. Agents are generally classified as targeted or activatable (Figure 1; Table).
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Targeted Imaging Agents
Targeted imaging agents are generally created by chemically attaching an affinity ligand such as an antibody, peptide, or small molecule to an isotope, fluorochrome, magnetic compound, or acoustically reflective microbubble. The oldest form of targeted agents represent isotope-labeled antibodies such as antimyosin.23 Although many antibody-based conjugates can be easily constructed and provide molecular specificity in vitro, some limitations diminish their ultimate utility in vivo. One drawback of targeted (as opposed to activatable) agents is that both the unbound and nonspecifically bound fractions of an agent produce an active signal, commonly resulting in high levels of background noise. Targeted agents thus require time for washout, a particularly important point to consider when using rapidly decaying isotopes. Long washout times are also impractical in certain acute disease scenarios (eg, myocardial infarction or vascular thrombosis). A second drawback of labeled antibodies has been their limited bioavailability beyond endothelial targets.24 Because of these limitations, most newer targeted imaging agents are based on modified antibodies or fragments,25 peptides and peptidomimetics,26 carbohydrate or lipid modified peptides,27 labeled small molecule agonists, binders and antagonists,28 multivalent constructs,29 or polyvalent nanoparticles30 among others. In addition, biological amplification strategies such as cellular trapping of imaging agents through targeting internalizing receptors,19,31 enzymatic conversion,32,33 and/or local binders34,35 are often used to further boost target/background ratios. Additional efforts to improve the imaging behavior of a given agent include optimization of pharmacological properties, size,36 and charge.
Activatable Imaging Agents
Activatable imaging agents (also known as "smart" agents, sensors, or beacons) are chemically engineered substrates that undergo a physicochemical change after interacting with their intended target. The resultant product is either easier to detect (eg, increase in fluorescence) or can be detected in a different channel (eg, shift reagents), thus resulting in increased target-to-background ratios through background suppression. Activatable imaging agents have been developed for magnetic compounds (with 2- to 10-fold signal increases18,30,37,38) and for fluorescent compounds (2- to 1000-fold signal increases39–43). Different chemical amplification strategies are summarized in Figure 1. These strategies can be further combined with biological amplification schemes to further increase target-to-background ratios.
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Agents for Different Imaging Modalities |
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Please see the Table for a comprehensive list of cardiovascular molecular imaging agents.
Magnetic Resonance Agents
Targeted MRI agents have largely been based on either superparamagnetic iron oxide nanoparticles44 or gadolinium chelates. Superparamagnetic iron oxide nanoparticles exert strong and reversible relaxation effects on their surrounding environment. Several forms of such iron oxides are in use, with some preparations under clinical investigation.45 Although these agents vary in size (10 to 300 nm), dispersion (monocrystalline, polycrystalline), surface coating (eg, dextran, carboxy dextran, carboxymethyl dextran, starch), and magnetic properties (R1, R2, susceptibility), only a few leading preparations will have utility as clinical imaging agents,45,46 targeting agents, or sensors.38 Efficient targeting often requires strategies such as caging of the dextran coat, which otherwise exists in an equilibrium of free and bound states surrounding the iron oxide core. Dextran-caging has been achieved by cross-linking the coating and resultant particles (cross-linked iron oxide, CLIO) have already been used as a platform to target receptors,20 enzymes,35 integrins,47 and specific cells.48,49 Using phage display technology and high-throughput screening approaches, it is likely that a myriad of CLIO-based cardiovascular imaging agents will be developed over the next few years, including VCAM-1, E-selectin, and macrophage-targeted preparations.
Gadolinium has also been used in the development of targeted MRI contrast agents, but its lower intrinsic relaxivity often necessitates larger-sized nanoparticles constructs such as polymerized liposomes, dendrimers, or perfluorocarbons nanoparticles to achieve high-magnetic payloads and longer intravascular lifetimes.50 Nonetheless, these agents have been successfully used to specifically image angiogenesis,51,52 progenitor cells,53 and thrombosis in vivo.54
Activatable smart agents have recently been developed for MRI and are generally based on one of two chemical principles: (1) enzymatic conversion of paramagnetic compounds18 or (2) assembly-disassembly of paramagnetic substrates37 or nanoparticles.38 In the first approach, investigators developed a contrast agent that is nearly magnetically silent at baseline. Suppression of the baseline MR signal occurs when cleavable high-affinity chelators are attached and block the access of water molecules to gadolinium, inhibiting its relaxation effects. The agent can be cleaved by ß-galactosidase (ß-gal), an enzyme encoded by the lacZ gene. After ß-gal cleavage, water access to the gadolinium molecule is irreversibly restored, and the measured T1 relaxivity triples, permitting high-resolution 3-D images of ß-gal mRNA inheritance patterns and lacZ gene expression in vivo.18
Enzyme-mediated polymerization of paramagnetic substrates into oligomers of higher magnetic relaxivity has been used to image nanomolar amounts of peroxidases37 and different affinity targets (eg, E-selectin) when used in conjunction with an anti–target-peroxidase conjugate. Another assembly/disassembly strategy for chemical amplification uses magnetic relaxation switches (MRSW).38,55–59 MRSW are iron oxide compounds that have been modified to include multiple copies of an affinity ligand on its dextran coat. When the target for the affinity ligand is encountered, the iron oxide particles begin form nanoassemblies. Of recent interest is the application of MRSW to sense the activity of myeloperoxidase,60 which has been recently shown to be predictive of myocardial infarction in patients with chest pain.61
Nuclear Imaging Agents (SPECT and PET)
Nuclear imaging agents have been developed for a larger number of cardiovascular processes and targets including apoptosis and angiogenesis, viability, atherosclerosis, and thrombosis (see reviews62–65). Targeted nuclear agents can also report on gene expression, for example by targeting a gene-transcribed extracellular protein or by detecting expression of a reporter gene such as herpes simplex virus thymidine kinase (HSV-Tk).10,21 In mammalian cells, exogenous HSV-Tk phosphorylates acycloguanosine residues, generating biological signal amplification when the phosphorylated radioisotopes are intracellularly trapped. Further improvements in PET imaging of gene expression are expected with modified reporter genes encoding highly active mutant thymidine kinases and substrates with improved biological behavior.66 Some of these paradigms have already been tested in clinical trials.67
Ultrasound Imaging Agents
Targeted ultrasound contrast agents have been developed by conjugating affinity ligands to acoustically active particulates, such as encapsulated microbubbles, liposomes, or perfluorocarbon nanoparticles.50 Biologically, targeted agents have been developed for imaging thrombosis,68–70 endothelial cell adhesion molecules,70–72 tissue factor,73 activated leukocytes,74,75 and angiogenesis.76,77 Possible limitations of the current generation of ultrasound-targeted contrast agents are their relatively larger size (>250 nm), impeding efficient tissue penetration and limiting many applications to endothelial targets.
Fluorescent Imaging Agents
Several groups have exploited the near infrared (NIR) bandwidth to develop more efficient fluorescent imaging agents for in vivo applications. A number of targeted NIR fluorescent agents have been reported (see review78), including those with specificity for tumor molecular signatures,31,79–81 apoptosis,82 and osteoblastic cellular activity.83
More recently, activatable NIRF agents have been developed for protease imaging.39–43 Molecular specificity is obtained by interposing a protease-specific peptide substrate between the fluorochrome and carrier vehicle. In the presence of the targeted proteolytic enzyme, the peptide substrate is cleaved, resulting in separation of the fluorochrome from the delivery vehicle. As a result, the NIRF signal increases by up to several hundred-fold in vivo. Protease-activatable agents have been designed to interrogate a number of enzymes including cathepsin S,39,40,84 matrix metalloproteinases,41 thrombin,42 and viral proteases.43 Limitations of NIR activatable agents include their higher synthetic complexity.
Bioluminescent Agents
Bioluminescence imaging (BLI) is performed on genetically modified cells and animals and refers to photocounting of a light-producing chemical reaction inside an organism without the need for an excitation light. Light is produced when a substrate, generically known as a luciferin, encounters its target enzyme, generically known as a luciferase. Although the vast majority of BLI studies rely on firefly and sea pansy luciferases (see review78), alternative red-shifted luciferases and luciferins are being developed.14,85 Collectively these different luciferase/luciferin combinations potentially allow for "multichannel imaging."13,86 Additional amplification strategies include incorporation of highly active transcriptional promoters to increase luciferase expression,87 as well as the development of activatable luciferases.88 In addition, luciferins can be modified so that they are only recognized by luciferase when they are chemically converted by an enzyme of interest. For example in our laboratory we have made synthetic luciferins with specificity for caspase-3, eg, Z-DEVD-luciferin.
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In Vivo Molecular Imaging of Cardiovascular Disease |
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Atherosclerosis
Atherosclerosis is the leading cause of morbidity and mortality in developed countries. Biologically, atherosclerosis is an inflammatory disease, with inflammation implicated in atheroma progression and plaque disruption.89,90 Consequently, a considerable research effort is aimed at detecting highly inflamed (high risk or "vulnerable") atherosclerotic lesions. By imaging high-risk lesions, investigators hope to better understand the link between inflammation and atherosclerosis, and to provide a new measure of clinical cardiovascular risk. A number of targeted nuclear imaging agents have already been developed to report on various high-risk features of atherosclerosis.64 In this section, we focus on recent advances in imaging agent development that permit high-resolution imaging of atherosclerosis.
Imaging of Protease Activity
Recently, our laboratory has demonstrated the ability to noninvasively image protease activity using a near-infrared fluorescent activatable imaging beacon.39 At baseline, the agent is self-quenched, but after cleavage of lysine-lysine bonds, its NIR fluorescence increases significantly. In particular, this agent can be cleaved by cathepsin B, an enzyme present in biologically active macrophages91 and implicated in the pathogenesis of atherosclerosis.92 We hypothesized that cathepsin B activity in atherosclerotic macrophages could activate this agent and serve as a new biomarker of plaque inflammation and vulnerability.84 To test this hypothesis, we injected the agent into atherosclerotic-prone apolipoprotein E–deficient (apoE-/-) mice and performed in vivo fluorescence mediated tomography (FMT). After 24 hours, submicromolar concentrations of the imaging agent were detectable (Figure 2), reflecting internal conversion by the enzyme. Animals were then euthanized, and the resected aortas underwent fluorescence reflectance imaging (FRI) followed by immunohistochemistry, Western blotting, and RT-PCR. FRI demonstrated substantial NIR signal from the aorta of apoE-/- but not from control mice, which correlated well with Sudan-stained lipid-rich areas (Figure 3). This study was the first to show that a protease can serve as an imaging biomarker for inflamed atherosclerotic lesions.
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Imaging of Matrix Metalloproteinase Activity
Matrix metalloproteinases (MMPs) are a diverse group of zinc-dependent proteolytic enzymes involved in degradation of the extracellular matrix.93 MMPs are classified based on their resident location (secreted or membrane-bound) and proteolytic target (eg, collagen, gelatin, stromelysin, or matrilysin). MMPs have been broadly implicated in a number of cardiovascular diseases, including atherosclerosis,90,94 aortic aneurysms,95 and heart failure,96 and therefore represent an important target for cardiovascular molecular imaging. In atherosclerosis, MMPs are expressed in macrophages and vascular cells, and are involved in atherosclerotic plaque disruption via enzymatic degradation of the fibrous cap or endothelial basement membrane.90,94 MMPs have also been associated with atherogenic vascular remodeling via several mechanisms, including smooth muscle cell migration and inflammatory cell recruitment to the atherosclerotic intima.94
Recently, we have demonstrated the ability to noninvasively image gelatinase MMP activity and therapeutic inhibition in vivo.41 Building on the NIRF activatable framework described earlier,39 the gelatinase MMP-2 peptide substrate PLGVR was conjugated to the carrier backbone. Using an MMP-2–positive human fibrosarcoma model, we demonstrated a 3-fold NIR tumor signal increase after injection of the agent. Furthermore, the NIRF signal was suppressible by a potent MMP-2–specific inhibitor.41 As MMP-2 has been suggested to be a specific mediator of fibrous cap destabilization,97 we are currently imaging gelatinase activity in human carotid endarterectomy specimens to better understand their role in the pathogenesis of stroke (Figure 4). Future efforts are aimed at developing more specific activatable MMP imaging agents.
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Imaging of Activated Macrophages
Macrophages are a essential component of the inflammatory response governing atherosclerosis and are implicated in lesion formation, progression, and disruption.90,98 Given their broad role in atherosclerosis, macrophages, particularly activated macrophages, are being increasingly recognized as an important treatment target for atherosclerosis.98
As described earlier, NIRF imaging of macrophage protease activity is one strategy for detecting activated macrophages.84 Another approach uses superparamagnetic iron oxide nanoparticles for high-resolution MRI. Atherosclerotic macrophages are known to phagocytose ferritin,99 and several groups have successfully imaged iron oxide–laden macrophages in atherosclerosis46,100–103 and cardiac transplant rejection.104 Mechanistically, macrophages appear to internalize dextranated nanoparticles, and the resultant iron oxide accumulation generates strong T2 relaxation and MRI contrast (Figure 4). It is anticipated that some iron oxide agents will become commercially available, allowing for clinical detection of atherosclerotic macrophages in situ, as well as for potentially detecting monocyte recruitment to atherosclerotic lesions.105
Imaging of Activated Endothelium
Via their interaction with leukocytes and platelets, activated endothelial cells are instrumental in atherogenesis.90,106 Although under normal conditions endothelial cells resist cell adhesion, atherogenic stimuli induce the expression of adhesion molecules on the endothelial cell surface, facilitating firm adhesion and transmigration of leukocytes into the arterial intima.90
Several ultrasound-targeted agents have been described for interrogating endothelial cell receptor presence. Specifically, acoustically reflective microbubbles or liposomes have been conjugated to monoclonal antibodies to target ICAM-170,71 and P-Selectin.72 One particular study using an ICAM-1–targeted liposome demonstrated significant transvascular and intravascular ultrasound enhancement of early atheroma in a swine model,70 although a limitation of this approach may be the limited biological role of ICAM-1 in atherogenesis.107
Thrombosis
Thrombosis is the pathological hallmark of a number of cardiovascular diseases, including myocardial infarction, stroke, and pulmonary embolism. The ability to specifically image molecules important in thrombogenesis could provide insight into their biological function and also serve as a highly specific diagnostic thrombosis imaging method. Several thrombosis-targeted nuclear imaging agents have been developed,65 including a clinically approved agent.108 In this section, we highlight new thrombosis agents for use with high-resolution MR, US, and NIRF imaging systems.
Imaging of Platelets
Platelets are an integral cellular component of arterial thrombi, where they become activated in the presence of abnormal endothelium or high shear.109 Historically, platelets have been a well-recognized target for nuclear imaging.65 Several radiolabeled platelet-targeted agents have been targeted to the activated 
IIbß3 integrin (also known as the GP IIb-IIIa receptor), known to mediate platelet stable adhesion and platelet aggregation.109 The activated IIbß3 integrin is a favorable molecular imaging target due its dynamically high concentration (50 000 to 100 000 receptors per platelet), and has been targeted using linear peptides, cyclic peptides (typically incorporating an RGD sequence), and natural polypeptides.65 Encouragingly, a recent report of an FDA-approved platelet GP IIb-IIIa receptor–targeted nuclear agent (99mTc-apcitide) has shown good sensitivity and specificity for detecting recurrent DVT.108 Similarly, activated IIbß3 integrin–targeted agents have been created for in vivo US and MR imaging,69,110 and show promise for high-resolution imaging of thrombi in vivo.
Imaging of Enzymes in Thrombosis
Imaging of Thrombin Activity
Thrombin, a serine protease, is an important enzyme in a wide array of normal and pathological processes including thrombogenesis, embryogenesis, and angiogenesis.111 During thrombogenesis, thrombin cleaves fibrinogen to form fibrin monomers, which subsequently polymerize to form fibrin, the scaffolding of thrombus. Thrombin also directly activates platelets and induces vasoconstriction to further promote thrombus propagation. The ability to locally image thrombin activity in vivo could provide new insight into the effects of thrombin in a range of homeostatic and pathological conditions and allow more precise assessment of anti-thrombin pharmacological therapies.
To image thrombin activity, we developed a new NIR activatable agent39–41 to report on thrombin enzyme activity.112 In human blood, thrombin strongly activated this NIR agent.42 Activation of the agent was suppressed by hirudin, a direct thrombin inhibitor. Using in vivo murine thrombosis models, the thrombin agent enabled high-resolution imaging of thrombin activity in experimental thrombi with intravital fluorescence microscopy (Figure 5).42 Strong NIR fluorescence was evident in acute thrombi and at the leading edges of thrombi, as expected biologically. In conjunction with a NIRF imaging catheter, the thrombin agent could permit detection of acute coronary thrombi. The NIR activatable agent approach is also well suited to study other important proteases involved in thrombosis and fibrinolysis, such as activated factor X and plasmin, respectively.
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Imaging of Activated Factor XIII Activity
Activated coagulation factor XIII (FXIIIa) is a tissue transglutaminase that cross-links fibrin chains and plasmin inhibitors such as 2-antiplasmin (2AP) to form mechanically and proteolytically stable thrombi.113 FXIIIa is important in fibrinolytic resistance114 and is a hallmark of biologically acute thrombi.115 Imaging of FXIIIa activity could provide important insight into thrombus formation and aging, anti-FXIIIa therapies, and factor XIII genetic polymorphisms.
Recently, a new FXIIIa-sensitive iron oxide agent has been described for MRI.35 This agent (F13-CLIO) consists of a dextran-coated caged iron oxide particle (CLIO) conjugated to an 2AP peptide fragment that can be cross-linked by factor XIIIa. In vitro F13-CLIO experiments with human plasma thrombi demonstrated marked thrombus contrast enhancement over control agents (Figure 5). Furthermore, gel electrophoresis and scanning electron microscopy revealed that F13-CLIO was covalently cross-linked into the thrombus. Additional factor XIIIa agents have been recently characterized for MRI and NIRF imaging,116 and are also under evaluation for imaging of FXIIIa activity in vivo.
Imaging of Fibrin
Through a series of proteolytic reactions of activated blood coagulation factors, fibrinogen is ultimately cleaved to produce fibrin, the scaffolding of thrombi.111 Fibrin is a favorable molecular imaging target because it is usually present in all types of thrombi (arterial and venous, acute and chronic) and is unlikely to be modified by standard antithrombotic pharmacological therapies such as aspirin, thrombin inhibitors (eg, heparin), or GP IIb-IIIa antagonists. Furthermore, fibrin is present in low plasma concentrations, minimizing background signal.
Fibrin-targeted molecular imaging agents have been developed for nuclear imaging,65 ultrasound imaging,68,70 and most recently, for high-resolution MRI.54,117 In one MRI example, investigators coated perfluorocarbon microemulsions with high densities of gadolinium using an avidin-biotin conjugation scheme, and then attached a modified antifibrin monoclonal antibody.54 In a canine model, surgically formed carotid thrombi were incubated with the fibrin-targeted nanoparticles during cessation of blood flow. After restoration of flow, nanoparticle-incubated thrombi demonstrated significant MR signal enhancement in vivo over native thrombi. In human carotid endarterectomy specimens, the nanoparticles also enhanced microthrombi overlying the atherosclerotic intima, demonstrating the potential for vulnerable plaque detection.54 Finally, another gadolinium-based fibrin-targeted probe has been recently reported in abstract form117 and shows promise for rapidly diagnosing vascular thrombi.
Heart Failure
Heart failure is a disabling illness that encompasses a broad array of pathological and clinical entities, and may be classified based on structural, functional, or molecular frameworks. Strategies to image-specific molecular and cellular targets are currently being developed with the ultimate goal of improving diagnosis, predicting prognosis, and assessing response to therapy.
Imaging of Myocardial Apoptosis
Cardiomyocyte apoptosis is a pathological feature of heart failure, ischemia/reperfusion injury, and transplant rejection.118 In explanted failing human hearts, cardiomyocyte apoptosis occurs much more frequently than in normal hearts.119 Recently, even a low-level of apoptosis has been shown to be sufficient to cause a lethal dilated cardiomyopathy in genetically engineered mice.120 Accordingly, several apoptosis-targeted imaging agents have been developed and are discussed herein.
Imaging of Phosphatidylserine
Phosphatidylserine (PS) is a phospholipid normally located on and restricted to the internal cell membrane by an energy-dependent aminophospholipid translocase.121 During apoptosis, this translocase is inactivated whereas other nearby enzymes such as phospholipid scramblase are activated, resulting in PS externalization to the outer cell membrane. Externalized PS avidly binds several proteins, including annexin V. Using intravital fluorescence microscopy, fluorescently labeled annexin V can image real-time apoptotic cell-membrane changes in the beating heart.122 Using radiolabeled annexin V, noninvasive imaging of apoptosis has been performed clinically in patients with acute myocardial infarction123 or transplant rejection.124 Because differentiation between bound and nonspecifically accumulated (ie, unbound) annexin V is difficult, we have recently developed dual-wavelength annexin reporters with active and inactive PS binding sites.125 Furthermore, to improve fluorescence imaging at greater depths, near infrared fluorochrome tagged annexins have been described.82,125
To overcome limitations of lower spatial resolution involved in nuclear imaging, alternative PS-targeted agents have been developed for high-resolution MRI. In one example, SPIO was conjugated to synaptotagmin I, another PS-binding protein, and used to image apoptotic tumor cells in vivo.126 Our laboratory has also developed an annexin V conjugated to MION capable of detecting apoptotic cells using 100-fold lower concentration than the synaptotagmin MR agent.127
Imaging of Caspase Activity
Caspases are specialized cysteine-dependent proteases involved in apoptosis via cytoplasmic and nuclear protein cleavage.128 In particular, caspase-3 activation has important functional myocardial consequences, including impaired contraction and infarct expansion.129 Recently, a novel caspase-3 reporter has been developed for in vivo BLI by using a luciferase-based fusion protein construct.88 Because BLI has already been used to detect cardiac gene expression,22 this agent could be readily applied for bioluminescence imaging of myocardial apoptosis, although at relatively low spatial resolution because of scattering of photons emanating from the heart.
Another approach to caspase imaging uses injectable reporters, ie, constructs that contain the caspase-3 cleavage region, a reporter label (eg, 99mTc or a quenched NIR fluorochrome), and a membrane translocation signal such as tat so that the molecule can be efficiently internalized into cells.130 Whereas the nuclear agents are trapped inside cells, the NIRF compounds could also potentially benefit from fluorescence activation.
Imaging of Matrix Metalloproteinase Activity in Heart Failure
MMPs have been implicated in heart failure and ventricular remodeling.96,131 In human explanted hearts, both ischemic and dilated cardiomyopathic tissue demonstrate altered patterns of collagenase, gelatinase, stromelysin, and TIMP expression compared with normal myocardium.132 In concert, transgenic murine experiments have confirmed a pathophysiological role for various MMPs in heart failure.133–135 Accordingly, in vivo detection of MMP activity will be important in both understanding the biology and treatment of heart failure.
Similarly as described in the atherosclerosis section, the gelatinase probe has been used to study MMP activity in cardiac remodeling after myocardial infarction (J. Chen, C.H. Tung, Q. Zhen, R. Weissleder, P.L. Huang, unpublished data, 2004). After imaging agent injection and subsequent euthanasia, NIRF imaging of myocardium correlated well with immunohistochemical staining for gelatinases. Increased MMP activity was confirmed by gelatinase zymography and Western blot analysis. Dual-label in vivo confocal microscopy showed colocalization of gelatinase activity with neutrophils on day 1, and colocalization with macrophages at later time points. These preliminary studies indicate that gelatinases may serve as a biomarker of tissue remodeling after myocardial infarction, and that specific agents can be used for biological imaging of MMP activity (J. Chen, C.H. Tung, Q. Zhen, R. Weissleder, P.L. Huang, unpublished data, 2004).
Imaging of Stem Cells for Myocardial Regeneration
The concept that stem cells could repair failing myocardium has engaged the scientific community.137 Several recent experimental investigations have demonstrated that transplanted adult bone marrow stem cells (BMSCs) can engraft in myocardium and differentiate into cardiomyocytes, endothelial cells, and vascular smooth muscle cells.138,139 In addition, stem cell therapy has been shown to improve cardiac function and survival in animal models of heart failure.140–142 Of note, two recent clinical studies of intracoronary stem cell therapy after acute myocardial infarction have demonstrated safety, feasibility, and improved ventricular function.143,144
Given the potential to serially track the presence, distribution, migration, durability, and molecular function of transplanted stem cells, cardiovascular imaging will likely play an important role in myocardial regeneration studies. Several imaging possibilities exist for detecting and tracking of stem cells in vivo. One approach is to transfect stem cells containing optical or nuclear reporter genes that can be noninvasively imaged in the heart.21,22,145 The other genetically intact approach, more likely to be used in human stem cell trials, is to label stem cells with magnetic nanoparticles. Encouragingly, MRI of magnetically labeled mesenchymal stem cells (MSCs) injected into porcine myocardium has recently been performed in vivo.146,147 In a myocardial infarction model, allogeneic, fluorescently labeled MSCs were incubated with commercially available magnetic particles for 24 to 48 hours. After ischemia and reperfusion, 
400 million magnetically labeled MSCs were intramyocardially injected under x-ray fluoroscopy. Serial MRI demonstrated progressively less intensely hypoenhancing lesions (Figure 6). Prussian blue staining demonstrated colocalization of the iron signal with the MSC-labeled fluorescent dyes, confirming that the magnetic particles remained within the intracellular space. In addition, another study demonstrated that relatively large magnetic and fluorescent particles (1-µm diameter) could also be used to image magnetically labeled MSCs injected into infarcted and normal porcine myocardium.147 These particles may be advantageous for stem cell labeling due to their high relaxivity and longer intracellular lifetime (at least 3 weeks), although labeling times are relatively long. Of note, other schemes for cell labeling have also been pursued. Using the transferrin receptor to shuttle iron oxide into the cell interior,19 oligodendrocyte progenitor cells have been tracked in spinal cords in vivo.148 Magnetodendrimers represent another class of derivatized magnetic particles useful for cell labeling.53 In addition, gadolinium labels have also been used for ex vivo confirmation of stem cell tracking.149
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Newer magnetic nanoparticle preparations such as CLIO-tat offer significant advantages including higher labeling efficiency, faster labeling (minutes instead of hours to days), chemical inertness, lack of immunogenicity and toxicity, dual labeling (magnetic and fluorescence capability), and higher signal (relaxivity) effects. These agents consist of cross-linked iron oxide (CLIO) conjugated to membrane translocation signals of the human immunodeficiency virus (HIV) Tat protein.48 Given the availability of the various magnetic cell labeling agents, and the ability to assess myocardial function and anatomy, MRI should play a leading role in assessing myocardial stem cell therapy.
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Conclusions |
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With the parallel advances in small animal imaging and reporter agent technology, investigators in the cardiovascular arena are well poised to apply and extend current capabilities to assay cardiovascular gene expression, stem cell biology, inflammation, apoptosis, and protease activity. It is further expected that clinical translation of molecular imaging technology will ultimately aid in the diagnosis and treatment of human cardiovascular disease.
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Acknowledgments |
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Sources of financial support for this work included the Donald W. Reynolds Foundation (R.W., F.J.), NIH P50-CA86355 (R.W.), and CMIR Development Fund (F.J.). The authors gratefully acknowledge the assistance of Peter Libby, MD, Guy L. Reed, MD, and Anthony Rosenzweig, MD, for their critical review of the manuscript and many helpful discussions.
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Footnotes |
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Original received August 21, 2003; resubmission received November 20, 2003; revised resubmission received January 15, 2004; accepted January 16, 2004.
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References |
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1. Weissleder R. Scaling down imaging: molecular mapping of cancer in mice. Nat Rev Cancer. 2002; 2: 11–18.[CrossRef][Medline] [Order article via Infotrieve]
2. Rudin M, Weissleder R. Molecular imaging in drug discovery and development. Nat Rev Drug Discov. 2003; 2: 123–131.[CrossRef][Medline] [Order article via Infotrieve]
3. Weissleder R, Mahmood U. Molecular imaging. Radiology. 2001; 219: 316–333.
4. Budinger TF, Benaron DA, Koretsky AP. Imaging transgenic animals. Annu Rev Biomed Eng. 1999; 1: 611–648.[CrossRef][Medline] [Order article via Infotrieve]
5. Cherry SR, Gambhir SS. Use of positron emission tomography in animal research. ILAR J. 2001; 42: 219–232.[Medline] [Order article via Infotrieve]
6. Balaban RS, Hampshire VA. Challenges in small animal noninvasive imaging. ILAR J. 2001; 42: 248–262.[Medline] [Order article via Infotrieve]
7. Paulus MJ, Gleason SS, Easterly ME, Foltz CJ. A review of high-resolution X-ray computed tomography and other imaging modalities for small animal research. Lab Anim. 2001; 30: 36–45.
8. Contag CH, Spilman SD, Contag PR, Oshiro M, Eames B, Dennery P, Stevenson DK, Benaron DA. Visualizing gene expression in living mammals using a bioluminescent reporter. Photochem Photobiol. 1997; 66: 523–531.[Medline] [Order article via Infotrieve]
9. Gambhir SS. Molecular imaging of cancer with positron emission tomography. Nat Rev Cancer. 2002; 2: 683–693.[CrossRef][Medline] [Order article via Infotrieve]
10. Blasberg RG, Tjuvajev JG. Molecular-genetic imaging: current and future perspectives. J Clin Invest. 2003; 111: 1620–1629.[CrossRef][Medline] [Order article via Infotrieve]
11. Massoud TF, Gambhir SS. Molecular imaging in living subjects: seeing fundamental biological processes in a new light. Genes Dev. 2003; 17: 545–580.
12. Sharma V, Luker GD, Piwnica-Worms D. Molecular imaging of gene expression and protein function in vivo with PET and SPECT. J Magn Reson Imaging. 2002; 16: 336–351.[CrossRef][Medline] [Order article via Infotrieve]
13. Hadjantonakis AK, Dickinson ME, Fraser SE, Papaioannou VE. Technicolour transgenics: imaging tools for functional genomics in the mouse. Nat Rev Genet. 2003; 4: 613–625.[Medline] [Order article via Infotrieve]
14. Contag CH, Ross BD. It’s not just about anatomy: in vivo bioluminescence imaging as an eyepiece into biology. J Magn Reson Imaging. 2002; 16: 378–387.[CrossRef][Medline] [Order article via Infotrieve]
15. Greer LF3rd, Szalay AA. Imaging of light emission from the expression of luciferases in living cells and organisms: a review. Luminescence. 2002; 17: 43–74.[CrossRef][Medline] [Order article via Infotrieve]
16. Weissleder R, Simonova M, Bogdanova A, Bredow S, Enochs WS, Bogdanov A Jr. MR imaging and scintigraphy of gene expression through melanin induction. Radiology. 1997; 204: 425–429.
17. Stegman LD, Rehemtulla A, Beattie B, Kievit E, Lawrence TS, Blasberg RG, Tjuvajev JG, Ross BD. Noninvasive quantitation of cytosine deaminase transgene expression in human tumor xenografts with in vivo magnetic resonance spectroscopy. Proc Natl Acad Sci U S A. 1999; 96: 9821–9826.
18. Louie AY, Huber MM, Ahrens ET, Rothbacher U, Moats R, Jacobs RE, Fraser SE, Meade TJ. In vivo visualization of gene expression using magnetic resonance imaging. Nat Biotechnol. 2000; 18: 321–325.[CrossRef][Medline] [Order article via Infotrieve]
19. Weissleder R, Moore A, Mahmood U, Bhorade R, Benveniste H, Chiocca EA, Basilion JP. In vivo magnetic resonance imaging of transgene expression. Nat Med. 2000; 6: 351–355.[CrossRef][Medline] [Order article via Infotrieve]
20. Ichikawa T, Hogemann D, Saeki Y, Tyminski E, Terada K, Weissleder R, Chiocca EA, Basilion JP. MRI of transgene expression: correlation to therapeutic gene expression. Neoplasia. 2002; 4: 523–530.[CrossRef][Medline] [Order article via Infotrieve]
21. Inubushi M, Wu JC, Gambhir SS, Sundaresan G, Satyamurthy N, Namavari M, Yee S, Barrio JR, Stout D, Chatziioannou AF, Wu L, Schelbert HR. Positron-emission tomography reporter gene expression imaging in rat myocardium. Circulation. 2003; 107: 326–332.
22. Wu JC, Inubushi M, Sundaresan G, Schelbert HR, Gambhir SS. Optical imaging of cardiac reporter gene expression in living rats. Circulation. 2002; 105: 1631–1634.
23. Khaw BA, Yasuda T, Gold HK, Leinbach RC, Johns JA, Kanke M, Barlai-Kovach M, Strauss HW, Haber E. Acute myocardial infarct imaging with indium-111-labeled monoclonal antimyosin Fab. J Nucl Med. 1987; 28: 1671–1678.
24. Zhu H, Baxter LT, Jain RK. Potential and limitations of radioimmunodetection and radioimmunotherapy with monoclonal antibodies. J Nucl Med. 1997; 38: 731–741.
25. Hu S, Shively L, Raubitschek A, Sherman M, Williams LE, Wong JY, Shively JE, Wu AM. Minibody: a novel engineered anti-carcinoembryonic antigen antibody fragment (single-chain Fv-CH3) which exhibits rapid, high-level targeting of xenografts. Cancer Res. 1996; 56: 3055–3061.
26. Urbain JL. Oncogenes, cancer and imaging. J Nucl Med. 1999; 40: 498–504.
27. Wester HJ, Schottelius M, Scheidhauer K, Meisetschlager G, Herz M, Rau FC, Reubi JC, Schwaiger M. PET imaging of somatostatin receptors: design, synthesis and preclinical evaluation of a novel 18F-labelled, carbohydrated analogue of octreotide. Eur J Nucl Med Mol Imaging. 2003; 30: 117–122.[CrossRef][Medline] [Order article via Infotrieve]
28. Wisniewski D, Lambek CL, Liu C, Strife A, Veach DR, Nagar B, Young MA, Schindler T, Bornmann WG, Bertino JR, Kuriyan J, Clarkson B. Characterization of potent inhibitors of the Bcr-Abl and the c-kit receptor tyrosine kinases. Cancer Res. 2002; 62: 4244–4255.
29. Goel A, Baranowska-Kortylewicz J, Hinrichs SH, Wisecarver J, Pavlinkova G, Augustine S, Colcher D, Booth BJ, Batra SK. 99mTc-labeled divalent and tetravalent CC49 single-chain Fv’s: novel imaging agents for rapid in vivo localization of human colon carcinoma. J Nucl Med. 2001; 42: 1519–1527.
30. Zhao M, Kircher MF, Josephson L, Weissleder R. Differential conjugation of tat peptide to superparamagnetic nanoparticles and its effect on cellular uptake. Bioconjug Chem. 2002; 13: 840–844.[CrossRef][Medline] [Order article via Infotrieve]
31. Moon WK, Lin Y, O’Loughlin T, Tang Y, Kim DE, Weissleder R, Tung CH. Enhanced tumor detection using a folate receptor-targeted near-infrared fluorochrome conjugate. Bioconjug Chem. 2003; 14: 539–545.[CrossRef][Medline] [Order article via Infotrieve]
32. Tjuvajev JG, Finn R, Watanabe K, Joshi R, Oku T, Kennedy J, Beattie B, Koutcher J, Larson S, Blasberg RG. Noninvasive imaging of herpes virus thymidine kinase gene transfer and expression: a potential method for monitoring clinical gene therapy. Cancer Res. 1996; 56: 4087–4095.
33. Gambhir SS, Barrio JR, Phelps ME, Iyer M, Namavari M, Satyamurthy N, Wu L, Green LA, Bauer E, MacLaren DC, Nguyen K, Berk AJ, Cherry SR, Herschman HR. Imaging adenoviral-directed reporter gene expression in living animals with positron emission tomography. Proc Natl Acad Sci U S A. 1999; 96: 2333–2338.
34. Chmura AJ, Orton MS, Meares CF. Antibodies with infinite affinity. Proc Natl Acad Sci U S A. 2001; 98: 8480–8484.
35. Jaffer FA, Tung CH, Houng AK, O’Loughin T, Reed GL, Weissleder R. MRI of blood coagulation factor XIII activity using a novel peptide-derivatized caged iron oxide nanoparticle (F13-CLIO). Mol Imaging. 2002; 1: 217–218.Abstract.
36. Weissleder R, Bogdanov A Jr, Tung CH, Weinmann HJ. Size optimization of synthetic graft copolymers for in vivo angiogenesis imaging. Bioconjug Chem. 2001; 12: 213–219.[CrossRef][Medline] [Order article via Infotrieve]
37. Bogdanov A, Matuszewski L, Bremer C, Petrovsky A, Weissleder R. Oligomerization of paramagnetic substrates result in signal amplification and can be used for MR imaging of molecular targets. Mol Imaging. 2002; 1: 1–9.[Medline] [Order article via Infotrieve]
38. Perez JM, Josephson L, O’Loughlin T, Hogemann D, Weissleder R. Magnetic relaxation switches capable of sensing molecular interactions. Nat Biotechnol. 2002; 20: 816–820.[Medline] [Order article via Infotrieve]
39. Weissleder R, Tung CH, Mahmood U, Bogdanov A. In vivo imaging of tumors with protease-activated near-infrared fluorescent probes. Nat Biotechnol. 1999; 17: 375–378.[CrossRef][Medline] [Order article via Infotrieve]
40. Tung C, Mahmood U, Bredow S, Weissleder R. In vivo imaging of proteolytic enzyme activity using a novel molecular reporter. Cancer Res. 2000; 2000: 4953–4958.
41. Bremer C, Tung CH, Weissleder R. In vivo molecular target assessment of matrix metalloproteinase inhibition. Nat Med. 2001; 7: 743–748.[CrossRef][Medline] [Order article via Infotrieve]
42. Jaffer FA, Tung CH, Gerszten RE, Weissleder R. In vivo imaging of thrombin activity in experimental thrombi with thrombin-sensitive near-infrared molecular probe. Arterioscler Thromb Vasc Biol. 2002; 22: 1929–1935.
43. Shah K, Tung CH, Chang CH, Slootweg E, O’Loughlin T, Breakefield XO, Weissleder R. In vivo imaging of HIV protease activity in amplicon vector transduced gliomas. Cancer Res. 2004; 64: 273–278.
44. Weissleder R, Elizondo G, Wittenberg J, Rabito CA, Bengele HH, Josephson L. Ultrasmall superparamagnetic iron oxide: characterization of a new class of contrast agents for MR imaging. Radiology. 1990; 175: 489–493.
45. Harisinghani MG, Barentsz J, Hahn PF, Deserno WM, Tabatabaei S, van de Kaa CH, de la Rosette J, Weissleder R. Noninvasive detection of clinically occult lymph-node metastases in prostate cancer. N Engl J Med. 2003; 348: 2491–2499.
46. Kooi ME, Cappendijk VC, Cleutjens KB, Kessels AG, Kitslaar PJ, Borgers M, Frederik PM, Daemen MJ, van Engelshoven JM. Accumulation of ultrasmall superparamagnetic particles of iron oxide in human atherosclerotic plaques can be detected by in vivo magnetic resonance imaging. Circulation. 2003; 107: 2453–2458.
47. Kang HW, Josephson L, Petrovsky A, Weissleder R, Bogdanov A Jr. Magnetic resonance imaging of inducible E-selectin expression in human endothelial cell culture. Bioconjug Chem. 2002; 13: 122–127.[CrossRef][Medline] [Order article via Infotrieve]
48. Lewin M, Carlesso N, Tung CH, Tang XW, Cory D, Scadden DT, Weissleder R. Tat peptide-derivatized magnetic nanoparticles allow in vivo tracking and recovery of progenitor cells. Nat Biotechnol. 2000; 18: 410–414.[CrossRef][Medline] [Order article via Infotrieve]
49. Kircher MF, Allport J, Graves EE, Love V, Josephson L, Lichtman A, Weissleder R. In vivo high resolution 3D imaging of antigen-specific cytotoxic T-lymphocyte trafficking to tumors. Cancer Res. 2003; 63: 6838–6846.
50. Dayton PA, Ferrara KW. Targeted imaging using ultrasound. J Magn Reson Imaging. 2002; 16: 362–377.[CrossRef][Medline] [Order article via Infotrieve]
51. Sipkins DA, Cheresh DA, Kazemi MR, Nevin LM, Bednarski MD, Li KC. Detection of tumor angiogenesis in vivo by Vß3-targeted magnetic resonance imaging. Nat Med. 1998; 4: 623–626.[CrossRef][Medline]
[Order article via Infotrieve]
52. Winter PM, Morawski AM, Caruthers SD, Fuhrhop RW, Zhang H, Williams TA, Allen JS, Lacy EK, Robertson JD, Lanza GM, Wickline SA. Molecular imaging of angiogenesis in early-stage atherosclerosis with vß3-integrin-targeted nanoparticles. Circulation. 2003; 108: 2270–2274.
53. Bulte JW, Douglas T, Witwer B, Zhang SC, Strable E, Lewis BK, Zywicke H, Miller B, van Gelderen P, Moskowitz BM, Duncan ID, Frank JA. Magnetodendrimers allow endosomal magnetic labeling and in vivo tracking of stem cells. Nat Biotechnol. 2001; 19: 1141–1147.[CrossRef][Medline] [Order article via Infotrieve]
54. Flacke S, Fischer S, Scott MJ, Fuhrhop RJ, Allen JS, McLean M, Winter P, Sicard GA, Gaffney PJ, Wickline SA, Lanza GM. Novel MRI contrast agent for molecular imaging of fibrin: implications for detecting vulnerable plaques. Circulation. 2001; 104: 1280–1285.
55. Josephson L, Perez JM, Weissleder R. Magnetic nanosensors for the detection of oligonucleotide sequences. Angewandte Chemie. 2001; 40: 3204–3206.[CrossRef]
56. Perez JM, O’Loughin T, Simeone FJ, Weissleder R, Josephson L. DNA-based magnetic nanoparticle assembly acts as a magnetic relaxation nanoswitch allowing screening of DNA-cleaving agents. J Am Chem Soc. 2002; 124: 2856–2857.[CrossRef][Medline] [Order article via Infotrieve]
57. Perez JM, Josephson L, Weissleder R. Magnetic nanosensors for DNA analysis. Eur Cell Mater. 2002; 3 (suppl 2): 181–182.
58. Zhao M, Josephson L, Tang Y, Weissleder R. Magnetic sensors for protease assays. Angew Chem Int Ed Engl. 2003; 42: 1375–1378.[CrossRef][Medline] [Order article via Infotrieve]
59. Perez JM, Simeone FJ, Saeki Y, Josephson L, Weissleder R. Viral-induced self-assembly of magnetic nanoparticles allows the detection of viral particles in biological media. J Am Chem Soc. 2003; 125: 10192–10193.[CrossRef][Medline] [Order article via Infotrieve]
60. Perez JM, Simeone FJ, Tsourkas A, Josephson L, Weissleder R. Peroxidase substrate nanosensors for MRI. Nano Lett. 2004; 4: 119–122.[CrossRef]
61. Brennan ML, Penn MS, Van Lente F, Nambi V, Shishehbor MH, Aviles RJ, Goormastic M, Pepoy ML, McErlean ES, Topol EJ, Nissen SE, Hazen SL. Prognostic value of myeloperoxidase in patients with chest pain. N Engl J Med. 2003; 349: 1595–1604.
62. Blankenberg FG, Strauss HW. Nuclear medicine applications in molecular imaging. J Magn Reson Imaging. 2002; 16: 352–361.[CrossRef][Medline] [Order article via Infotrieve]
63. Khaw BA. The current role of infarct avid imaging. Semin Nucl Med. 1999; 29: 259–270.[CrossRef][Medline] [Order article via Infotrieve]
64. Mari C, Strauss HW. Radiotracer characterization of coronary artery lesions. Nucl Med Commun. 2002; 23: 703–706.[CrossRef][Medline] [Order article via Infotrieve]
65. Knight LC. Radiolabeled peptide ligands for imaging thrombi and emboli. Nucl Med Biol. 2001; 28: 515–526.[CrossRef][Medline] [Order article via Infotrieve]
66. Gambhir SS, Bauer E, Black ME, Liang Q, Kokoris MS, Barrio JR, Iyer M, Namavari M, Phelps ME, Herschman HR. A mutant herpes simplex virus type 1 thymidine kinase reporter gene shows improved sensitivity for imaging reporter gene expression with positron emission tomography. Proc Natl Acad Sci U S A. 2000; 97: 2785–2790.
67. Jacobs A, Voges J, Reszka R, Lercher M, Gossmann A, Kracht L, Kaestle C, Wagner R, Wienhard K, Heiss WD. Positron-emission tomography of vector-mediated gene expression in gene therapy for gliomas. Lancet. 2001; 358: 727–729.[CrossRef][Medline] [Order article via Infotrieve]
68. Lanza GM, Wallace KD, Scott MJ, Cacheris WP, Abendschein DR, Christy DH, Sharkey AM, Miller JG, Gaffney PJ, Wickline SA. A novel site-targeted ultrasonic contrast agent with broad biomedical application. Circulation. 1996; 94: 3334–3340.
69. Takeuchi M, Ogunyankin K, Pandian NG, McCreery TP, Sweitzer RH, Caldwell VE, Unger EC, Avelar E, Sheahan M, Connolly R. Enhanced visualization of intravascular and left atrial appendage thrombus with the use of a thrombus-targeting ultrasonographic contrast agent (MRX-408A1): in vivo experimental echocardiographic studies. J Am Soc Echocardiogr. 1999; 12: 1015–1021.[CrossRef][Medline] [Order article via Infotrieve]
70. Demos SM, Alkan-Onyuksel H, Kane BJ, Ramani K, Nagaraj A, Greene R, Klegerman M, McPherson DD. In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement. J Am Coll Cardiol. 1999; 33: 867–875.
71. Villanueva FS, Jankowski RJ, Klibanov S, Pina ML, Alber SM, Watkins SC, Brandenburger GH, Wagner WR. Microbubbles targeted to intercellular adhesion molecule-1 bind to activated coronary artery endothelial cells. Circulation. 1998; 98: 1–5.
72. Lindner JR, Song J, Christiansen J, Klibanov AL, Xu F, Ley K. Ultrasound assessment of inflammation and renal tissue injury with microbubbles targeted to P-selectin. Circulation. 2001; 104: 2107–2112.
73. Lanza GM, Abendschein DR, Hall CS, Scott MJ, Scherrer DE, Houseman A, Miller JG, Wickline SA. In vivo molecular imaging of stretch-induced tissue factor in carotid arteries with ligand-targeted nanoparticles. J Am Soc Echocardiogr. 2000; 13: 608–614.[CrossRef][Medline] [Order article via Infotrieve]
74. Lindner JR, Song J, Xu F, Klibanov AL, Singbartl K, Ley K, Kaul S. Noninvasive ultrasound imaging of inflammation using microbubbles targeted to activated leukocytes. Circulation. 2000; 102: 2745–2750.
75. Christiansen JP, Leong-Poi H, Klibanov AL, Kaul S, Lindner JR. Noninvasive imaging of myocardial reperfusion injury using leukocyte-targeted contrast echocardiography. Circulation. 2002; 105: 1764–1767.
76. Leong-Poi H, Christiansen J, Klibanov AL, Kaul S, Lindner JR. Noninvasive assessment of angiogenesis by ultrasound and microbubbles targeted to v-integrins. Circulation. 2003; 107: 455–460.
77. Ellegala DB, Leong-Poi H, Carpenter JE, Klibanov AL, Kaul S, Shaffrey ME, Sklenar J, Lindner JR. Imaging tumor angiogenesis with contrast ultrasound and microbubbles targeted to vß3. Circulation. 2003; 108: 336–341.
78. Weissleder R, Ntziachristos V. Shedding light onto live molecular targets. Nat Med. 2003; 9: 123–128.[CrossRef][Medline] [Order article via Infotrieve]
79. Neri D, Carnemolla B, Nissim A, Leprini A, Querze G, Balza E, Pini A, Tarli L, Halin C, Neri P, Zardi L, Winter G. Targeting by affinity-matured recombinant antibody fragments on an angiogenesis associated fibronectin isoform. Nat Biotechnol. 1997; 15: 1271–1275.[CrossRef][Medline] [Order article via Infotrieve]
80. Achilefu S, Dorshow RB, Bugaj JE, Rajagopalan R. Novel receptor-targeted fluorescent contrast agents for in vivo tumor imaging. Invest Radiol. 2000; 35: 479–485.[CrossRef][Medline] [Order article via Infotrieve]
81. Becker A, Hessenius C, Licha K, Ebert B, Sukowski U, Semmler W, Wiedenmann B, Grotzinger C. Receptor-targeted optical imaging of tumors with near-infrared fluorescent ligands. Nat Biotechnol. 2001; 19: 327–331.[CrossRef][Medline] [Order article via Infotrieve]
82. Petrovsky A, Schellenberger E, Josephson L, Weissleder R, Bogdanov A Jr. Near-infrared fluorescent imaging of tumor apoptosis. Cancer Res. 2003; 63: 1936–1942.
83. Zaheer A, Lenkinski RE, Mahmood A, Jones AG, Cantley LC, Frangioni JV. In vivo near-infrared fluorescence imaging of osteoblastic activity. Nat Biotechnol. 2001; 19: 1148–1154.[CrossRef][Medline] [Order article via Infotrieve]
84. Chen J, Tung CH, Mahmood U, Ntziachristos V, Gyurko R, Fishman MC, Huang PL, Weissleder R. In vivo imaging of proteolytic activity in atherosclerosis. Circulation. 2002; 105: 2766–2771.
85. Branchini BR. Chemical synthesis of firefly luciferin analogs and inhibitors. Methods Enzymol. 2000; 305: 188–195.[Medline] [Order article via Infotrieve]
86. Shah K, Tang Y, Breakefield X, Weissleder R. Real time imaging of TRAIL induced apoptosis of glioma tumors in vivo. Oncogene. 2003; 22: 6865–6872.[CrossRef][Medline] [Order article via Infotrieve]
87. Iyer M, Wu L, Carey M, Wang Y, Smallwood A, Gambhir SS. Two-step transcriptional amplification as a method for imaging reporter gene expression using weak promoters. Proc Natl Acad Sci U S A. 2001; 98: 14595–14600.
88. Laxman B, Hall DE, Bhojani MS, Hamstra DA, Chenevert TL, Ross BD, Rehemtulla A. Noninvasive real-time imaging of apoptosis. Proc Natl Acad Sci U S A. 2002; 99: 16551–16555.
89. Glass CK, Witztum JL. Atherosclerosis: the road ahead. Cell. 2001; 104: 503–516.[CrossRef][Medline] [Order article via Infotrieve]
90. Libby P. Inflammation in atherosclerosis. Nature. 2002; 420: 868–874.[CrossRef][Medline] [Order article via Infotrieve]
91. Reddy VY, Zhang QY, Weiss SJ. Pericellular mobilization of the tissue-destructive cysteine proteinases, cathepsins B, L, and S, by human monocyte-derived macrophages. Proc Natl Acad Sci U S A. 1995; 92: 3849–3853.
92. Leake DS, Peters TJ. Proteolytic degradation of low density lipoproteins by arterial smooth muscle cells: the role of individual cathepsins. Biochim Biophys Acta. 1981; 664: 108–116.[Medline] [Order article via Infotrieve]
93. Visse R, Nagase H. Matrix metalloproteinases and tissue inhibitors of metalloproteinases: structure, function, and biochemistry. Circ Res. 2003; 92: 827–839.
94. Galis ZS, Khatri JJ. Matrix metalloproteinases in vascular remodeling and atherogenesis: the good, the bad, and the ugly. Circ Res. 2002; 90: 251–262.
95. Pyo R, Lee JK, Shipley JM, Curci JA, Mao D, Ziporin SJ, Ennis TL, Shapiro SD, Senior RM, Thompson RW. Targeted gene disruption of matrix metalloproteinase-9 (gelatinase B) suppresses development of experimental abdominal aortic aneurysms. J Clin Invest. 2000; 105: 1641–1649.[Medline] [Order article via Infotrieve]
96. Lee RT, Libby P. Matrix metalloproteinases: not-so-innocent bystanders in heart failure. J Clin Invest. 2000; 106: 827–828.[Medline] [Order article via Infotrieve]
97. Galis ZS, Sukhova GK, Lark MW, Libby P. Increased expression of matrix metalloproteinases and matrix degrading activity in vulnerable regions of human atherosclerotic plaques. J Clin Invest. 1994; 94: 2493–2503.[Medline] [Order article via Infotrieve]
98. Li AC, Glass CK. The macrophage foam cell as a target for therapeutic intervention. Nat Med. 2002; 8: 1235–1242.[CrossRef][Medline] [Order article via Infotrieve]
99. Gerrity RG. The role of the monocyte in atherogenesis, I: transition of blood-borne monocytes into foam cells in fatty lesions. Am J Pathol. 1981; 103: 181–190.[Abstract]
100. Schmitz SA, Coupland SE, Gust R, Winterhalter S, Wagner S, Kresse M, Semmler W, Wolf KJ. Superparamagnetic iron oxide-enhanced MRI of atherosclerotic plaques in Watanabe hereditable hyperlipidemic rabbits. Invest Radiol. 2000; 35: 460–471.[CrossRef][Medline] [Order article via Infotrieve]
101. Ruehm SG, Corot C, Vogt P, Kolb S, Debatin JF. Magnetic resonance imaging of atherosclerotic plaque with ultrasmall superparamagnetic particles of iron oxide in hyperlipidemic rabbits. Circulation. 2001; 103: 415–422.
102. Schmitz SA, Taupitz M, Wagner S, Wolf KJ, Beyersdorff D, Hamm B. Magnetic resonance imaging of atherosclerotic plaques using superparamagnetic iron oxide particles. J Magn Reson Imaging. 2001; 14: 355–361.[CrossRef][Medline] [Order article via Infotrieve]
103. Schmitz SA, Taupitz M, Wagner S, Coupland SE, Gust R, Nikolova A, Wolf KJ. Iron-oxide–enhanced magnetic resonance imaging of atherosclerotic plaques: postmortem analysis of accuracy, inter-observer agreement, and pitfalls. Invest Radiol. 2002; 37: 405–411.[CrossRef][Medline] [Order article via Infotrieve]
104. Kanno S, Wu YJ, Lee PC, Dodd SJ, Williams M, Griffith BP, Ho C. Macrophage accumulation associated with rat cardiac allograft rejection detected by magnetic resonance imaging with ultrasmall superparamagnetic iron oxide particles. Circulation. 2001; 104: 934–938.
105. Litovsky S, Madjid M, Zarrabi A, Casscells SW, Willerson JT, Naghavi M. Superparamagnetic iron oxide-based method for quantifying recruitment of monocytes to mouse atherosclerotic lesions in vivo: enhancement by tissue necrosis factor-, interleukin-1ß, and interferon-
. Circulation. 2003; 107: 1545–1549.
106. Massberg S, Brand K, Gruner S, Page S, Muller E, Muller I, Bergmeier W, Richter T, Lorenz M, Konrad I, Nieswandt B, Gawaz M. A critical role of platelet adhesion in the initiation of atherosclerotic lesion formation. J Exp Med. 2002; 196: 887–896.
107. Cybulsky MI, Iiyama K, Li H, Zhu S, Chen M, Iiyama M, Davis V, Gutierrez-Ramos JC, Connelly PW, Milstone DS. A major role for VCAM-1, but not ICAM-1, in early atherosclerosis. J Clin Invest. 2001; 107: 1255–1262.[Medline] [Order article via Infotrieve]
108. Bates SM, Lister-James J, Julian JA, Taillefer R, Moyer BR, Ginsberg JS. Imaging characteristics of a novel technetium Tc 99m-labeled platelet glycoprotein IIb/IIIa receptor antagonist in patients with acute deep vein thrombosis or a history of deep vein thrombosis. Arch Intern Med. 2003; 163: 452–456.
109. Ruggeri ZM. Platelets in atherothrombosis. Nat Med. 2002; 8: 1227–1234.[CrossRef][Medline] [Order article via Infotrieve]
110. Johansson LO, Bjornerud A, Ahlstrom HK, Ladd DL, Fujii DK. A targeted contrast agent for magnetic resonance imaging of thrombus: implications of spatial resolution. J Magn Reson Imaging. 2001; 13: 615–618.[CrossRef][Medline] [Order article via Infotrieve]
111. Coughlin SR. Thrombin signalling and protease-activated receptors. Nature. 2000; 407: 258–264.[CrossRef][Medline] [Order article via Infotrieve]
112. Tung CH, Gerszten RE, Jaffer FA, Weissleder R. A novel near-infrared fluorescence sensor for detection of thrombin activation in blood. Chembiochem. 2002; 3: 207–211.[CrossRef][Medline] [Order article via Infotrieve]
113. Ariens RA, Lai TS, Weisel JW, Greenberg CS, Grant PJ. Role of factor XIII in fibrin clot formation and effects of genetic polymorphisms. Blood. 2002; 100: 743–754.
114. Reed GL, Houng AK. The contribution of activated factor XIII to fibrinolytic resistance in experimental pulmonary embolism. Circulation. 1999; 99: 299–304.
115. Robinson BR, Houng AK, Reed GL. Catalytic life of activated factor XIII in thrombi: implications for fibrinolytic resistance and thrombus aging. Circulation. 2000; 102: 1151–1157.
116. Tung C, Ho N-H, Zeng Q, Tang Y, Jaffer FA, Reed GL, Weissleder R. Novel factor XIII probes for blood coagulation imaging. Chem Biol Chem. 2003; 4: 897–899.
117. Barrett JA, Kolodziej AF, Caravan PD, Nair S, Looby R, Witte S, Costello CR, Meslia MA, Drezwecki L, Cesna C, Pratt C, McMurry TJ, Lauffer RB, Yucel EK, Zhao L, Weisskoff RM, Carpenter AP, Graham PB. EP-1873, a gadolinium (Gd) labeled fibrin specific agent that rapidly detects arterial and venous thrombi with MRI. Circulation. 2002; 106 (suppl II): II-120.Abstract.
118. Kang PM, Izumo S. Apoptosis and heart failure: a critical review of the literature. Circ Res. 2000; 86: 1107–1113.
119. Narula J, Haider N, Virmani R, DiSalvo TG, Kolodgie FD, Hajjar RJ, Schmidt U, Semigran MJ, Dec GW, Khaw BA. Apoptosis in myocytes in end-stage heart failure. N Engl J Med. 1996; 335: 1182–1189.
120. Wencker D, Chandra M, Nguyen K, Miao W, Garantziotis S, Factor SM, Shirani J, Armstrong RC, Kitsis RN. A mechanistic role for cardiac myocyte apoptosis in heart failure. J Clin Invest. 2003; 111: 1497–1504.[CrossRef][Medline] [Order article via Infotrieve]
121. Gottlieb RA, Kitsis RN. Seeing death in the living. Nat Med. 2001; 7: 1277–1278.[CrossRef][Medline] [Order article via Infotrieve]
122. Dumont EA, Reutelingsperger CP, Smits JF, Daemen MJ, Doevendans PA, Wellens HJ, Hofstra L. Real-time imaging of apoptotic cell-membrane changes at the single-cell level in the beating murine heart. Nat Med. 2001; 7: 1352–1355.[CrossRef][Medline] [Order article via Infotrieve]
123. Hofstra L, Liem IH, Dumont EA, Boersma HH, van Heerde WL, Doevendans PA, De Muinck E, Wellens HJ, Kemerink GJ, Reutelingsperger CP, Heidendal GA. Visualisation of cell death in vivo in patients with acute myocardial infarction. Lancet. 2000; 356: 209–212.[CrossRef][Medline] [Order article via Infotrieve]
124. Narula J, Acio ER, Narula N, Samuels LE, Fyfe B, Wood D, Fitzpatrick JM, Raghunath PN, Tomaszewski JE, Kelly C, Steinmetz N, Green A, Tait JF, Leppo J, Blankenberg FG, Jain D, Strauss HW. Annexin-V imaging for noninvasive detection of cardiac allograft rejection. Nat Med. 2001; 7: 1347–1352.[CrossRef][Medline] [Order article via Infotrieve]
125. Schellenberger EA, Bogdanov A Jr, Petrovsky A, Ntziachristos V, Weissleder R, Josephson L. Optical imaging of apoptosis as a biomarker of tumor response to chemotherapy. Neoplasia. 2003; 5: 187–192.[Medline] [Order article via Infotrieve]
126. Zhao M, Beauregard DA, Loizou L, Davletov B, Brindle KM. Non-invasive detection of apoptosis using magnetic resonance imaging and a targeted contrast agent. Nat Med. 2001; 7: 1241–1244.[CrossRef][Medline] [Order article via Infotrieve]
127. Schellenberger EA, Bogdanov A Jr, Hogemann D, Weissleder R, Josephson L, Tait J. Annexin V-CLIO: a nanoparticle for detecting apoptosis by MRI. Mol Imaging. 2002; 1: 1–6.[Medline] [Order article via Infotrieve]
128. Borutaite V, Brown GC. Mitochondria in apoptosis of ischemic heart. FEBS Lett. 2003; 541: 1–5.[CrossRef][Medline] [Order article via Infotrieve]
129. Condorelli G, Roncarati R, Ross J Jr, Pisani A, Stassi G, Todaro M, Trocha S, Drusco A, Gu Y, Russo MA, Frati G, Jones SP, Lefer DJ, Napoli C, Croce CM. Heart-targeted overexpression of caspase 3 in mice increases infarct size and depresses cardiac function. Proc Natl Acad Sci U S A. 2001; 98: 9977–9982.
130. Polyakov V, Sharma V, Dahlheimer JL, Pica CM, Luker GD, Piwnica-Worms D. Novel Tat-peptide chelates for direct transduction of technetium-99m and rhenium into human cells for imaging and radiotherapy. Bioconjug Chem. 2000; 11: 762–771.[CrossRef][Medline] [Order article via Infotrieve]
131. Tyagi SC, Ratajska A, Weber KT. Myocardial matrix metalloproteinase(s): localization and activation. Mol Cell Biochem. 1993; 126: 49–59.[CrossRef][Medline] [Order article via Infotrieve]
132. Spinale FG, Coker ML, Heung LJ, Bond BR, Gunasinghe HR, Etoh T, Goldberg AT, Zellner JL, Crumbley AJ. A matrix metalloproteinase induction/activation system exists in the human left ventricular myocardium and is upregulated in heart failure. Circulation. 2000; 102: 1944–1949.
133. Heymans S, Luttun A, Nuyens D, Theilmeier G, Creemers E, Moons L, Dyspersin GD, Cleutjens JP, Shipley M, Angellilo A, Levi M, Nube O, Baker A, Keshet E, Lupu F, Herbert JM, Smits JF, Shapiro SD, Baes M, Borgers M, Collen D, Daemen MJ, Carmeliet P. Inhibition of plasminogen activators or matrix metalloproteinases prevents cardiac rupture but impairs therapeutic angiogenesis and causes cardiac failure. Nat Med. 1999; 5: 1135–1142.[CrossRef][Medline] [Order article via Infotrieve]
134. Ducharme A, Frantz S, Aikawa M, Rabkin E, Lindsey M, Rohde LE, Schoen FJ, Kelly RA, Werb Z, Libby P, Lee RT. Targeted deletion of matrix metalloproteinase-9 attenuates left ventricular enlargement and collagen accumulation after experimental myocardial infarction. J Clin Invest. 2000; 106: 55–62.[Medline] [Order article via Infotrieve]
135. Kim HE, Dalal SS, Young E, Legato MJ, Weisfeldt ML, D’Armiento J. Disruption of the myocardial extracellular matrix leads to cardiac dysfunction. J Clin Invest. 2000; 106: 857–866.[Medline] [Order article via Infotrieve]
137. Orlic D, Hill JM, Arai AE. Stem cells for myocardial regeneration. Circ Res. 2002; 91: 1092–1102.
138. Orlic D, Kajstura J, Chimenti S, Jakoniuk I, Anderson SM, Li B, Pickel J, McKay R, Nadal-Ginard B, Bodine DM, Leri A, Anversa P. Bone marrow cells regenerate infarcted myocardium. Nature. 2001; 410: 701–705.[CrossRef][Medline] [Order article via Infotrieve]
139. Jackson KA, Majka SM, Wang H, Pocius J, Hartley CJ, Majesky MW, Entman ML, Michael LH, Hirschi KK, Goodell MA. Regeneration of ischemic cardiac muscle and vascular endothelium by adult stem cells. J Clin Invest. 2001; 107: 1395–1402.[CrossRef][Medline] [Order article via Infotrieve]
140. Orlic D, Kajstura J, Chimenti S, Limana F, Jakoniuk I, Quaini F, Nadal-Ginard B, Bodine DM, Leri A, Anversa P. Mobilized bone marrow cells repair the infarcted heart, improving function and survival. Proc Natl Acad Sci U S A. 2001; 98: 10344–10349.
141. Kocher AA, Schuster MD, Szabolcs MJ, Takuma S, Burkhoff D, Wang J, Homma S, Edwards NM, Itescu S. Neovascularization of ischemic myocardium by human bone-marrow-derived angioblasts prevents cardiomyocyte apoptosis, reduces remodeling and improves cardiac function. Nat Med. 2001; 7: 430–436.[CrossRef][Medline] [Order article via Infotrieve]
142. Mangi AA, Noiseux N, Kong D, He H, Rezvani M, Ingwall JS, Dzau VJ. Mesenchymal stem cells modified with Akt prevent remodeling and restore performance of infarcted hearts. Nat Med. 2003; 9: 1195–1201.[CrossRef][Medline] [Order article via Infotrieve]
143. Strauer BE, Brehm M, Zeus T, Kostering M, Hernandez A, Sorg RV, Kogler G, Wernet P. Repair of infarcted myocardium by autologous intracoronary mononuclear bone marrow cell transplantation in humans. Circulation. 2002; 106: 1913–1918.
144. Assmus B, Schachinger V, Teupe C, Britten M, Lehmann R, Dobert N, Grunwald F, Aicher A, Urbich C, Martin H, Hoelzer D, Dimmeler S, Zeiher AM. Transplantation of Progenitor Cells and Regeneration Enhancement in Acute Myocardial Infarction (TOPCARE-AMI). Circulation. 2002; 106: 3009–3017.
145. Wu JC, Chen IY, Sundaresan G, Min JJ, De A, Qiao JH, Fishbein MC, Gambhir SS. Molecular imaging of cardiac cell transplantation in living animals using optical bioluminescence and positron emission tomography. Circulation. 2003; 108: 1302–1305.
146. Kraitchman DL, Heldman AW, Atalar E, Amado LC, Martin BJ, Pittenger MF, Hare JM, Bulte JW. In vivo magnetic resonance imaging of mesenchymal stem cells in myocardial infarction. Circulation. 2003; 107: 2290–2293.
147. Hill JM, Dick AJ, Raman VK, Thompson RB, Yu ZX, Hinds KA, Pessanha BS, Guttman MA, Varney TR, Martin BJ, Dunbar CE, McVeigh ER, Lederman RJ. Serial cardiac magnetic resonance imaging of injected mesenchymal stem cells. Circulation. 2003; 108: 1009–1014.
148. Bulte JW, Zhang S, van Gelderen P, Herynek V, Jordan EK, Duncan ID, Frank JA. Neurotransplantation of magnetically labeled oligodendrocyte progenitors: magnetic resonance tracking of cell migration and myelination. Proc Natl Acad Sci U S A. 1999; 96: 15256–15261.
149. Modo M, Cash D, Mellodew K, Williams SC, Fraser SE, Meade TJ, Price J, Hodges H. Tracking transplanted stem cell migration using bifunctional, contrast agent-enhanced, magnetic resonance imaging. Neuroimage. 2002; 17: 803–811.[CrossRef][Medline] [Order article via Infotrieve]
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