Application of (68)Ga-PRGD2 PET/CT for αvβ3-integrin imaging of myocardial infarction and stroke

Global research trends and emerging opportunities for integrin adhesion complexes in cardiac repair: a scientometric analysis

Objective

Cardiac regenerative medicine has gained significant attention in recent years, and integrins are known to play a critical role in mediating cardiac development and repair, especially after an injury from the myocardial infarction (MI). Given the extensive research history and interdisciplinary nature of this field, a quantitative retrospective analysis and visualization of related topics is necessary.

Materials and methods

We performed a scientometric analysis of published papers on cardiac integrin adhesion complexes (IACs), including analysis of annual publications, disciplinary evolution, keyword co-occurrence, and literature co-citation.

Results

A total of 2,664 publications were finally included in the past 20 years. The United States is the largest contributor to the study and is leading this area of research globally. The journal Circulation Research attracts the largest number of high-quality publications. The study of IACs in cardiac repair/regenerative therapies involves multiple disciplines, particularly in materials science and developmental biology. Keywords of research frontiers were represented by Tenasin-C (2019-2023) and inflammation (2020-2023).

Conclusion

Integrins are topics with ongoing enthusiasm in biological development and tissue regeneration. The rapidly emerging role of matricellular proteins and non-protein components of the extracellular matrix (ECM) in regulating matrix structure and function may be a further breakthrough point in the future; the emerging role of IACs and their downstream molecular signaling in cardiac repair are also of great interest, such as induction of cardiac proliferation, differentiation, maturation, and metabolism, fibroblast activation, and inflammatory modulation.

Molecular Imaging of Heart Failure: An Update and Future Trends

Molecular imaging can detect and quantify pathophysiological processes underlying heart failure, complementing evaluation of cardiac structure and function with other imaging modalities. Targeted tracers have enabled assessment of various cellular and subcellular mechanisms of heart failure aiming for improved phenotyping, risk stratification, and personalized therapy. This review outlines the current status of molecular imaging in heart failure, accompanied with discussion on novel developments. The focus is on radionuclide methods with data from clinical studies. Imaging of myocardial metabolism can identify left ventricle dysfunction caused by myocardial ischemia that may be reversible after revascularization in the presence of viable myocardium. In vivo imaging of active inflammation and amyloid deposition have an established role in the detection of cardiac sarcoidosis and transthyretin amyloidosis. Innervation imaging has well documented prognostic value in predicting heart failure progression and arrhythmias. Tracers specific for inflammation, angiogenesis and myocardial fibrotic activity are in earlier stages of development, but have demonstrated potential value in early characterization of the response to myocardial injury and prediction of cardiac function over time. Early detection of disease activity is a key for transition from medical treatment of clinically overt heart failure towards a personalized approach aimed at supporting repair and preventing progressive cardiac dysfunction.

Imaging of Cardiac Fibrosis: How Far Have We Moved From Extracellular to Cellular?

Cardiovascular disease is the leading cause of morbidity and mortality worldwide. Myocardial fibrosis plays an important role in adverse outcomes such as heart failure and arrhythmias. As the pathological response and degree of scarring, and therefore clinical presentation varies from patient to patient, early detection of fibrosis is crucial for identifying the appropriate treatment approach and forecasting the progression of a disease along with the likelihood of disease-related mortality. Current imaging modalities provides information about either decreased function or extracellular signs of fibrosis. Targeting activated fibroblasts represents a burgeoning approach that could offer insights prior to observable functional alterations, presenting a promising focus for potential anti-fibrotic therapeutic interventions at cellular level. In this article, we provide an overview of imaging cardiac fibrosis and discuss the role of different advanced imaging modalities with the focus on novel non-invasive imaging of activated fibroblasts.

Imaging of Myocardial αvβ3 Integrin Expression for Evaluation of Myocardial Injury After Acute Myocardial Infarction

[68Ga]Ga-NODAGA-Arg-Gly-Asp (RGD) is a PET tracer targeting αvβ3 integrin, which is upregulated during angiogenesis soon after acute myocardial infarction (AMI). We prospectively evaluated determinants of myocardial uptake of [68Ga]Ga-NODAGA-RGD and its associations with left ventricular (LV) function in patients after AMI. Methods: Myocardial blood flow and [68Ga]Ga-NODAGA-RGD uptake (60 min after injection) were evaluated by PET in 31 patients 7.7 ± 3.8 d after primary percutaneous coronary intervention for ST-elevation AMI. Transthoracic echocardiography of LV function was performed on the day of PET and at the 6-mo follow-up. Results: PET images showed increased uptake of [68Ga]Ga-NODAGA-RGD in the ischemic area at risk (AAR), predominantly in injured myocardial segments. The SUV in the segment with the highest uptake (SUVmax) in the ischemic AAR was higher than the SUVmean of the remote myocardium (0.73 ± 0.16 vs. 0.51 ± 0.11, P < 0.001). Multivariable predictors of [68Ga]Ga-NODAGA-RGD uptake in the AAR included high peak N-terminal pro-B-type natriuretic peptide (P < 0.001), low LV ejection fraction, low global longitudinal strain (P = 0.01), and low longitudinal strain in the AAR (P = 0.01). [68Ga]Ga-NODAGA-RGD uptake corrected for myocardial blood flow and perfusable tissue fraction in the AAR predicted improvement in global longitudinal strain at follow-up (P = 0.002), independent of peak troponin, N-terminal pro-B-type natriuretic peptide, and LV ejection fraction. Conclusion: [68Ga]Ga-NODAGA-RGD uptake shows increased αvβ3 integrin expression in the ischemic AAR early after AMI that is associated with regional and global systolic dysfunction, as well as increased LV filling pressure. Increased [68Ga]Ga-NODAGA-RGD uptake predicts improvement of global LV function 6 mo after AMI.

Imaging of Angiogenesis in White Matter Hyperintensities

Background White matter hyperintensities (WMHs) are areas of increased signal intensity on T2-weighted magnetic resonance imaging (MRI). WMH penumbra may be a potential target for early intervention in WMHs. We explored the relationship between angiogenesis and WMH penumbra in patients with WMHs. Methods and Results Twenty-one patients with confluent WMHs of Fazekas grade ≥2 were included. All the participants underwent 68Ga-NOTA-PRGD2 positron emission tomography/magnetic resonance imaging. WMH penumbra was analyzed with masks created for the WMH and 7 normal-appearing white matter layers; each layer was dilated away from the WMH by 2 mm. Angiogenesis array and ELISA were used to detect the serum levels of angiogenic factors, inflammatory factors, HIF-1 alpha, and S100B. Fourteen patients with increased 68Ga-NOTA-PRGD2 maximum standardized uptake (>0.17) were classified into group 2. Seven patients with maximum standardized uptake ≤0.17 were classified as group 1. WMH volume and serum levels of integrin αvβ3, vascular endothelial growth factor receptor 22, and interleukin-1β tended to be higher in group 2 than in group 1. In group 2, 68Ga-NOTA-PRGD2 uptake was significantly increased at the border between the WMH and normal-appearing white matter than in WMHs (P=0.004). The structure penumbra, defined by fractional anisotropy, was wider in group 2 (8 mm) than in group 1 (2 mm). The cerebral blood flow penumbra was 12 mm in both groups. Angiogenesis showed a correlation with reduced cerebral blood flow and microstructure integrity. Conclusions Our study provides evidence that angiogenesis occurs in the WMH penumbra. Further studies are warranted to verify the effect of angiogenesis on WMH growth.

Nanotechnology in coronary heart disease

Coronary heart disease (CHD) is one of the major causes of death and disability worldwide, especially in low- and middle-income countries and among older populations. Conventional diagnostic and therapeutic approaches have limitations such as low sensitivity, high cost and side effects. Nanotechnology offers promising alternative strategies for the diagnosis and treatment of CHD by exploiting the unique properties of nanomaterials. In this review, we use bibliometric analysis to identify research hotspots in the application of nanotechnology in CHD and provide a comprehensive overview of the current state of the art. Nanomaterials with enhanced imaging and biosensing capabilities can improve the early detection of CHD through advanced contrast agents and high-resolution imaging techniques. Moreover, nanomaterials can facilitate targeted drug delivery, tissue engineering and modulation of inflammation and oxidative stress, thus addressing multiple aspects of CHD pathophysiology. We discuss the application of nanotechnology in CHD diagnosis (imaging and sensors) and treatment (regulation of macrophages, cardiac repair, anti-oxidative stress), and provide insights into future research directions and clinical translation. This review serves as a valuable resource for researchers and clinicians seeking to harness the potential of nanotechnology in the management of CHD. STATEMENT OF SIGNIFICANCE: Coronary heart disease (CHD) is the one of leading cause of death and disability worldwide. Nanotechnology offers new strategies for diagnosing and treating CHD by exploiting the unique properties of nanomaterials. This review uses bibliometric analysis to uncover research trends in the use of nanotechnology for CHD. We discuss the potential of nanomaterials for early CHD detection through advanced imaging and biosensing, targeted drug delivery, tissue engineering, and modulation of inflammation and oxidative stress. We also offer insights into future research directions and potential clinical applications. This work aims to guide researchers and clinicians in leveraging nanotechnology to improve CHD patient outcomes and quality of life.

[68Ga]Ga-NODAGA-E[(cRGDyK)]2 angiogenesis PET following myocardial infarction in an experimental rat model predicts cardiac functional parameters and development of heart failure

BACKGROUND

Angiogenesis has increasingly been a target for imaging and treatment over the last decade. The integrin αvβ3 is highly expressed in cells during angiogenesis and are therefore a promising target for imaging. In this study, we aimed to investigate the PET tracer [68Ga]Ga-RGD as a marker of angiogenesis following MI and its ability to predict cardiac functional parameters.

METHODS

First, the real-time interaction between [68Ga]Ga-RGD and integrin αvβ3 was investigated using surface plasmon resonance (SPR). Second, an animal study was performed to investigate the [68Ga]Ga-RGD uptake in the infarcted area after one and four weeks following MI in a rat model (MI = 68, sham surgery = 36). Finally, the specificity of the [68Ga]Ga-RGD tracer was evaluated ex vivo using histology, autoradiography, gamma counting and flow cytometry.

RESULTS

SPR showed that [68Ga]Ga-RGD has a high affinity for integrin αvβ3, forming a strong and stable binding. PET/CT showed a significantly higher uptake of [68Ga]Ga-RGD in the infarcted area compared to sham one week (p < 0.001) and four weeks (p < 0.001) after MI. The uptake of [68Ga]Ga-RGD after one week correlated to end diastolic volume (r = 0.74, p < 0.001) and ejection fraction (r = - 0.71, p < 0.001) after four weeks.

CONCLUSION

This study demonstrates that [68Ga]Ga-RGD has a high affinity for integrin αvβ3, which enables the evaluation of angiogenesis and remodeling. The [68Ga]Ga-RGD uptake after one week indicates that [68Ga]Ga-RGD may be used as an early predictor of cardiac functional parameters and possible development of heart failure after MI. These encouraging data supports the clinical translation and future use in MI patients.

Overview of the RGD-Based PET Agents Use in Patients With Cardiovascular Diseases: A Systematic Review

Studies using arginine–glycine–aspartate (RGD)-PET agents in cardiovascular diseases have been recently published. The aim of this systematic review was to perform an updated, evidence-based summary about the role of RGD-based PET agents in patients with cardiovascular diseases to better address future research in this setting. Original articles within the field of interest reporting the role of RGD-based PET agents in patients with cardiovascular diseases were eligible for inclusion in this systematic review. A systematic literature search of PubMed/MEDLINE and Cochrane library databases was performed until October 26, 2021. Literature shows an increasing role of RGD-based PET agents in patients with cardiovascular diseases. Overall, two main topics emerged: the infarcted myocardium and atherosclerosis. The existing studies support that α_vβ₃ integrin expression in the infarcted myocardium is well evident in RGD PET/CT scans. RGD-based PET radiotracers accumulate at the site of infarction as early as 3 days and seem to be peaking at 1–3 weeks post myocardial infarction before decreasing, but only 1 study assessed serial changes of myocardial RGD-based PET uptake after ischemic events. RGD-based PET uptake in large vessels showed correlation with CT plaque burden, and increased signal was found in patients with prior cardiovascular events. In human atherosclerotic carotid plaques, increased PET signal was observed in stenotic compared with non-stenotic areas based on MR or CT angiography data. Histopathological analysis found a co-localization between tracer accumulation and areas of α_vβ₃ expression. Promising applications using RGD-based PET agents are emerging, such as prediction of remodeling processes in the infarcted myocardium or detection of active atherosclerosis, with potentially significant clinical impact.

Prototype device for endoventricular beta-emitting radiotracer detection and molecularly-guided intervention

BACKGROUND

We have set out to develop a catheter-based theranostic system that: (a) identifies diseased and at-risk myocardium via endocardial detection of systemically delivered β-emitting radiotracers and (b) utilizes molecular signals to guide delivery of therapeutics to appropriate tissue via direct intramyocardial injection.

METHODS

Our prototype device consists of a miniature β-radiation detector contained within the tip of a flexible intravascular catheter. The catheter can be adapted to incorporate an injection port and retractable needle for therapeutic delivery. The performance of the β-detection catheter was assessed in vitro with various β-emitting radionuclides and ex vivo in hearts of pigs following systemic injection of 18F-fluorodeoxyglucose (18F-FDG) at 1-week post-myocardial infarction. Regional catheter-based endocardial measurements of 18F activity were compared to regional tissue activity from PET/CT images and gamma counting.

RESULTS

The β-detection catheter demonstrated sensitive in vitro detection of β-radiation from 22Na (β+), 18F (β+), and 204Tl (β-), with minimal sensitivity to γ-radiation. For 18F, the catheter demonstrated a sensitivity of 4067 counts/s/μCi in contact and a spatial resolution of 1.1 mm FWHM. Ex vivo measurements of endocardial 18F activity with the β-detection catheter in the chronic pig infarct model demonstrated good qualitative and quantitative correlation with regional tissue activity from PET/CT images and gamma counting.

CONCLUSION

The prototype β-detection catheter demonstrates sensitive and selective detection of β- and β+ emissions over a wide range of energies and enables high-fidelity ex vivo characterization of endocardial activity from systemically delivered 18F-FDG.

Positron Emission Tomography Techniques to Measure Active Inflammation, Fibrosis and Angiogenesis: Potential for Non-invasive Imaging of Hypertensive Heart Failure

Heart failure, which is responsible for a high number of deaths worldwide, can develop due to chronic hypertension. Heart failure can involve and progress through several different pathways, including: fibrosis, inflammation, and angiogenesis. Early and specific detection of changes in the myocardium during the transition to heart failure can be made via the use of molecular imaging techniques, including positron emission tomography (PET). Traditional cardiovascular PET techniques, such as myocardial perfusion imaging and sympathetic innervation imaging, have been established at the clinical level but are often lacking in pathway and target specificity that is important for assessment of heart failure. Therefore, there is a need to identify new PET imaging markers of inflammation, fibrosis and angiogenesis that could aid diagnosis, staging and treatment of hypertensive heart failure. This review will provide an overview of key mechanisms underlying hypertensive heart failure and will present the latest developments in PET probes for detection of cardiovascular inflammation, fibrosis and angiogenesis. Currently, selective PET probes for detection of angiogenesis remain elusive but promising PET probes for specific targeting of inflammation and fibrosis are rapidly progressing into clinical use.

Comparison of a New 68Ga-Radiolabelled PET Imaging Agent sCD146 and RGD Peptide for In Vivo Evaluation of Angiogenesis in Mouse Model of Myocardial Infarction

Ischemic vascular diseases are associated with elevated tissue expression of angiomotin (AMOT), a promising molecular target for PET imaging. On that basis, we developed an AMOT-targeting radiotracer, ⁶⁸Ga-sCD146 and performed the first in vivo evaluation on a myocardial infarction mice model and then, compared AMOT expression and α_vβ₃-integrin expression with ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ imaging. After myocardial infarction (MI) induced by permanent ligation of the left anterior descending coronary artery, myocardial perfusion was evaluated by Doppler ultrasound and by ¹⁸F-FDG PET imaging. ⁶⁸Ga-sCD146 and ⁶⁸Ga-RGD₂ PET imaging were performed. In myocardial infarction model, heart-to-muscle ratio of ⁶⁸Ga-sCD146 imaging showed a significantly higher radiotracer uptake in the infarcted area of MI animals than in sham (* p = 0.04). Interestingly, we also observed significant correlations between ⁶⁸Ga-sCD146 imaging and delayed residual perfusion assessed by ¹⁸F-FDG (* p = 0.04), with lowest tissue fibrosis assessed by histological staining (* p = 0.04) and with functional recovery assessed by ultrasound imaging (** p = 0.01). ⁶⁸Ga-sCD146 demonstrated an increase in AMOT expression after MI. Altogether, significant correlations of early post-ischemic ⁶⁸Ga-sCD146 uptake with late heart perfusion, lower tissue fibrosis and better functional recovery, make ⁶⁸Ga-sCD146 a promising radiotracer for tissue angiogenesis assessment after MI.

Association between [68Ga]NODAGA-RGDyK uptake and dynamics of angiogenesis in a human cell-based 3D model

Radiolabeled RGD peptides targeting expression of α_vβ₃ integrin have been applied to in vivo imaging of angiogenesis. However, there is a need for more information on the quantitative relationships between RGD peptide uptake and the dynamics of angiogenesis. In this study, we sought to measure the binding of [⁶⁸Ga]NODAGA-RGDyK to α_vβ₃ integrin in a human cell-based three-dimensional (3D) in vitro model of angiogenesis, and to compare the level of binding with the amount of angiogenesis. Experiments were conducted using a human cell-based 3D model of angiogenesis consisting of co-culture of human adipose stem cells (hASCs) and of human umbilical vein endothelial cells (HUVECs). Angiogenesis was induced with four concentrations (25%, 50%, 75%, and 100%) of growth factor cocktail resulting in a gradual increase in the density of the tubule network. Cultures were incubated with [⁶⁸Ga]NODAGA-RGDyK for 90 min at 37 °C, and binding of radioactivity was measured by gamma counting and digital autoradiography. The results revealed that tracer binding increased gradually with neovasculature density. In comparison with vessels induced with a growth factor concentration of 25%, the uptake of [⁶⁸Ga]NODAGA-RGDyK was higher at concentrations of 75% and 100%, and correlated with the amount of neovasculature, as determined by visual evaluation of histological staining. Uptake of [⁶⁸Ga]NODAGA-RGDyK closely reflected the amount of angiogenesis in an in vitro 3D model of angiogenesis. These results support further evaluation of RGD-based approaches for targeted imaging of angiogenesis.

PET Imaging of Post-infarct Myocardial Inflammation

PURPOSE OF REVIEW

To examine the use of positron emission tomography (PET) for imaging post-infarct myocardial inflammation and repair.

RECENT FINDINGS

Dysregulated immune responses after myocardial infarction are associated with adverse cardiac remodelling and an increased likelihood of ischaemic heart failure. PET imaging utilising novel tracers can be applied to visualise different components of the post-infarction inflammatory and repair processes. This approach could offer unique pathophysiological insights that could prove useful for the identification and risk-stratification of individuals who would ultimately benefit most from emerging immune-modulating therapies. PET imaging could also bridge the clinical translational gap as a surrogate measure of drug efficacy in early-stage clinical trials in patients with myocardial infarction. The use of hybrid PET/MR imaging, in particular, offers the additional advantage of simultaneous in vivo molecular imaging and detailed assessment of myocardial function, viability and tissue characterisation. Further research is needed to realise the true clinical translational value of PET imaging after myocardial infarction.

Imaging Inflammation with Positron Emission Tomography

The impact of inflammation on the outcome of many medical conditions such as cardiovascular diseases, neurological disorders, infections, cancer, and autoimmune diseases has been widely acknowledged. However, in contrast to neurological, oncologic, and cardiovascular disorders, imaging plays a minor role in research and management of inflammation. Imaging can provide insights into individual and temporospatial biology and grade of inflammation which can be of diagnostic, therapeutic, and prognostic value. There is therefore an urgent need to evaluate and understand current approaches and potential applications for imaging of inflammation. This review discusses radiotracers for positron emission tomography (PET) that have been used to image inflammation in cardiovascular diseases and other inflammatory conditions with a special emphasis on radiotracers that have already been successfully applied in clinical settings.

First report of 68Ga-PRGD2 PET/MRI molecular imaging of vaso-occlusion in a patient with sickle cell disease

Increased vascular cell adhesion (hyperadhesion) to the endothelium is responsible for the hallmark acute pain episodes, or vaso-occlusive crises (VOC), of sickle cell disease. The integrin α_vβ₃ plays an important role in VOC since it mediates sickle red blood cell adhesion to the endothelium, a process that leads to ischemia and painful bone infarction. In the pilot study presented herein, we hypothesized that real-time imaging of hyperadhesion could quantify VOC severity and identify the most vulnerable anatomical sites. We also hypothesized that harnessing hyperadhesion as a proximate event in VOC would provide sensitive, objective evidence of VOC before pain has developed. Specifically, we tested whether positron emission tomography (PET) imaging of integrin α_vβ₃ using the PET tracer ⁶⁸Ga-PRGD2 would successfully image hyperadhesion associated with VOC in a patient with sickle cell disease. We observed persistently higher tracer uptake in the femurs during VOC compared to baseline. In the vessel, after an initial and transient increase during VOC, blood pool activity was similar between baseline and VOC. These findings suggest that PET imaging of integrin α_vβ₃ may be a valuable strategy for imaging of VOC.

Multiparametric PET and MRI of myocardial damage after myocardial infarction: correlation of integrin αvβ3 expression and myocardial blood flow

Purpose

Increased angiogenesis after myocardial infarction is considered an important favorable prognostic parameter. The αvβ3 integrin is a key mediator of cell-cell and cell-matrix interactions and an important molecular target for imaging of neovasculature and repair processes after MI. Thus, imaging of αvβ3 expression might provide a novel biomarker for assessment of myocardial angiogenesis as a prognostic marker of left ventricular remodeling after MI. Currently, there is limited data available regarding the association of myocardial blood flow and αvβ3 integrin expression after myocardial infarction in humans.

Methods

Twelve patients were examined 31 ± 14 days after MI with PET/CT using [¹⁸F]Galacto-RGD and [¹³N]NH₃ and with cardiac MRI including late enhancement on the same day. Normal myocardium (remote) and areas of infarction (lesion) were identified on the [¹⁸F]Galacto-RGD PET/CT images by correlation with [¹³N]NH₃ PET and cardiac MRI. Lesion/liver-, lesion/blood-, and lesion/remote ratios were calculated. Blood flow and [¹⁸F]Galacto-RGD uptake were quantified and correlated for each myocardial segment (AHA 17-segment model).

Results

In 5 patients, increased [¹⁸F]Galacto-RGD uptake was notable within or adjacent to the infarction areas with a lesion/remote ratio of 46% (26–83%; lesion/blood 1.15 ± 0.06; lesion/liver 0.61 ± 0.18). [¹⁸F]Galacto-RGD uptake correlated significantly with infarct size (R = 0.73; p = 0.016). Moreover, it correlated significantly with restricted blood flow for all myocardial segments (R = − 0.39; p < 0.0001) and even stronger in severely hypoperfused areas (R = − 0.75; p < 0.0001).

Conclusion

[¹⁸F]Galacto-RGD PET/CT allows the visualization and quantification of myocardial αvβ3 expression as a key player in angiogenesis in a subset of patients after MI. αvβ3 expression was more pronounced in patients with larger infarcts and was generally more intense but not restricted to areas with more impaired blood flow, proving that tracer uptake was largely independent of unspecific perfusion effects. Based on these promising results, larger prospective studies are warranted to evaluate the potential of αvβ3 imaging for assessment of myocardial angiogenesis and prediction of ventricular remodeling.

Non-oncological applications of RGD-based single-photon emission tomography and positron emission tomography agents

INTRODUCTION

Non-invasive imaging techniques (especially single-photon emission tomography and positron emission tomography) apply several RGD-based imaging ligands developed during a vast number of preclinical and clinical investigations. The RGD (Arg-Gly-Asp) sequence is a binding moiety for a large selection of adhesive extracellular matrix and cell surface proteins. Since the first identification of this sequence as the shortest sequence required for recognition in fibronectin during the 1980s, fundamental research regarding the molecular mechanisms of integrin action have paved the way for development of several pharmaceuticals and radiopharmaceuticals with clinical applications. Ligands recognizing RGD may be developed for use in the monitoring of these interactions (benign or pathological). Although RGD-based molecular imaging has been actively investigated for oncological purposes, their utilization towards non-oncology applications remains relatively under-exploited.

METHODS AND SCOPE

This review highlights the new non-oncologic applications of RGD-based tracers (with the focus on single-photon emission tomography and positron emission tomography). The focus is on the last 10 years of scientific literature (2009-2020). It is proposed that these imaging agents will be used for off-label indications that may provide options for disease monitoring where there are no approved tracers available, for instance Crohn's disease or osteoporosis. Fundamental science investigations have made progress in elucidating the involvement of integrin in various diseases not pertaining to oncology. Furthermore, RGD-based radiopharmaceuticals have been evaluated extensively for safety during clinical evaluations of various natures.

CONCLUSION

Clinical translation of non-oncological applications for RGD-based radiopharmaceuticals and other imaging tracers without going through time-consuming extensive development is therefore highly plausible. Graphical abstract.

Imaging tools for assessment of myocardial fibrosis in humans: the need for greater detail

Myocardial fibrosis is recognized as a key pathological process in the development of cardiac disease and a target for future therapeutics. Despite this recognition, the assessment of fibrosis is not a part of routine clinical practice. This is primarily due to the difficulties in obtaining an accurate assessment of fibrosis non-invasively. Moreover, there is a clear discrepancy between the understandings of myocardial fibrosis clinically where fibrosis is predominately studied with comparatively low-resolution medical imaging technologies like MRI compared with the basic science laboratories where fibrosis can be visualized invasively with high resolution using molecularly specific fluorescence microscopes at the microscopic and nanoscopic scales. In this article, we will first review current medical imaging technologies for assessing fibrosis including echo and MRI. We will then highlight the need for greater microscopic and nanoscopic analysis of human tissue and how this can be addressed through greater utilization of human tissue available through endomyocardial biopsies and cardiac surgeries. We will then describe the relatively new field of molecular imaging that promises to translate research findings to the clinical practice by non-invasively monitoring the molecular signature of fibrosis in patients.

Review: PET imaging with macro- and middle-sized molecular probes

Recent progress in radiolabeling of macro- and middle-sized molecular probes has been extending possibilities to use PET molecular imaging for dynamic application to drug development and therapeutic evaluation. Theranostics concept also accelerated the use of macro- and middle-sized molecular probes for sharpening the contrast of proper target recognition even the cellular types/subtypes and proper selection of the patients who should be treated by the same molecules recognition. Here, brief summary of the present status of immuno-PET, and then further development of advanced technologies related to immuno-PET, peptidic PET probes, and nucleic acids PET probes are described.

A 64 Cu-porphyrin-based dual-modal molecular probe with integrin αv β3 targeting function for tumour imaging

Pyropheophorbide-a (Pyro) is a promising multifunctional molecule for multimodal tumour imaging and photodynamic therapy, but its clinical applications are seriously restricted by the limited tumour accumulation capability. Here, we designed and synthesized a small-molecule probe that achieved specific dual-modal tumour imaging based on Pyro. Briefly, a novel molecule combining Pyro, an RGD dimer peptide (3PRGD₂ ) and ⁶⁴ Cu, was designed and synthesized, and the obtained molecule, ⁶⁴ Cu-Pyro-3PRGD₂ , exhibited high tumour specificity in both positron emission tomography and optical imaging in vivo. c (RGDfk) peptide blocking significantly reduced the efficacy of the probe, which confirmed the integrin α_V β₃ targeting of this molecular probe. ⁶⁴ Cu-Pyro-3PRGD₂ had very low accumulation in normal organs and could be rapidly cleared through kidney metabolism, which prevented the potential damage to adjacent normal tissues. Overall, combining tumour targeting, dual-modal imaging, and biosafety, ⁶⁴ Cu-Pyro-3PRGD₂ has the potential for clinical use as a molecular imaging probe for tumour diagnosis.

Infection and Inflammation Imaging: Beyond FDG

This review discusses nuclear imaging of inflammation using molecular probes beyond fluoro-d-glucose, is structured by cellular targets, and focuses on those tracers that have been successfully applied clinically.

In vivo alpha-V beta-3 integrin expression in human aortic atherosclerosis

OBJECTIVES

Intraplaque angiogenesis and inflammation are key promoters of atherosclerosis and are mediated by the alpha-V beta-3 (αvβ3) integrin pathway. We investigated the applicability of the αvβ3-integrin receptor-selective positron emission tomography (PET) radiotracer 18F-fluciclatide in assessing human aortic atherosclerosis.

METHODS

Vascular 18F-fluciclatide binding was evaluated using ex vivo analysis of carotid endarterectomy samples with autoradiography and immunohistochemistry, and in vivo kinetic modelling following radiotracer administration. Forty-six subjects with a spectrum of atherosclerotic disease categorised as stable (n=27) or unstable (n=19; recent myocardial infarction) underwent PET and CT imaging of the thorax after administration of 229 (IQR 217-237) MBq 18F-fluciclatide. Thoracic aortic 18F-fluciclatide uptake was quantified on fused PET-CT images and corrected for blood-pool activity using the maximum tissue-to-background ratio (TBRmax). Aortic atherosclerotic burden was quantified by CT wall thickness, plaque volume and calcium scoring.

RESULTS

18F-Fluciclatide uptake co-localised with regions of increased αvβ3 integrin expression, and markers of inflammation and angiogenesis. 18F-Fluciclatide vascular uptake was confirmed in vivo using kinetic modelling, and on static imaging correlated with measures of aortic atherosclerotic burden: wall thickness (r=0.57, p=0.001), total plaque volume (r=0.56, p=0.001) and aortic CT calcium score (r=0.37, p=0.01). Patients with recent myocardial infarction had greater aortic 18F-fluciclatide uptake than those with stable disease (TBRmax 1.29 vs 1.21, p=0.02).

CONCLUSIONS

In vivo expression of αvβ3 integrin in human aortic atheroma is associated with plaque burden and is increased in patients with recent myocardial infarction. Quantification of αvβ3 integrin expression with 18F-fluciclatide PET has potential to assess plaque vulnerability and disease activity in atherosclerosis.

Molecular Imaging of the Heart

Multimodality cardiovascular imaging is routinely used to assess cardiac function, structure, and physiological parameters to facilitate the diagnosis, characterization, and phenotyping of numerous cardiovascular diseases (CVD), as well as allows for risk stratification and guidance in medical therapy decision-making. Although useful, these imaging strategies are unable to assess the underlying cellular and molecular processes that modulate pathophysiological changes. Over the last decade, there have been great advancements in imaging instrumentation and technology that have been paralleled by breakthroughs in probe development and image analysis. These advancements have been merged with discoveries in cellular/molecular cardiovascular biology to burgeon the field of cardiovascular molecular imaging. Cardiovascular molecular imaging aims to noninvasively detect and characterize underlying disease processes to facilitate early diagnosis, improve prognostication, and guide targeted therapy across the continuum of CVD. The most-widely used approaches for preclinical and clinical molecular imaging include radiotracers that allow for high-sensitivity in vivo detection and quantification of molecular processes with single photon emission computed tomography and positron emission tomography. This review will describe multimodality molecular imaging instrumentation along with established and novel molecular imaging targets and probes. We will highlight how molecular imaging has provided valuable insights in determining the underlying fundamental biology of a wide variety of CVDs, including: myocardial infarction, cardiac arrhythmias, and nonischemic and ischemic heart failure with reduced and preserved ejection fraction. In addition, the potential of molecular imaging to assist in the characterization and risk stratification of systemic diseases, such as amyloidosis and sarcoidosis will be discussed. © 2019 American Physiological Society. Compr Physiol 9:477-533, 2019.

Imaging Diagnosis of Transient Ischemic Attack in Clinic and Traditional Chinese Medicine

Neuroimaging plays a pivotal role in Transient Ischemic Attack (TIA). Generally, clinicians focus on the specific changes in morphology and function, but the diagnosis of TIA often depends on imaging evidence. Whereas Traditional Chinese Medicine (TCM) is concerned with the performance of clinical symptoms, they began to use imaging methods to diagnose TIA. CT and MRI are the recommended modality to diagnose TIA and image ischemic lesions. In addition, Transcranial Doppler sonography (TCD) and Digital Subtraction Angiography (DSA) are two acceptable alternatives for diagnosing TIA patients. This article elaborates the update of imaging modalities in clinic and the development of imaging modalities in TCM. Besides, multiple joint imaging technologies also will be evaluated whether enhanced diagnostic yields availably.

Radionuclide generators: the prospect of availing PET radiotracers to meet current clinical needs and future research demands

Targeted molecular imaging with positron emission tomography (PET) constitutes a successful technique for detecting and diagnosing disease conditions promptly and accurately, and for effectively prognosticating outcomes and treating patients with a tailored and more individualized intervention. In order to expand the success of PET in nuclear medicine, it is important to assure access to radiotracers of desired quantities and qualities. In this context, the benefit of accessing PET radiotracers through a radionuclide generator (RNG) cannot be overstated, as generators offer the potential of enriching the PET radiotracer arsenal at the medical centers both with and without onsite cyclotrons. While RNG technology to avail PET tracers is in its infancy, their use is expected to revitalize current PET practices and seems poised to broaden the palette of PET in nuclear medicine in the foreseeable future. In this review, we discuss the principles of RNGs, assess major parent/daughter pairs of interest for PET, RNGs currently in use in clinical PET, and identify the potentially useful RNGs which have made substantial progress or are likely to be used in daily clinical practices in the near future. Availability of the parent radionuclides required for PET RNGs is an important criterion and hence their production will also be reviewed. This overview outlines a critical assessment of RNGs to avail PET tracers, the contemporary status of RNGs, and key challenges and apertures to the near future.

Roles of blood-brain barrier integrins and extracellular matrix in stroke

Ischemicstroke is a leading cause of death and disability in the United States, but recent advances in treatments [i.e., endovascular thrombectomy and tissue plasminogen activator (t-PA)] that target the stroke-causing blood clot, while improving overall stroke mortality rates, have had much less of an impact on overall stroke morbidity. This may in part be attributed to the lack of therapeutics targeting reperfusion-induced injury after the blood clot has been removed, which, if left unchecked, can expand injury from its core into the surrounding at risk tissue (penumbra). This occurs in two phases of increased permeability of the blood-brain barrier, a physical barrier that under physiologic conditions regulates brain influx and efflux of substances and consists of tight junction forming endothelial cells (and transporter proteins), astrocytes, pericytes, extracellular matrix, and their integrin cellular receptors. During, embryonic development, maturity, and following stroke reperfusion, cerebral vasculature undergoes significant changes including changes in expression of integrins and degradation of surrounding extracellular matrix. Integrins, heterodimers with α and β subunits, and their extracellular matrix ligands, a collection of proteoglycans, glycoproteins, and collagens, have been modestly studied in the context of stroke compared with other diseases (e.g., cancer). In this review, we describe the effect that various integrins and extracellular matrix components have in embryonic brain development, and how this changes in both maturity and in the poststroke environment. Particular focus will be on how these changes in integrins and the extracellular matrix affect blood-brain barrier components and their potential as diagnostic and therapeutic targets for ischemic stroke.

3D Fusion Framework for Infarction and Angiogenesis Analysis in a Myocardial Infarct Minipig Model

The combination of different modality images can provide detailed and comprehensive information for the prognostic assessment and therapeutic strategy of patients with ischemic heart disease. In this study, a 3D fusion framework is designed to integrate coronary computed tomography (CT) angiography (CTA), 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]DG) positron emission tomography (PET)/CT, and [⁶⁸Ga]-1,4,7-triazacyclononane-1,4,7-triacetic acid-(Arg-Gly-Asp)2 ([⁶⁸Ga]-NOTA-PRGD2) PET/CT images of the myocardial infarction model in minipigs. First, the structural anatomy of the heart in coronary CTA and CT is segmented using a multi-atlas-based method. Then, the hearts are registered using the B-spline-based free form deformation. Finally, the [¹⁸F]DG and [⁶⁸Ga]-NOTA-PRGD2 signals are mapped into the heart in coronary CTA, which produces a single fusion image to delineate both the cardiac structural anatomy and the functional information of myocardial viability and angiogenesis. Heart segmentation demonstrates high accuracy with good agreement between manual delineation and automatic segmentation. The fusion result intuitively reflects the extent of the [¹⁸F]DG uptake defect as well as the location where the [⁶⁸Ga]-NOTA-PRGD2 signal appears. The fusion result verified the occurrence of angiogenesis based on the in vivo noninvasive molecular imaging approach. The presented framework is helpful in facilitating the study of the relationship between infarct territories and blocked coronary arteries as well as angiogenesis.

Imaging angiogenesis using 68Ga-NOTA-PRGD2 positron emission tomography/computed tomography in patients with severe intracranial atherosclerotic disease

Angiogenesis is a critical compensation route, which has been demonstrated in the brain following ischemic stroke; however, few studies have investigated angiogenesis in chronic intracranial atherosclerosis disease (ICAD). We used ⁶⁸Ga-NOTA-PRGD2 positron emission tomography/computed tomography based imaging to detect angiogenesis in chronic ICAD and to explore the factors that may have affected it. A total of 21 participants with unilateral severe chronic ICAD were included in the study. Of the 21 participants, 19 were men; the mean (SD) age was 52 (15) years. In 18 participants, we observed elevated ⁶⁸Ga-NOTA-PRGD2 uptake in the peri-infarct, subcortical, and periventricular regions of the lesioned side, with a higher ⁶⁸Ga-NOTA-PRGD2 SUV_max compared to that in the contralateral hemisphere (0.15 vs. 0.06, p=0.001). The ¹⁸F-FDG PET SUV_max was significantly lower on the lesioned side (11.28 vs. 13.92, p=0.001). Subgroup analyses revealed that the recent group (<6 months) had a higher lesion-to-contralateral region ratio SUV_max than the remote group (>6 months) (6.73 vs. 2.36, p<0.05). Our results provide molecular imaging evidence of angiogenesis in patients with severe chronic ICAD. Furthermore, the extent of angiogenesis in chronic ICAD may be affected by the post-qualified event time interval, and not by infarction itself or the severity of the arterial lesion.

Imaging of αvβ3 integrin expression in experimental myocardial ischemia with [68Ga]NODAGA-RGD positron emission tomography

Background

Radiolabeled RGD peptides detect α_vβ₃ integrin expression associated with angiogenesis and extracellular matrix remodeling after myocardial infarction. We studied whether cardiac positron emission tomography (PET) with [⁶⁸Ga]NODAGA-RGD detects increased α_vβ₃ integrin expression after induction of flow-limiting coronary stenosis in pigs, and whether α_vβ₃ integrin is expressed in viable ischemic or injured myocardium.

Methods

We studied 8 Finnish landrace pigs 13 ± 4 days after percutaneous implantation of a bottleneck stent in the proximal left anterior descending coronary artery. Antithrombotic therapy was used to prevent stent occlusion. Myocardial uptake of [⁶⁸Ga]NODAGA-RGD (290 ± 31 MBq) was evaluated by a 62 min dynamic PET scan. The ischemic area was defined as the regional perfusion abnormality during adenosine-induced stress by [¹⁵O]water PET. Guided by triphenyltetrazolium chloride staining, tissue samples from viable and injured myocardial areas were obtained for autoradiography and histology.

Results

Stent implantation resulted in a partly reversible myocardial perfusion abnormality. Compared with remote myocardium, [⁶⁸Ga]NODAGA-RGD PET showed increased tracer uptake in the ischemic area (ischemic-to-remote ratio 1.3 ± 0.20, p = 0.0034). Tissue samples from the injured areas, but not from the viable ischemic areas, showed higher [⁶⁸Ga]NODAGA-RGD uptake than the remote non-ischemic myocardium. Uptake of [⁶⁸Ga]NODAGA-RGD correlated with immunohistochemical detection of α_vβ₃ integrin that was expressed in the injured myocardial areas.

Conclusions

Cardiac [⁶⁸Ga]NODAGA-RGD PET demonstrates increased myocardial α_vβ₃ integrin expression after induction of flow-limiting coronary stenosis in pigs. Localization of [⁶⁸Ga]NODAGA-RGD uptake indicates that it reflects α_vβ₃ integrin expression associated with repair of recent myocardial injury.

First in-human radiation dosimetry of 68Ga-NODAGA-RGDyK

Background

Integrin-targeting radiopharmaceuticals have potential broad applications, spanning from cancer theranostics to cardiovascular diseases. We have previously reported preclinical dosimetry results of ⁶⁸Ga-NODAGA-RGDyK in mice. This study presents the first human dosimetry of ⁶⁸Ga-NODAGA-RGDyK in the five consecutive patients included in a clinical imaging protocol of carotid atherosclerotic plaques. Five male patients underwent whole-body time-of-flight (TOF) PET/CT scans 10, 60 and 120 min after tracer injection (200 MBq). Quantification of ⁶⁸Ga activity concentration was first validated by a phantom study. To be used as input in OLINDA/EXM, time-activity curves were derived from manually drawn regions of interest over the following organs: brain, thyroid, lungs, heart, liver, spleen, stomach, kidneys, red marrow, pancreas, small intestine, colon, urinary bladder and whole body. A separate dosimetric analysis was performed for the choroid plexuses. Female dosimetry was extrapolated from male data. Effective doses (EDs) were estimated according to both ICRP60 and ICRP103 assuming 30-min and 1-h voiding cycles.

Results

The body regions receiving the highest dose were urinary bladder, kidneys and choroid plexuses. For a 30-min voiding cycle, the EDs were 15.7 and 16.5 μSv/MBq according to ICRP60 and ICRP103, respectively. The extrapolation to female dosimetry resulted in organ absorbed doses 17% higher than those of male patients, on average.

The 1-h voiding cycle extrapolation resulted in EDs of 19.3 and 19.8 μSv/MBq according to ICRP60 and ICRP103, respectively. A comparison is made with previous mouse dosimetry and with other human studies employing different RGD-based radiopharmaceuticals.

Conclusions

According to ICRP60/ICRP103 recommendations, an injection of 200 MBq ⁶⁸Ga-NODAGA-RGDyK leads to an ED in man of 3.86/3.92 mSv. For future therapeutic applications, specific attention should be directed to delivered dose to kidneys and potentially also to the choroid plexuses.

Trial registration

Clinical trial.gov, NCT01608516

Cardiac αVβ3 integrin expression following acute myocardial infarction in humans

Objective

Maladaptive repair contributes towards the development of heart failure following myocardial infarction (MI). The α_vβ₃ integrin receptor is a key mediator and determinant of cardiac repair. We aimed to establish whether α_vβ₃ integrin expression determines myocardial recovery following MI.

Methods

¹⁸F-Fluciclatide (a novel α_vβ₃-selective radiotracer) positron emission tomography (PET) and CT imaging and gadolinium-enhanced MRI (CMR) were performed in 21 patients 2 weeks after ST-segment elevation MI (anterior, n=16; lateral, n=4; inferior, n=1). CMR was repeated 9 months after MI. 7 stable patients with chronic total occlusion (CTO) of a major coronary vessel and nine healthy volunteers underwent a single PET/CT and CMR.

Results

¹⁸F-Fluciclatide uptake was increased at sites of acute infarction compared with remote myocardium (tissue-to-background ratio (TBR_mean) 1.34±0.22 vs 0.85±0.17; p<0.001) and myocardium of healthy volunteers (TBR_mean 1.34±0.22 vs 0.70±0.03; p<0.001). There was no ¹⁸F-fluciclatide uptake at sites of established prior infarction in patients with CTO, with activity similar to the myocardium of healthy volunteers (TBR_mean 0.71±0.06 vs 0.70±0.03, p=0.83). ¹⁸F-Fluciclatide uptake occurred at sites of regional wall hypokinesia (wall motion index≥1 vs 0; TBR_mean 0.93±0.31 vs 0.80±0.26 respectively, p<0.001) and subendocardial infarction. Importantly, although there was no correlation with infarct size (r=0.03, p=0.90) or inflammation (C reactive protein, r=−0.20, p=0.38), ¹⁸F-fluciclatide uptake was increased in segments displaying functional recovery (TBR_mean 0.95±0.33 vs 0.81±0.27, p=0.002) and associated with increase in probability of regional recovery.

Conclusion

¹⁸F-Fluciclatide uptake is increased at sites of recent MI acting as a biomarker of cardiac repair and predicting regions of recovery.

Trial registration number

NCT01813045; Post-results.

Molecular Imaging of Angiogenesis in Cardiac Regeneration

PURPOSE OF REVIEW

Myocardial infarction (MI) leading to heart failure displays an important cause of death worldwide. Adequate restoration of blood flow to prevent this transition is a crucial factor to improve long-term morbidity and mortality. Novel regenerative therapies have been thoroughly investigated within the past decades.

RECENT FINDINGS

Increased angiogenesis in infarcted myocardium has shown beneficial effects on the prognosis of MI; therefore, the proangiogenic capacity of currently tested treatments is of specific interest. Molecular imaging to visualize formation of new blood vessels in vivo displays a promising option to monitor proangiogenic effects of regenerative substances.

SUMMARY

Based on encouraging results in preclinical models, molecular angiogenesis imaging has recently been applied in a small set of patients. This article reviews recent literature on noninvasive in vivo molecular imaging of angiogenesis after MI as an integral part of cardiac regeneration.

SPECT and PET imaging of angiogenesis and arteriogenesis in pre-clinical models of myocardial ischemia and peripheral vascular disease

Purpose

The extent of neovascularization determines the clinical outcome of coronary artery disease and other occlusive cardiovascular disorders. Monitoring of neovascularization is therefore highly important. This review article will elaborately discuss preclinical studies aimed at validating new nuclear angiogenesis and arteriogenesis tracers. Additionally, we will briefly address possible obstacles that should be considered when designing an arteriogenesis radiotracer.

Methods

A structured medline search was the base of this review, which gives an overview on different radiopharmaceuticals that have been evaluated in preclinical models.

Results

Neovascularization is a collective term used to indicate different processes such as angiogenesis and arteriogenesis. However, while it is assumed that sensitive detection through nuclear imaging will facilitate translation of successful therapeutic interventions in preclinical models to the bedside, we still lack specific tracers for neovascularization imaging. Most nuclear imaging research to date has focused on angiogenesis, leaving nuclear arteriogenesis imaging largely overlooked.

Conclusion

Although angiogenesis is the process which is best understood, there is no scarcity in theoretical targets for arteriogenesis imaging.

Angiogenesis PET Tracer Uptake ((68)Ga-NODAGA-E[(cRGDyK)]₂) in Induced Myocardial Infarction in Minipigs

Angiogenesis is part of the healing process following an ischemic injury and is vital for the post-ischemic repair of the myocardium. Therefore, it is of particular interest to be able to noninvasively monitor angiogenesis. This might, not only permit risk stratification of patients following myocardial infarction, but could also facilitate development and improvement of new therapies directed towards stimulation of the angiogenic response. During angiogenesis endothelial cells must adhere to one another to form new microvessels. αvβ₃ integrin has been found to be highly expressed in activated endothelial cells and has been identified as a critical modulator of angiogenesis. (68)Ga-NODAGA-E[c(RGDyK)]₂ (RGD) has recently been developed by us as an angiogenesis positron-emission-tomography (PET) ligand targeted towards αvβ₃ integrin. In the present study, we induced myocardial infarction in Göttingen minipigs. Successful infarction was documented by (82)Rubidium-dipyridamole stress PET and computed tomography. RGD uptake was demonstrated in the infarcted myocardium one week and one month after induction of infarction by RGD-PET. In conclusion, we demonstrated angiogenesis by noninvasive imaging using RGD-PET in minipigs hearts, which resemble human hearts. The perspectives are very intriguing and might permit the evaluation of new treatment strategies targeted towards increasing the angiogenetic response, e.g., stem-cell treatment.

Clinical Application of Radiolabeled RGD Peptides for PET Imaging of Integrin αvβ3

Molecular imaging for non-invasive assessment of angiogenesisis is of great interest for clinicians because of the wide-spread application of anti-angiogenic cancer therapeutics. Besides, many other interventions that involve the change of blood vessel/tumor microenvironment would also benefit from such imaging strategies. Of the imaging techniques that target angiogenesis, radiolabeled Arg-Gly-Asp (RGD) peptides have been a major focus because of their high affinity and selectivity for integrin α_vβ₃--one of the most extensively examined target of angiogenesis. Since the level of integrin α_vβ₃ expression has been established as a surrogate marker of angiogenic activity, imaging α_vβ₃ expression can potentially be used as an early indicator of effectiveness of antiangiogenic therapy at the molecular level. In this review, we summarize RGD-based PET tracers that have already been used in clinical trials and intercompared them in terms of radiosynthesis, dosimetry, pharmacokinetics and clinical applications. A perspective of their future use in the clinic is also provided.

The role of molecular imaging in the evaluation of myocardial and peripheral angiogenesis

Angiogenesis, or the formation of new microvasculature, is a physiological process that may occur in the setting of chronic tissue ischemia and can play an important role in improving tissue perfusion and blood flow following myocardial infarction or in the presence of peripheral vascular disease (PVD). Molecular imaging of angiogenesis within the cardiovascular system is a developing field of study. Targeted imaging of angiogenesis has the potential for non-invasive assessment of the underlying molecular signaling events associated with the angiogenic process and, when applied in conjunction with physiological perfusion imaging, may be utilized to predict and evaluate clinical outcomes in the setting of ischemic heart disease or PVD. This review discusses the developing radiotracer-based imaging techniques and technology currently in use that possess potential for clinical translation, with specific focus on PET and SPECT imaging of myocardial and peripheral angiogenesis.