Simultaneous positron emission tomography and magnetic resonance imaging (PET‐MRI) combines the anatomical detail and tissue characterization of MRI with the functional information from PET. Within the coronary arteries, this hybrid technique can be used to identify biological activity combined with anatomically high‐risk plaque features to better understand the processes underlying coronary atherosclerosis. Furthermore, the downstream effects of coronary artery disease on the myocardium can be characterized by providing information on myocardial perfusion, viability, and function. This review will describe the current capabilities of PET‐MRI in coronary artery disease and discuss the limitations and future directions of this emerging technique.Level of Evidence5Technical EfficacyStage 3
The identification of intracoronary thrombus and atherothrombosis is central to the diagnosis of acute myocardial infarction, with the differentiation between type 1 and type 2 myocardial infarction being crucial for immediate patient management. Invasive coronary angiography has remained the principal imaging modality used in the investigation of patients with myocardial infarction. More recently developed invasive intravascular imaging approaches, such as angioscopy, intravascular ultrasound and optical coherence tomography, can be used as adjunctive imaging modalities to provide more direct visualisation of coronary atheroma and the causes of myocardial infarction as well as to improve the sensitivity of thrombus detection. However, these invasive approaches have practical and logistic constraints that limit their widespread and routine application. Non-invasive angiographic techniques, such as CT and MRI, have become more widely available and have improved the non-invasive visualisation of coronary artery disease. Although they also have a limited ability to reliably identify intracoronary thrombus, this can be overcome by combining their anatomical and structural characterisation of coronary anatomy with positron emission tomography. Specific radiotracers which bind with high specificity and sensitivity to components of thrombus, such as activated platelets, fibrin and factor XIIIa, hold promise for the non-invasive detection of intracoronary thrombus. The development of these novel non-invasive approaches has the potential to inform clinical decision making and patient management as well as to provide a non-invasive technique to assess the efficacy of novel antithrombotic therapies or interventional strategies. However, these have yet to be realised in routine clinical practice.
BACKGROUND: 18 F-GP1 is a novel positron-emitting radiotracer that is highly specific for activated platelets and thrombus. In a proof-of-concept study, we aimed to determine its potential clinical application in establishing the role and origin of thrombus in ischemic stroke. METHODS: Eleven patients with recent ischemic stroke (n=9) or transient ischemic attack (n=2) underwent 18 F-GP1 positron emission tomography and computed tomography angiography at a median of 11 (range, 2–21) days from symptom onset. 18 F-GP1 uptake (maximum target-to-background ratio) was assessed in the carotid arteries and brain. RESULTS: 18 F-GP1 uptake was identified in 10 of 11 patients: 4 in the carotid arteries only, 3 in the brain only, and 3 in both the brain and carotid arteries. In those with carotid uptake, 4 participants had >50% stenosis and 3 had nonstenotic disease. One case had bilateral stenotic disease (>70%), but only the culprit carotid artery demonstrated 18 F-GP1 uptake. The average uptake was higher in the culprit (median maximum target-to-background ratio, 1.55 [interquartile range, 1.26–1.82]) compared with the contralateral nonculprit carotid artery (maximum target-to-background ratio, 1.22 [1.19–1.6]). In those with brain 18 F-GP1 uptake (maximum target-to-background ratio, 6.45 [4.89–7.65]), areas of acute infarction on computed tomography correlated with brain 18 F-GP1 uptake in 6 cases. Ex vivo autoradiography of postmortem infarcted brain tissue showed focal uptake corresponding to intraluminal thrombus within the culprit vessel and downstream microvasculature. There was also evidence of diffuse uptake within some of the infarcted brain tissue reflecting parenchymal petechial hemorrhage. CONCLUSIONS: 18 F-GP1 positron emission tomography and computed tomography angiography is a novel noninvasive method of identifying in vivo cerebrovascular thrombosis, which holds major promise in understanding the role and origin of thrombosis in stroke. REGISTRATION: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT03943966.
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