Qualitative and quantitative analysis of 18F-GP1 positron emission tomography in thrombotic cardiovascular disease

¹⁸F-GP1 is a novel highly specific radiotracer that binds to activated platelets and thrombus. We aimed to establish the observer repeatability of coronary, carotid and cerebral ¹⁸F-GP1 uptake in patients presenting with acute myocardial infarction or ischaemic stroke. Forty-three patients presenting with acute myocardial infarction or ischaemic stroke underwent hybrid positron emission tomography (PET) and computed tomography (CT) angiography. Qualitative and quantitative assessment of ¹⁸F-GP1 uptake was performed on coronary arteries, carotid arteries and brain parenchyma. Qualitative uptake of ¹⁸F-GP1 had excellent intraobserver and interobserver agreement, with complete agreement for the presence or absence of visual ¹⁸F-GP1 uptake. For quantitative analysis, there were excellent intraclass correlation coefficients for intraobserver repeatability for coronary artery, carotid artery and brain parenchymal SUV_max and TBR_max measurements (all ≥ 0.92). Coronary artery and brain parenchymal analyses showed the strongest agreement in SUV_max values with mean biases of - 0.04 (limits of agreement - 0.21 to 0.20) and 0.02 (limits of agreement - 0.29 to 0.32) respectively. There was good interclass correlation coefficients for interobserver repeatability for coronary artery, carotid artery and brain parenchymal SUV_max and TBR_max measurements (all ≥ 0.89). The strongest interobserver agreement was seen with brain parenchymal SUV_max (mean SUV_max 1.95 ± 0.94) and TBR_max (mean TBR_max 9.55 ± 6.56) with mean biases of - 0.05 (limits of agreement - 0.37 to 0.27) and 0.04 (limits of agreement - 0.59 to 0.52) respectively. Visual qualitative and quantitative ¹⁸F-GP1 PET-CT image analyses provide robust and repeatable measurements of activated platelets and thrombi within the coronary arteries, carotid arteries and brain parenchyma.