Noninvasive In Vivo Thrombus Imaging in Patients With Ischemic Stroke or Transient Ischemic Attack-Brief Report

Long Axial Field of View PET/CT: Technical Aspects in Cardiovascular Diseases

Positron emission tomography / computed tomography (PET/CT) plays a pivotal role in the assessment of cardiovascular diseases (CVD), particularly in the context of ischemic heart disease. Nevertheless, its application in other forms of CVD, such as infiltrative, infectious, or inflammatory conditions, remains limited. Recently, PET/CT systems with an extended axial field of view (LAFOV) have been developed, offering greater anatomical coverage and significantly enhanced PET sensitivity. These advancements enable head-to-pelvis imaging with a single bed position, and in systems with an axial field of view (FOV) of approximately 2 meters, even total body (TB) imaging is feasible in a single scan session. The application of LAFOV PET/CT in CVD presents a promising opportunity to improve systemic cardiovascular assessments and address the limitations inherent to conventional short axial field of view (SAFOV) devices. However, several technical challenges, including procedural considerations for LAFOV systems in CVD, complexities in data processing, arterial input function extraction, and artefact management, have not been fully explored. This review aims to discuss the technical aspects of LAFOV PET/CT in relation to CVD by highlighting key opportunities and challenges and examining the impact of these factors on the evaluation of most relevant CVD.

Quantification of carotid artery plaque and peri-vascular adipose tissue attenuation on computed tomography

Aims

Quantitative assessment of carotid artery plaque on computed tomography (CT) may identify high-risk phenotypes associated with culprit lesions and subsequent ischaemic stroke or transient ischaemic attack.

Methods and results

Carotid CT angiography was performed in 48 patients with acute ischaemic stroke or transient ischaemic attack within 21 days. Quantitative plaque assessment was performed in the proximal 6 cm of the internal and external carotid artery, distal 6 cm of the common carotid artery, and residual common carotid artery. Semi-automated quantification included assessment of non-calcified, calcified, low-attenuation, and total plaque, area and diameter stenosis, and peri-vascular adipose tissue attenuation. In 48 patients (mean age 71 ± 11 years, 67% male), 96 vessels were assessed with 30 (31%) identified as culprit vessels. Culprit internal carotid arteries had greater area [83 (65, 94) vs. 64 (55, 77)%] and diameter [56 (39, 74) vs. 32 (21, 48)%] stenosis and more non-calcified [563 (413, 965) vs. 428 (283 649) mm3, P = 0.04], low-attenuation [33.7 (6.9, 72.4) vs. 16.3 (3.35, 54.3) mm3, P = 0.01], and total [699 (455, 1057) vs. 492 (311, 809), P = 0.04] plaque. There was no difference in calcified plaque or peri-vascular adipose tissue attenuation between culprit and non-culprit internal carotid arteries. There were no differences in quantitative plaque or peri-vascular adipose tissue attenuation in the external carotid artery or common carotid artery.

Conclusion

Carotid atherosclerotic plaque characteristics are the principal features associated with culprit plaques with little or no demonstrable relationship with calcified plaque or increased peri-vascular adipose tissue attenuation.

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 SUVmax and TBRmax measurements (all ≥ 0.92). Coronary artery and brain parenchymal analyses showed the strongest agreement in SUVmax 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 SUVmax and TBRmax measurements (all ≥ 0.89). The strongest interobserver agreement was seen with brain parenchymal SUVmax (mean SUVmax 1.95 ± 0.94) and TBRmax (mean TBRmax 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.

Translational molecular imaging: Thrombosis imaging with positron emission tomography

A key focus of cardiovascular medicine is the detection, treatment, and prevention of disease, with a move towards more personalized and patient-centred treatments. To achieve this goal, novel imaging approaches that allow for early and accurate detection of disease and risk stratification are needed. At present, the diagnosis, monitoring, and prognostication of thrombotic cardiovascular diseases are based on imaging techniques that measure changes in structural anatomy and biological function. Molecular imaging is emerging as a new tool for the non-invasive detection of biological processes, such as thrombosis, that can improve identification of these events above and beyond current imaging modalities. At the forefront of these evolving techniques is the use of high-sensitivity radiotracers in conjunction with positron emission tomography imaging that could revolutionise current diagnostic paradigms by improving our understanding of the role and origin of thrombosis in a range of cardiovascular diseases.