PET/CT challenge for the non-invasive diagnosis of coronary artery disease

Recent technologies in cardiac imaging

Cardiac imaging allows physicians to view the structure and function of the heart to detect various heart abnormalities, ranging from inefficiencies in contraction, regulation of volumetric input and output of blood, deficits in valve function and structure, accumulation of plaque in arteries, and more. Commonly used cardiovascular imaging techniques include x-ray, computed tomography (CT), magnetic resonance imaging (MRI), echocardiogram, and positron emission tomography (PET)/single-photon emission computed tomography (SPECT). More recently, even more tools are at our disposal for investigating the heart's physiology, performance, structure, and function due to technological advancements. This review study summarizes cardiac imaging techniques with a particular interest in MRI and CT, noting each tool's origin, benefits, downfalls, clinical application, and advancement of cardiac imaging in the near future.

High-risk plaque features can be detected in non-stenotic carotid plaques of patients with ischaemic stroke classified as cryptogenic using combined (18)F-FDG PET/MR imaging

PURPOSE

The aim of this study was to investigate in 18 patients with ischaemic stroke classified as cryptogenic and presenting non-stenotic carotid atherosclerotic plaques the morphological and biological aspects of these plaques with magnetic resonance imaging (MRI) and (18)F-fluoro-deoxyglucose positron emission tomography ((18)F-FDG PET) imaging.

METHODS

Carotid arteries were imaged 150 min after injection of (18)F-FDG with a combined PET/MRI system. American Heart Association (AHA) lesion type and plaque composition were determined on consecutive MRI axial sections (n = 460) in both carotid arteries. (18)F-FDG uptake in carotid arteries was quantified using tissue to background ratio (TBR) on corresponding PET sections.

RESULTS

The prevalence of complicated atherosclerotic plaques (AHA lesion type VI) detected with high-resolution MRI was significantly higher in the carotid artery ipsilateral to the ischaemic stroke as compared to the contralateral side (39 vs 0 %; p = 0.001). For all other AHA lesion types, no significant differences were found between ipsilateral and contralateral sides. In addition, atherosclerotic plaques classified as high-risk lesions with MRI (AHA lesion type VI) were associated with higher (18)F-FDG uptake in comparison with other AHA lesions (TBR = 3.43 ± 1.13 vs 2.41 ± 0.84, respectively; p < 0.001). Furthermore, patients presenting at least one complicated lesion (AHA lesion type VI) with MRI showed significantly higher (18)F-FDG uptake in both carotid arteries (ipsilateral and contralateral to the stroke) in comparison with carotid arteries of patients showing no complicated lesion with MRI (mean TBR = 3.18 ± 1.26 and 2.80 ± 0.94 vs 2.19 ± 0.57, respectively; p < 0.05) in favour of a diffuse inflammatory process along both carotid arteries associated with complicated plaques.

CONCLUSION

Morphological and biological features of high-risk plaques can be detected with (18)F-FDG PET/MRI in non-stenotic atherosclerotic plaques ipsilateral to the stroke, suggesting a causal role for these plaques in stroke. Combined (18)F-FDG PET/MRI systems might help in the evaluation of patients with ischaemic stroke classified as cryptogenic.

Value of Hybrid Imaging with PET/CT to Guide Percutaneous Revascularization of Chronic Total Coronary Occlusion

Chronic total coronary occlusions (CTO) are documented in approximately one fifth of diagnostic invasive coronary angiographies (ICA). Percutaneous coronary interventions (PCI) of CTO are challenging and are accompanied by higher complication and lower success rates in comparison with non-CTO PCI. Scrutinous evaluation of ischemia and viability to justify percutaneous revascularization is therefore of importance to select eligible patients for such a procedure. Furthermore, knowledge of the anatomical features of the occlusion may predict the chances of success of PCI CTO and could even guide the procedural strategy to augment the likelihood of recanalization. Positron emission tomography (PET) is unequivocally accepted as the reference standard for ischemia and viability testing, whereas coronary computed tomography angiography (CCTA) currently allows for non-invasive detailed three-dimensional imaging of the coronary anatomy that adds morphological information over two-dimensional ICA. Hybrid PET/CT could therefore be useful for optimal patient selection as well as procedural planning. This review discusses the potential value of PET/CT to guide PCI in CTOs.

Biomechanical rationale of coronary artery bypass grafting of multivessel disease

The biomechanical model of human coronary arteries was modified for improving the quality of diagnosis and surgical treatment for coronary heart disease. The problem of hemodynamics in the left coronary artery with multivessel bed disease - 45% stenosis of the anterior descending branch and 75% stenosis of the circumflex branch - was particularly considered. Numerical simulation of the coronary arterial bypass of the main trunk was carried out to estimate the functional condition of the coronary arteries after restoring myocardial blood supply by surgery.

Advanced tracers in PET imaging of cardiovascular disease

Cardiovascular disease is the leading cause of death worldwide. Molecular imaging with targeted tracers by positron emission tomography (PET) allows for the noninvasive detection and characterization of biological changes at the molecular level, leading to earlier disease detection, objective monitoring of therapies, and better prognostication of cardiovascular diseases progression. Here we review, the current role of PET in cardiovascular disease, with emphasize on tracers developed for PET imaging of cardiovascular diseases.

Myocardial perfusion imaging with PET

PET-myocardial perfusion imaging (MPI) allows accurate measurement of myocardial perfusion, absolute myocardial blood flow and function at stress and rest in a single study session performed in approximately 30 min. Various PET tracers are available for MPI, and rubidium-82 or nitrogen-13-ammonia is most commonly used. In addition, a new fluorine-18-based PET-MPI tracer is currently being evaluated. Relative quantification of PET perfusion images shows very high diagnostic accuracy for detection of obstructive coronary artery disease. Dynamic myocardial blood flow analysis has demonstrated additional prognostic value beyond relative perfusion imaging. Patient radiation dose can be reduced and image quality can be improved with latest advances in PET/CT equipment. Simultaneous assessment of both anatomy and perfusion by hybrid PET/CT can result in improved diagnostic accuracy. Compared with SPECT-MPI, PET-MPI provides higher diagnostic accuracy, using lower radiation doses during a shorter examination time period for the detection of coronary artery disease.

Motion Artifacts in Oncological and Cardiac PET Imaging

Image quality in PET examinations is influenced by several factors. Patient motion during PET data acquisition is a substantial problem that potentially leads to smearing artifacts, resulting in the loss of diagnostic accuracy both in visual and quantitative image analyses. In hybrid imaging, coregistration of functional (PET) and morphologic (CT or MR imaging) data can be hampered by patient movement between the acquisitions, resulting in additional sources of error. This article describes the artifacts due to patient movement.

Advances in nuclear cardiac instrumentation with a view towards reduced radiation exposure

Recent advances in nuclear cardiology instrumentation have enabled myocardial perfusion imaging (MPI) with improved image quality and faster scan times. These developments also can be exploited to reduce the effective radiation dose to the patient. In this review, we discuss these technologies including new single photon emission computed tomography (SPECT) and positron emission tomography (PET) scanners, as well as novel reconstruction software with regard to their potential for the reduction of the patient radiation dose. New advances in nuclear cardiology instrumentation will allow routine rest/stress MPI imaging with low radiation doses (<5 mSv) and fast imaging times, even by the software-only solutions. It is possible to further reduce the MPI radiation dose to less than 2 to 3 mSv range with standard acquisition times. PET perfusion imaging also can be performed with very low doses especially by the three-dimensional scanners allowing hybrid PET/computed tomographic angiography (CTA) imaging with low overall dose. In addition, stress-only protocols can be utilized to further reduce the radiation dose and the overall test time.

PET and PET/CT in cardiovascular disease

The present review provides an overview of the role of cardiac positron emission tomography in the diagnosis and management of cardiovascular disease. It expands on the relative advantages and disadvantages over other imaging modalities as well as the available evidence supporting its value in the diagnosis and management of patients with coronary artery disease, the assessment of myocardial viability, and evaluation of the cardiac sympathetic nervous system. Furthermore, the recent developments, such as the implementation of high-end computed tomography devices to form hybrid systems, and the advances of molecular imaging probes in experimental applications are briefly discussed.