Alavi–Carlsen Calcification Score (ACCS): A Simple Measure of Global Cardiac Atherosclerosis Burden

Abstract

Multislice cardiac CT characterizes late stage macrocalcification in epicardial arteries as opposed to PET/CT, which mirrors early phase arterial wall changes in epicardial and transmural coronary arteries. With regard to tracer, there has been a shift from using mainly 18F-fluorodeoxyglucose (FDG), indicating inflammation, to applying predominantly 18F-sodium fluoride (NaF) due to its high affinity for arterial wall microcalcification and more consistent association with cardiovascular risk factors. To make NaF-PET/CT an indispensable adjunct to clinical assessment of cardiac atherosclerosis, the Alavi–Carlsen Calcification Score (ACCS) has been proposed. It constitutes a global assessment of cardiac atherosclerosis burden in the individual patient, supported by an artificial intelligence (AI)-based approach for fast observer-independent segmentation. Common measures for characterizing epicardial coronary atherosclerosis by NaF-PET/CT as the maximum standardized uptake value (SUV) or target-to-background ratio are more versatile, error prone, and less reproducible than the ACCS, which equals the average cardiac SUV. The AI-based approach ensures a quick and easy delineation of the entire heart in 3D to obtain the ACCS expressing ongoing global cardiac atherosclerosis, even before it gives rise to CT-detectable coronary calcification. The quantification of global cardiac atherosclerotic burden by the ACCS is suited for management triage and monitoring of disease progression with and without intervention.

Molecular imaging in atherosclerosis

“…However, assessment of the overall disease burden may provide more valuable information than a lesion-based approach in risk stratification [34]. Additionally, measurements using easily identifiable and well-defined structures allow for easily replicable approaches analysis amenable to analysis by artificial intelligence [35]. Previous studies have demonstrated the superiority of this approach in measuring CVD burden in various disease conditions such as multiple myeloma and type 2 diabetes [36,37].…”

PET-Based Imaging with 18F-FDG and 18F-NaF to Assess Inflammation and Microcalcification in Atherosclerosis and Other Vascular and Thrombotic Disorders

“…In the current state of research, the prognostic value and implementation of FDG-PET for the assessment of the atherosclerotic risk remain to be further tested. There has been no clear association between the FDG uptake and CT calcium burden, nor a prospective study in noncancerous patients that correlates an increased FDG uptake with adverse cardiovascular outcomes [91]. The CAMONA (Cardio-vascular Molecular Calcification Assessed by 18 F-NaF PET/CT) study involving 50 patients with angina pectoris and 89 healthy controls, for instance, revealed no significant correlation of FDG uptake in the thoracic aorta and 10-year Framingham Risk Score (FRS) [34].…”

“…There currently has not been any human studies establishing a clear link between arterial NaF uptake by macrocalcification and the subsequent transformation into CT-detectable macrocalcification; the clearest association with early NaF uptake and corresponding coronary macrocalcification was demonstrated using an Ossabaw miniature swine model for metabolic syndrome [ 19 ]. Therefore, the development of well-powered, prognostic studies conducted with longitudinal design remains necessary to fill this void and confirm the potential of NaF-PET for the clinical assessment of atherosclerosis [ 91 ].…”

“…The regions of interest (ROIs) can easily be defined based on gross structures seen in CT or the cardiac silhouette in 3D. Since the score is measured based on clearly defined and delineated anatomical boundaries, it is less subject to human bias and variations in measurements, even allowing for artificial intelligence (AI)-based approaches with a reproducibility of 100% [ 91 ].…”

Can Target-to-Background Ratio Measurement Lead to Detection and Accurate Quantification of Atherosclerosis With FDG PET? Likely Not

“…By adopting NaF PET, this limitation is overcome, and the presence of the plaques in the coronaries can be successfully assessed 35,36 . By adopting global disease assessment approach with PET, it is logical to determine the extent of the disease in the entire coronary arteries 37 . This advantage will also have a revolutionary impact on the role of PET in this very important and common disease.…”