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Coronary computed tomographic angiography (CCTA) is becoming the first-line investigation for establishing the presence of coronary artery disease and, with fractional flow reserve (FFRCT), its haemodynamic significance. In patients without significant epicardial obstruction, its role is either to rule out atherosclerosis or to detect subclinical plaque that should be monitored for plaque progression/regression following prevention therapy and provide risk classification. Ischaemic non-obstructive coronary arteries are also expected to be assessed by non-invasive imaging, including CCTA. In patients with significant epicardial obstruction, CCTA can assist in planning revascularisation by determining the disease complexity, vessel size, lesion length and tissue composition of the atherosclerotic plaque, as well as the best fluoroscopic viewing angle; it may also help in selecting adjunctive percutaneous devices (e.g., rotational atherectomy) and in determining the best landing zone for stents or bypass grafts.

The introduction of FDG in 1976 started a new discipline and enhanced the role of molecular imaging in medicine. While the initial intent with this tracer was to determine brain function in a variety of neuropsychiatric disorders, over time, this powerful approach has made a major impact on managing many other diseases and disorders. During the past 2 decades, FDG PET has been used to detect inflammatory lesions in the atherosclerotic plaques and in other settings. However, the suboptimal spatial resolution of PET limits its ability to visualize plaques that are very small in size. Furthermore, this tracer remains in the blood for an extended period and therefore provides suboptimal results. Target-to-background ratio (TBR) has been suggested to correct for this source of error. Unfortunately, TBR values vary substantially, depending on the timing of image acquisition. Delayed imaging at later time points (3-4 hours) may obviate the need for TBR measurement, but it is impractical with conventional PET instruments. Recently, 18F-sodium fluoride (NaF) has been used for detection and quantification of molecular calcification in the plaques. This tracer is highly specific for calcification and is rapidly cleared from the circulation. In addition, global atherosclerotic burden as measured by NaF PET can be determined accurately either in the heart or major arteries throughout the body. Therefore, the role of FDG PET-based TBR measurement for detection and quantification of atherosclerotic plaques is questionable at this time.

BACKGROUND AND PURPOSE To determine the prognostic value for ischemic stroke or transitory ischemic attack (TIA) of plaque surface echogenicity alone or combined to degree of stenosis in a Swiss multicenter cohort METHODS: Patients with ≥60% asymptomatic or ≥50% symptomatic carotid stenosis were included. Grey-scale based colour mapping was obtained of the whole plaque and of its surface defined as the regions between the lumen and respectively 0-0.5, 0-1, 0-1.5, and 0-2 mm of the outer border of the plaque. Red, yellow and green colour represented low, intermediate or high echogenicity. Proportion of red color on surface (PRCS) reflecting low echogenictiy was considered alone or combined to degree of stenosis (Risk index, RI). RESULTS We included 205 asymptomatic and 54 symptomatic patients. During follow-up (median/mean 24/27.7 months) 27 patients experienced stroke or TIA. In the asymptomatic group, RI ≥0.25 and PRCS ≥79% predicted stroke or TIA with a hazard ratio (HR) of respectively 8.7 p = 0.0001 and 10.2 p < 0.0001. In the symptomatic group RI ≥0.25 and PRCS ≥81% predicted stroke or TIA occurrence with a HR of respectively 6.1 p = 0.006 and 8.9 p = 0.001. The best surface parameter was located at 0-0.5mm. Among variables including age, sex, degree of stenosis, stenosis progression, RI, PRCS, grey median scale values and clinical baseline status, only PRCS independently prognosticated stroke (p = 0.005). CONCLUSION In this pilot study including patients with at least moderate degree of carotid stenosis, PRCS (0-0.5mm) alone or combined to degree of stenosis strongly predicted occurrence of subsequent cerebrovascular events.