To conduct a systematic review of articles on PET imaging of carotid atherosclerosis with emphasis on clinical usefulness and comparison with other imaging modalities.
Research articles reporting carotid artery PET imaging with different radiotracers until 30 November 2018 were systematically searched for in Medline/PubMed, Scopus, Embase, Google Scholar, and Cochrane Library. Duplicates were removed, and editorials, case studies, and investigations on feasibility or reproducibility of PET imaging and of patients with end-stage diseases or immunosuppressive medications were omitted. After quality assessment of included articles using Joanna Briggs Institute checklists, all eligible articles were reviewed.
Of 1718 primary hits, 53 studies comprising 4472 patients, aged 47–91 years (78.8% males), were included and grouped under the following headlines: diagnostic performance, risk factors, laboratory findings, imaging modalities, and treatment. 18F-fluorodeoxyglucose (FDG) (49/53) and 18F-sodium fluoride (NaF) (5/53) were the most utilized tracers to visualize carotid wall inflammation and microcalcification, respectively. Higher carotid FDG uptake was demonstrated in patients with than without symptomatic carotid atherosclerosis. Normal carotid arteries presented with the lowest FDG uptake. In symptomatic atherosclerosis, carotid arteries ipsilateral to a cerebrovascular event had higher FDG uptake than the contralateral carotid artery. FDG uptake was significantly associated with age, male gender, and body mass index in healthy individuals, and in addition with arterial hypertension, hypercholesterolemia, and diabetes mellitus in patients. Histological assessment indicated a strong correlation between microcalcification and NaF uptake in symptomatic patients. Histological evidence of calcification correlated inversely with FDG uptake, which was associated with increased macrophage and CD68 count, both accounting for increased local inflammatory response.
FDG-PET visualizes the inflammatory part of carotid atherosclerosis enabling risk stratification to a certain degree, whereas NaF-PET seems to indicate long-term consequences of ongoing inflammation by demonstrating microcalcification allowing discrimination of atherosclerotic from normal arteries and suggesting clinically significant carotid atherosclerosis.