In PET Scans, 2 Tracers Shed Light on Carotid Wall Inflammation and Microcalcification

In positron emission tomography (PET) imaging of carotid atherosclerosis, ¹⁸F-fluorodeoxyglucose (FDG)-PET visualizes different inflammatory phases of disease, and ¹⁸F-sodium fluoride (NaF)-PET appears to indicate long-term consequences of ongoing inflammation, according to a study in the European Journal of Nuclear Medicine and Molecular Imaging.

Researchers conducted a systematic review of articles about PET imaging of carotid atherosclerosis, emphasizing clinical usefulness and comparison with other imaging modalities. Articles publishedthrough November 30, 2018 were reviewed.

A total of 53 studies with 4472 patients (mean age, 58 years [range, 47-91]; 78.8% male) were included and grouped according to the following: diagnostic performance, risk factors, laboratory findings, imaging modalities, and treatment. FDG (n=49) and NaF (n=5) were the most frequently used tracers to visualize carotid wall inflammation and microcalcification, respectively. The study designs included cross-sectional (n=45), case-control (n=4), and interventional trials (n=4).

The researchers found that higher carotid FDG uptake was shown in patients with symptomatic carotid atherosclerosis than in those without symptomatic carotid atherosclerosis. Patients with normal carotid arteries presented with the lowest FDG uptake. In symptomatic atherosclerosis, carotid arteries ipsilateral to the location of a cerebrovascular event had higher FDG uptake compared with the contralateral carotid artery.

In addition, FDG uptake was significantly associated with age, male gender, and body mass index among healthy individuals as well as with arterial hypertension, hypercholesterolemia, and diabetes mellitus in all patients. Among symptomatic patients, histologic assessment indicated a strong correlation between microcalcification and NaF uptake. Also, histologic evidence of calcification correlated inversely with FDG uptake, which was associated with increased macrophage and CD68 count, both accounting for increased local inflammatory response.

“Histologic and immunohistochemical findings were the most coherent with PET findings because of the shared focus on molecular aspects,” the researchers commented. “It was shown that pro-inflammatory changes especially those in relation to count and activity of macrophages in carotid arteries correlated with PET findings.”

A main limitation, according to the study authors, was the different measures and scales that were used to express tracer uptake. Another limitation was the variation in PET imaging acquisition technique, timing of PET imaging following a complication due to a carotid plaque, and the fact that PET was used for multiple purposes.

“Molecular PET imaging appears to be an interesting modality for investigation of atherosclerotic carotid artery disease,” the investigators concluded. “FDG-PET visualizes different inflammatory phases of carotid atherosclerosis development and its complications, while NaF-PET seems to mirror and monitor more long-term consequences by demonstrating arterial wall microcalcification allowing discrimination between atherosclerotic and normal carotid arteries.”

Reference

Piri R, Gerke O, Høilund-Carlsen PF. Molecular imaging of carotid artery atherosclerosis with PET: a systematic review. Eur J Nucl Med Mol Imaging. 2020;47(8):2016-2025. doi: 10.1007/s00259-019-04622-y