PET/MRI may uncover atherosclerosis at early stage

Hybrid PET/MRI revealed inflammation in plaque-free arterial segments in a sizable proportion of patients with subclinical atherosclerosis, suggesting the imaging technique may provide a lens into early stages of cardiovascular disease.  

Researchers with Centro Nacional de Investigaciones Cardiovasculares (CNIC) in Madrid performed 18F-fluorodeoxyglucose (18F-FDG) PET/MRI in 755 asymptomatic participants with plaques detected via vascular ultrasound or coronary artery calcium scanning. The patients were 49.6 years old on average and 83.7 percent were men.

Arterial inflammation, detected by increased 18F-FDG uptake, was found in 48.2 percent of participants. Plaques were detected in 90.1 percent of individuals with PET/MRI, while coincident 18F-FDG uptakes were only present in 11 percent of plaques—highlighting that many inflamed regions didn’t yet have plaque.

“Arterial inflammation is highly prevalent in middle-aged individuals with known subclinical atherosclerosis,” lead author Leticia Fernandez-Friera, MD, PhD, and colleagues wrote in the Journal of the American College of Cardiology.

“Large-scale multiterritorial PET/MRI allows characterization of atherosclerosis-related arterial inflammation and demonstrates 18F-FDG uptake in plaque-free arterial segments and, less frequently, within plaques. These findings suggest an arterial inflammatory state at early stages of atherosclerosis.”

The prevalence of arterial inflammation differed by territory: 24.4 percent femoral, 19.3 percent aorta, 15.8 percent carotid and 9.3 percent iliac. Plaques were detected most often in the femoral territories as well.

Plaque burden, defined by the presence, number and volume of plaques, was significantly higher in those with arterial inflammation than those without, but 61.5 percent of 18F-FDG uptakes were detected in segments free of plaque. Unsurprisingly, older participants and those with more cardiovascular risk factors were most likely to have arterial inflammation.

“While inflammation extent correlated with plaque burden, inflammation uptakes and plaques frequently did not coincide, suggesting that they are distinct processes in atherogenesis,” the authors wrote. “The reason for preferential uptake in the carotid and femoral territories compared with the iliac territory requires further investigation, but may be related to local wall shear stress conditions, different stages of atherosclerosis development in each vascular territory, and more physiological uptake in the abdominal organs, leading to potential pitfalls in imaging interpretation.”

Fernandez-Friera et al. said they couldn’t prove that inflammation precedes or contributes to plaque formation due to the cross-sectional design of the study. Future investigations should look to answer this question along with the value of quantifying inflammation for cardiovascular risk prediction, they wrote.

In a related editorial, three researchers from Brigham and Women’s Hospital and Harvard Medical School noted that cost considerations also must be considered.

“The expense of MRI and FDG imaging precludes the feasibility of the routine use of these modalities in screening unselected populations,” wrote Ron Blankstein, MD, Peter Libby, MD, and Deepak L. Bhatt, MD, MPH. “Thus, we need future studies to determine the best methods to detect plaque or inflammation and whether the detection of such findings would enhance risk prediction or alter patient management in a way that would improve patient outcomes.”