Correlation of noninvasive imaging of vulnerable carotid artery plaque using NaF and FDG PET/CT and black-blood MRI with cerebral ischemia on brain MRI

Objectives: Stroke is associated with vulnerable carotid artery plaques. Carotid black-blood (BB) magnetic resonance imaging (MRI) is widely used for assessing carotid artery plaques. Recent researchers tried to identify high-risk plaque features using positron emission tomography (PET). F-18 fluorodeoxyglucose (FDG) and F-18 sodium fluoride (NaF) has been promising PET tracer for assessing carotid artery plaques. The purpose of this study was to evaluate the correlation of noninvasive imaging of vulnerable carotid artery plaque using NaF and FDG PET/CT and BB MRI with cerebral ischemic changes on brain MRI. [Material and methods] A total of 31 patients with carotid artery stenosis of 50% or greater determined by using ultrasonography were examined with NaF and FDG PET/CT studies and carotid BB and brain MRI studies. In one patient, only unilateral carotid artery was used because of indwelling stent. PET emission scanning of the neck region with a 15-min acquisition of one bed position was performed at 60 min after each radiotracer injection. Images of bilateral carotids and brain were obtained on a 1.5T or 3.0T MRI scanner. NaF and FDG uptake in carotid arteries were quantified using maximum standardized uptake value (SUV). Carotid BB MRI findings were characterized as vulnerable plaque and non-vulnerable plaque. Brain MRI findings were characterized as mild ischemic changes (grade 1), moderate ischemic changes (grade 2), and severe ischemic changes (grade 3) in bilateral cerebral hemispheres. [Results] Thirty-three hemispheres were considered grade 1; 21, grade 2; and 7, grade 3 on brain MRI. The mean (±S.D.) NaF SUV in grade 3 (3.48±0.83) was significantly higher than that in grade 1 (2.09±0.53) and grade 2 (2.17±0.51) (p=0.005 and 0.006, respectively). There was no significant association between FDG SUV and ischemic changes on brain MRI. Thirty-four carotid plaques were considered as vulnerable plaque and 27 as non-vulnerable plaque on BB MRI. There was no significant association between carotid plaque findings on BB MRI and ischemic changes on brain MRI.[Conclusion] These preliminary results suggest that NaF uptake in carotid artery seems to correlate with cerebral ischemic changes.