Carotid plaque inflammatory activity assessed by 2-[18F]FDG-PET imaging decrease after a neurological thromboembolic event

Abstract

Background: Atherosclerotic plaque vulnerability is comprised by plaque composition driven by inflammatory activity and these features can be depicted with 3D ultrasound and 2-[18F]FDG-PET, respectively. The study investigated timely changes in carotid artery plaque inflammation and morphology after a thromboembolic event with PET/CT and novel ultrasound volumetric grayscale median (GSM) readings. Patients with a single hemisphere-specific neurological symptom and the presence of an ipsilateral carotid artery atherosclerotic plaque were prospectively included to both 2-[18F]FDG PET/CT and 3D ultrasound scans of the plaque immediately after their event and again three months later. On PET/CT images the maximum standardized uptake value (SUV_max) was measured and the volumetric ultrasound acquisitions were analyzed using a semiautomated software measuring GSM values.

Results: Baseline scans were performed by a mean of 7 days (range 2-14) after the symptom and again after 98 days (range 91-176). For the entire group (n = 14), we found a decrease in average SUV_max from baseline to follow-up of - 0.18 (95% confidence interval: - 0.34 to - 0.02, P = 0.034). GSM did not increase significantly over time (mean change: + 2.21, 95% confidence interval: - 17.02 to 21.44, P = 0.808).

Conclusion: A decrease in culprit lesion 2-[18F]FDG-uptake 3 months after an event indicates a decrease in inflammatory activity, suggesting that carotid plaque stabilization over time. 3D ultrasound morphological quantitative differences in GSM were not detectable after 3 months.

Keywords: 3D ultrasound; Carotid artery plaque; FDG PET; Inflammation; Vulnerable plaque.

Fig. 1

Schematic example of the calculated average max standardized uptake value (aSUV_max) and grayscale median (GSM). ECA = external carotid artery. ICA = internal carotid artery. CCA = common carotid artery. The 3D ultrasound acquisition of the plaque was sliced in 2-mm segments from the flow divider, and the slice containing the maximum plaque thickness was identified. The slice with the maximum plaque thickness and the two slices on each side were used in analyses. For the PET/CT, the flow divider was used as landmark for alignment of SUV_max readings to the ultrasound readings. An average SUV_max was calculated for this 1 cm long plaque volume. GSM was automatically calculated by the software for the volume of the 10-mm-long plaque segment

Fig. 2

Flowchart of the included patients. Of the 19 included four were excluded. Two were excluded after withdrawal of consent, one died because of an, at the time of inclusion, undiagnosed cancer and one scan was lost

Fig. 3

Change in average maximum standardized uptake values (aSUV_max) from baseline to follow-up. The black diamonds represent the mean aSUV_max at baseline and follow-up with the 95% confidence interval as the dotted line. Mean difference in aSUV_max of − 0.18, CI95%: − 0.34 to − 0.02, P = 0.034. The light blue lines represent each patient with the circles marking the aSUV_max at baseline and follow-up. The patient with recurrent symptoms undergoing carotid endarterectomy before the follow-up scan is marked as a filled circle

Fig. 4

Baseline and follow-up patient example of 2-[18F]FDG-PET / CT-angiography and ultrasound images. Images from one patient. To the left 2-[18F]FDG-PET/CT angiography fusion, frontal MPR and to the right ultrasound images, axial plane. The top images are from baseline and the bottom follow-up. The white arrow points to the plaque on the symptomatic side