Multimodality imaging of atherosclerotic plaque activity and composition using FDG-PET/CT and MRI in carotid and femoral arteries

Abstract

Purpose To evaluate the relationship between atherosclerotic plaque inflammation, as assessed by FDG-Positron Emission Tomography/Computed Tomography (FDG-PET/CT), and plaque morphology and composition, as assessed by magnetic resonance imaging (MRI), in the carotid and femoral arteries. Materials and methods Sixteen patients underwent FDG-PET/CT and MRI (T2 weighted (T2W) and Proton density weighted (PDW)) of the carotid and femoral arteries. For every image slice, two observers determined the corresponding regions of the FDG-PET/CT and MRI image sets by matching CT and T2W axial images. Each plaque was then classified into one of three groups according to the CT appearance and T2W/PDW signal: 1) collagen, 2) lipid-necrotic core and 3) calcium. Arterial FDG uptake was measured for each plaque and normalized to vein FDG activity to produce a blood-normalized artery activity called the target to background ratio (TBR). The vessel wall thickness (VWT), the vessel wall area and the total vessel wall area were measured from the T2W MR images. Results The TBR value was higher in the lipid-necrotic core group compared to the collagen and calcium groups, (p < 0.001). The lipid-necrotic core group demonstrated a significant TBR variation according to the median of the VWT (TBR = 1.26 ± 0.25 vs. TBR = 1.50 ± 0.12). There was no correlation with other morphological MR parameters. Conclusions This study demonstrates the complementary value of non-invasive FDG-PET/CT and MR imaging for the evaluation of atherosclerotic plaque composition and activity. Lipid-rich plaques are more inflamed than either calcified or collagen-rich plaques.

Vascular imaging with positron emission tomography

“…No correlation was found between FDG uptake and plaque thickness, area or smooth muscle staining. It has since been shown that FDG can quantify inflammation in the aorta, iliac and peripheral arteries, with excellent short-term and interobserver reproducibility [49][50][51][52]. This has proved important in the search for quantitative measures of inflammation that can be used to test the impact of new therapies.…”

“…Arterial uptake in one vascular region correlates strongly with its anatomical pair, and more strongly with neighbouring regions than more distally. Plaques with high-risk features on MRI (large lipid core [49] or intraplaque haemorrhage [63]) or ultrasound [64,65] (echolucency) have higher FDG than more stable phenotypes. Aortic uptake has been shown to correlate with circulating biomarkers matrix metalloproteases 1, 3 and 9 [54,66], and an inverse correlation has been reported with the atheroprotective biomarkers adiponectin and plasminogen activator inhibitor 1 [54,66].…”

Investigating Vulnerable Atheroma Using Combined 18F-FDG PET/CT Angiography of Carotid Plaque with Immunohistochemical Validation

“…Indeed, this combined approach has now been applied to carotid plaque imaging (12,13). However, the findings have been conflicting with respect to the relationship between uptake on PET and anatomic imaging: lipid-rich necrotic core plaques demonstrated higher 18 F-FDG uptake than calcified or collagen plaques in one study (12), but no strong correlations between 18 F-FDG uptake and the CT-or MRI-assessed composition of the plaques existed in another (13). Moreover, gold standard histologic comparison was unavailable for either of these studies.…”

Advances in imaging vascular inflammation

“…It has been shown to be reproducible, with low levels of inter-observer and short-term variability [29]. In carotid imaging, high FDG uptake correlates well with features of vulnerability noted on other modalities, for example, echolucency on ultrasound [30] and lipid rich cores on MRI [31]. Vascular FDG PET is being used to investigate the excess cardiovascular risk associated with other chronic inflammatory diseases such as HIV [32], chronic obstructive pulmonary disease [33] and rheumatoid arthritis [34].…”