18F-FDG PET/CT in rabbit model of vulnerable plaque and its correlation with 99Tcm-RGD imaging

Objective To evaluate 18F-fluorodeoxyglucose (FDG) PET/CT in the rabbit model of vulnerable plaques by correlation with 99Tcm-Arg-Gly-Asp (RGD) SPECT/CT imaging, lipid levels, pathological and immunohistochemical results. Methods Sixteen male New Zealand white rabbits were randomly divided into normal diet group (group A, n=4), stable plaque group (group B, n=4) and vulnerable plaque group (group C, n=8) using completely random grouping method. The animals were given abdominal aorta sham operation (groups A and B) or balloon injury of the abdominal aorta (group C) 2 weeks after feeding. Animals were injected with 18F-FDG and 99Tcm-RGD respectively at the end of 4, 8 and 12 weeks. PET/CT was performed at 1, 2 and 3 h post-injection. SPECT/CT was performed at 30 min post-injection. One rabbit was sacrificed at the end of 4 and 8 weeks after imaging studies, respectively. The others were sacrificed at the end of 12 weeks after imaging studies. All abdominal aortas were harvested. Pathology and immunohistochemistry analysis were performed. The data were analyzed by one-way analysis of variance and Pearson correlation analysis. Results There was no uptake in any group at 4th week and no uptake in group A or group B at 8th week. There was mild uptake in group B at 12th week and group C at 8th week. There was intense uptake in group C at 12th week, whereas both mean standardized uptake value (SUVmean) and maximum standardized uptake value (SUVmax) were significantly higher than the other two groups (F values: 7.952, 14.279, both P<0.05). In group C, SUVmax (0.43±0.08, 0.68±0.06, 1.74±0.63) and SUVmean (0.37±0.03, 0.56±0.03, 1.26±0.23) had significant difference at 3 h post-injection for imaging at 4th, 8th and 12th week (F values: 10.939, 39.747, both P<0.05). At 12th week, there was a strong correlation between the uptake of 18F-FDG and target/non-target (T/NT) ratio of 99Tcm-RGD in all groups(r values: 0.748, 0.709, both P<0.05). Histopathology results showed that the plaques had rich macrophages and a small amount of smooth muscle cells in group C, little macrophages in group B, while no macrophages in group A. Conclusion 18F-FDG PET/CT might be an effective noninvasive method for early assessment of aortic vulnerability to atherosclerotic plaque. Key words: Plaque, atherosclerotic; Positron-emission tomography; Tomography, X-ray computed; Tomography, emission-computed, single-photon; Rabbits; Deoxyglucose; Arg-Gly-Asp