RESUMO
BACKGROUND: Vagus nerve activation impacts inflammation. Therefore, we hypothesized that vagal nerve stimulation (VNS) influenced arterial wall inflammation as measured by 18F-FDG uptake. RESULTS: Ten patients with left-sided VNS for refractory epilepsy were studied during stimulation (VNS-on) and in the hours after stimulation was switched off (VNS-off). In nine patients, 18F-FDG uptake was measured in the right carotid artery, aorta, bone marrow, spleen, and adipose tissue. Target-to-background ratios (TBRs) were calculated to normalize the respective standardized uptake values (SUVs) for venous blood pool activity. Median values are shown with interquartile range and compared using the Wilcoxon signed-rank test. Arterial SUVs tended to be higher during VNS-off than VNS-on [SUVmax all vessels 1.8 (1.5-2.2) vs. 1.7 (1.2-2.0), p = 0.051]. However, a larger difference was found for the venous blood pool at this time point, reaching statistical significance in the vena cava superior [meanSUVmean 1.3 (1.1-1.4) vs. 1.0 (0.8-1.1); p = 0.011], resulting in non-significant lower arterial TBRs during VNS-off than VNS-on. Differences in the remaining tissues were not significant. Insulin levels increased after VNS was switched off [55.0 pmol/L (45.9-96.8) vs. 48.1 pmol/L (36.9-61.8); p = 0.047]. The concurrent increase in glucose levels was not statistically significant [4.8 mmol/L (4.7-5.3) vs. 4.6 mmol/L (4.5-5.2); p = 0.075]. CONCLUSIONS: Short-term discontinuation of VNS did not show a consistent change in arterial wall 18F-FDG-uptake. However, VNS did alter insulin and 18F-FDG blood levels, possibly as a result of sympathetic activation.
RESUMO
PURPOSE: The aim of this study was to investigate the effect of positron range on visualization and quantification in (18)F, (68)Ga and (124)I positron emission tomography (PET)/CT of lung-like tissue. METHODS: Different sources were measured in air, in lung-equivalent foams and in water, using a clinical PET/CT and a microPET system. Intensity profiles and curves with the cumulative number of annihilations were derived and numerically characterized. RESULTS: (68)Ga and (124)I gave similar results. Their intensity profiles in lung-like foam had a peak similar to that for (18)F, and tails of very low intensity, but extending over distances of centimetres and containing a large fraction of all annihilations. For 90% recovery, volumes of interest with diameters up to 50 mm were required, and recovery within the 10% intensity isocontour was as low as 30%. In contrast, tailing was minor for (18)F. CONCLUSION: Lung lesions containing (18)F, (68)Ga or (124)I will be visualized similarly, and at least as sharp as in soft tissue. Nevertheless, for quantification of (68)Ga and (124)I large volumes of interest are needed for complete activity recovery. For clinical studies containing noise and background, new quantification approaches may have to be developed.
