18F-NaF uptake by atherosclerotic plaque on PET/CT imaging: Inverse correlation between calcification density and mineral metabolic activity

Several studies have highlighted the role of vascular (18)F-NaF uptake as a marker of ongoing calcium deposition. However, accumulation of (18)F-NaF is often inconsistent with localization of arterial plaque. Calcification activity and thus (18)F-NaF uptake might prevail in the earlier plaque stages. To test this hypothesis, we evaluated (18)F-NaF uptake in plaque of 3 different densities, using density as a marker of calcification progression. We also tested whether attenuation-weighted image reconstruction affects (18)F-NaF uptake in the different plaque stages. METHODS: Sixty-four oncologic patients (14 men and 50 women; mean age, 65.3 \ub1 8.2 y; range, 26-81 y) underwent (18)F-NaF PET/CT. A volume of interest was drawn on each plaque within the infrarenal aorta to assess mean standardized uptake value and attenuation (in Hounsfield units [HU]). Plaque was then categorized as light (<210 HU), medium (211-510 HU), or heavy (>510 HU). Standardized uptake value was normalized for blood (18)F-NaF activity to obtain the plaque target-to-background ratio (TBR). During this process, several focal, noncalcified areas of (18)F-NaF were identified (hot spots). The TBR of the hot spots was computed after isocontour thresholding. The TBR of a noncalcified control region was also calculated. In 35 patients, the TBR of non-attenuation-corrected images was calculated. RESULTS: The average TBR was highest in light plaque (2.21 \ub1 0.88), significantly lower in medium plaque (1.59 \ub1 0.63, P < 0.001), and lower still in heavy plaque (1.14 \ub1 0.37, P < 0.0001 with respect to both light and medium plaque). The TBR of the control region was not significantly different from that of heavy plaque but was significantly lower than that of light and medium plaque (P < 0.01). Hot spots had the highest absolute TBR (3.89 \ub1 1.87, P < 0.0001 vs. light plaque). TBRs originating from non-attenuation-corrected images did not significantly differ from those originating from attenuation-corrected images. CONCLUSION: Our results support the concept that (18)F-NaF is a feasible option in imaging molecular calcium deposition in the early stages of plaque formation, when active uptake mechanisms are the main determinants of calcium presence, but that retention of (18)F-NaF progressively decreases with increasing calcium deposition in the arterial wall. Our data suggest that non-attenuation-corrected reconstruction does not significantly affect evaluation of plaque of any thickness

18F-FDG micro-PET imaging for research investigations in the Octopus vulgaris: applications and future directions in invertebrate neuroscience and tissue regeneration

This study aimed at developing a method for administration of 18F-Fludeoxyglucose (18F-FDG) in the common octopus and micro-positron emission tomography (micro-PET) bio-distribution assay for the characterization of glucose metabolism in body organs and regenerating tissues. Methods: Seven animals (two with one regenerating arm) were anesthetized with 3.7% MgCl2 in artificial seawater. Each octopus was injected with 18-30 MBq of isosmotic 18F-FDG by accessing the branchial heart or the anterior vena cava. After an uptake time of ~50 minutes, the animal was sacrificed, placed on a bed of a micro-PET scanner and submitted to 10 min static 3-4 bed acquisitions to visualize the entire body. To confirm the interpretation of images, internal organs of interest were collected. The level of radioactivity of each organ was counted with a \u3b3-counter. Results: Micro-PET scanning documented a good 18F-FDG full body distribution following vena cava administration. A high mantle mass radioactivity facing a relatively low tracer uptake in the arms was revealed. In particular, the following organs were clearly identified and measured for their uptake: brain (standardized uptake value, SUV max of 6.57\ub11.86), optic lobes (SUV max of 7.59\ub11.66) and arms (SUV max of 1.12\ub10.06). Interestingly, 18F-FDG uptake was up to threefold higher in the regenerating arm stumps at the level of highly proliferating areas. Conclusion: This study represents a stepping-stone over the use of non-invasive functional techniques to address questions relevant to invertebrate neuroscience and regenerative medicine