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In both clinical and preclinical scenarios, 2-deoxy-2[18F]fluoro-D-glucose ([18F]FDG) is the radiotracer most widely used to study brain glucose metabolism with positron emission tomography (PET). In clinical practice, there is a worldwide standardized protocol for preparing patients for [18F]FDG-PET studies, which specifies the room lighting. However, this standard is typically not observed in the preclinical field, although it is well known that animal handling affects the biodistribution of [18F]FDG. The present study aimed to evaluate the effect of ambient lighting on brain [18F]FDG uptake in mice. Two [18F]FDG-PET studies were performed on each animal, one in light and one in dark conditions. Thermal video recordings were acquired to analyse animal motor activity in both conditions. [18F]FDG-PET images were analysed with the Statistical Parametric Mapping method. The results showed that [18F]FDG uptake is higher in darkness than in light condition in mouse nucleus accumbens, hippocampus, midbrain, hindbrain, and cerebellum. The SPM analysis also showed an interaction between the illumination condition and the sex of the animal. Mouse activity was significantly different (p = 0.01) between light conditions (632 ± 215 s of movement) and dark conditions (989 ± 200 s), without significant effect of sex (p = 0.416). We concluded that room illumination conditions during [18F]FDG uptake in mice affected the brain [18F]FDG biodistribution. Therefore, we highlight the importance to control this factor to ensure more reliable and reproducible mouse brain [18F]FDG-PET results.

INTRODUCTION:Retention of 2-deoxy-2-[18F]fluoro-D-glucose 18F-FDG in the bladder causes more problems in small animal research than in human research owing to the smaller size of the subject. Catheterization has been proposed to reduce bladder spillover both in human studies and in small animal research. Noninvasive alternatives such as hydration plus furosemide also seem to be a promising pre-imaging strategy for decreasing bladder spillover. Our main goal was to measure the effects of the combination of furosemide and hydration for reducing bladder signal directly on mouse bowel 18F-FDG-PET images. METHODS:Nine mice were divided into two groups: the control group (C, n = 4) and the treatment group (n = 5). The clearance protocol combines hyperhydration and a single furosemide dose during the 18F-FDG uptake period. Two images were acquired on different days in treated mice to evaluate two different furosemide doses (low dose, LD, 3.5 mg/kg; and high dose, HD, 7 mg/kg). A region of interest was drawn on each computed tomography image (bladder, kidneys, liver, muscle, and bone marrow). To quantify bladder spillover, two different areas of the colon were selected. RESULTS:A remarkable reduction in bladder spillover was achieved on 18F-FDG -PET in both groups. Our imaging findings were quantified, and both furosemide doses induced a decrease in mean standard uptake values (SUVmean) compared with the controls (LD 1.46 ± 0.54 and HD 1.05 ± 0.29; controls: 8.90 ± 3.4 [p-value < 0.05]). CONCLUSION:We validated a non-invasive, easy, and harmless pre-imaging alternative for decreasing 18F-FDG bladder spillover. Our study shows the effect of furosemide on bladder spillover directly on 18F-FDG-PET images by measuring SUVmean in the bladder, colon, liver, muscle, and bone marrow.

Besides its application in oncology, 18F-FDG PET-CT imaging is also useful in the diagnosis of certain lung infections, inflammatory diseases, and atherosclerotic plaques. Myocardial uptake of 18F-FDG may hamper visualization of the lesions caused by these diseases. Two approaches have been proposed for reducing myocardial uptake in preclinical studies, namely, calcium channel blockers (verapamil) and high-fat diets such as commercial ketogenic diets and sunflower seed diets. The objective of this study was to compare the efficacy of these approaches in reducing myocardial uptake of 18F-FDG in mice.We performed two experiments. In experiment A, each animal underwent four 18F-FDG PET/CT scans in the following order: baseline, after administration of verapamil, after two days on ketogenic diet and after two days on sunflower seeds. PET scans were performed 60 minutes after injection of 18.5 MBq of 18F-FDG. In experiment B, the best protocol of the three (ketogenic diet) was evaluated in a lung inflammation model to assess the efficacy of reducing myocardial uptake of 18F-FDG.Compared with baseline (SUV 2.03 ± 1.21); the greatest reduction in uptake of 18F-FDG was with ketogenic diet (SUV 0.79 ± 0.16; p = 0.008), followed by sunflower seeds (SUV 0.91 ± 0.13; p = 0.015); the reduction in myocardial uptake produced by verapamil was not statistically significant (SUV 1.78 ± 0.79; p = NS). In experiment B, complete suppression of myocardial uptake noticeably improved the visualization of inflamed areas near the heart, while in the case of null or partial myocardial suppression, it was much harder to distinguish lung inflammation from myocardial spillover.A high-fat diet appeared to be the most effective method for decreasing myocardial uptake of 18F-FDG in healthy mice, outperforming verapamil. Our findings also demonstrate that ketogenic diet actually improves visualization of inflammatory lesions near the heart.

Reporter gene (RG) imaging of cell-based therapies provides a direct readout of therapeutic efficacy by assessing the fate of implanted cells. To permit long-term cellular imaging, RGs are traditionally required to be integrated into the cellular genome. This poses a potential safety risk and regulatory bottleneck for clinical translation as integration can lead to cellular transformation. To address this issue, we have developed non-integrative, replicating minicircles (MCs) as an alternative platform for safer monitoring of cells in living subjects. We developed both plasmids and minicircles containing the scaffold/matrix attachment regions (S/MAR) of the human interferon-beta gene, driven by the CMV promoter, and expressing the bioluminescence RG firefly luciferase. Constructs were transfected into breast cancer cells, and expanded S/MAR minicircle clones showed luciferase signal for greater than 3 months in culture and minicircles remained as episomes. Importantly, luciferase activity in clonal populations was slowly lost over time and this corresponded to a loss of episome, providing a way to reversibly label cells. To monitor cell proliferation in vivo, 1.5 × 10(6) cells carrying the S/MAR minicircle were implanted subcutaneously into mice (n = 5) and as tumors developed significantly more bioluminescence signal was noted at day 35 and 43 compared to day 7 post-implant (p