Abstract
2-Deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) has been widely used for imaging brain metabolism. Tracer injection in anesthetized animals is a prerequisite for performing dynamic positron emission tomography (PET) scanning. Since preconditioning, as well as anesthesia, has been described to potentially influence brain [18F] FDG levels, this study evaluated how these variables globally and regionally affect both [18F] FDG uptake and kinetics in murine brain. Sixty-minute dynamic [18F] FDG PET scans were performed in adult male C57BL/6 mice anesthetized with isoflurane [control (in 100% O2), in medical air, in 100% O2 + insulin pre-treatment, and in 100% O2 after 18h fasting], ketamine/xylazine, sevoflurane, and chloral hydrate. An additional group was scanned after awake uptake. Blood glucose levels were determined, and data was analyzed by comparing percent injected dose per cc tissue (%ID/cc) and glucose influx rate and metabolic rate (MRGlu) calculated by Patlak plot. Ketamine/xylazine and chloral hydrate anesthesia induced a lower whole-brain uptake of [18F] FDG (2.86 ± 0.67%ID/cc, p < 0.001; 4.25 ± 0.28%ID/cc, p = 0.0179, respectively) compared to isoflurane anesthesia (5.04 ± 0.19%ID/cc). In addition, protocols affected differently distribution of [18F] FDG uptake in brain regions. Ketamine/xylazine reduced [18F] FDG influx rate in murine brain (0.0135 ± 0.0009 vs 0.0247 ± 0.0014ml/g/min; p < 0.005) and chloral hydrate increased MRGlu (66.72 ± 3.75 vs 41.55 ± 3.06μmol/min/100ml; p < 0.01) compared to isoflurane. Insulin-pretreated animals showed a higher influx rate (0.0477 ± 0.0101ml/min/g; p < 0.05) but a reduced MRGlu (21.92 ± 3.12μmol/min/100ml; p < 0.01). Blood glucose levels were negatively correlated to [18F] FDG uptake and influx rate, but positively correlated to MRGlu. Choice of anesthesia and pre-conditioning affect not only [18F] FDG uptake but also kinetics and regional distribution in the mouse brain. Both anesthesia and pre-conditioning should be carefully considered in the interpretation of [18F] FDG studies due to its great influence on the uptake and distribution of the tracer along the brain regions.
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