| Summary: | The aim of this study was to evaluate the impact of different anesthetics on 3′-[ 18 F]fluoro-3′-deoxythymidine ([ 18 F]FLT) uptake in carcinomas and arthritic ankles. To determine the amount of [ 18 F]FLT uptake in subcutaneous CT26 colon carcinomas or arthritic ankles, spontaneously room air/medical air–breathing mice were anesthetized with isoflurane, a combination of medetomidine/midazolam, or ketamine/xylazine. Mice were kept conscious or anesthetized during [ 18 F]FLT uptake before the 10-minute static positron emission tomographic (PET) investigations. [ 18 F]FLT uptake in CT26 colon carcinomas and arthritic ankles was calculated by drawing regions of interest. We detected a significantly reduced (4.4 ± 0.9 %ID/cm 3 ) [ 18 F]FLT uptake in the carcinomas of ketamine/xylazine-anesthetized mice compared to the [ 18 F]FLT-uptake in carcinomas of medetomidine/midazolam- (7.0 ± 1.5 %ID/cm 3 ) or isoflurane-anesthetized mice (6.4 ± 1.5 %ID/cm 3 ), whereas no significant differences were observed in arthritic ankles regardless of whether mice were anesthetized or conscious during tracer uptake. The time-activity curves of carcinomas and arthritic ankles yielded diverse [ 18 F]FLT accumulation related to the used anesthetics. [ 18 F]FLT uptake dynamics are different in arthritic ankles and carcinoma, and the magnitude and pharmacokinetics of [ 18 F]FLT uptake are sensitive to anesthetics. Thus, for preclinical in vivo [ 18 F]FLT PET studies in experimental tumor or inflammation models, we recommend the use of isoflurane anesthesia as it yields a stable tracer uptake and is easy to handle.
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