18F-FDG and 18F-FET uptake in experimental soft tissue infection

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Abstract
The aim of this study was to compare the uptake of 18F-fluoroethyl-L-tyrosine (18F-FET) with that of 18F-fluorodeoxyglucose (18F-FDG) in activated inflammatory white blood cells. Unilateral thigh muscle abscesses were induced in 11 rats by intramuscular inoculation of 0.1 ml of a bacterial suspension (S. aureus, 1.2×109 CFU/ml). Four animals were intraperitoneally injected with 130–180 MBq 18F-FDG, four with 140–170 MBq 18F-FET and three with a mixture of 140–170 MBq 18F-FET and 1.8 MBq 14C-deoxyglucose. Autoradiography (10 µm slice thickness) of the abscess and the contralateral muscle was performed and detailed spatial correlation of autoradiography and histopathology (haematoxylin-eosin staining) was obtained. Regions of interest were placed on the abscess wall and the grey values (digitised image intensities) measured were converted to kBq/cc per kBq injected activity per gram (SUV). Areas with increased 18F-FDG uptake corresponded to cellular inflammatory infiltrates mainly consisting of granulocytes. The SUV was calculated to be 4.08±0.65 (mean±SD). The uptake of 18F-FET in activated white blood cells was not increased: the SUV of the abscess wall, at 0.74±0.14, was even below that of contralateral muscle. The low uptake of 18F-FET in non-neoplastic inflammatory cells promises a higher specificity for the detection of tumour cells than is achieved with 18F-FDG, since the immunological host response will not be labelled and inflammation can be excluded.

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