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

The aim of this study was to compare the uptake of F-18-fluoroethyl-L-tyrosine (F-18-FET) with that of F-18-fluorodeoxyglucose (F-18-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, 1.2x10(9) CFU/ml). Four animals were intraperitoneally injected with 130-180 MBq F-18-FDG. four with 140-170 MBq F-18-FET and three with a mixture of 140-170 MBq F-18-FET and 1.8 MBq C-14-deoxy glucose. Autoradiography (10 mum 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 F-18-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 F-18-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 F-18-FET in non-neoplastic inflammatory cells promises a higher specificity for the detection of tumour cells than is achieved with F-18-FDG, since the immunological host response will not be labelled and inflammation can be excluded.