Uptake of 18F-fluorocholine, 18F-fluoro-ethyl-L-tyrosine and 18F-fluoro-2-deoxyglucose in F98 gliomas in the rat

Introduction: The positron emission tomography (PET) tracers F-18-fluoro-ethyl-L-tyrosine (FET), F-18-fluorocholine (N, N-dimethyl-N-[F-18] fluoromethyl-2- hydroxyethylammonium (FCH]) and F-18-fluoro-2-deoxyglucose (FDG) are used in the diagnosis of brain tumours. The aim of this study was threefold: ( a) to assess the uptake of the different tracers in the F98 rat glioma, (b) to evaluate the impact of blood-brain barrier (BBB) disruption and microvessel density (MVD) on tracer uptake and ( c) to compare the uptake in the tumours to that in the radiation injuries ( induced by proton irradiation of healthy rats) of our previous study. Methods: F98 gliomas were induced in 26 rats. The uptake of FET, FCH and FDG was measured using autoradiography and correlated with histology, disruption of the BBB and MVD. Results: The mean FET, FCH and FDG standardised uptake values (SUVs) in the tumour and the contralateral normal cortex ( in parentheses) were 4.19 +/- 0.86 (1.32 +/- 0.26), 2.98 +/- 0.58 (0.51 +/- 0.11) and 11.02 +/- 3.84 (4.76 +/- 1.77) respectively. MVD was significantly correlated only with FCH uptake. There was a trend towards a negative correlation between the degree of BBB disruption and FCH uptake and a trend towards a positive correlation with FET uptake. The ratio of the uptake in tumours to that in the radiation injuries was 1.97 ( FCH), 2.71 ( FET) and 2.37 ( FDG). Conclusion: MVD displayed a significant effect only on FCH uptake. The degree of BBB disruption seems to affect the accumulation of FET and FCH, but not FDG. Mean tumour uptake for all tracers was significantly higher than the accumulation in radiation injuries.