Comparison of O-(2-18F-Fluoroethyl)-L-Tyrosine and L-3H-Methionine Uptake in Cerebral Hematomas

Radiolabeled amino acids are useful for brain tumor diagnosis, but unspecific uptake near the cerebral hematoma may complicate the differentiation of a neoplastic from a nonneoplastic origin of the hematoma. The aim of this study was to investigate the pattern and time course of O-(2-F-18-fluorethyl)-L-tyrosine (F-18-FET) and L-H-3-methionine (H-3-MET) uptake in rats with cerebral hematomas. Methods: Intracerebral hematomas were induced in the striatum of 25 Fischer 344 CDF rats by inoculation of bacterial collagenase. F-18-FET and H-3-MET were injected intravenously at different times up to 4 wk after bleeding. One hour after tracer injection, brains were cut in coronal sections and evaluated by dual-tracer autoradiography. Lesion-to-brain (L/B) ratios were calculated by dividing maximal uptake near the hematomas and mean uptake in normal brain tissue. An L/B ratio greater than 1.5 was considered as indicative of pathologic uptake. The autoradiograms were compared with histology and immunostainings for astrogliosis (glial fibrillary acidic protein) and macrophage infiltration (CD68). Results: F-18-FET exhibited significantly increased uptake near the hematomas between 3 and 14 d after bleeding. The time course of pathologic H-3-MET uptake was similar, but after 3-4 wk there was still borderline uptake in single animals. The L/B ratios exceeded the cutoff level of 1.5 in 10 of 23 animals for F-18-FET and in 12 of 22 animals for H-3-MET but did not exceed a value of 3. Immunostainings indicated that increased uptake of both tracers correlated with reactive astrogliosis, whereas H-3-MET uptake was additionally increased in areas with macrophage infiltration. Conclusion: F-18-FET, like H-3-MET, may exhibit significantly increased uptake near cerebral hematomas, especially during the first 2 wk after bleeding, complicating the differentiation between a neoplastic and a nonneoplastic origin of cerebral hematomas.