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DNA synthesis rate (2) and the [‘8F]fluorodeoxyglucose (FDG) PET method allows noninvasive measurement of tumor grade, prognosis and recurrence (3—10).However, FDG uptakeinvolves a process common to both tumorand nontumor tissues. In tumor tissues, FDG uptake is related to inflammatory and neoplastic cells (11); in nontumor tissues (i.e., normal brain, abscesses, scar or epileptic focus), the tracer uptake could hamper the interpretation of the tumor's uptake (12). These potential drawbacks could be circumvented by developing a more selective tumor tracer. During the last decade, PET imaging with “C-labeledthymidine (Tdr) was developed to measure noninvasively cellular proliferation (13,14). Previous data obtained in a partial hepatectomized rat model showed a correlation between PET-Tdr images and the DNA sy