[en] Positron emission tomography (PET) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) has been established in the diagnosis of brain tumors. FDG enables the detection of brain tumor because of increased glucose consumption. However, high cortical glucose metabolism limits the capacity of FDG-PET to distinguish tumor tissue from normal brain tissue. PET with L-[methyl-¹¹C]methionine (MET) provides information on the amino acid uptake in brain tumors. MET-PET has been shown to possess high specificity in tumor detection, tumor delineation, and differentiation between malignant and benign lesions. Various studies have demonstrated a significant correlation between tumor grade and MET uptake in glioma. Our recent experience revealed a significant difference in maximum standardized uptake value (SUV_max) of MET between grade II (3.05±1.42, n=14) and grade IV (4.08±1.05, n=13) gliomas (P<0.001). However, no significant difference was observed in MET SUV_max between grade II and grade III (3.99±1.46, n=14) gliomas. More specifically, studies have demonstrated relationships between MET uptake and tumor proliferation and angiogenesis. A positive correlation was observed between the individual MET SUV_max and Ki-67 indices in our patients (r=0.49, P=0.0011). MET-PET has also been applied for the guidance of stereotactic biopsy and open tumor resection. Many studies have reported the use of MET-PET to investigate the effectiveness of therapy and prognosis of glioma. Moreover, MET-PET is highly sensitive for differentiating between tumor recurrence and radiation necrosis following radiotherapy in patients with glioma and metastatic brain tumor. In spite of several limitations, MET-PET has become a recent 'gold standard' in brain tumor diagnosis and treatment strategy design, especially in glioma. PET with [¹⁸F]-fluoro-3'-deoxy-3'-L-fluoro-thymidine (FLT) provides information about cellular proliferation activity and has been examined in malignant brain tumors. FLT-PET is sensitive in detecting malignant glioma due to the very low background uptake in normal brain tissue. However, the ability to detect low grade glioma and tumor extension appears to be lower for FLT than for MET. Recent studies have found a correlation between World Health Organization (WHO) tumor grade and FLT uptake in gliomas. Our recent experience demonstrated a significant difference in FLT SUV_max between grade II (0.27±0.06, n=6) and grade IV (2.18±0.93, n=10) glioma (P<0.0001), and grade III (0.70±0.45, n=7) and grade IV glioma (P<0.001). FLT uptake showed a significantly higher correlation with the Ki-67 index (r=0.86, P<0.0001) than did MET uptake in gliomas. Studies have also reported the use of FLT-PET to investigate the effectiveness of therapy and prognosis in glioma. Increased FLT accumulation is also observed in other brain tumors including malignant lymphoma and metastatic brain tumor. Additional investigation and understanding of each PET tracer characteristics may further validate the use of PET imaging in brain tumor diagnosis and treatment. Advancement of PET molecular imaging technique using [¹⁸F]fluoromisonidazole (FMISO) provides a noninvasive assessment of hypoxia in malignant glioma and is prognostic for treatment outcome. FMISO-PET may have a further role in directing patients towards targeted hypoxic therapies. (author)