The aim of the study is to compare the two imaging modalities perfusion weighted MR-imaging and FET-PET in their ability to provide an accurate histological evaluation of low grade glioma and to reveal focal abnormalities within a homogeneously appearing tumor. Additionally, therapeutic effects should be assessed during a time period of two years.

Inclusion Criteria:

• neuroradiologically suspected low grade glioma (Astrocytoma WHOI-II, Oligodendroglioma WHO II, Oligoastrocytoma WHO II)
• histological verification will be obtained either by microsurgery or by stereotactic biopsy
• patients older than 18 years
• Karnofsky Performance Score >=70
• pregnant or nursing female patients will not be included in this study

Exclusion Criteria:

• patients in whom informed consent cannot be obtained due to organic brain syndrome or insufficient language skills
• patients who cannot lie quiet for a time period of app. two hours during the FET-PEt scan
• medical history of a metastatic brain disease
• patients in whom an MRI scan cannot be performed due to claustrophobia metallic protheses or pacemakers etc.

Patients with a suspected referred to a Neurosurgical Department in order to provide a diagnosis and therapy