No predictive factors are known for the response to the bevacizumab anti-angiogenic molecule (Avastin) given in the event of relapse of glioblastoma (GBM) following radiochemotherapy. Classical MRI with gadolinium injection and perfusion is not sufficient to predict survival and response or duration. We propose to evaluate the prognostic interest for 6-month survival of spectroscopic biomarkers of proliferation, glial reaction, infiltration and glutaminergic metabolism or glycolytic metabolism recorded at 7 and 28 days of application of the treatment.