<prompt> Radiation-induced brain necrosis is diagnosed byPET scanMRICT scanBiopsy  <response>: radiation-induced necrosis diagnosis is difficult to confirm withoutsurgical tissue sampling craniotomy or biopsyAdvanced imaging techniques such as DTI ADC and fractional anisotropy ratios, perfusion MR imaging CBV, rPH, and relative PSR, MR spectroscopy, and PET hold promise for better differentiation between radiation necrosis and recurrent tumor. Diagnosis in individual cases is complicated by the coexistence of tumor and radiation necrosis.Ref: Ritu Shah, MD, et al Radiation Necrosis in the Brain: Imaging Features and Differentiation from Tumor Recurrence 