This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
Radiation-induced brain necrosis is diagnosed by 
Select and explain. 
A. PET scan, B. MRI, C. CT scan, D. Biopsy
A: PET scan
Answer: A: PET scan 
Explanation: radiation-induced necrosis diagnosis is difficult to confirm withoutsurgical tissue sampling (craniotomy or biopsy)Advanced 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)