This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Radiology
[{'content': 'Which of the following techniques is the best for differentiating recurrence of brain tumour from radiation therapy-induced necrosis? \nSelect and explain. \nA. MRI, B. Contrast enhanced MRI, C. PET scan, D. CT scan', 'role': 'user'}, {'content': 'Answer: C \nExplanation: "MRI or CT scans are often unable to distinguish radiation necrosis from recurrent tumor, but PET or SPECT scans may demonstrate that glucose metabolism is increased in tumor tissue but decreased in radiation necrosis."', 'role': 'assistant'}]