This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S., Subject name: Medicine
[{'content': 'Which of the following imaging techniques is best able to measure regional brain substrate uptake and metabolic kinetics? \nSelect and explain. \nA. magnetic resonance imaging (MRI), B. computed tomography (CT), C. positron emission tomography (PET), D. serial thallium scintigrams', 'role': 'user'}, {'content': 'Answer: C \nExplanation: PET scans use glucose analogues to demonstrate metabolic activity. They are rarely available, however, and functional MRI scans are now being used extensively to assess areas of brain activity.', 'role': 'assistant'}]