This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Magnetic Resonance Imaging, Subject name: Radiology
[{'content': 'Which MRI sequence is used to detect cytotoxic edema before vasogenic edema? \nSelect and explain. \nA. T1WI, B. T2WI, C. SWI, D. DWI', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Vasogenic edema shows HyperIntense T2 and FLAIR signals, which do not show Restricted diffusion.(Cytotoxic cerebral edema, which shows diffusion restriction). The one sequence which is able to identify cytotoxic oedema, and was thus responsible for a revolution in the imaging of acute Ischaemic stroke, is Diffusion Weighted Imaging (DWI).', 'role': 'assistant'}]