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
[{'content': 'Brain infarct is detected at the earliest by \nSelect and explain. \nA. NCCT, B. CECT, C. X ray, D. Diffusion weighted MRI', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Diffusion weighted imaging (DWI) is the most sensitive sequence for stroke imaging, becomes positive within minutes in >95% cases"Diffusion-negative" acute strokes may be Small (lacunar) infarcts, Brainstem lesions, Rapid clot lysis/recanalization, and Transient/fluctuating hypoperfusionDiffusion tensor imaging (DTI) is even more sensitive than DWI, especially for pontine and medullary lesionsOn CT Early signs of ischemiaHypo attenuating brain tissueObscuration of the lentiform nucleusInsular Ribbon signDense MCA signHemorrhagic infarcts(Osborn\'s Brain: Imaging, Pathology, and Anatomy, page 189,190,191)', 'role': 'assistant'}]