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
Cerebral infarcts at its earliest is detected by 
Select and explain. 
A. Diffusion weighted MRI, B. MRI, C. Contrast enhanced CT, D. PET scan
A: Diffusion weighted MRI
Answer: A: Diffusion weighted MRI 
Explanation: Diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) is the use of specific MRI sequences as well as software that generates images from the resulting data that uses the diffusion of water molecules to generate contrast in MR images The most common application of conventional DWI (without DTI) is in acute brain ischemia. DWI directly visualizes the ischemic necrosis in cerebral infarction in the form of a cytotoxic edema,appearing as a high DWI signal within minutes of aerial occlusion.With perfusion MRI detecting both the infarcted core and the salvageable penumbra, the latter can be quantified by DWI and perfusion MRI Ref Harrison20th edition pg 2234