Brain infarct is detected at the earliest by

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)