Establishing the true time of symptom onset is one of the most important and often challenging aspects of acute ischaemic stroke management. In many cases, stroke onset time cannot be reliably established, notably when patients wake with symptoms. In addition, susceptibility to ischaemia does vary between patients. Thus, tissue salvage may be possible for several hours in some patients, but not at all in others. Imaging techniques that provide temporal information related to the evolution of tissue injury would therefore be extremely useful in the acute setting. Although standard diffusion-weighted images (DWI) do evolve over time, changes in image intensity, or corresponding apparent diffusion coefficient (ADC) values, are …