A method and system for processing imaging data of a tissue in an individual following a change in oxygenation or blood flow in tissue, for assessing tissue function. Test images are registered with a baseline image, providing registered images. The registered images may be compared to assess variations in the change in the tissue in response to changes in oxygenation or blood flow of the tissue shown in the images. The change in oxygenation or blood flow in the tissue may be quantified and plotted in a parametric plot or displayed in a parametric map to assess whether the change in oxygenation or blood flow, corresponding to a change in signal intensity, is abnormal following a stress event or under other conditions, to assess microvascular or macrovascular function.