1. A method for estimating a measure of a penumbra size of a penumbra in biological tissue, the method comprising: receiving a first image, the first image comprising data representative of a spatially resolved perfusion parameter, receiving a second image, the second image comprising data representative of a spatially resolved diffusion parameter, identifying a first area on the first image, which first area corresponds to a perfusion lesion, identifying a second area on the second image, which second area corresponds to a diffusion lesion, estimating the measure of the penumbra size based on the first and second area, applying a first image processing method on the first image, the first image processing method comprising a level set method, and applying a second image processing method on the second image, the second image processing method comprising a grayscale morphological reconstruction.