1. A method for determining a region of gray matter in a brain starting from a time-dependent computed tomography image data record from a perfusion CT examination, the method comprising: calculating a plurality of time-independent images from the time-dependent computed tomography image data record; performing a plurality of threshold histogram analyses in order to determine regions of the brain which are assignable to one or more types of cerebral matter; and subsequently determining a region of gray matter from the information obtained with respect to the determined regions and types of the cerebral matter using at least one logical combination and at least one exclusion method.