1. A method for determining a plausibility of a MTT parameter map generated based on perfusion image data, comprising: selecting a first vessel in the image data; selecting a second vessel in the image data; determining an estimated mean MTT value from contrast flow based on the selected first and second vessels; computing a mean MTT value from the MTT parameter map; comparing the estimated and the computed mean MTT value; and validating the MTT parameter map only when a plausibility for the MTT map satisfies a pre-set perfusion parameter plausibility criteria.