In a method and apparatus for determining perfusion within a tissue region of the human or animal body, the tissue region being supplied by at least two input vessels, a time series of perfusion measurements is acquired, a first concentration/time curve at a first input vessel is determined, a second concentration/time curve at a second input vessel is determined, and a third concentration/time curve in the tissue region is determined. A weighting factor of the supply to the tissue region by the first input vessel and/or the second input vessel is determined by maximizing a residue function that is a function of the weighting factor.
