Patlak analysis can be derived from a two-compartment model that describes the one-way transfer of contrast material from the intravascular space to the extravascular space, i.e. there is no significant backflow during the examination time. At any time point, the tissue concentration of contrast material is equivalent to the sum of the intravascular and extravascular concentrations of contrast material as denoted by the following equation: where C(t) is the concentration of contrast material within the tissue, CBV is the cerebral blood volume, C A(t) is the concentration of contrast material in blood (the arterial input function AIF) and K Trans is the volume transfer constant [29]; ∆t describes the time it takes the input function to travel to the tissue voxel; ∆t is determined automatically by cross correlation analysis of the AIF with the voxel TAC separately for every voxel.