A method for determining a patient-specific contrast medium impulse response function includes providing patient-specific test bolus contrast medium behavior data and a number of basic impulse response functions on the basis of a defined test bolus input function. Simulated test bolus contrast medium behavior functions are generated by combining the basic impulse response functions with the test bolus input function. The simulated functions and the patient-specific data are fitted to one another by varying a number of fitting parameters to obtain optimum fitting parameter values, and the patient-specific contrast medium impulse response function is then created based on the basic impulse response functions and the optimum fitting parameter values. A method for predicting a likely contrast medium behavior and a method for controlling a medical imaging system are also described. Additionally a corresponding apparatus, a control device and an imaging system having such a control device are also described.