A method of determining at least one patient physiological parameter from an imaging procedure includes at least the steps of measuring time enhancement outputs for at least two different regions of interest, and determining at least one difference between the time enhancement outputs to provide a measure of the at least one patient physiological parameter. The physiological parameter can be a parameter of the cardiopulmonary system. It can also be the cardiac output, the blood volume in a region, a rate transfer term or a transit delay. A first time enhancement output may be measured in the ascending aorta or the descending aorta and a second time enhancement output may be measured in the pulmonary artery trunk.