A method for determining a quantity of interest of a patient, comprising the following steps: a) receiving (302, 402) patient data of the patient at a first physiological state; b) determining (304, 404) a value of a quantity of interest (QoI, 206) of the patient at the first physiological state based on the patient data, the quantity of interest(QoI, 206) representing a medical characteristic of the patient; c1) extracting (306, 406)) features from the patient data, c2) wherein the features which are extracted (306, 406) are based on the quantity of interest (QoI, 216) to be determined for the patient at a second physiological state; and d) mapping (308, 408) the value of the quantity of interest (QoI, 2016) of the patient at the first physiological state to a value of the quantity of interest of the patient at the second physiological state based on the extracted features using a mapping function (f); e) said method adapted as a method for determining fractional flow reserve for a coronary stenosis of a patient at a hyperemia state, comprising: in said step a): receiving patient data of the patient at a rest state; in said step b): calculating a value of a pressure drop over the coronary stenosis of the patient at the rest state based on the patient data; in said step c1): extracting features from the patient data; wherein in said step c2): the features which are extracted are based on the pressure drop to be determined for the patient at the hyperemia state; in said step d): mapping the value of the pressure drop over the coronary stenosis of the patient at the rest state to a value of the pressure drop over the coronary stenosis of the patient at the hyperemia state based on the extracted features; and in said step e): outputting the FFR for the coronary stenosis of the patient based on the pressure drop over the coronary stenosis of the patient at the hyperemia state. a) receiving (302, 402) patient data of the patient at a first physiological state; b) determining (304, 404) a value of a quantity of interest (QoI, 206) of the patient at the first physiological state based on the patient data, the quantity of interest(QoI, 206) representing a medical characteristic of the patient; c1) extracting (306, 406)) features from the patient data, c2) wherein the features which are extracted (306, 406) are based on the quantity of interest (QoI, 216) to be determined for the patient at a second physiological state; and d) mapping (308, 408) the value of the quantity of interest (QoI, 2016) of the patient at the first physiological state to a value of the quantity of interest of the patient at the second physiological state based on the extracted features using a mapping function (f); e) said method adapted as a method for determining fractional flow reserve for a coronary stenosis of a patient at a hyperemia state, comprising: in said step a): receiving patient data of the patient at a rest state; in said step b): calculating a value of a pressure drop over the coronary stenosis of the patient at the rest state based on the patient data; in said step c1): extracting features from the patient data; wherein in said step c2): the features which are extracted are based on the pressure drop to be determined for the patient at the hyperemia state; in said step d): mapping the value of the pressure drop over the coronary stenosis of the patient at the rest state to a value of the pressure drop over the coronary stenosis of the patient at the hyperemia state based on the extracted features; and in said step e): outputting the FFR for the coronary stenosis of the patient based on the pressure drop over the coronary stenosis of the patient at the hyperemia state. in said step a): receiving patient data of the patient at a rest state; in said step b): calculating a value of a pressure drop over the coronary stenosis of the patient at the rest state based on the patient data; in said step c1): extracting features from the patient data; wherein in said step c2): the features which are extracted are based on the pressure drop to be determined for the patient at the hyperemia state; in said step d): mapping the value of the pressure drop over the coronary stenosis of the patient at the rest state to a value of the pressure drop over the coronary stenosis of the patient at the hyperemia state based on the extracted features; and in said step e): outputting the FFR for the coronary stenosis of the patient based on the pressure drop over the coronary stenosis of the patient at the hyperemia state.