Systems and methods are disclosed for estimating patient-specific blood flowcharacteristics. One method includes acquiring, for each of a plurality ofindividuals, ageometric model and estimated blood flow characteristics of at least part oftheindividual's vascular system； executing a machine learning algorithm on thegeometricmodel and estimated blood flow characteristics for each of the plurality ofindividuals；identifying, using the machine learning algorithm, features predictive ofblood flowcharacteristics corresponding to a plurality of points in the geometricmodels； acquiring,for a patient, a geometric model of at least part of the patient's vascularsystem； andusing the identified features to produce estimates of the patient's blood flowcharacteristic for each of a plurality of points in the patient's geometricmodel.
