Systems and methods are disclosed for estimating patient-specific blood flow characteristics. One method includes acquiring, for each of a plurality of individuals, a geometric model and estimated blood flow characteristics of at least part of the individual's vascular system； executing a machine learning algorithm on the geometric model and estimated blood flow characteristics for each of the plurality of individuals； identifying, using the machine learning algorithm, features predictive of blood flow characteristics corresponding to a plurality of points in the geometric models； acquiring, for a patient, a geometric model of at least part of the patient's vascular system； and using the identified features to produce estimates of the patient's blood flow characteristic for each of a plurality of points in the patient's geometric model.
