1. A computer-implemented method for determining patient-specific hemodynamic information using at least one computer system, the computer-implemented method comprising: receiving, at the at least one computer system, a patient-specific anatomic model of at least a portion of a patient's vasculature and at least a portion of tissue supplied with blood from the portion of the patient's vasculature; determining, non-invasively from an estimation of blood flow through the patient-specific anatomic model by a processor of the at least one computer system, one or more first values of a blood flow characteristic within the portion of the patient's vasculature or the portion of tissue; determining, non-invasively from the patient-specific anatomic model and the one or more first values of the blood flow characteristic by the processor, a first fractional flow reserve value that indicates a risk of low blood flow to the portion of tissue; modifying, using the at least one computer system, at least a portion of the patient-specific anatomic model to produce a modified patient-specific anatomic model, based on at least one treatment option for treating the portion of the patient's vasculature; determining, non-invasively from a second estimation of blood flow through the modified patient-specific anatomic model by the processor, one or more second values of the blood flow characteristic within the portion of the patient's vasculature or the portion of tissue; determining, non-invasively from the modified patient-specific anatomic model and the one or more second values of the blood flow characteristic by a processor of the at least one computer system, a second fractional flow reserve value that indicates a risk of low blood flow to the portion of tissue; and generating a visualization of one or more of the modified patient-specific anatomic model, the second fractional flow reserve value, and an assessment of the at least one treatment option based on the second fractional flow reserve value.