1. A computer-implemented method of simulating or optimizing an occlusive procedure, the method comprising: obtaining a patient-specific anatomic model of a patient's vasculature; obtaining an initial computational model of blood flow through the patient's vasculature based on the patient-specific anatomic model; receiving a selected occlusive procedure for treatment at a location of the patient's vasculature; modifying the patient-specific anatomic model by modeling the removal of a portion of the patient's vasculature at or beyond the location of the received occlusive procedure, wherein the removal is modeled by the creation of one or more cross-sectional outlets, surfaces, or boundaries in the modeled vasculature of the patient-specific anatomic model; modifying the initial computational model to generate a second computational model of blood flow through the modified patient-specific anatomic model; modeling redistribution of blood flow based on the occlusive procedure using the second computational model of blood flow; generating or calculating a post-treatment blood flow characteristic of blood flow through the modified patient-specific anatomic model using the modeled redistribution of blood flow; and outputting an electronic representation of the post-treatment blood flow characteristic.