1. A method for predicting a post-stenting hemodynamic metric for a coronary artery stenosis from pre-stenting medical image data, comprising: extracting a pre-stenting patient-specific anatomical model of the coronary arteries from medical image data of a patient; directly modifying one or more parameters of a pressure-drop model that computes a pressure-drop over a target stenosis region in the pre-stenting anatomical model of the coronary arteries without modifying the pre-stenting patient-specific anatomical model of the coronary arteries, resulting in a modified pressure-drop model that simulates an effect of stenting on the target stenosis region; simulating blood flow in the pre-stenting patient-specific anatomical model of the coronary arteries with the modified pressure-drop model used for computing the pressure-drop over the target stenosis region in the pre-stenting patient-specific anatomical model of the coronary arteries, wherein the modified pressure-drop model simulates the effect of stenting on the target stenosis region; and calculating a predicted post-stenting hemodynamic metric for the target stenosis region based on the pressure-drop over the target stenosis region computed using the modified pressure-drop model.