1. One or more non-transitory computer-readable media embodying instructions executable by machine to perform operations for angiographic roadmapping comprising: projecting a four-dimensional (4D) digital subtraction angiography (DSA) image volume at a predetermined angle to generate a series of two-dimensional (2D) digitally reconstructed radiograph (DRR) images, wherein the 4D DSA image volume is a time-varying three-dimensional (3D) volume with additional flow information about a contrast flow through a vasculature over a time period, wherein the predetermined angle is substantially equal to a projection angle used to acquire a live fluoroscopic image, wherein the series of 2D DRR images show the contrast flow in an image volume within the time period; registering the series of 2D DRR images with the live fluoroscopic image; generating a maximally opacified image from at least one of the registered 2D DRR images, wherein pixels of the maximally opacified image represent peak contrast levels over a window of time; integrating the maximally opacified image with the live fluoroscopic image to generate a roadmapping fluoroscopic image; and displaying the roadmapping fluoroscopic image for angiographic roadmapping.