1. An X-ray diagnostic imaging system for conducting live fluoroscopic subtraction imaging, comprising: an X-ray source for directing X-ray radiation to a patient being examined; an X-ray imaging device positioned for receiving the X-ray radiation and acquiring images in response thereto; a processor configured to communicate with the X-ray source and X-ray imaging device to control acquisition of a contrast-enhanced mask image frame and a live image frame without contrast enhancement, to conduct a pixel shift vector calculation operation based on a small, user-defined region of interest (ROI) having a location selectable by a user within a displayed image frame during live X-ray imaging and comprising a plurality of adjacent pixels to realize a pixel shift vector derived from the plurality of pixels to correct for motion between an individual live image frame of successive live image frames and a mask image frame, to shift pixels comprising the mask image frame by pixel shift directions defined by the pixel shift vector, and to subtract the shifted mask image frame from the live image frame to realize a live roadmapping image frame; a display for displaying live roadmapping image frames; and a user interface that allows a user to define and capture the small ROI in the displayed image frame for use by the processor conducting the pixel shift calculation.