The present invention relates to vessel segmentation. In order to provide an improved way of providing segmentation information with reduced X-ray dose, an X-ray image processing device (10) is provided that comprises an interface unit (12), and a data processing unit (14). The interface unit is configured to provide a sequence of time series angiographic 2D images of a vascular structure obtained after a contrast agent injection. The data processing unit is configured to determine an arrival time index of a predetermined characteristic related to the contrast agent injection for each of a plurality of determined pixels along the time series, and to compute a connectivity index for each of the plurality of the determined pixels based on the arrival time index. The data processing unit is configured to generate segmentation data of the vascular structure from the plurality of the determined pixels, wherein the segmentation data is based on the connectivity index of the pixels. The data processing unit is configured to provide the segmentation data for further purposes.