1. An x-ray image acquisition system comprising: an x-ray image acquisition system configured to acquire successive x-ray images of an examination subject; an optical image acquisition system configured to acquire successive optical images of the examination subject; and a control unit connected to said x-ray image acquisition system and to said optical image acquisition system to control respective acquisition of said successive x-ray images and said successive optical images, said control unit being configured to detect respective identifiers in respective ones of said successive optical images, and to trigger acquisition of said x-ray images only when the respective identifiers are detected in said ones of said optical images, to cause said x-ray image acquisition system to acquire a first plurality of said successive x-ray images that is less than a second plurality of said optical images acquired by said optical image acquisition unit, with substantially no overlap between said successive x-ray images.