Contrast agent for X-ray imaging, consisting of a halogenated, especially iodinated or brominated, derivative of boron, having characteristics necessary for its use in X-ray imaging. The contrast agent may be used for imaging a corporeal situs by radiological techniques, comprising delivery to the corporeal situs of an imagingly effectively amount of a physiologically acceptable composition comprising the boron reagent. A variety of illustrative boron reagents is described, including vectorised boron derivatives, e.g., boron derivatives encapsulated within liposomes, fixed on or bonded to macromolecules or polymers, etc. The contrast agents, formulations, and method of the present invention may be employed for a wide variety of radiological imaging applications, e.g., excretory urography, angiocardiography, aortography, etc.