1. A medical system comprising: a medical instrument to be guided in a patient body, an X-Ray acquisition system which acquires a two-dimensional X-ray image of said medical instrument, an ultrasound acquisition system for acquiring a three-dimensional ultrasound data set of said medical instrument using an ultrasound probe, a localizer which provides a localization of said ultrasound probe within a referential of said X-ray acquisition system, a selector operable to selecting a region of interest around said medical instrument in the three-dimensional ultrasound data set, that defines a first localization of said region of interest within a referential of said ultrasound acquisition system, a convertor which converts said first localization of said region of interest within said referential of the ultrasound acquisition system into a second localization of said region of interest within said referential of the X-ray acquisition system, using said localization of the ultrasound probe, a generation and display screen which displays a bi-modal representation of said medical instrument in which said two-dimensional X-ray image and the three-dimensional ultrasound data included in said region of interest are combined using said second localization.