1. A method for locating an implant in an ultrasound coordinate system, comprising: obtaining positions of a plurality of implants in a fluoroscopy coordinate system; estimating positions of said plurality of implants in an ultrasound coordinate system; determining an initial transformation matrix based at least in part on said obtained positions and said estimated positions of said plurality of implants; and determining a position of an implant in said ultrasound coordinate system based at least in part on said initial transformation.