An expansion mechanism that includes an elongate instrument and a plurality of struts arranged around the elongate instrument provides radial expansion of a medical device. Each strut has a first end pivotally connected to the elongate instrument and a second strut that expands radially outward. Each strut further carries a flexible line which has a proximal end and a distal end. The distal end of each line passes beyond the second end of the strut which carries it and is attached to the strut immediately adjacent the strut which carries it. Methods of using such an expansion mechanism are also disclosed, particularly to provide deployment of medical devices within a patient's blood vascular system.