The present invention is directed to a surgical instrument used in minimally invasive procedures performed under either direct, endoscopic, fluoroscopic, or other visualization. The surgical instrument includes a frame which can be retracted into and extended from a sheath to form a loop and a sack having a mouth that is attached to the loop. The sack is used to encircle and capture foreign objects in body canals, cavities or organs. The wire frame is formed of a shape-memory-effect alloy wire in a super elastic state and previously trained to form the loop, the loop forming when the said wire frame is extended beyond the sheath. An invertor is connected to a closed end of the sack for urging the closed end of the sack toward the mouth of the sack.