An apparatus, method and system for detecting a position within a body are provided. A dipole that is free to rotate or oscillate within a capsule is inserted at a target location within the body. The dipole can be either electric or magnetic, and the dipole rotates or oscillates within the capsule when an alternating or rotating electric or magnetic field is applied in the vicinity of the dipole. Ultrasound energy is impinged upon the target location and a position of the dipole is determined based on detected ultrasound reflections.
