A medical instrument may include a tube, a sheath provided around and coaxial with the tube, and an inflatable balloon at a distal end of the sheath. The balloon may receive a fluid from a lumen of the sheath, and may have a central opening along a longitudinal axis thereof, and into which the tube extends, a proximal portion, a middle portion adjacent to and distal of the proximal portion, and a distal portion adjacent to and proximal of the middle portion. When the balloon is inflated with the fluid, a maximum diameter of the middle portion may be less than a maximum diameter of the proximal portion, and less than a maximum diameter of the distal portion. The medical instrument may also include an extraction member provided at a distal end of the tube, distal to the balloon, and movable axially relative to the balloon.