The decision between US guidance versus US mapping is influenced primarily by the degree of inherent danger of the procedure. Perform procedures that carry a higher risk or have greater technical difficulty (e.g., central venous access, pericardiocentesis, or foreign body removal) under US guidance. Perform lower risk procedures (e.g., thoracentesis, paracentesis, or abscess I&D) with US mapping. Another factor is sonographer experience. The experienced sonographer is more technically adept and comfortable doing procedures under real-time US guidance. Novice sonographers who do not have as much psychomotor training and experience may find it easier to use US mapping.