1. The Pain Management Center of Long Island; Rockville Centre; New York; U.S.A
2. Department of Anesthesiology; Advocate Illinois Masonic Medical Center; Chicago; Illinois; U.S.A
3. The Center for Pain Relief; Charleston; West Virginia; U.S.A
4. Department of Anesthesiology; The Hospitals of the University of Pennsylvania; Philadelphia; Pennsylvania; U.S.A