title: Navigation by parallax in three-dimensional space during fluoroscopy: application in guide wire-directed axillary/subclavian vein puncture.
abstract: BACKGROUND
  Fluoroscopy is range ambiguous--the relative positions in three-dimensional space of two structures with superimposed silhouettes cannot be ascertained. The parallax effect can be used to overcome this problem, and was used to develop a technique of axillary/subclavian vein puncture.
  
  
  METHODS
  Patients requiring axillary/subclavian vein puncture were considered for the new technique. The vein was marked by a guide wire placed inside. In the postero-anterior (P-A) caudal projection, the needle was advanced dorsally from medial to the coracoid process at an arbitrary angle until its tip overlay the guide wire over the first intercostal space. Depending on whether the needle tip appeared caudad or cephalad of the guide wire in the P-A projection, the needle was advanced farther into or withdrawn back from the body, with its tip maintained over the guide wire in the P-A caudal projection at all times. Maneuvering of the needle stopped when the needle tip overlay the guide wire in both the P-A caudal and P-A projections or blood was aspirated.
  
  
  RESULTS
  Forty-one separate successful punctures were performed in 20 patients. No complications were recorded. Each puncture took no more than 1 minute, and the image intensifier needed to swing between the P-A caudal and the P-A projections only twice.
  
  
  CONCLUSIONS
  The new technique was effective, efficient, and safe when implemented in clinical practice, justifying the parallax principles on which it is based. The parallax principles may be applied to other invasive medical procedures with due modifications.
authors.affiliation: Department of Cardiology, Royal Victoria Hospital, Belfast, United Kingdom. ernest.lau@btinternet.com
authors.forename: Ernest W
authors.initials: EW
authors.lastname: Lau
mesh_terms: D001367:Axillary Vein / Q000000981:diagnostic imaging / Q000601:surgery*; D002404:Catheterization / Q000295:instrumentation / Q000379:methods*; D005260:Female; D005471:Fluoroscopy / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D010690:Phlebography / Q000379:methods; D011677:Punctures / Q000295:instrumentation / Q000379:methods*; D013350:Subclavian Vein / Q000000981:diagnostic imaging / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000379:methods*