title: Implementation of an electromagnetic tracking system for accurate intrahepatic puncture needle guidance: accuracy results in an in vitro model.
abstract: OBJECTIVE
  Electromagnetic tracking potentially may be used to guide percutaneous needle-based interventional procedures. The accuracy of electromagnetic guided-needle puncture procedures has not been specifically characterized. This article reports the functional accuracy of a needle guidance system featuring real-time tracking of respiratory-related target motion.
  
  
  METHODS
  A needle puncture algorithm based on a "free-hand" needle puncture technique for percutaneous intrahepatic portocaval systemic shunt was employed. Preoperatively obtained computed tomographic images were displayed on a graphical user interface and registered with the electromagnetically tracked needle position. The system and procedure was tested on an abdominal torso phantom containing a liver model mounted on a motor-driven platform to simulate respiratory excursion. The liver model featured two hollow tubes to simulate intrahepatic vessels. Registration and respiratory motion tracking was performed using four skin fiducials and a needle fiducial within the liver. Success rates for 15 attempts at simultaneous puncture of the two "vessels" of different luminal diameters guided by the electromagnetic tracking system were recorded.
  
  
  RESULTS
  Successful "vessel" puncture occurred in 0%, 33%, and 53% of attempts for 3-, 5-, and 7-mm diameter "vessels," respectively. Using a two-dimensional accuracy prediction analysis, predicted accuracy exceeded actual puncture accuracy by 25%-35% for all vessel diameters. Accuracy outcome improved when depth-only errors were omitted from the analysis.
  
  
  CONCLUSIONS
  Actual puncture success rate approximates predicted rates for target vessels 5 mm in diameter or greater when depth errors are excluded. Greater accuracy for smaller diameter vessels would be desirable for implementation in a broader range of clinical applications.
authors.affiliation: Department of Radiology, Section of Interventional Radiology, Medstar-Georgetown University Hospital, 3800 Reservoir Road, NW, Washington, DC 20007, USA. levye@gunet.georgetown.edu
authors.forename: Elliot B
authors.initials: EB
authors.lastname: Levy
authors.forename: Jonathan
authors.initials: J
authors.lastname: Tang
authors.forename: David
authors.initials: D
authors.lastname: Lindisch
authors.forename: Neil
authors.initials: N
authors.lastname: Glossop
authors.forename: Filip
authors.initials: F
authors.lastname: Banovac
authors.forename: Kevin
authors.initials: K
authors.lastname: Cleary
mesh_terms: D000465:Algorithms; D055590:Electromagnetic Phenomena; D006801:Humans; D008099:Liver; D009339:Needles; D019047:Phantoms, Imaging; D011677:Punctures / Q000295:instrumentation; D014057:Tomography, X-Ray Computed