title: Tracked ultrasonography snapshots enhance needle guidance for percutaneous renal access: a pilot study.
abstract: OBJECTIVE
  Although ultrasonography-guided percutaneous nephrostomy is relatively safe, a number of factors make it challenging for inexperienced operators. A computerized needle navigation technique using tracked ultrasonography snapshots was investigated to determine whether performance of percutaneous nephrostomy by inexperienced users could be improved.
  
  
  METHODS
  Ten operators performed the procedure on a phantom model with alternating needle guidance between conventional ultrasonography and tracked ultrasonography snapshots. The needle was reinserted until fluid backflow confirmed calyceal access. Needle trajectories were recorded using the real time needle navigation system for offline evaluation of operator performance. Recorded needle trajectories were used to measure needle motion path length inside the phantom tissue, number of reinsertions, total procedure time, and needle insertion time as end points of this study.
  
  
  RESULTS
  Needle path length measured inside the phantom tissue was significantly lower with ultrasonography snapshots guidance (295.0±23.1 mm, average±standard error of the mean) compared with control procedures (977.9±144.4 mm, P<0.01). This was associated with a significantly lower number of needle insertion attempts with ultrasonography snapshots (average 1.27±0.10 vs 2.83±0.31, P<0.01). The total procedure time and the needle insertion time were also significantly lower with ultrasonography snapshots guidance.
  
  
  CONCLUSIONS
  Tracked ultrasonography snapshots appear to improve the performance of percutaneous nephrostomy in these preliminary investigations, justifying further validation studies. The presented navigation system is reproducible because of commercially available hardware and open-source software components, facilitating its potential role in clinical practice.
authors.affiliation: 1 Laboratory for Percutaneous Surgery, School of Computing, Queen's University , Kingston, Ontario, Canada .
authors.forename: Tamas
authors.initials: T
authors.lastname: Ungi
authors.forename: Darren
authors.initials: D
authors.lastname: Beiko
authors.forename: Michael
authors.initials: M
authors.lastname: Fuoco
authors.forename: Franklin
authors.initials: F
authors.lastname: King
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Holden
authors.forename: Gabor
authors.initials: G
authors.lastname: Fichtinger
authors.forename: D Robert
authors.initials: DR
authors.lastname: Siemens
mesh_terms: D006801:Humans; D009339:Needles; D009403:Nephrostomy, Percutaneous / Q000379:methods*; D019047:Phantoms, Imaging; D010865:Pilot Projects; D018084:Ultrasonography, Interventional / Q000379:methods*