title: Computer-assisted navigation applied to fetal cardiac intervention.
abstract: BACKGROUND
  Prenatal cardiac interventions (PCI) for human fetal aortic valve (AoV) stenosis can reduce left ventricular hypoplasia and restore ventricular growth and function. However, 'freehand' needle delivery from the maternal skin through the uterine wall, fetal chest and ventricular apex to cross the fetal AoV remains technically challenging and time intensive, and is the rate-limiting step in the procedure.
  
  
  METHODS
  We developed a computer-assisted navigation (CANav) system that tracks the position and orientation of a two-dimensional (2D) ultrasound image relative to the trajectory of an electromagnetic (EM) embedded needle and stylet. We tested the CANav system in vitro using a water bath phantom, then in vivo using adult rats and pregnant (fetal) sheep.
  
  
  RESULTS
  The CANav system accurately tracked the delivered needle position in both in vitro phantom and adult rat model experiments. We performed 22 PCI attempts with or without CANav in a fetal sheep model. Maternal laparotomy was required to adjust the fetal position in 50% of the procedures. The time required to deliver the needle from the skin into the left ventricle (LV) using CANav was 2.9 +/- 1.7 (range 2-7) min (n = 14) vs. 5.5 +/- 4.3 (range 1-12) min (n = 8) without CANav (p < 0.05). The time needed to cross the aortic valve once the needle was within the LV was similar with and without CANav (p = 0.19).
  
  
  CONCLUSIONS
  CANav reduces the PCI time required to accurately deliver a needle to the fetal heart. Adaptations of this technical approach may be relevant to other congenital cardiac conditions and ultrasound-guided medical procedures.
authors.affiliation: Department of Obstetrics and Gynecology, Magee-Women's Hospital, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Emery
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Kreutzer
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Sherman
authors.forename: Kazuro L
authors.initials: KL
authors.lastname: Fujimoto
authors.forename: Branislav
authors.initials: B
authors.lastname: Jaramaz
authors.forename: Constantinos
authors.initials: C
authors.lastname: Nikou
authors.forename: Kimimasa
authors.initials: K
authors.lastname: Tobita
authors.forename: Bradley B
authors.initials: BB
authors.lastname: Keller
mesh_terms: D000818:Animals; D001024:Aortic Valve Stenosis / Q000000981:diagnostic imaging / Q000601:surgery*; D013504:Cardiovascular Surgical Procedures / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006330:Heart Defects, Congenital / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D009339:Needles; D051381:Rats; D011917:Rats, Inbred Lew; D012371:Robotics / Q000295:instrumentation* / Q000379:methods; D025321:Surgery, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D018084:Ultrasonography, Interventional / Q000295:instrumentation* / Q000379:methods; D016216:Ultrasonography, Prenatal / Q000295:instrumentation* / Q000379:methods