title: Cochlear coordinates in regard to cochlear implantation: a clinically individually applicable 3 dimensional CT-based method.
abstract: METHODS
  Cochlear implant (CI)/tertiary referral center.
  
  
  METHODS
  Twenty-five patients implanted with an Advanced Bionics HiRes90K HiFocus1J CI. STUDY DESIGN/MAIN OUTCOME MEASURES: A 3-dimensional cylindrical coordinate system is introduced using the basal turn of the cochlea as the x and y planes and the center of the modiolus as the z axis. The 0-degree angle is defined by the most lateral point of the horizontal semicircular canal. It is applied to both preoperative and postoperative computed tomographies in 25 patients. The angular position of the round window is examined. Interobserver reproducibility is tested by localization of all electrode contacts within the coordinate system. To observe realignment over time, electrode coordinates in postoperative images were projected on preoperative images. Additionally, comparison to existing imaging-related coordinate systems was made.
  
  
  RESULTS
  The angular position of the center of the round window is 34.6 +/- 0.4 degrees (standard deviation) with an intraclass coefficient of 1.00. The intraclass coefficient for interobserver reproducibility of the 16 electrode contacts ranged from 0.74 to 1 for the rotational angle (phi) and 0.77 to 1 for the distance to the modiolus (rho). In 21 of 25 patients, a perfect match or minimal displacement of up to 3 electrode contacts was seen. Comparison to existing systems showed good correlation.
  
  
  CONCLUSIONS
  A 3-dimensional cochlear coordinate system easily applicable in clinical patients is described, which fulfills the requirements set by an international consensus.
authors.affiliation: Departments of *Radiology and daggerOtolaryngology, Leiden University Medical Center, Leiden, The Netherlands. b.m.verbist@lumc.nl
authors.forename: Berit M
authors.initials: BM
authors.lastname: Verbist
authors.forename: Raoul M S
authors.initials: RM
authors.lastname: Joemai
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: Briaire
authors.forename: Wouter M
authors.initials: WM
authors.lastname: Teeuwisse
authors.forename: Wouter J H
authors.initials: WJ
authors.lastname: Veldkamp
authors.forename: Johan H M
authors.initials: JH
authors.lastname: Frijns
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003051:Cochlea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D019929:Cochlear Implantation; D003054:Cochlear Implants; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007223:Infant; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009925:Organ of Corti / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D055815:Young Adult