title: Digital live-tracking 3-dimensional minisensors for recording head orientation during image acquisition.
abstract: BACKGROUND
  Our objective was to test the value of minisensors for recording unrestrained head position with 6 degrees of freedom during 3-dimensional stereophotogrammetry.
  
  
  METHODS
  Four 3-dimensional pictures (3dMD, Atlanta, Ga) were taken of 20 volunteers as follows: (1) in unrestrained head position, (2) a repeat of picture 1, (3) in unrestrained head position wearing a headset with 3-dimensional live tracking sensors (3-D Guidance trackSTAR; Ascension Technology, Burlington, Vt), and (4) a repeat of picture 3. The sensors were used to track the x, y, and z coordinates (pitch, roll, and yaw) of the head in space. The patients were seated in front of a mirror and asked to stand and take a walk between each acquisition. Eight landmarks were identified in each 3-dimensional picture (nasion, tip of nose, subnasale, right and left lip commissures, midpoints of upper and lower lip vermilions, soft-tissue B-point). The distances between correspondent landmarks were measured between pictures 1 and 2 and 3 and 4 with software. The Student t test was used to test differences between unrestrained head position with and without sensors.
  
  
  RESULTS
  Interlandmark distances for pictures 1 and 2 (head position without the sensors) and pictures 3 and 4 (head position with sensors) were consistent for all landmarks, indicating that roll, pitch, and yaw of the head are controlled independently of the sensors. However, interlandmark distances were on average 17.34 ± 0.32 mm between pictures 1 and 2. Between pictures 3 and 4, the distances averaged 6.17 ± 0.15 mm. All interlandmark distances were significantly different between the 2 methods (P <0.001).
  
  
  CONCLUSIONS
  The use of 3-dimensional live-tracking sensors aids the reproducibility of patient head positioning during repeated or follow-up acquisitions of 3-dimensional stereophotogrammetry. Even with sensors, differences in spatial head position between acquisitions still require additional registration procedures.
authors.affiliation: Department of Orthodontics, School of Dentistry, University of North Carolina, Chapel Hill, NC, USA. lkoerich@gmail.com
authors.forename: Leonardo Koerich
authors.initials: LK
authors.lastname: de Paula
authors.forename: James L
authors.initials: JL
authors.lastname: Ackerman
authors.forename: Felipe de Assis Ribeiro
authors.initials: Fde A
authors.lastname: Carvalho
authors.forename: Lindsey
authors.initials: L
authors.lastname: Eidson
authors.forename: Lucia Helena Soares
authors.initials: LH
authors.lastname: Cevidanes
mesh_terms: D059925:Anatomic Landmarks; D006257:Head / Q000502:physiology*; D019416:Head Movements; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D056888:Patient Positioning; D010780:Photogrammetry / Q000295:instrumentation; D011187:Posture; D019252:Radiography, Dental, Digital / Q000295:instrumentation*; D015203:Reproducibility of Results