Digital Live-tracking 3D Sensors for Head Orientation

Objective: To test a new methodology for recording natural head position (NHP) with 6 degrees of freedom during 3D stereophotogrammetry. Methods: Four different 3D pictures (3dMD) were taken from 20 volunteers as follows: (1) in NHP, (2) a repeat of picture 1, (3) patient in NHP wearing a headset with 3D live tracking sensors (3D Guidance trackSTAR, Ascension); and (4) a repeat of picture 3. The sensors were used to track the X, Y and Z coordinates in space and pitch, yaw and roll of the subject head in NHP. The patients were positioned sitting in front of a mirror and asked to stand and walk between each acquisition. Eight landmarks were identified in each 3D picture (nasion, tip of nose, subnasale, right and left lip commissures, midpoints of upper and lower lip vermillions, soft tissue B-point). The distances between correspondent landmarks were measured between pictures 1 to 2, and 3 to 4 using CMF Application software. Student's t-test was used to test differences between NHP with and without sensor. Results: Inter-landmark distances for acquisitions 1 and 2 (NHP without sensors) and acquisitions 3 and 4 (NHP with sensors) were consistent for all landmarks indicating that roll, pitch and yaw of the head are controlled independent of the use of sensors. However inter-landmark distances were in average 17.34 ± 0.32mm between acquisitions 1 and 2 (NHP without sensors). Between acquisitions 3 and 4, the distances averaged 6.17 ±0.15mm. All the inter-landmark distances were significantly different between the two methods ( p-values < 0.001). Conclusion: The use of 3D live tracking sensors aids reproducibility of patient head positioning repeated or follow up acquisitions of 3D stereophotogrammetry. Even with the use of sensors, differences in spatial head position between acquisitions still require registration procedures. Support: DE017727, DE018962, DE005215.