J Korean Assoc Oral Maxillofac Surg.  2017 Aug;43(4):256-261. 10.5125/jkaoms.2017.43.4.256.

Recording natural head position using an accelerometer and reconstruction from computed tomographic images

• Park IK
• Lee KY
• Jeong YK
• Kim RH
• Kwon DG
• Yeon S
• Kwon KH

• KMID: 2391356
• DOI: http://doi.org/10.5125/jkaoms.2017.43.4.256

Abstract

OBJECTIVES
The concept of natural head position (NHP) was first introduced by Broca in 1862, and was described as a person's stable physiologic position "when a man is standing and his visual axis is horizontal." NHP has been used routinely for clinical examination; however, a patient's head position is random during cone-beam computed tomography (CBCT) acquisition. To solve this problem, we developed an accelerometer to record patients' NHP and reproduce them for CBCT images. In this study, we also tested the accuracy and reproducibility of our accelerometer.
MATERIALS AND METHODS
A total of 15 subjects participated in this study. We invented an accelerometer that measured acceleration on three axes and that could record roll and pitch calculations. Recorded roll and pitch data for each NHP were applied to a reoriented virtual image using three-dimensional (3D) imaging software. The data between the 3D models and the clinical photos were statistically analyzed side by side. Paired t-tests were used to statistically analyze the measurements.
RESULTS
The average difference in the angles between the clinical photograph and the 3D model was 0.04° for roll and 0.29° for pitch. The paired ttests for the roll data (P=0.781) and the pitch data (P=0.169) showed no significant difference between the clinical photographs and the 3D model (P>0.05).
CONCLUSION
By overcoming the limitations of previous NHP-recording techniques, our new method can accurately record patient NHP in a time-efficient manner. Our method can also accurately transfer the NHP to a 3D virtual model.

Keyword

Surgical diagnostic techniques; Cone-beam computed tomography; Three-dimensional imaging

MeSH Terms

Acceleration
Cone-Beam Computed Tomography
Diagnostic Techniques, Surgical
Head*
Humans
Imaging, Three-Dimensional
Methods

Figure

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  Fig. 1 The accelerometer and three lingual buttons. We made a small accelerometer (3×3×2 cm, 60 g) using the TinyDuino Platform (TinyCircuits, USA) with a Nordic BLE nRF8001 bluetooth 4.0 chip and Bosch BMA250 3-axis accelerator chip on it. Roll and pitch are calculated per 0.5 second with inverse trigonometric function.

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  Fig. 2 Measuring roll and pitch with an application. Roll and pitch data of the device were transmitted to android smartphone application (nRF UART v2.0). Averaged last five data were used in this study.

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  Fig. 3 Clinical photo (lateral side). Two lingual buttons, one on the periauricular and another on the right zygomatic area are shown. To compare the pitch value, we made a line connecting those buttons, and the angle was calculated.

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  Fig. 4 Clinical photo (frontal side). Two lingual buttons on the bilateral zygomatic area are shown. To compare the roll value, we made a line between those buttons, and the angle was measured.

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  Fig. 5 Clinical photo room. The mirror on the wall was used to orient patient's natural head position by mirror-guided technique. The mirror is 150 cm far from the chair. The studio-stand on the bottom of the picture was set to be parallel to the gravity line, vertically, and perpendicular to the gravity line, horizontally by using a fluid level.

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  Fig. 6 Three-dimensional (3D) model reorientation. The cone-beam computed tomography data were reconstructed to 3D model by virtual imaging software (OnDemand3D ver. 1.0; Cybermed Inc., USA), and the 3D model was reoriented as the axis' of the device and the computed tomography images' were parallel to each other.

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  Fig. 7 Recreated natural head position (NHP) on three-dimensional (3D) simulator, frontal side. The 3D model was re-oriented to the NHP based on the roll and pitch data acquired by the device. Then the angle between two lingual buttons on both zygoma in the frontal side was calculated to compare the roll value.

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  Fig. 8 Recreated natural head position (NHP) on three-dimensional (3D) simulator. The 3D model was re-oriented to the NHP based on the roll and pitch data acquired by the device. Then the angle between two lingual buttons on periauricula and zygomatic area in the lateral side was calculated to compare the pitch value.

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