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Research Papers

Estimating Endoscopic Orientation in Static and Dynamic States With Inertial Sensors

[+] Author and Article Information
Hung V. Dao

Graduate School of Engineering and Science,
Shibaura Institute of Technology,
Saitama City,
Saitama 337-8570, Japan
e-mail: nb13503@shibaura-it.ac.jp

Takashi Komeda

Professor
Bioscience and Engineering,
Shibaura Institute of Technology,
Saitama City,
Saitama 337-8570, Japan
e-mail: komeda@se.shibaura-it.ac.jp

Manuscript received September 17, 2015; final manuscript received March 14, 2016; published online August 5, 2016. Assoc. Editor: Carl Nelson.

J. Med. Devices 10(4), 041003 (Aug 05, 2016) (7 pages) Paper No: MED-15-1261; doi: 10.1115/1.4033332 History: Received September 17, 2015; Revised March 14, 2016

This paper presents a new method for estimating the tilt angles of endoscopic images. Disorientation is one of the major challenges during natural orifice translumenal endoscopic surgery (NOTES). Reorientation allows surgeons or gastroenterologists to work in off-axis conditions and provides an important reference for coupling a secondary image. Some published studies of angle estimation for NOTES still have the limitation under the influence of movement or vibration. This study proposes a new sensor-fusion method for reducing the shock-based error. A triaxial accelerometer measures the gravitational vector (g-components) in all static states. When motion appears, the angular velocity from a triaxial gyroscope is used to calculate the elemental changes in g-components. A so-called predict-and-choose process relies on this data to predict the future state by giving many prediction values. The relationship between these values, the newest accelerometer readings, and their variation determine the final choice. Hence, under all conditions, the gravitational components are iteratively estimated to calculate the tilt angles. The result is evaluated by being applied in a well-known application, endoscopic horizon stabilization. Compared with the reference method, the proposed method has notable advantages. The simulation and experimental results show small errors, smooth angle change, and a small delay time. The tilt angles are reliable without any cumulative error under the prolonged motion. Therefore, this study gives surgeons or gastroenterologists an improved rectified image for reorienting under off-axis conditions. Further research will identify more applications for the development of surgical instruments for NOTES.

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Figures

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Fig. 1

System overview with key components and key processes in the basic application

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Fig. 2

Tip of the flexible endoscope: (a) position of the IMU and (b) definition of the three elemental rotations

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Fig. 3

Sensor fusion in the predict-and-choose process

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Fig. 4

Gravitational vector changes caused by each elemental rotation: (a) rotation about Z-axis changes gx and gy, (b) rotation about the X-axis changes gy and gz, and rotation about the Y-axis changes gz and gx

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Fig. 5

Generating the simulation data by the virtual IMU: (a) schematic diagram of the virtual IMU and (b) original tilt angles for conditions (iii) and (iv); here, Φ changes as a sine function while Θ changes as a linear function

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Fig. 6

Simulation results under condition (ii), linear acceleration only: akmax=3 m/s2 and ω = 0

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Fig. 7

Simulation results under condition (iii), rotation with small background vibration: akmax=0.5 m/s2 and ω≠0

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Fig. 8

Simulation results under condition (iv), combined linear acceleration and rotation: akmax=3 m/s2 and ω≠0

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Fig. 9

Simulation results under condition (iv), combined linear acceleration and rotation: akmax=10 m/s2 and ω≠0

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Fig. 10

Rotation frame used in the experiments

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Fig. 11

Experimental results when the motion noise is small

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Fig. 12

Experimental results under the strong motion

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Fig. 13

Using the output angles of both methods to stabilize the horizon under some conditions: (a) static state, (b) weak motion, (c) strong motion, and (d) continuous strong motion

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