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Research Papers

Self-Contained Image Recalibration in a Scanning Fiber Endoscope Using Piezoelectric Sensing

[+] Author and Article Information
I. L. Yeoh

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195
e-mail: ivanyeoh@uw.edu

P. G. Reinhall, M. C. Berg, E. J. Seibel

Department of Mechanical Engineering,
University of Washington,
Seattle, WA 98195

Manuscript received April 11, 2014; final manuscript received September 15, 2014; published online November 14, 2014. Assoc. Editor: Rafael V. Davalos.

J. Med. Devices 9(1), 011004 (Mar 01, 2015) (9 pages) Paper No: MED-14-1168; doi: 10.1115/1.4028652 History: Received April 11, 2014; Revised September 15, 2014; Online November 14, 2014

The scanning fiber endoscope (SFE) is a new ultrathin (1.2 mm diameter) medical imaging device that utilizes a unique mechanical scanning technique to image large (120 deg) fields of view (FOVs). A single 80 μm optical fiber is circularly vibrated by a piezo-electric tube to illuminate a field while the reflected light is collected to construct an image pixel-by-pixel. Accurate scanning of the optical fiber is paramount to image quality. Previously, an optical calibration chamber in the base station was used to calibrate the scanning of the optical fiber. This analytical and experimental work eliminates the use of the calibration chamber by implementing a new piezoelectric sensing approach enabling self-contained recalibration to maintain high-image quality during long medical procedures and also reducing the cost, size, and power consumption of the SFE. This work provides a major step toward self-calibration through adaptive control without additional sensors.

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Figures

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Fig. 1

(a) The new ultrathin forward-viewing SFC. (b) Schematic of the SFE scope probe.

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Fig. 2

(a) Images of a USD20 bill taken with the SFE. By bringing the endoscope closer to the object, we get high-resolution zoom-in images. (b) Undistorted SFE image. (c) Distorted SFE image requiring system recalibration. (d) Inserting the scope probe (upper right) into the calibration chamber for recalibration, a procedure eliminated by methods presented in this paper.

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Fig. 3

(a) Simplified first mode of optical fiber vibration. (b) The piezoelectric tube axes (vertical and horizontal axes) do not align with the eigendirections (rotated axes) due to random fiber ovularity. (c) Elliptical path response or whirling motion that is explained by our analysis.

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Fig. 4

(a) Piezoelectric drive signal during different phases of the scanning profile. (b) Scanner response during different phases of the scanning profile.

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Fig. 5

(a) First extended mode shape and (b) second extended mode shape, where previously ignored piezoelectric tube deflections are considered

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Fig. 6

(a) Lumped-element model of the piezoelectric sensing circuit. (b) Circuit model when V_Drive is off.

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Fig. 7

(a) Experimental setup. (b) Signals from the sensing circuit, showing that after actuation is turned off, the same electrical channel can be used for sensing the piezoelectric tube deflections.

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Fig. 8

(a) Whirling motion (low flatness) when φ ≠ θ. (b) Straight-line response (maximal flatness) when φ = θ, from piezoelectric sensing data. (c) Verification of straight-line response, from optical position sensor data.

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Fig. 9

Identifying first damped natural frequency from the prominent peak in the FFT magnitude spectrum

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Fig. 10

(a) FFT magnitude peak height changes with different braking phases. (b) Optimum braking phase identified from minimum FFT magnitude peak height. (c) Piezoelectric sensing signal after braking. (d) Optical position sensor signal after braking, showing that the scanner is brought rapidly to rest.

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Fig. 11

Piezoelectric sensing data over changing operating temperature (T) from 24 °C to 44 °C: (a) Tracking eigendirections. (b) Tracking damped first natural frequency. (c) Tracking phase. (d) Piezoelectric sensing signals show that scan control and braking is much more effective after recalibrating for temperature changes (heating from 24 °C to 44 °C).

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