Scanning and Actuation Techniques for Cantilever-Based Fiber Optic Endoscopic Scanners-A Review

Abstract

Endoscopes are used routinely in modern medicine for in-vivo imaging of luminal organs. Technical advances in the micro-electro-mechanical system (MEMS) and optical fields have enabled the further miniaturization of endoscopes, resulting in the ability to image previously inaccessible small-caliber luminal organs, enabling the early detection of lesions and other abnormalities in these tissues. The development of scanning fiber endoscopes supports the fabrication of small cantilever-based imaging devices without compromising the image resolution. The size of an endoscope is highly dependent on the actuation and scanning method used to illuminate the target image area. Different actuation methods used in the design of small-sized cantilever-based endoscopes are reviewed in this paper along with their working principles, advantages and disadvantages, generated scanning patterns, and applications.

Keywords: MEMS actuators; electromagnetic; electrostatic; electrothermal; endoscopes; medical imaging; piezoelectric; scanning patterns; shape memory alloys.

Figure 1

Block diagram of a confocal micro-endoscope.

Figure 2

Fluorescence confocal imaging developed by Pentax: (a) schematic design of the micro-endoscope; (b) an en face image of rectal mucosa showing the crypt lumens (taken with the permission of [73]).

Figure 3

Schematic diagram of a PARS-OCT probe: (a) distal tip; (b) circular motion generation by rotating just one lens; (c) linear scan by rotation of both lenses (taken with permission of [74]) © The Optical Society.

Figure 4

Endoscopic OCT image of the gill structure of a tadpole: (a) photograph of probe relative to the tadpole; (b,c) OCT images showing gill pockets indicated with g (taken with the permission of [74]). © The Optical Society.

Figure 5

Euler–Bernoulli beam and a free body diagram of an element of the beam.

Figure 6

Deformation of a cantilever beam at resonance.

Figure 7

Piezoelectric bending actuator: (a) schematic diagram; (b) working principle.

Figure 8

Multiple patterns generating fiber scanner: (A) schematic diagram of the scanner; (B) achieved scanning patterns projected on a USAF target (taken with permission of [104]).

Figure 9

Raster scanning endoscope: (A) mechanical assembly; (B) developed prototype; (C) optical path diagram; (D) fluorescence image of an unstained ex vivo lung tissue (taken with the permission of [105]).

Figure 10

Schematic diagram of a scanning fiber endoscope (taken with permission of [15]).

Figure 11

In vivo images of airways of a pig acquired with (a) conventional Pentax bronchoscope; (b) scanning fiber endoscope (taken with permission of [15]).

Figure 12

Nonlinear optical endoscope: (a) schematic diagram; (b) two-photon and second harmonic generation structural image of a resected mouse liver (taken with permission of [106]).

Figure 13

Fourier-plane fiber scanner: (a) schematic diagram; (b) cross-sectional tomogram of human finger (taken with permission of [107]).

Figure 14

Electrothermally actuated confocal endo-microscope: (a) schematic diagram; (b) working principle (taken with permission of [65]).

Figure 15

Cantilevered fiber scanner using chevron actuator: (a) schematic diagram; (b) reconstructed image of a resolution target.

Figure 16

Schematic diagram of a non-resonant fiber scanner using bimorph electrothermal actuation technique (taken with the permission of [95]).

Figure 17

Forward-viewing OCT probe based on electromagnetic actuation: (a) schematic diagram; (b) real-time image of conjunctiva (taken with the permission of [132]) © The Optical Society.

Figure 18

Schematic of an electromagnetically driven fiber scanner (taken with the permission of [133]).

Figure 19

Schematic design of a fiber scanner excited at second resonance mode using an electromagnetic actuator (taken with the permission of [64]).

Figure 20

Schematic of a magnetically actuated fiber-based imaging system (reprinted with permission from [141]).

Figure 21

Electrostatically driven fiber scanner: (a) schematic diagram; (b) Doppler OCT image of a tadpole heart (taken with permission of [150]) © The Optical Society.

Figure 22

Schematic design of endoscopic tip guided using SMA coils (taken with the permission of [153]).

Figure 23

Active bending endoscope using SMA coil actuators: (a) endoscope design; (b) enlarged view of the actuation mechanism (taken with the permission of [155]).