Fiber-optic raster scanning two-photon endomicroscope using a tubular piezoelectric actuator

Abstract

Abstract. A nonresonant, fiber-optic raster scanning endomicroscope was developed using a quarter-tubular piezoelectric (PZT) actuator. A fiber lever mechanism was utilized to enhance the small actuation range of the tubular PZT actuator and to increase its field-of-view. Finite element method simulation of the endoscopic probe was conducted for various conditions to maximize its scanning range. After fabricating the probe using a double clad fiber, we obtained two-photon fluorescence images using raster beam scanning of the fiber. The outer diameter of the probe was 3.5 mm and its rigid distal length was 30 mm including a high numerical aperture gradient index lens. These features are sufficient for input into the instrumental channel of a commercial colonoscope or gastroscope to obtain high resolution images in vivo.

Development of tunable miniature piezoelectric-based scanners validated by the combination of two scanners in a direct image relay technique

“…As has been described in previous publications, the resonant frequency of the PZT is determined by the geometry of the cantilever tip (optical fiber) while the scanning range depends on both the cantilever and PZT size. 9,15,16,20 It has been shown that the resonant frequency of the fiber can be theoretically calculated as $$f=\frac{\pi \sqrt{E}}{16\sqrt{\rho }}\frac{R}{L^2}{B}_n^2,$$ where E is the Young’s modulus, ρ is the density of the fiber, R is the radius of the fiber, L is the fiber length, and B n is a numerical constant equal to 1.194, 2.988, …. 16 Without changing any parameters besides fiber length L , we can expect an inverse correlation with resonant frequency.…”

“…These operating parameters are comparable to a similarly sized PZT. 9 To find the maximum displacement, the frequency was swept across a range from 50 to 1500 Hz, allowing for observation of both the first and second mode resonances. The experiments were repeated for the east–west electrodes and at varying lengths (15, 10, 9, and 7 mm).…”

“…Additionally, miniaturization of the distal end optics reduces discomfort to patients and allows for the exploration of small bodily orifices for observation of luminal organs and tissues. For example, miniature PZTs have been utilized in endomicroscopy to provide widefield full-color imaging, 6 three-dimensional (3-D) optical coherence tomography imaging, 7,8 two-photon fluorescence imaging, 9 confocal imaging, 10 and to increase the ablation region of laser surgical probes. 11 Confined to a few millimeters in diameter (between 2.7 to 4 mm in middle-ear probes 12 and typically <5 mm for endomicroscopic systems), these probes typically consist of a miniature lens to focus light onto a PZT-controlled optical fiber, which is vibrated at its resonance frequency in order to image an area as defined by the actuator deflection, fiber mechanical properties, and imaging optics.…”

“…The image reconstruction strategy, algorithm, and technique depend on the imaging modality employed by the scanner. 7,9,10,13 For most systems, the light leaving the optical fiber is focused onto a point detector and is converted to an electrical signal. Using the known coordinates of the scan at each point, which is typically either a spiral or a Lissajous pattern depending on the driving signal, a reconstruction algorithm assigns the voltage of the signal to a pixel as an intensity value.…”

Microscanners for optical endomicroscopic applications

“…Piyawattanametha et al have successfully demonstrated raster scanning with two resonant MEMS mirrors [11] but the MEMS mirror with a low resonant frequency is vulnerable to the external mechanical shock due to a small spring constant. Do et al also presented raster scanning endomicroscope using a non-resonant tubular piezoelectric actuator [12]. The non-resonant raster scanner readily changes the FOV with both uniform scanning density and a stable orthogonal shape but it still requires high driving voltages.…”