Scanning Fiber Research Articles

Rapid, k-space linear wavelength scanning laser source based on recirculating frequency shifter.

We propose and successfully demonstrate a k-space linear and self-clocked wavelength scanning fiber laser source based on recirculating frequency shifting (RFS). The RFS is realized with a high speed electro-optic dual parallel Mach-Zehnder modulator operating at the state of carrier suppressed single sideband modulation. A gated short pulse is injected into an amplified RFS loop to generate the wavelength scanning pulse train. We find that the accumulation of in-band amplified spontaneous emission (ASE) noise over multiple scanning periods will saturate the erbium-doped fiber amplifier and impede the amplification to the pulse signal in the RFS loop. To overcome the degradation of temporal signal due to the accumulation of ASE noise over multiple scanning periods, we insert a modulated optical switch into the RFS loop to completely attenuate the in-band ASE noise at the end of each scanning period. The signal to noise ratio of the temporal pulsed signal is greatly enhanced. K-space linear and self-clocked wavelength scanning fiber laser sources in 6.1 nm/7.2 nm scanning range with 20 GHz/30 GHz frequency shifting are successfully demonstrated.

The effects of humidity on the surface modification of wool fabric through atmospheric pressure plasma jet

Current research was carried out on hydrophilic wool fibers at three different humidity conditions through atmospheric pressure plasma jet (APPJ). Samples were taken to evaluate surface microscopic morphology, surface roughness, directional friction effect (DFE), and surface chemical composition. The scanning electron microscope (SEM) and fiber friction coefficient test (FFT) results show that wetting pretreatment has significant effect on surface etching and DFE, but very limited effect on surface roughness. Allworden reaction and X-ray photoelectron spectroscopy (XPS) results reveal that extra moisture changes C, O, N, S contents and their related characteristic functional groups, therefore increases etching degree on wool fiber surface scales. It was concluded that APPJ treatment is effective in processing wool fiber with high moisture contents.

109 Multimodal Endovascular Endoscopy in Carotid Atherosclerotic Disease

Disruption of vulnerable atherosclerotic plaque is the precipitating factor that culminates in thrombosis and ischemia. Current technologies do not have sufficient power to identify subtle thrombogenic lesions (ie, ulcers) in the arterial endoluminal surfaces nor reliably predict markers for future symptomatology. We developed an ultra-thin scanning fiber endoscope (SFE) to directly visualize the endoluminal surface of carotid arteries and identify structural, chemical, and biological markers of vulnerable and complicated atherosclerotic plaques. 1.2 mm and 2.1 mm endoscopes containing single optical fiber scanned by a piezoelectric drive mechanism were developed to illuminate tissue surfaces with red, blue, and green laser beams (RBG). Laser-induced backscattering (reflectance) and tissue fluorescence collected by a ring of optical fibers were then digitalized to reconstruct color videos with large fields of view. Then, SFE was studied ex vivo in human carotid arteries and in vivo in a rabbit model of atherosclerosis. After imaging, specimens were processed for histology; lesions were independently reviewed by 2 pathologists and matched to endoscopic images with analysis of variance. High-definition structural and chemical images of 20 carotid arteries harvested during hospital autopsies revealed 42 lesions. Based on anatomical features and tissue fluorescence, we developed a classifier that enabled identification of: healthy endovascular regions (smooth surfaces with strong homogeneous fluorescence); early plaques (dot or streak-like elevated lesions with low fluorescence); advance plaques (irregular elevated lesions with minimal to absent fluorescence); and complicated plaques (ulcers: punch-out dark-gray lesions with raised irregular bead-like borders and speckled fluorescence pattern; hematoma: absent reflection, black regions, and fluorescence). The image quality and validity of the classifier were reproduced in vivo in an atherogenic rabbit model. Multimodal SFE generates high-definition structural and label-free chemical images, and detects with high sensitivity and specificity small intravascular thrombi and subtle surface thrombogenic lesions in nonstenosing complicated plaques, even in cases not detected by conventional diagnostic modalities. Therefore, it holds the potential for becoming a new imaging platform in cerebrovascular and cardiovascular disease.

Electromechanical Modeling and Adaptive Feedforward Control of a Self-Sensing Scanning Fiber Endoscope

Precise image capture using a mechanical scanning endoscope is framed as a resonant structural-deflection control problem in a novel application. A bipolar piezoelectric self-sensing circuit is introduced to retrofit the piezoelectric tube as a miniature sensor. A data-driven electromechanical modeling approach is presented using system identification and system inversion methods that together represent the first online-adaptive control strategy for the scanning fiber endoscope (SFE). Trajectory tracking experiments show marked improvements in scan accuracy over previous control methods and significantly, the ability of the new method to adapt to changing operating environments.

(Invited) Spectral Triangulation: A Novel 3D Method for Locating Single-Walled Carbon Nanotubes In Vivo

Nanomaterials with luminescence in the short-wave infrared (SWIR) region are of special interest for biological research and medical diagnostics because of relatively favorable tissue transparency in that region. Single-walled carbon nanotubes (SWCNTs) show sharp SWIR spectral signatures and therefore have the potential for noninvasive detection and imaging of cancerous tumors when linked to selective targeting agents such as antibodies. However, such applications face the challenge of detecting and localizing the source of light emission from inside tissues. We present here a new method, called spectral triangulation, for sensitively locating SWCNT emission sources in three dimensions using only optical measurements at the specimen surface. SWCNTs inside tissue phantoms are excited by an LED array, and resulting SWIR emission is captured by a scanning fiber optic probe coupled to an InGaAs spectrometer or avalanche photodiode detector. Because of water absorption, attenuation of the SWCNT fluorescence in tissues is strongly wavelength-dependent. We can therefore gauge the distance between SWCNTs and probe by analyzing differential changes in the measured SWCNT emission spectra. SWCNT fluorescence is clearly detected though as much as 22.5 mm of tissue phantom, and the three-dimensional locations of SWCNT samples are deduced with sub-millimeter accuracy at depths up to 10 mm. Our method can also distinguish and locate dual SWCNT sources within tissues.

Design and Fabrication of a Disposable Dental Handpiece for Clinical Use of a New Laser-Based Therapy-Monitoring System

Dental caries, the breakdown of tooth enamel by bacteria infection that causes cavities in the enamel, is the most common chronic disease in individuals 6–19 years of age in the U.S. Optical detection of caries has been shown to be sensitive to the presence of bacteria and the resulting demineralization of enamel. The scanning fiber endoscope (SFE) is a miniature camera system that can detect early stages of caries by performing high-quality imaging and laser fluorescence spectroscopy with 405 nm excitation. Because optical imaging of caries does not involve radiation risk, repeated imaging of the teeth is acceptable during treatment of the bacterial infection to monitor healing. A disposable handpiece was designed and fabricated to position the flexible fiber optic SFE probe for quantitative measurements. Plastic 3D-printed handpiece prototypes were tested with the SFE and a fluorescence calibration standard to verify mechanical fit and absence of signal contamination. Design feedback was provided by pediatric dentists and staff engineers to guide iterations. The final design configuration was based on the need to image interproximal regions (contact surfaces between adjacent teeth), ergonomics, and probe safety. The final handpiece design: (1) is safe for both the patient and the probe, (2) allows easy SFE insertion and removal, (3) does not interfere with spectral measurements, (4) standardizes the SFE's positioning during imaging by maintaining a consistent distance from the target surface, and (5) is significantly less expensive to produce and use than purchasing sanitary endoscope sheaths. The device will be used to help determine if new medicinal therapies can arrest caries and repair early interproximal demineralization under the clinical monitoring program. Ultimately, we anticipate that this handpiece will help us move closer toward widespread implementation of a dental diagnostic laser system that is safer and more sensitive than conventional methods for early caries detection.

A non-resonant fiber scanner based on an electrothermally-actuated MEMS stage

Scanning fiber tips provides the most convenient way for forward-viewing fiber-optic microendoscopy. In this paper, a distal fiber scanning method based on a large-displacement MEMS actuator is presented. A single-mode fiber is glued on the micro-platform of an electrothermal MEMS stage to realize large range non-resonant scanning. The micro-platform has a large piston scan range of up to 800μm at only 6V. The tip deflection of the fiber can be further amplified by placing the MEMS stage at a proper location along the fiber. A quasi-static model of the fiber-MEMS assembly has been developed and validated experimentally. The frequency response has also been studied and measured. A fiber tip deflection of up to 1650μm for the 45mm-long movable fiber portion has been achieved when the MEMS electrothermal stage was placed 25mm away from the free end. The electrothermally-actuated MEMS stage shows a great potential for forward viewing fiber scanning and optical applications.

Rapid scanning catheterscope for expanded forward-view volumetric imaging with optical coherence tomography.

We demonstrate a novel catheterscope, based on scanning fiber endoscopy, for volumetric imaging with optical coherence tomography (OCT), which possesses a high resonance frequency (>2 kHz) and a small outer diameter (OD) (1.07mm). Our design is the fastest volumetric-scanning, forward-viewing catheterscope for OCT, and the scanning package has the smallest OD of any such OCT package published to date. Using a proof-of-operation catheterscope with commercial lenses, we demonstrate high-quality in vivo and ex vivo volumetric imaging and extend the 1.1mm diameter field of view more than 200-fold by mosaicking. Due to its small OD, short rigid tip length, and fast scan rate, this scope is the leading candidate design to enable early detection and staging of bladder cancer during flexible white light cystoscopy.

Axial-Stereo 3-D Optical Metrology for Inner Profile of Pipes Using a Scanning Laser Endoscope

As the rapid progress in the development of optoelectronic components and computational power, 3-D optical metrology becomes more and more popular in manufacturing and quality control due to its flexibility and high speed. However, most of the optical metrology methods are limited to external surfaces. This article proposed a new approach to measure tiny internal 3-D surfaces with a scanning fiber endoscope and axial-stereo vision algorithm. A dense, accurate point cloud of internally machined threads was generated to compare with its corresponding X-ray 3-D data as ground truth, and the quantification was analyzed by Iterative Closest Points algorithm.

Microelectromagnetic actuator based on a 3D printing process for fiber scanner application

A novel electromagnetic-actuated fiber scanner has been proposed for ultra-thin scanning fiber endoscope application. A free-fixed optical fiber cantilever with a cylindrical magnet can be driven and vibrated by a tilted coil on a tube surface under electromagnetic force. The tiny coil with a large tilt angle as the actuator is fabricated by a new three-dimensional (3D) printing technology and handmade hybrid process. It is an efficient and low-cost method for fabricating tiny 3D tilted coils compared with the complicated micromachining process. A 2.0 mm outer diameter tilted coil has been successfully developed. The line pitch, tilt angle, resistance and turns of this fabricated coil are 75 µm, 60°, 20 Ω and 100 turns, respectively. The scanning motion of the assembled scanner utilizing the fabricated 3D coil, fiber and a small magnet has been measured by a high-speed camera. The scanner consists of a 9 mm-length optical fiber, a 2 mm outer diameter cylindrical magnet, a jig and a fabricated tilted coil.The displacement of the fiber tip in the scanner is observed and measured when the alternative current-driven voltage was applied to the tilted coil, and 126.8 µm maximum displacement has been obtained. The present fiber scanner with 3D tilted coil has promise for use as an important inspecting device for biomedical endoscope application.

Bound constrained bundle adjustment for reliable 3D reconstruction.

Bundle adjustment (BA) is a common estimation algorithm that is widely used in machine vision as the last step in a feature-based three-dimensional (3D) reconstruction algorithm. BA is essentially a non-convex non-linear least-square problem that can simultaneously solve the 3D coordinates of all the feature points describing the scene geometry, as well as the parameters of the camera. The conventional BA takes a parameter either as a fixed value or as an unconstrained variable based on whether the parameter is known or not. In cases where the known parameters are inaccurate but constrained in a range, conventional BA results in an incorrect 3D reconstruction by using these parameters as fixed values. On the other hand, these inaccurate parameters can be treated as unknown variables, but this does not exploit the knowledge of the constraints, and the resulting reconstruction can be erroneous since the BA optimization halts at a dramatically incorrect local minimum due to its non-convexity. In many practical 3D reconstruction applications, unknown variables with range constraints are usually available, such as a measurement with a range of uncertainty or a bounded estimate. Thus to better utilize these pre-known, constrained, but inaccurate parameters, a bound constrained bundle adjustment (BCBA) algorithm is proposed, developed and tested in this study. A scanning fiber endoscope (the camera) is used to capture a sequence of images above a surgery phantom (the object) of known geometry. 3D virtual models are reconstructed based on these images and then compared with the ground truth. The experimental results demonstrate BCBA can achieve a more reliable, rapid, and accurate 3D reconstruction than conventional bundle adjustment.

Solvent‐free acetylation of lignocellulosic fibers at room temperature: Effect on fiber structure and surface properties

ABSTRACTAcetylation is one of the most interesting chemical treatments to improve the affinity of lignocellulosic fibers with polymeric matrices for the elaboration of several types of composites. In this paper, the acetylation of flax and wood pulp (bleached softwood Kraft pulp and thermomechanical pulp) fibers was carried out at room temperature in a solvent‐free system with acetic anhydride in the presence of sulfuric acid as catalyst. The effect of acetylation on the fine structure of fibers was investigated by spectroscopic methods, while the extent of acetylation was quantified by weight percent gain. The effect of reaction time on fiber morphology was studied at macro‐ and microscale using scanning electron microscopy, optical microscopy, and fiber quality analysis. The evolution of the hydrophobic/hydrophilic character of fibers was determined by contact angle measurements. The wettability of fibers by liquid epoxy resin was also evaluated to confirm the improvement of the affinity of acetylated fibers with the epoxy matrix. It was found that the hydrophilic character of fibers decrease with increasing reaction time, whereas the trend was less pronounced beyond specific reaction times. Acetylated fibers can therefore be potential candidates for replacing nonbiodegradable reinforcing materials in composite applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42247.

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

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.

Accurate three-dimensional virtual reconstruction of surgical field using calibrated trajectories of an image-guided medical robot.

Brain tumor margin removal is challenging because diseased tissue is often visually indistinguishable from healthy tissue. Leaving residual tumor leads to decreased survival, and removing normal tissue causes life-long neurological deficits. Thus, a surgical robotics system with a high degree of dexterity, accurate navigation, and highly precise resection is an ideal candidate for image-guided removal of fluorescently labeled brain tumor cells. To image, we developed a scanning fiber endoscope (SFE) which acquires concurrent reflectance and fluorescence wide-field images at a high resolution. This miniature flexible endoscope was affixed to the arm of a RAVEN II surgical robot providing programmable motion with feedback control using stereo-pair surveillance cameras. To verify the accuracy of the three-dimensional (3-D) reconstructed surgical field, a multimodal physical-sized model of debulked brain tumor was used to obtain the 3-D locations of residual tumor for robotic path planning to remove fluorescent cells. Such reconstruction is repeated intraoperatively during margin clean-up so the algorithm efficiency and accuracy are important to the robotically assisted surgery. Experimental results indicate that the time for creating this 3-D surface can be reduced to one-third by using known trajectories of a robot arm, and the error from the reconstructed phantom is within 0.67mm in average compared to the model design.

Micromachined tethered silicon oscillator for an endomicroscopic Lissajous fiber scanner.

This work reports micromachined tethered silicon oscillators (MTSOs) for endoscopic Lissajous fiber scanners. An MTSO comprises an offset silicon spring for stiffness modulation of a scanning fiber and additional mass for modulation of resonant scanning frequency in one body. MTSOs were assembled with a resonant fiber scanner and enhanced scanning reliability of the scanner by eliminating mechanical cross coupling. The fiber scanner with MTSOs was fully packaged as an endomicroscopic catheter and coupled with a conventional laparoscope and spectral domain OCT system. The endomicroscope was maneuvered with the integrated laparoscope and in vivo swine tissue OCT imaging was successfully demonstrated during open surgery. This new component serves as an important element inside an endoscopic Lissajous fiber scanner for early cancer detection or on-demand minimum lesional margin decision during noninvasive endoscopic biopsy.

Target-to-background enhancement in multispectral endoscopy with background autofluorescence mitigation for quantitative molecular imaging.

Fluorescence molecular imaging with exogenous probes improves specificity for the detection of diseased tissues by targeting unambiguous molecular signatures. Additionally, increased diagnostic sensitivity is expected with the application of multiple molecular probes. We developed a real-time multispectral fluorescence-reflectance scanning fiber endoscope (SFE) for wide-field molecular imaging of fluorescent dye-labeled molecular probes at nanomolar detection levels. Concurrent multichannel imaging with the wide-field SFE also allows for real-time mitigation of the background autofluorescence (AF) signal, especially when fluorescein, a U.S. Food and Drug Administration approved dye, is used as the target fluorophore. Quantitative tissue AF was measured for the ex vivo porcine esophagus and murine brain tissues across the visible and nearinfrared spectra. AF signals were then transferred to the unit of targeted fluorophore concentration to evaluate the SFE detection sensitivity for sodium fluorescein and cyanine. Next, we demonstrated a real-time AF mitigation algorithm on a tissue phantom, which featured molecular probe targeted cells of high-grade dysplasia on a substrate containing AF species. The target-to-background ratio was enhanced by more than one order of magnitude when applying the real-time AF mitigation algorithm. Furthermore, a quantitative estimate of the fluorescein photodegradation (photobleaching) rate was evaluated and shown to be insignificant under the illumination conditions of SFE. In summary, the multichannel laser-based flexible SFE has demonstrated the capability to provide sufficient detection sensitivity, image contrast, and quantitative target intensity information for detecting small precancerous lesions in vivo.

High-resolution angioscopic imaging during endovascular neurosurgery.

Endoluminal optical imaging, or angioscopy, has not seen widespread application during neurointerventional procedures, largely as a result of the poor imaging resolution of existing angioscopes. Scanning fiber endoscopes (SFEs) are a novel endoscopic platform that allows high-resolution video imaging in an ultraminiature form factor that is compatible with currently used distal access endoluminal catheters. To test the feasibility and potential utility of high-resolution angioscopy with an SFE during common endovascular neurosurgical procedures. A 3.7-French SFE was used in a porcine model system to image endothelial disruption, ischemic stroke and mechanical thrombectomy, aneurysm coiling, and flow-diverting stent placement. High-resolution, video-rate imaging was shown to be possible during all of the common procedures tested and provided information that was complementary to standard fluoroscopic imaging. SFE angioscopy was able to assess novel factors such as aneurysm base coverage fraction and side branch patency, which have previously not been possible to determine with conventional angiography. Endovascular imaging with an SFE provides important information on factors that cannot be assessed fluoroscopically and is a novel platform on which future neurointerventional techniques may be based because it allows for periprocedural inspection of the integrity of the vascular system and the deployed devices. In addition, it may be of diagnostic use for inspecting the vascular wall and postprocedure device evaluation.

Scanning fiber endoscopy: a novel platform for cholangioscopy

Indeterminate pancreaticobiliary strictures remain a difficult diagnostic dilemma with currently available endoscopic imaging. Currently available pancreaticobiliary endoscopic systems have improved the sensitivity of directed biopsy; however, they are limited by image quality. We present scanning fiber endoscopy (SFE) as a novel platform for improving diagnostic accuracy. This endoscopic platform works through a standard side-viewing endoscope. SFE works by using a single-mode optical fiber whose distal tip is resonantly scanned in a spiral pattern.

A Contamination Sensor Based on an Array of Microfibers with Nanoscale-Structured Film

A contamination sensor based on an array of microfibers with nanoscale-structured film using evanescent field is proposed and demonstrated theoretically and experimentally. When the molecular contaminants deposit on the nanoscale-structured film, the refractive index of the film will change and the additional loss will be produced due to the disturbance of evanescent field. The possibility of the sensor is demonstrated theoretically by using three-dimensional finite-difference time domain (3D-FDTD). The corresponding experiments have also been carried out in order to demonstrate the theoretical results. Microfibers are fabricated by using hydrogen-oxygen flame-heated scanning fiber drawing method and the nanoscale-structured film coated on the surface of microfibers is deposited by using dip coating process. Then an array of microfibers is assembled to demonstrate the feasibility of the device. The experimental results show that contaminants detection with the device can agree well with the results measured by the laser-scattering particle counter, which demonstrates the feasibility of the new type of contaminant sensor. The device can be used to monitor contaminants on-line in the high-power laser system.

Mitigating fluorescence spectral overlap in wide-field endoscopic imaging

The number of molecular species suitable for multispectral fluorescence imaging is limited due to the overlap of the emission spectra of indicator fluorophores, e.g., dyes and nanoparticles. To remove fluorophore emission cross-talk in wide-field multispectral fluorescence molecular imaging, we evaluate three different solutions: (1) image stitching, (2) concurrent imaging with cross-talk ratio subtraction algorithm, and (3) frame-sequential imaging. A phantom with fluorophore emission cross-talk is fabricated, and a 1.2-mm ultrathin scanning fiber endoscope (SFE) is used to test and compare these approaches. Results show that fluorophore emission cross-talk could be successfully avoided or significantly reduced. Near term, the concurrent imaging method of wide-field multispectral fluorescence SFE is viable for early stage cancer detection and localization in vivo. Furthermore, a means to enhance exogenous fluorescence target-to-background ratio by the reduction of tissue autofluorescence background is demonstrated.