New Endoscopic Imaging Technology Based on MEMS Sensors and Actuators

High-speed forward-viewing optical coherence tomography probe based on Lissajous sampling and sparse reconstruction

We present a novel endoscopy probe using optical coherence tomography (OCT) that combines sparse Lissajous scanning and compressed sensing (CS) for faster data collection. This compact probe is only 4 mm in diameter and achieves a large field of view (FOV) of 2.25 mm2 and a 10 mm working distance. Unlike traditional OCT systems that use bulky raster scanning, our design features a dual-axis piezoelectric mechanism for efficient Lissajous pattern scanning. It employs compressive data reconstruction algorithms that minimize data collection requirements for efficient, high-speed imaging. This approach significantly enhances imaging speed by over 40%, substantially improving miniaturization and performance for endoscopic applications.

OneSLAM to map them all: a generalized approach to SLAM for monocular endoscopic imaging based on tracking any point

PURPOSE

Monocular SLAM algorithms are the key enabling technology for image-based surgical navigation systems for endoscopic procedures. Due to the visual feature scarcity and unique lighting conditions encountered in endoscopy, classical SLAM approaches perform inconsistently. Many of the recent approaches to endoscopic SLAM rely on deep learning models. They show promising results when optimized on singular domains such as arthroscopy, sinus endoscopy, colonoscopy or laparoscopy, but are limited by an inability to generalize to different domains without retraining.

METHODS

To address this generality issue, we propose OneSLAM a monocular SLAM algorithm for surgical endoscopy that works out of the box for several endoscopic domains, including sinus endoscopy, colonoscopy, arthroscopy and laparoscopy. Our pipeline builds upon robust tracking any point (TAP) foundation models to reliably track sparse correspondences across multiple frames and runs local bundle adjustment to jointly optimize camera poses and a sparse 3D reconstruction of the anatomy.

RESULTS

We compare the performance of our method against three strong baselines previously proposed for monocular SLAM in endoscopy and general scenes. OneSLAM presents better or comparable performance over existing approaches targeted to that specific data in all four tested domains, generalizing across domains without the need for retraining.

CONCLUSION

OneSLAM benefits from the convincing performance of TAP foundation models but generalizes to endoscopic sequences of different anatomies all while demonstrating better or comparable performance over domain-specific SLAM approaches. Future research on global loop closure will investigate how to reliably detect loops in endoscopic scenes to reduce accumulated drift and enhance long-term navigation capabilities.

Towards OCT-Guided Endoscopic Laser Surgery-A Review

Optical Coherence Tomography (OCT) is an optical imaging technology occupying a unique position in the resolution vs. imaging depth spectrum. It is already well established in the field of ophthalmology, and its application in other fields of medicine is growing. This is motivated by the fact that OCT is a real-time sensing technology with high sensitivity to precancerous lesions in epithelial tissues, which can be exploited to provide valuable information to clinicians. In the prospective case of OCT-guided endoscopic laser surgery, these real-time data will be used to assist surgeons in challenging endoscopic procedures in which high-power lasers are used to eradicate diseases. The combination of OCT and laser is expected to enhance the detection of tumors, the identification of tumor margins, and ensure total disease eradication while avoiding damage to healthy tissue and critical anatomical structures. Therefore, OCT-guided endoscopic laser surgery is an important nascent research area. This paper aims to contribute to this field with a comprehensive review of state-of-the-art technologies that may be exploited as the building blocks for achieving such a system. The paper begins with a review of the principles and technical details of endoscopic OCT, highlighting challenges and proposed solutions. Then, once the state of the art of the base imaging technology is outlined, the new OCT-guided endoscopic laser surgery frontier is reviewed. Finally, the paper concludes with a discussion on the constraints, benefits and open challenges associated with this new type of surgical technology.

Two-Photon Endoscopy: State of the Art and Perspectives

In recent years, the demand for non-destructive deep-tissue imaging modalities has led to interest in multiphoton endoscopy. In contrast to bench top systems, multiphoton endoscopy enables subcellular resolution imaging in areas not reachable before. Several groups have recently presented their development towards the goal of producing user friendly plug and play system, which could be used in biological research and, potentially, clinical applications. We first present the technological challenges, prerequisites, and solutions in two-photon endoscopic systems. Secondly, we focus on the applications already found in literature. These applications mostly serve as a quality check of the built system, but do not answer a specific biomedical research question. Therefore, in the last part, we will describe our vision on the enormous potential applicability of adult two-photon endoscopic systems in biological and clinical research. We will thus bring forward the concept that two-photon endoscopy is a sine qua non in bringing this technique to the forefront in clinical applications.

A hydraulic soft microgripper for biological studies

We have developed a microscale hydraulic soft gripper and demonstrated the handling of an insect without damage. This gripper is built on Polydimethylsiloxane (PDMS) with the soft material casting technique to form three finger-like columns, which are placed on a circular membrane. The fingers have a length of 1.5 mm and a diameter of 300 µm each; the distance between the two fingers is 600 µm of center-to-center distance. A membrane as a 150 µm soft film is built on top of a cylindrical hollow space. Applying pressure to the interior space can bend the membrane. Bending the membrane causes the motion of opening/closing of the gripper, and as a result, the three fingers can grip an object or release it. The PDMS was characterized, and the experimental results were used later in Abaqus software to simulate the gripping motion. The range of deformation of the gripper was investigated by simulation and experiment. The result of the simulation agrees with the experiments. The maximum 543 µN force was measured for this microfluidic-compatible microgripper and it could lift a ball that weighs 168.4 mg and has a 0.5 mm diameter. Using this microgripper, an ant was manipulated successfully without any damage. Results showed fabricated device has great a potential as micro/bio manipulator.

Miniaturized structured illumination microscopy using two 3-axis MEMS micromirrors

We present the development and performance characterisation of a novel structured illumination microscope (SIM) in which the grating pattern is generated using two optical beams controlled via 2 micro-electro-mechanical system (MEMS) three-axis scanning micromirrors. The implementation of MEMS micromirrors to accurately and repeatably control angular, radial and phase positioning delivers flexible control of the fluorescence excitation illumination, with achromatic beam delivery through the same optical path, reduced spatial footprint and cost-efficient integration being further benefits. Our SIM architecture enables the direct implementation of multi-color imaging in a compact and adaptable package. The two-dimensional SIM system approach is enabled by a pair of 2 mm aperture electrostatically actuated three-axis micromirrors having static angular tilt motion along the x- and y-axes and static piston motion along the z-axis. This allows precise angular, radial and phase positioning of two optical beams, generating a fully controllable spatial interference pattern at the focal plane by adjusting the positions of the beam in the back-aperture of a microscope objective. This MEMS-SIM system was applied to fluorescent bead samples and cell specimens, and was able to obtain a variable lateral resolution improvement between 1.3 and 1.8 times the diffraction limited resolution.

Cellular shape micromachined actuator ribbons

This work presents a new class of micromachined electrostatic actuators capable of producing output force and displacement unprecedented for MEMS electrostatic actuators. The actuators feature submicron high aspect ratio transduction gaps lined up in two-dimensional arrays. Such an arrangement of microscale actuator cells allows the addition of force and displacements of a large number of cells (up to 7600 in one demonstrated array), leading to displacements ranging in the hundreds of microns and several gram forces of axial force. For 50 µm thick actuators with horizontal dimensions in the 1-4 millimeter range, an out-of-plane displacement of up to 678 µm at 46 V, a bending moment of up to 2.0 µNm, i.e., 0.08 N (~8 gram-force) of axial force over a 50 µm by 2 mm cross-sectional area of the actuator (800 kPa of electrostatically generated stress), and an energy density (mechanical work output per stroke per volume) up to 1.42 mJ/cm³ was demonstrated for the actuators.

Sensitivity-Bandwidth Optimization of PMUT with Acoustical Matching Using Finite Element Method

A new model in finite element method to study round-trip performance of piezoelectric micromachined ultrasonic transducers (pMUTs) is established. Most studies on the performance of pMUT are based only on the transmission sensibility, but the reception capacity is as much important as the transmission one, and is quite different from this latter. In this work, the round-trip sensitivity of pMUT is defined as the product of the frequency response of transmitted far field pressure to source voltage excitation and that of reception output to return wave pressure. Based on this sensitivity characteristic, firstly, a multi-parameter optimization for a cavity pMUT is performed using the sensitivity-bandwidth product parameter SBW as criterion. The radii of the electrode and the piezoelectric layer, the thicknesses of the piezoelectric layer and the vibration diaphragm are adjusted to maximize the performance. Secondly, an acoustic matching method is proposed and applied to pMUTs for the first time. As a result, the round-trip sensitivity can be evaluated and the pulse-echo response of wide-band excitation can be simulated, giving the most quantitative and intuitive feedback for pMUT design. The optimization enhances the sensitivity-bandwidth product by 52% when the top electrode and piezoelectric layer are both etched to 75% radius of the cavity beneath; the introduction of an acoustic matching layer shows significant bandwidth expansion in both the transmitting and receiving process.

Investigation of Cylindrical Piezoelectric and Specific Multi-Channel Circular MEMS-Transducer Array Resonator of Ultrasonic Ablation

BACKGROUND

A cylindrical piezoelectric element and a specific multi-channel circular microelectromechanical systems (MEMS)-transducer array of ultrasonic system were used for ultrasonic energy generation and ablation. A relatively long time is required for the heat to be conducted to the target position. Ultrasound thermal therapy has great potential for treating deep hyperplastic tissues and tumors, such as breast cancer and liver tumors.

METHODS

Ultrasound ablation technology produces thermal energy by heating the surface of a target, and the heat gradually penetrates to the target's interior. Beamforming was performed to observe energy distribution. A resonance method was used to generate ablation energy for verification. Energy was generated according to the coordinates of geometric graph positions to reach the ablation temperature.

RESULTS

The mean resonance frequency of Channels 1-8 was 2.5 MHz, and the cylindrical piezoelectric ultrasonic element of Channel A was 4.2546 Ω at 5.7946 MHz. High-intensity ultrasound has gradually been applied in clinical treatment. Widely adopted, ultrasonic hyperthermia involves the use of high-intensity ultrasound to heat tissues at 42-45 °C for 30-60 min.

CONCLUSION

In the ultrasonic energy method, when the target position reaches a temperature that significantly reduces the cell viability (46.9 °C), protein surface modification occurs on the surface of the target.

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

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.

A Silicon Optical Bench-Based Forward-View Two-Axis Scanner for Microendoscopy Applications

Optical microendoscopy enabled by a microelectromechanical system (MEMS) scanning mirror offers great potential for in vivo diagnosis of early cancer inside the human body. However, an additional beam folding mirror is needed for a MEMS mirror to perform forward-view scanning, which drastically increases the diameter of the resultant MEMS endoscopic probe. This paper presents a new monolithic two-axis forward-view optical scanner that is composed of an electrothermally driven MEMS mirror and a beam folding mirror both vertically standing and integrated on a silicon substrate. The mirror plates of the two mirrors are parallel to each other with a small distance of 0.6 mm. The laser beam can be incident first on the MEMS mirror and then on the beam folding mirror, both at 45°. The MEMS scanner has been successfully fabricated. The measured optical scan angles of the MEMS mirror were 10.3° for the x axis and 10.2° for the y axis operated under only 3 V. The measured tip-tilt resonant frequencies of the MEMS mirror were 1590 Hz and 1850 Hz, respectively. With this compact MEMS design, a forward-view scanning endoscopic probe with an outer diameter as small as 2.5 mm can be made, which will enable such imaging probes to enter the subsegmental bronchi of an adult patient.

MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications

Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given.

Towards a Low-Cost and Portable Photoacoustic Microscope for Point-of-Care and Wearable Applications

Several breakthrough applications in biomedical imaging have been reported in the recent years using advanced photoacoustic microscopy imaging systems. While two photon and other optical microscopy systems have recently emerged in portable and wearable form, there is much less work reported on the portable and wearable photoacoustic microscopy (PAM) systems. Working towards this goal, we report our studies on a low-cost and portable photoacoustic microscopy system that uses a custom fabricated 2.5 mm diameter ring ultrasound transducer integrated with a fiber-coupled laser diode. The ultrasound transducer is centered at 17.25 MHz, and shows ~ 45% and ~ 100% fractional bandwidths for ultrasound pulse-echo and photoacoustic A-line signals respectively. To achieve overall system portability, besides the imaging head, other backend imaging system components need to be readily portable as well. In this direction, we have studied the potential use of compact pre-amplifiers, scanning stages and microcontroller based data acquisition and reconstruction for photoacoustic imaging. The portable PAM system is validated by imaging phantoms embedded with light absorbing targets. Future directions that will likely help achieve a completely portable and wearable photoacoustic microscopy system are discussed.

Damage Identification in Structural Health Monitoring: A Brief Review from its Implementation to the Use of Data-Driven Applications

The damage identification process provides relevant information about the current state of a structure under inspection, and it can be approached from two different points of view. The first approach uses data-driven algorithms, which are usually associated with the collection of data using sensors. Data are subsequently processed and analyzed. The second approach uses models to analyze information about the structure. In the latter case, the overall performance of the approach is associated with the accuracy of the model and the information that is used to define it. Although both approaches are widely used, data-driven algorithms are preferred in most cases because they afford the ability to analyze data acquired from sensors and to provide a real-time solution for decision making; however, these approaches involve high-performance processors due to the high computational cost. As a contribution to the researchers working with data-driven algorithms and applications, this work presents a brief review of data-driven algorithms for damage identification in structural health-monitoring applications. This review covers damage detection, localization, classification, extension, and prognosis, as well as the development of smart structures. The literature is systematically reviewed according to the natural steps of a structural health-monitoring system. This review also includes information on the types of sensors used as well as on the development of data-driven algorithms for damage identification.

Swept-source optical coherence tomography microsystem with an integrated Mirau interferometer and electrothermal micro-scanner

In the rapid evolution of gastrointestinal endomicroscopy, optical coherence tomography (OCT) has found many diverse applications. Until recently, the micro-opto-electro-mechanical systems (MOEMS) technology has been playing a key role in shaping the miniaturization of these components. We report here, to the best of our knowledge, a novel endoscopic microsystem. It is based on a spectrally tuned MOEMS Mirau micro-interferometer integrated with micro-electro-mechanical systems (MEMS) electro-thermal micro-scanner, operating in the regime of swept-source (SS) OCT imaging. This Letter validates our initial proof-of-concept toward the development of such MOEMS probe and the presentation of experimental performances of the resulting SS-OCT microsystem.

Ring ultrasound transducer based miniaturized photoacoustic imaging system

In recent years photoacoustic microscopy systems have attracted significant attention from biomedical researchers due to its ability to provide label-free imaging of hemoglobin (vasculature), lipids, and melanin with high spatial and temporal resolutions even from deeper (> 1 mm) depths inside biological tissue. This work reports the development of a low-cost and miniaturized photoacoustic (PA) imaging device for microscopy applications. A ring ultrasound transducer with 2.5 mm outer diameter and 0.5 mm inner diameter is fabricated using a 150 μm thick PZT element as the piezoelectric layer. The ring ultrasound transducer is integrated with a pulsed laser diode with integrated optical fiber which is coaxially fed through the transducer. Raster scanning of the integrated device is used to obtain 3 dimensional images of a tissue-mimicking phantom.