Development of a Mechanical Scanning Device With High-Frequency Ultrasound Transducer for Ultrasonic Capsule Endoscopy

Novel ultrasound capsule endoscopy for gastrointestinal scanning: An in vivo animal study

Background and objectives

EUS is an important modality for diagnosis and assessment of gastrointestinal (GI) subepithelial lesions. However, EUS is invasive and operator-dependent and requires sedation in most cases. The newly developed ultrasound capsule endoscopy (USCE) system, with both white-light and ultrasound imaging modalities, is a minimally invasive method for superficial and submucosal imaging of the esophagus. This animal study aimed to evaluate the feasibility and efficacy of the USCE system for upper GI tract and small bowel scanning.

Methods

Three Bama miniature pigs were selected to scan their esophagus, stomach, small bowel, and simulated submucosal lesions. USCE was performed first, followed by EUS. The feasibility of USCE was measured by obtaining ultrasound images of normal GI walls and submucosal lesions under the guidance of optical viewing. The efficacy of USCE was evaluated by comparing tissue structures and lesion features shown on ultrasound images obtained with both instruments.

Results

Under the optical mode of USCE, the GI tract was well visualized, and all simulated lesions were located. Clear ultrasound images of normal GI tract and submucosal lesions were acquired. Ultrasound images of the esophagus, stomach, and small bowel were characterized by differentiated multilayer structures on USCE, which was consistent with the structures displayed on EUS. And the visualization of submucosal lesions, using both USCE and EUS, was characterized by a hypoechoic and well-demarcated mass in the layer of submucosa.

Conclusions

This animal study indicated the feasibility and potential clinical efficacy of this USCE for simultaneous optical mucosal visualization and transmural ultrasound imaging of upper GI tract and small bowel, providing possibility of using this technology for a wider range of GI tract.

Thin-Film Piezoelectric Micromachined Ultrasound Transducers in Biomedical Applications: A Review

Thin-film piezoelectric micromachined ultrasound transducers (PMUTs) are an increasingly relevant and well-researched field, and their biomedical importance has been growing as the technology continues to mature. This review article briefly discusses their history in biomedical use, provides a simple explanation of their principles for newer readers, and sheds light on the materials selection for these devices. Primarily, it discusses the significant applications of PMUTs in the biomedical industry and showcases recent progress that has been made in each application. The biomedical applications covered include common historical uses of ultrasound such as ultrasound imaging, ultrasound therapy, and fluid sensing, but additionally new and upcoming applications such as drug delivery, photoacoustic imaging, thermoacoustic imaging, biometrics, and intrabody communication. By including a device comparison chart for different applications, this review aims to assist microelectromechanical systems (MEMS) designers that work with PMUTs by providing a benchmark for recent research works. Furthermore, it puts forth a discussion on the current challenges being faced by PMUTs in the biomedical field, current and likely future research trends, and opportunities for PMUT development areas, as well as sharing the opinions and predictions of the authors on the state of this technology as a whole. The review aims to be a comprehensive introduction to these topics without diving excessively deep into existing literature.

A Flexible Implant for Multi-Day Monitoring of Colon Segment Activity

Monitoring of colon activity is currently limited to tethered systems like anorectal manometry. These systems have significant drawbacks, but fundamentally limit the observation time of colon activity, reducing the likelihood of detecting specific clinical events. While significant technological advancement has been directed to mobile sensor capsules, this work describes the development and feasibility of a stationary sensor for describing the coordinated activity between neighboring segments of the colon. Unlike wireless capsules, this device remains in position and measures propagating pressure waves and impedances between colon segments to describe activity and motility. This low-power, flexible, wireless sensor-the colon monitor to capture activity (ColoMOCA) was validated in situ and in vivo over seven days of implantation. The ColoMOCA diameter was similar to common endoscopes to allow for minimally invasive diagnostic placement. The ColoMOCA included two pressure sensors, and three impedance-sensing electrodes arranged to describe the differential pressures and motility between adjacent colon segments. To prevent damage after placement in the colon, the ColoMOCA was fabricated with a flexible polyimide circuit board and a silicone rubber housing. The resulting device was highly flexible and suitable for surgical attachment to the colon wall. In vivo testing performed in eleven animals demonstrated suitability of both short term (less than 3 hours) and 7-day implantations. Data collected wirelessly from animal experiments demonstrated the ColoMOCA described colon activity similarly to wired catheters and allowed untethered, conscious monitoring of organ behavior.

New US capsule endoscopy for superficial and submucosal imaging of the esophagus: the first-in-human study

BACKGROUND AND AIMS

EUS is essential in diagnosing and staging of esophageal subepithelial lesions and tumors. However, EUS is invasive, relies on highly trained endoscopists, and typically requires sedation. The newly developed US capsule endoscopy (USCE), which incorporates both white-light and US imaging modalities into a tethered capsule, is a minimally invasive method for obtaining superficial and submucosal information of the esophagus. This study aimed to assess the feasibility and safety of this USCE system.

METHODS

Twenty participants were enrolled: 10 healthy volunteers and 10 patients with esophageal lesions indicated for EUS. Participants first underwent USCE and subsequently EUS within 48 hours. The primary outcome was the technical success rate of USCE. Secondary outcomes were safety, visualization of the esophagus, and comfort assessment.

RESULTS

The technical success rate of USCE was 95% because 1 patient failed to swallow the capsule. No adverse events were observed. The esophagus was well visualized, and all lesions were detected under USCE optical mode in 19 participants. For healthy volunteers, the US images of normal esophageal walls were all characterized by differentiated 7-layer architecture under both USCE and EUS. For 9 patients, the features of esophageal lesions were recognized clearly under USCE, and presumptive diagnoses derived from USCE were all consistent with those from EUS. Most participants preferred USCE to EUS.

CONCLUSIONS

The novel USCE is feasible and safe to observe the esophageal mucosa and acquire submucosal information, which has the potential to be widely used in the clinic. (Clinical trial registration number: NCT05054933.).

Structural Design and Experimental Studies of Resonant Fiber Optic Scanner Driven by Co-Fired Multilayer Piezoelectric Ceramics

Piezo-driven resonant fiber optic scanners are gaining more and more attention due to their simple structure, weak electromagnetic radiation, and non-friction loss. Conventional piezo-driven resonant fiber optic scanners typically use quadrature piezoelectric tubes (piezo tubes) operating in 31-mode with high drive voltage and low excitation efficiency. In order to solve the abovementioned problem, a resonant fiber scanner driven by co-fired multilayer piezoelectric ceramics (CMPCs) is proposed in which four CMPCs drive a cantilevered fiber optic in the first-order bending mode to achieve efficient and fast space-filling scanning. In this paper, the cantilever beam vibration model with base displacement excitation was derived to provide a theoretical basis for the design of the fiber optic scanner. The finite element method was used to guide the dynamic design of the scanner. Finally, the dynamics characteristics and scanning trajectory of the prepared scanner prototype were tested and compared with the theoretical and simulation calculation results. Experimental results showed that the scanner can achieve three types of space-filling scanning: spiral, Lissajous, and propeller. Compared with the structure using piezo tubes, the designed scanner achieved the same scanning range with smaller axial dimensions, lower drive voltage, and higher efficiency. The scanner can achieve a free end displacement of 10 mm in both horizontal and vertical directions under a sinusoidal excitation signal of 50 V_p-p and 200 Hz. The theoretical, simulation and experimental results validate the feasibility of the proposed scanner structure and provide new ideas for the design of resonant fiber optic scanners.

3-D High Frequency Ultrasound Imaging by Piezo-Driving a Single-Element Transducer

Electronic scanning of two-dimensional (2-D) arrays and mechanical or freehand scanning of one-dimensional (1-D) arrays have been mostly utilized for conventional three-dimensional (3-D) ultrasound (US) imaging. However, the development of 2-D arrays and the hardware systems are complicated and expensive, while freehand systems with positioning sensors and mechanical systems are mostly bulky. This article represents a novel scanning strategy for achieving high-quality 3-D US imaging with a high-frequency single-element transducer. A 42-MHz US transducer with a compact structure was designed and fabricated, which was excited in the 2-D vibration by a tubular piezoelectric actuator. A dedicated imaging system was set up and both B-mode and 3-D US imaging of a custom wire phantom have been carried out to evaluate the performance of the proposed transducer. Compared to the results obtained with the motorized linear translation stage, the reconstructed images obtained by the proposed resonance scanning method are accurate, demonstrating the feasibility of 3-D US imaging with a vibrating single-element US transducer.

Recent Advancements in Ultrasound Transducer: From Material Strategies to Biomedical Applications

Ultrasound is extensively studied for biomedical engineering applications. As the core part of the ultrasonic system, the ultrasound transducer plays a significant role. For the purpose of meeting the requirement of precision medicine, the main challenge for the development of ultrasound transducer is to further enhance its performance. In this article, an overview of recent developments in ultrasound transducer technologies that use a variety of material strategies and device designs based on both the piezoelectric and photoacoustic mechanisms is provided. Practical applications are also presented, including ultrasound imaging, ultrasound therapy, particle/cell manipulation, drug delivery, and nerve stimulation. Finally, perspectives and opportunities are also highlighted.

Modeling Pulsed High-Power Spikes in Tunable HV Capacitive Drivers of Piezoelectric Wideband Transducers to Improve Dynamic Range and SNR for Ultrasonic Imaging and NDE

The signal-to-noise ratios (SNR) of ultrasonic imaging and non-destructive evaluation (NDE) applications can be greatly improved by driving each piezoelectric transducer (single or in array) with tuned HV capacitive-discharge drivers. These can deliver spikes with kW pulsed power at PRF ≈ 5000 spikes/s, achieving levels higher even than in CW high-power ultrasound: up to 5 kWpp. These conclusions are reached here by applying a new strategy proposed for the accurate modeling of own-design re-configurable HV capacitive drivers. To obtain such rigorous spike modeling, the real effects of very high levels of pulsed intensities (3-10 A) and voltages (300-700 V) were computed. Unexpected phenomena were found: intense brief pulses of driving power and probe emitted force, as well as nonlinearities in semiconductors, though their catalog data include only linear ranges. Fortunately, our piezoelectric and circuital devices working in such an intense regime have not shown serious heating problems, since the finally consumed "average" power is rather small. Intensity, power, and voltage, driving wideband transducers from our capacitive drivers, are researched here in order to drastically improve (∆ >> 40 dB) their ultrasonic "net dynamic range available" (NDRA), achieving emitted forces > 240 Newtonspp and receiving ultrasonic signals of up to 76-205 Vpp. These measurements of ultrasonic pulsed voltages, received in NDE and Imaging, are approximately 10,000 larger than those usual today. Thus, NDRA ranges were optimized for three laboratory capacitive drivers (with six commercial transducers), which were successfully applied in the aircraft industry for imaging landing flaps in Boeing wings, despite suffering acoustic losses > 120 dB.

Capsule Endoscopy: Pitfalls and Approaches to Overcome

Capsule endoscopy of the gastrointestinal tract is an innovative technology that serves to replace conventional endoscopy. Wireless capsule endoscopy, which is mainly used for small bowel examination, has recently been used to examine the entire gastrointestinal tract. This method is promising for its usefulness and development potential and enhances convenience by reducing the side effects and discomfort that may occur during conventional endoscopy. However, capsule endoscopy has fundamental limitations, including passive movement via bowel peristalsis and space restriction. This article reviews the current scientific aspects of capsule endoscopy and discusses the pitfalls and approaches to overcome its limitations. This review includes the latest research results on the role and potential of capsule endoscopy as a non-invasive diagnostic and therapeutic device.

Optimized integrated design of a high-frequency medical ultrasound transducer with genetic algorithm

Designing efficient acoustic stack and elements for high-frequency (HF) medical ultrasound (US) transducers involves various interrelated parameters. So far, optimizing spatial resolution and acoustic field intensity simultaneously has been a daunting task in the area of HF medical US imaging. Here, we introduce optimized design for a 50-MHz US probe for skin tissue imaging. We have developed an efficient design and simulation approach using Krimholtz, Leedom and Matthaei (KLM) equivalent circuit model and spatial impulse response method by means of Field II software. These KLM model and Field II software are integrated, and a GA algorithm is used to optimize the design of the US transducer to obtain the best imaging performance. As a result, a 50-MHz single element probe is effectively optimized with 5 mm acoustic focal length, 72 $$\upmu {\text{m}}$$ μ m lateral, and 42 $$\upmu {\text{m}}$$ μ m axial imaging resolution, with an enhancement in imaging resolution over the conventionally designed and simulated probe by 10%. This work has the potential to benefit many applications that require a fast, high-resolution and strong US focus in skin imaging.

Development of a low-cost six-axis alignment instrument for flexible 2D and 3D ultrasonic probes

BACKGROUND:

The pulse-echo test is used to evaluate the performance of ultrasonic probes before manufacturing ultrasonic systems. However, commercial alignment instruments are very large and use complex programs with long operation times.

OBJECTIVE:

To develop a low-cost alignment instrument used in the pulse-echo test for evaluating the performance of various 2D and 3D ultrasonic probes.

METHODS:

The developed alignment instrument can be aligned with the X, Y, Z, azimuth, elevation, and tilt axes with manual structure to support mounting fixtures that hold 2D and 3D ultrasonic probes. Each axis has a manual lever and is designed to have no movement when fixed. In particular, tilt and azimuth directions are designed to move more than 5∘ left and right.

RESULTS:

The probe mounted in the X, Y, and Z axes can move at above 50 mm. The probe mounted in the azimuth, elevation, and tilt axes can move more than 5∘ in the left and right directions. The pulse-echo test using commercial ultrasonic probes showed maximum error rate of less than 5%.

CONCLUSIONS:

Our developed alignment instrument can reduce costs by eliminating the need for shortening inspection times for probe manufacturers.

Photoacoustic endoscopy: A progress review

Endoscopy has been widely used in biomedical imaging and integrated with various optical and acoustic imaging modalities. Photoacoustic imaging (PAI), one of the fastest growing biomedical imaging modalities, is a noninvasive and nonionizing method that owns rich optical contrast, deep acoustic penetration depth, multiscale and multiparametric imaging capability. Hence, it is preferred to miniaturize the volume of PAI and develop an emerged endoscopic imaging modality referred to as photoacoustic endoscopy (PAE). It has been developed for more than one decade since the first report of PAE. Unfortunately, until now, there is no mature photoacoustic endoscopic technique recognized in clinic due to various technical limitations. To address this concern, recent development of new scanning mechanisms, adoption of novel optical/acoustic devices, utilization of superior computation methods and exploration of multimodality strategies have significantly promoted the progress of PAE toward clinic. In this review, we comprehensively reviewed recent progresses in single- and multimodality PAE with new physics, mechanisms and strategies to achieve practical devices for potential applicable scenarios including esophageal, gastrointestinal, urogenital and intravascular imaging. We ended this review with challenges and prospects for future development of PAE.

Post-Voltage-Boost Circuit-Supported Single-Ended Class-B Amplifier for Piezoelectric Transducer Applications

Piezoelectric transducers are important devices that are triggered by amplifier circuits in mobile ultrasound systems. Therefore, amplifier performance is vital because it determines the acoustic piezoelectric transducer performances. Particularly, mobile ultrasound applications have strict battery performance and current consumption requirements; hence, amplifier devices should exhibit good efficiency because the direct current (DC) voltage in the battery are provided to the supply voltages of the amplifier, thus limiting the maximum DC drain voltages of the main transistors in the amplifier. The maximum DC drain voltages are related with maximum output power if the choke inductor in the amplifier is used. Therefore, a need to improve the amplifier performance of piezoelectric transducers exists for mobile ultrasound applications. In this study, a post-voltage-boost circuit-supported class-B amplifier used for mobile ultrasound applications was developed to increase the acoustic performance of piezoelectric transducers. The measured voltage of the post-voltage-boost circuit-supported class-B amplifier (62 V_P-P) is higher than that of only a class-B amplifier (50 V_P-P) at 15 MHz and 100 mV_P-P input. By performing the pulse-echo measurement test, the echo signal with the post-voltage-boost circuit-supported class-B amplifier (10.39 mV_P-P) was also noted to be higher than that with only a class-B amplifier (6.15 mV_P-P). Therefore, this designed post-voltage-boost circuit can help improve the acoustic amplitude of piezoelectric transducers used for mobile ultrasound applications.

Ex Vivo and In Vivo Imaging Study of Ultrasound Capsule Endoscopy

Wireless capsule endoscopy (WCE) has revolutionized the capacity for evaluation of the gastrointestinal (GI) tract, but its evaluation is limited to the mucosal surface. To overcome this, ultrasound capsule endoscopy (UCE) that can evaluate the deeper structures beyond the mucosal surface has been proposed and several studies focusing on technology development have demonstrated promising results. However, investigations of the potential for clinical utility of this technology are lacking. This work had two main goals: perform ex vivo and in vivo imaging studies in a swine model to (1) evaluate if acoustic coupling between a capsule with a specific size and GI tract can be achieved only through peristalsis autonomously without any human control and (2) identify key issues and challenges to help guide further research. The images acquired in these studies were able to visualize the wall of the GI tract as well as the structures within demonstrating that achieving adequate acoustic coupling through peristalsis is possible. Critical challenges were identified including level of visualization and area of coverage; these require further in-depth investigation before potential clinical utility of UCE technology can be concluded.

Ingestible Sensors and Sensing Systems for Minimally Invasive Diagnosis and Monitoring: The Next Frontier in Minimally Invasive Screening

Ingestible electronic systems that are capable of embedded sensing, particularly within the gastrointestinal (GI) tract and its accessory organs, have the potential to screen for diseases that are difficult if not impossible to detect at an early stage using other means. Furthermore, these devices have the potential to (1) reduce labor and facility costs for a variety of procedures, (2) promote research for discovering new biomarker targets for associated pathologies, (3) promote the development of autonomous or semiautonomous diagnostic aids for consumers, and (4) provide a foundation for epithelially targeted therapeutic interventions. These technological advances have the potential to make disease surveillance and treatment far more effective for a variety of conditions, allowing patients to lead longer and more productive lives. This review will examine the conventional techniques, as well as ingestible sensors and sensing systems that are currently under development for use in disease screening and diagnosis for GI disorders. Design considerations, fabrication, and applications will be discussed.

Ultrasound Capsule Endoscopy With a Mechanically Scanning Micro-ultrasound: A Porcine Study

Wireless capsule endoscopy has been used for the clinical examination of the gastrointestinal (GI) tract for two decades. However, most commercially available devices only utilise optical imaging to examine the GI wall surface. Using this sensing modality, pathology within the GI wall cannot be detected. Micro-ultrasound (μUS) using high-frequency (>20 MHz) ultrasound can provide a means of transmural or cross-sectional image of the GI tract. Depth of imaging is approximately 10 mm with a resolution of between 40-120 μm that is sufficient to differentiate between subsurface histologic layers of the various regions of the GI tract. Ultrasound capsule endoscopy (USCE) uses a capsule equipped with μUS transducers that are capable of imaging below the GI wall surface, offering thereby a complementary sensing technique to optical imaging capsule endoscopy. In this work, a USCE device integrated with a ∼30 MHz ultrasonic transducer was developed to capture a full 360° image of the lumen. The performance of the device was initially evaluated using a wire phantom, indicating an axial resolution of 69.0 μm and lateral resolution of 262.5 μm. Later, in vivo imaging performance was characterised in the oesophagus and small intestine of anaesthetized pigs. The reconstructed images demonstrate clear layer differentiation of the lumen wall. The tissue thicknesses measured from the B-scan images show good agreement with ex vivo images from the literature. The high-resolution ultrasound images in the in vivo porcine model achieved with this device is an encouraging preliminary step in the translation of these devices toward future clinical use.

Development of a Class-C Power Amplifier with Diode Expander Architecture for Point-of-Care Ultrasound Systems

Point-of-care ultrasound systems are widely used in ambulances and emergency rooms. However, the excessive heat generated from ultrasound transmitters has an impact on the implementation of piezoelectric transducer elements and on battery consumption, thereby affecting the system’s sensitivity and resolution. Non-linear power amplifiers, such as class-C amplifiers, could substitute linear power amplifiers, such as class-A amplifiers, which are currently used in point-of-care ultrasound systems. However, class-C power amplifiers generate less output power, resulting in a reduction of system sensitivity. To overcome this issue, we propose a new diode expander architecture dedicated to power amplifiers to reduce the effects of sinusoidal pulses toward the power supply. Thus, the proposed architecture could increase the input pulse amplitudes applied to the main transistors in the power amplifiers, hence increasing the output voltage of such amplifiers. To verify the proposed concept, pulse-echo responses from an ultrasonic transducer were tested with the developed class-C power amplifier using a resistor divider and the designed diode expander architecture. The peak-to-peak amplitude of the echo signals of the ultrasonic transducers when using a class-C power amplifier with a diode expander architecture (2.98 V_p–p) was higher than that for the class-C power amplifier with a resistor divider architecture (2.51 V_p–p). Therefore, the proposed class-C power amplifier with diode expander architecture is a potential candidate for improving the sensitivity performance of piezoelectric transducers for point-of-care ultrasound systems.

Gastrointestinal diagnosis using non-white light imaging capsule endoscopy

Capsule endoscopy (CE) has proved to be a powerful tool in the diagnosis and management of small bowel disorders since its introduction in 2001. However, white light imaging (WLI) is the principal technology used in clinical CE at present, and therefore, CE is limited to mucosal inspection, with diagnosis remaining reliant on visible manifestations of disease. The introduction of WLI CE has motivated a wide range of research to improve its diagnostic capabilities through integration with other sensing modalities. These developments have the potential to overcome the limitations of WLI through enhanced detection of subtle mucosal microlesions and submucosal and/or transmural pathology, providing novel diagnostic avenues. Other research aims to utilize a range of sensors to measure physiological parameters or to discover new biomarkers to improve the sensitivity, specificity and thus the clinical utility of CE. This multidisciplinary Review summarizes research into non-WLI CE devices by organizing them into a taxonomic structure on the basis of their sensing modality. The potential of these capsules to realize clinically useful virtual biopsy and computer-aided diagnosis (CADx) is also reported.

Miniaturized High-Resolution Integrated 360° Electronic Radial Ultrasound Endoscope for Digestive Tract Imaging

To improve the accuracy and operating flexibility of digestive diagnostic applications in situ, this paper demonstrates the design, fabrication, and evaluation of a miniaturized high-resolution integrated 360° electronic radial ultrasound endoscope. To improve the uniformity between elements of the radial array transducer, an optimal fabrication procedure based on a flexible matching layer was developed. The radial ultrasound endoscope has a 128.3° 5-million-pixel camera module integrated with an approximately 8-MHz 128-element radial ultrasonic array in a package with an outer diameter of 9.5 mm. The results showed that the array has a center frequency of 8.2 MHz, a -6-dB fractional bandwidth of 83.4%, and a two-way insertion loss of 39.62 dB at the center frequency. Annulus and wire phantoms can be distinctly imaged with the radial array. Printed eight-point font can be distinctly imaged with both a large view and a 3-18-mm depth of field in lumen short-range optical imaging. A porcine esophagus can be distinctly imaged in vitro with the integrated endoscope. The results indicate that the fabrication method based on a flexible matching layer can achieve high uniformity between elements of a radial array transducer. In addition, the proposed ultrasound endoscope demonstrates a good image resolution.

A Dual-Mode Imaging Catheter for Intravascular Ultrasound Application

Both the morphological anatomy and functional parameters such as flow speed of the artery provide valuable information for the evaluation of cardiovascular diseases. Direct measurement of the arterial wall can be achieved by intravascular optical/ultrasound imaging methods, and however, no functional data are acquired with these methods. Fractional flow reserve and Doppler wire have been used to assess the blood flow information, but do not provide cross-sectional images of the artery. This paper is the first to design and fabricate a dual-mode imaging catheter that contains a forward-looking ultrasonic transducer and a side-looking ultrasonic transducer together in one catheter. This dual-mode catheter not only provides morphological information about the artery, but also a precise measurement of functional flow. The data indicate that the proposed catheter can be used to acquire multiple parameters of the artery with a one-time procedure. This novel one-catheter approach could be used for the functional diagnosis of atherosclerotic arteries.

Development of a KNN Ceramic-Based Lead-Free Linear Array Ultrasonic Transducer

High-frequency array transducers can provide higher imaging resolution than traditional transducers, thus resolving smaller features and producing finer images. Commercially available ultrasonic transducers are mostly made with lead-based piezoelectric materials, which are harmful to the environment and public health. This paper presents the development of the 64-elements high-frequency (18.3 MHz) lead-free linear array ultrasonic transducer based on (K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.1Sb_0.04)O₃ (KNLNTS) piezoceramic. Array elements were spaced at a 75- pitch, and interconnected via a custom flexible circuit. The two matching layers and a light backing material were used to improve the performance of the array. The developed KNLNTS ceramic-based lead-free linear array exhibited a center frequency of 18.3 MHz, an average -6-dB bandwidth of 42%, an average two-way insertion loss of 41.8 dB, and a crosstalk between the adjacent elements of less than -53 dB near the center frequency. An image of a tungsten wire phantom was acquired using a Verasonics Vantage research ultrasound system. Results from imaging tests demonstrated a good imaging capability with a spatial resolution of axially and laterally, indicating that the lead-free linear array ultrasonic transducer based on KNLNTS ceramics is a promising alternative to lead-based transducers for ultrasound medical imaging.

In-Vivo Evaluation of Microultrasound and Thermometric Capsule Endoscopes

Clinical endoscopy and colonoscopy are commonly used to investigate and diagnose disorders in the upper gastrointestinal tract and colon, respectively. However, examination of the anatomically remote small bowel with conventional endoscopy is challenging. This and advances in miniaturization led to the development of video capsule endoscopy (VCE) to allow small bowel examination in a noninvasive manner. Available since 2001, current capsule endoscopes are limited to viewing the mucosal surface only due to their reliance on optical imaging. To overcome this limitation with submucosal imaging, work is under way to implement microultrasound (μUS) imaging in the same form as VCE devices. This paper describes two prototype capsules, termed Sonocap and Thermocap, which were developed respectively to assess the quality of μUS imaging and the maximum power consumption that can be tolerated for such a system. The capsules were tested in vivo in the oesophagus and small bowel of porcine models. Results are presented in the form of μUS B-scans as well as safe temperature readings observed up to 100 mW in both biological regions. These results demonstrate that acoustic coupling and μUS imaging can be achieved in vivo in the lumen of the bowel and the maximum power consumption that is possible for miniature μUS systems.

Design and Simulation of a Ring-Shaped Linear Array for Microultrasound Capsule Endoscopy

Video capsule endoscopy (VCE) has significantly advanced visualization of the gastrointestinal tract since its introduction in the last 20 years. Work is now under way to combine VCE with microultrasound imaging. However, small maximum capsule dimensions, coupled with the electronics required to integrate ultrasound imaging capabilities, pose significant design challenges. This paper describes a simulation process for testing transducer geometries and imaging methodologies to achieve satisfactory imaging performance within the physical limitations of the capsule size and outlines many of the tradeoffs needed in the design of this new class of ultrasound capsule endoscopy (USCE) device. A hybrid MATLAB model is described, incorporating Krimholtz-Leedom-Matthaei circuit elements and digitizing and beamforming elements to render a gray-scale B-mode. This model is combined with a model of acoustic propagation to generate images of point scatterers. The models are used to demonstrate the performance of a USCE transducer configuration comprising a single, unfocused transmit ring of radius 5 mm separated into eight segments for electrical impedance control and a 512-element receive linear array, also formed into a ring. The MATLAB model includes an ultrasonic pulser circuit connected to a piezocrystal composite transmit transducer with a center frequency of 25 MHz. B-scan images are simulated for wire target phantoms, multilayered phantoms, and a gut wall model. To demonstrate the USCE system's ability to image tissue, a digital phantom was created from single-element ultrasonic transducer scans of porcine small bowel ex vivo obtained at a frequency of 45 MHz.

Machine Learning in Ultrasound Computer-Aided Diagnostic Systems: A Survey

The ultrasound imaging is one of the most common schemes to detect diseases in the clinical practice. There are many advantages of ultrasound imaging such as safety, convenience, and low cost. However, reading ultrasound imaging is not easy. To support the diagnosis of clinicians and reduce the load of doctors, many ultrasound computer-aided diagnosis (CAD) systems are proposed. In recent years, the success of deep learning in the image classification and segmentation led to more and more scholars realizing the potential of performance improvement brought by utilizing the deep learning in the ultrasound CAD system. This paper summarized the research which focuses on the ultrasound CAD system utilizing machine learning technology in recent years. This study divided the ultrasound CAD system into two categories. One is the traditional ultrasound CAD system which employed the manmade feature and the other is the deep learning ultrasound CAD system. The major feature and the classifier employed by the traditional ultrasound CAD system are introduced. As for the deep learning ultrasound CAD, newest applications are summarized. This paper will be useful for researchers who focus on the ultrasound CAD system.

Acoustic Sensing and Ultrasonic Drug Delivery in Multimodal Theranostic Capsule Endoscopy

Video capsule endoscopy (VCE) is now a clinically accepted diagnostic modality in which miniaturized technology, an on-board power supply and wireless telemetry stand as technological foundations for other capsule endoscopy (CE) devices. However, VCE does not provide therapeutic functionality, and research towards therapeutic CE (TCE) has been limited. In this paper, a route towards viable TCE is proposed, based on multiple CE devices including important acoustic sensing and drug delivery components. In this approach, an initial multimodal diagnostic device with high-frequency quantitative microultrasound that complements video imaging allows surface and subsurface visualization and computer-assisted diagnosis. Using focused ultrasound (US) to mark sites of pathology with exogenous fluorescent agents permits follow-up with another device to provide therapy. This is based on an US-mediated targeted drug delivery system with fluorescence imaging guidance. An additional device may then be utilized for treatment verification and monitoring, exploiting the minimally invasive nature of CE. While such a theranostic patient pathway for gastrointestinal treatment is presently incomplete, the description in this paper of previous research and work under way to realize further components for the proposed pathway suggests it is feasible and provides a framework around which to structure further work.