Transparent High-Frequency Ultrasonic Transducer for Photoacoustic Microscopy Application

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.

High spatiotemporal mapping of cortical blood flow velocity with an enhanced accuracy

Cerebral blood flow velocity is one of the most essential parameters related to brain functions and diseases. However, most existing mapping methods suffer from either inaccuracy or lengthy sampling time. In this study, we propose a particle-size-related calibration method to improve the measurement accuracy and a random-access strategy to suppress the sampling time. Based on the proposed methods, we study the long-term progress of cortical vasculopathy and abnormal blood flow caused by glioma, short-term variations of blood flow velocity under different anesthetic depths, and cortex-wide connectivity of the rapid fluctuation of blood flow velocities during seizure onset. The experimental results demonstrate that the proposed calibration method and the random-access strategy can improve both the qualitative and quantitative performance of velocimetry techniques and are also beneficial for understanding brain functions and diseases from the perspective of cerebral blood flow.

An ultrasensitive and broadband transparent ultrasound transducer for ultrasound and photoacoustic imaging in-vivo

Transparent ultrasound transducers (TUTs) can seamlessly integrate optical and ultrasound components, but acoustic impedance mismatch prohibits existing TUTs from being practical substitutes for conventional opaque ultrasound transducers. Here, we propose a transparent adhesive based on a silicon dioxide-epoxy composite to fabricate matching and backing layers with acoustic impedances of 7.5 and 4-6 MRayl, respectively. By employing these layers, we develop an ultrasensitive, broadband TUT with 63% bandwidth at a single resonance frequency and high optical transparency ( > 80%), comparable to conventional opaque ultrasound transducers. Our TUT maximises both acoustic power and transfer efficiency with maximal spectrum flatness while minimising ringdowns. This enables high contrast and high-definition dual-modal ultrasound and photoacoustic imaging in live animals and humans. Both modalities reach an imaging depth of > 15 mm, with depth-to-resolution ratios exceeding 500 and 370, respectively. This development sets a new standard for TUTs, advancing the possibilities of sensor fusion.

Transparent Dual-Frequency CMUT Arrays for Photoacoustic Imaging

The opaque ultrasound transducers used in conventional photoacoustic imaging systems necessitate oblique light delivery, which gives rise to some disadvantages such as inefficient target illumination and bulky system size. This work proposes a transparent capacitive micromachined ultrasound transducer (CMUT) linear array with dual-band operation for through-illumination photoacoustic imaging. Fabricated using an adhesive wafer bonding method, the array consists of optically transparent conductors [indium tin oxide (ITO)] as both top and bottom electrodes, a transparent polymer [bisbenzocyclobutene (BCB)] as the sidewall and adhesive material, and largely transparent silicon nitride as the membrane. The fabricated device had a maximum optical transparency of 76.8% in the visible range. Furthermore, to simultaneously maintain higher spatial resolution and deeper imaging depth, this dual-frequency array consists of low- and high-frequency channels with 4.2- and 9.3-MHz center frequencies, respectively, which are configured in an interlaced architecture to minimize the grating lobes in the receive point spread function (PSF). With a wider bandwidth compared to the single-frequency case, the fabricated transparent dual-frequency CMUT array was used in through-illumination photoacoustic imaging of wire targets demonstrating an improved spatial resolution and imaging depth.

Broadband transparent ultrasound transducer with polymethyl methacrylate as matching layer for in vivo photoacoustic microscopy

Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and in vivo small animal imaging.

Noise-insensitive defocused signal and resolution enhancement for optical-resolution photoacoustic microscopy via deep learning

Optical-resolution photoacoustic microscopy suffers from narrow depth of field and a significant deterioration in defocused signal intensity and spatial resolution. Here, a method based on deep learning was proposed to enhance the defocused resolution and signal-to-noise ratio. A virtual optical-resolution photoacoustic microscopy based on k-wave was used to obtain the datasets of deep learning with different noise levels. A fully dense U-Net was trained with randomly distributed sources to improve the quality of photoacoustic images. The results show that the PSNR of defocused signal was enhanced by more than 1.2 times. An over 2.6-fold enhancement in lateral resolution and an over 3.4-fold enhancement in axial resolution of defocused regions were achieved. The large volumetric and high-resolution imaging of blood vessels further verified that the proposed method can effectively overcome the deterioration of the signal and the spatial resolution due to the narrow depth of field of optical-resolution photoacoustic microscopy.

A Miniature Multi-Functional Photoacoustic Probe

Photoacoustic technology is a promising tool to provide morphological and functional information in biomedical research. To enhance the imaging efficiency, the reported photoacoustic probes have been designed coaxially involving complicated optical/acoustic prisms to bypass the opaque piezoelectric layer of ultrasound transducers, but this has led to bulky probes and has hindered the applications in limited space. Though the emergence of transparent piezoelectric materials helps to save effort on the coaxial design, the reported transparent ultrasound transducers were still bulky. In this work, a miniature photoacoustic probe with an outer diameter of 4 mm was developed, in which an acoustic stack was made with a combination of transparent piezoelectric material and a gradient-index lens as a backing layer. The transparent ultrasound transducer exhibited a high center frequency of ~47 MHz and a -6 dB bandwidth of 29.4%, which could be easily assembled with a pigtailed ferrule of a single-mode fiber. The multi-functional capability of the probe was successfully validated through experiments of fluid flow sensing and photoacoustic imaging.

Review on ultrasound-guided photoacoustic imaging for complementary analyses of biological systems in vivo

Photoacoustic imaging has been developed as a new biomedical molecular imaging modality. Due to its similarity to conventional ultrasound imaging in terms of signal detection and image generation, dual-modal photoacoustic and ultrasound imaging has been applied to visualize physiological and morphological information in biological systems in vivo. By complementing each other, dual-modal photoacoustic and ultrasound imaging showed synergistic advances in photoacoustic imaging with the guidance of ultrasound images. In this review, we introduce our recent progresses in dual-modal photoacoustic and ultrasound imaging systems at various scales of study, from preclinical small animals to clinical humans. A summary of the works reveals various strategies for combining the structural information of ultrasound images with the molecular information of photoacoustic images.

Transparent microfiber Fabry-Perot ultrasound sensor with needle-shaped focus for multiscale photoacoustic imaging

Photoacoustic tomography emerged as a promising tool for noninvasive biomedical imaging and diseases diagnosis. However, most of the current piezoelectric ultrasound transducers suffer optical opacity and tissue-mismatched acoustic impedance, hindering the miniaturization and integration of the system for multiscale and multimodal imaging. Here, a transparent polydimethylsiloxane (PDMS) encapsulated optical microfiber ultrasound sensor was demonstrated for photoacoustic imaging with scalable spatial resolution and penetration depth. The sensor comprised a microfiber loop sandwiched by a pair of in-line Bragg gratings, which formed an ultrasound-sensitive Fabry-Perot cavity allowing free delivery of ultrasound/light beams and unique needle-shaped ultrasound focusing along the penetration depth. The sensor with a detection limit of ∼ 700 Pa and a bandwidth of ∼ 10 MHz was applied for multiscale photoacoustic imaging of mouse ear and brain vasculatures. With advantages of flexibility, optical transparence and focusing capability, the sensor offers new opportunities for developing photoacoustic/ultrasound imaging devices for biomedical and clinic applications.

Ultrahigh Frequency Ultrasonic Transducers (150MHz) Based on Silicon Lenses

Acoustic microscopes and acoustic tweezers have great value in the application of microparticle manipulation, biomedical research and non-destructive testing. Ultrahigh frequency (UHF) ultrasonic transducers act as the key component in acoustic microscopes, and acoustic tweezers and acoustic lenses are essential parts of UHF ultrasonic transducers. Therefore, the preparation of acoustic lenses is crucial. Silicon is a suitable material for preparing acoustic lenses because of its high acoustic velocity, low acoustic attenuation and excellent machinability. In previous research, silicon lenses were mainly prepared by etching. However, etching has some drawbacks. The etching of large sizes is complex, time-consuming and expensive. Furthermore, vertical etching is preferred to spherical etching. Thus, a new method of ultra-precision machining was introduced to prepare silicon lenses. In this paper, silicon lenses with an aperture of 892 μm and a depth of 252 μm were prepared. Then, UHF ultrasonic transducers with a center frequency of 157 MHz and a -6-dB bandwidth of 52% were successfully prepared based on silicon lenses. The focal distance of the transducers was 736 μm and the F-number was about 0.82. The transducers had a lateral resolution of 11 μm and could distinguish the 13 μm slots on silicon wafers clearly.

High-speed wide-field photoacoustic microscopy using a cylindrically focused transparent high-frequency ultrasound transducer

Combining focused optical excitation and high-frequency ultrasound detection, optical-resolution photoacoustic microscopy (OR-PAM) can provide micrometer-level spatial resolution with millimeter-level penetration depth and has been employed in a variety of biomedical applications. However, it remains a challenge for OR-PAM to achieve a high imaging speed and a large field of view at the same time. In this work, we report a new approach to implement high-speed wide-field OR-PAM, using a cylindrically-focused transparent ultrasound transducer (CFT-UT). The CFT-UT is made of transparent lithium niobate coated with indium-tin-oxide as electrodes. A transparent cylindrical lens is attached to the transducer surface to provide an acoustic focal line with a length of 9 mm. The excitation light can pass directly through the CFT-UT from the above and thus enables a reflection imaging mode. High-speed imaging is achieved by fast optical scanning of the focused excitation light along the CFT-UT focal line. With the confocal alignment of the optical excitation and acoustic detection, a relatively high detection sensitivity is maintained over the entire scanning range. The CFT-UT-based OR-PAM system has achieved a cross-sectional frame rate of 500 Hz over the scanning range of 9 mm. We have characterized the system's performance on phantoms and demonstrated its application on small animal models in vivo. We expect the new CFT-UT-based OR-PAM will find matched biomedical applications that need high imaging speed over a large field of view.

Photoacoustic imaging for microcirculation

Microcirculation facilitates the blood-tissue exchange of nutrients and regulates blood perfusion. It is, therefore, essential in maintaining tissue health. Aberrations in microcirculation are potentially indicative of underlying cardiovascular and metabolic pathologies. Thus, quantitative information about it is of great clinical relevance. Photoacoustic imaging (PAI) is a capable technique that relies on the generation of imaging contrast via the absorption of light and can image at micron-scale resolution. PAI is especially desirable to map microvasculature as hemoglobin strongly absorbs light and can generate a photoacoustic signal. This paper reviews the current state of the art for imaging microvascular networks using photoacoustic imaging. We further describe how quantitative information about blood dynamics such as the total hemoglobin concentration, oxygen saturation, and blood flow rate is obtained using PAI. We also discuss its importance in understanding key pathophysiological processes in neurovascular, cardiovascular, ophthalmic, and cancer research fields. We then discuss the current challenges and limitations of PAI and the approaches that can help overcome these limitations. Finally, we provide the reader with an overview of future trends in the field of PAI for imaging microcirculation.

A Novel Matching Layer Design for Improving the Performance of Transparent Ultrasound Transducers

Transparent ultrasound transducer (TUT) technology allows easy co-alignment of optical and acoustic beams in the development of compact photoacoustic imaging (PAI) devices with minimum acoustic coupling. However, TUTs suffer from narrow bandwidth and low pulse-echo sensitivity due to the lack of suitable transparent acoustic matching and backing layers. Here, we studied translucent glass beads (GB) in transparent epoxy as an acoustic matching layer for the transparent lithium niobate piezoelectric material-based TUTs (LN-TUTs). The acoustic and optical properties of various volume fractions of GB matching layers were studied using theoretical calculations, simulations, and experiments. These results demonstrated that the GB matching layer has significantly enhanced the pulse-echo sensitivity and bandwidth of the TUTs. Moreover, the GB matching layer served as a light diffuser to help achieve uniform optical fluence on the tissue surface and also improved the photoacoustic (PA) signal bandwidth. The proposed GB matching layer fabrication is low cost, easy to manufacture using conventional ultrasound transducer fabrication tools, acoustically compatible with soft tissue, and minimizes the use of the acoustic coupling medium.

A Transparent Ultrasound Array for Real-Time Optical, Ultrasound, and Photoacoustic Imaging

Objective and Impact Statement. Simultaneous imaging of ultrasound and optical contrasts can help map structural, functional, and molecular biomarkers inside living subjects with high spatial resolution. There is a need to develop a platform to facilitate this multimodal imaging capability to improve diagnostic sensitivity and specificity. Introduction. Currently, combining ultrasound, photoacoustic, and optical imaging modalities is challenging because conventional ultrasound transducer arrays are optically opaque. As a result, complex geometries are used to coalign both optical and ultrasound waves in the same field of view. Methods. One elegant solution is to make the ultrasound transducer transparent to light. Here, we demonstrate a novel transparent ultrasound transducer (TUT) linear array fabricated using a transparent lithium niobate piezoelectric material for real-time multimodal imaging. Results. The TUT-array consists of 64 elements and centered at ~6 MHz frequency. We demonstrate a quad-mode ultrasound, Doppler ultrasound, photoacoustic, and fluorescence imaging in real-time using the TUT-array directly coupled to the tissue mimicking phantoms. Conclusion. The TUT-array successfully showed a multimodal imaging capability and has potential applications in diagnosing cancer, neurological, and vascular diseases, including image-guided endoscopy and wearable imaging.

A Review of High-Frequency Ultrasonic Transducers for Photoacoustic Imaging Applications

Photoacoustic imaging (PAI) is a new and rapidly growing hybrid biomedical imaging modality that combines the virtues of both optical and ultrasonic (US) imaging. The nature of the interaction between light and ultrasound waves allows PAI to make good use of the rich contrast produced by optics while retaining the imaging depths in US imaging. High-frequency US transducers are an important part of the PAI systems, used to detect the high-frequency and broad-bandwidth photoacoustic signals excited by the target tissues irradiated by short laser pulses. Advancement in high-frequency US transducer technology has influenced the boost of PAI to broad applications. Here, we present a review on high-frequency US transducer technologies for PAI applications, including advanced piezoelectric materials and representative transducers. In addition, we discuss the new challenges and directions facing the development of high-frequency US transducers for PAI applications.

Reversibly Photoswitching Upconversion Nanoparticles for Super-Sensitive Photoacoustic Molecular Imaging

Photoacoustic (PA) imaging uses light excitation to generate the acoustic signal for detection and improves tissue penetration depth and spatial resolution in the clinically relevant depth of living subjects. However, strong background signals from blood and pigments have significantly compromised the sensitivity of PA imaging with exogenous contrast agents. Here we report a nanoparticle-based probe design that uses light to reversibly modulate the PA emission to enable photoacoustic photoswitching imaging (PAPSI) in living mice. Such a nanoprobe is built with upconverting nanocrystals and photoswitchable small molecules and can be switched on by NIR light through upconversion to UV energy. Reversibly photoswitching of the nanoprobe reliably removed strong tissue background, increased the contrast-to-noise ratio, and thus improved imaging sensitivity. We have shown that PAPSI can image 0.05 nM of the nanoprobe in hemoglobin solutions and 10⁴ labeled cancer cells after implantation in living mice using a commercial PA imager.

A backward-mode optical-resolution photoacoustic microscope for 3D imaging using a planar Fabry-Pérot sensor

Optical-resolution photoacoustic microscopy (OR-PAM) combines high spatial resolution and strong absorption-based contrast in tissue, which has enabled structural and spectroscopic imaging of endogenous chromophores, primarily hemoglobin. Conventional piezoelectric ultrasound transducers are typically placed far away from the photoacoustic source due to their opacity, which reduces acoustic sensitivity. Optical ultrasound sensors are an alternative as their transparency allows them to be positioned close to the sample with minimal source-detector distances. In this work, a backward-mode OR-PAM system based on a planar Fabry-Pérot ultrasound sensor and coaxially aligned excitation and interrogation beams was developed. Two 3D imaging modes, using raster-scanning for enhanced image quality and continuous-scanning for fast imaging, were implemented and tested on a leaf skeleton phantom. In fast imaging mode, a scan-rate of 100,000 A-lines/s was achieved. 3D images of a zebrafish embryo were acquired in vivo in raster-scanning mode. The transparency of the FP sensor in the visible and near-infrared wavelength region makes it suitable for combined functional and molecular imaging applications using OR-PAM and multi-photon fluorescence microscopy.

A High Sensitivity Transparent Ultrasound Transducer based on PMN-PT for Ultrasound and Photoacoustic Imaging

We recently introduced piezoelectric lithium niobate (LN) based transparent ultrasound transducers (TUT) as a new platform for developing multimodal optical, ultrasound and photoacoustic imaging systems. However, LN based TUT is limited in its signal-to-noise ratio due to material's low piezoelectricity (d ₃₃). In this paper, we report, for the first time, a 0.2 mm thick transparent lead magnesium niobate-lead titanate (PMN-PT) based TUT (PMN-PT-TUT) for ultrasound and photoacoustic applications and compared its performance with a 0.25 mm thick transparent LN based TUT (LN-TUT). To improve the ultrasound energy transmission efficiency, TUTs were fabricated with a two-matching-layer design. This resulted in a dual frequency response with center frequencies of 7.8 MHz/13.2 MHz and corresponding bandwidths of 28.2%/66.67% for PMN-PT-TUT, and center frequencies of 7.2 MHz/11.8 MHz and bandwidths of 36.1%/62.7% for LN-TUT. The optical transmission rate of PMN-PT-TUTs and LN-TUTs are measured as ~73% and ~91% respectively at 532 nm optical wavelength. The PMN-PT-TUT exhibited higher sensitivity compared to LN-TUT with a nearly three-fold higher pulse echo amplitude and more than two-fold higher photoacoustic amplitude. Furthermore, optical resolution photoacoustic microscopy (ORPAM) experiments on phantom targets demonstrated lateral resolutions of 7 μm and 5.1 μm, and axial resolutions of 285.6 μm and 375.9 μm for PMN-PT-TUT and LN-TUT respectively. These results indicated that PMN-PT is a viable alternative to LN for developing TUT based multimodal ultrasound and photoacoustic imaging systems.

A Review of Transparent Sensors for Photoacoustic Imaging Applications

Photoacoustic imaging is a new type of noninvasive, nonradiation imaging modality that combines the deep penetration of ultrasonic imaging and high specificity of optical imaging. Photoacoustic imaging systems employing conventional ultrasonic sensors impose certain constraints such as obstructions in the optical path, bulky sensor size, complex system configurations, difficult optical and acoustic alignment, and degradation of signal-to-noise ratio. To overcome these drawbacks, an ultrasonic sensor in the optically transparent form has been introduced, as it enables direct delivery of excitation light through the sensors. In recent years, various types of optically transparent ultrasonic sensors have been developed for photoacoustic imaging applications, including optics-based ultrasonic sensors, piezoelectric-based ultrasonic sensors, and microelectromechanical system-based capacitive micromachined ultrasonic transducers. In this paper, the authors review representative transparent sensors for photoacoustic imaging applications. In addition, the potential challenges and future directions of the development of transparent sensors are discussed.

The Core of Medical Imaging: State of the Art and Perspectives on the Detectors

In this review, the roles of detectors in various medical imaging techniques were described. Ultrasound, optical (near-infrared spectroscopy and optical coherence tomography) and thermal imaging, magnetic resonance imaging, computed tomography, single-photon emission tomography, positron emission tomography were the imaging modalities considered. For each methodology, the state of the art of detectors mainly used in the systems was described, emphasizing new technologies applied.

Acoustic-resolution photoacoustic microscopy based on an optically transparent focused transducer with a high numerical aperture

This Letter reports acoustic-resolution-photoacoustic microscopy (AR-PAM) based on a new optically transparent focused polyvinylidene fluoride (PVDF) transducer with a high acoustic numerical aperture (NA) of 0.64. Owing to the improved fabrication process, the new transducer has a much higher NA (0.64) than the previously reported low-NA transducer (NA=0.23). The acoustic center frequency and (pulse-echo) bandwidth are also increased to 36 and 44 MHz, respectively, which provides a 38 µm acoustic focal spot size and 210 µm acoustic depth of focus. For demonstration, AR-PAM was conducted on a twisted wire target in water and chicken breast tissue, and in vivo on a mouse tail. The imaging results show that high acoustic resolution and sensitivity can be achieved with a simple and compact setup to resolve the target at different depths. Such capabilities can be useful for the development of new AR-PAM systems for handheld, wearable, and even endoscopic imaging applications.

Centimeter-scale wide-field-of-view laser-scanning photoacoustic microscopy for subcutaneous microvasculature in vivo

We developed a simple and compact laser-scanning photoacoustic microscopy (PAM) for imaging large areas of subcutaneous microvasculature in vivo. The reflection-mode PAM not only retains the advantage of high scanning speed for optical scanning, but also offers an imaging field-of-view (FOV) up to 20 × 20 mm², which is the largest FOV available in laser-scanning models so far. The lateral resolution of the PAM system was measured to be 17.5 µm. Image experiments on subcutaneous microvasculature in in vivo mouse ears and abdomen demonstrate the system's potential for fast and high-resolution imaging for injuries and diseases of large tissues and organs.

Quadruple ultrasound, photoacoustic, optical coherence, and fluorescence fusion imaging with a transparent ultrasound transducer

Ultrasound and optical imagers are used widely in a variety of biological and medical applications. In particular, multimodal implementations combining light and sound have been actively investigated to improve imaging quality. However, the integration of optical sensors with opaque ultrasound transducers suffers from low signal-to-noise ratios, high complexity, and bulky form factors, significantly limiting its applications. Here, we demonstrate a quadruple fusion imaging system using a spherically focused transparent ultrasound transducer that enables seamless integration of ultrasound imaging with photoacoustic imaging, optical coherence tomography, and fluorescence imaging. As a first application, we comprehensively monitored multiparametric responses to chemical and suture injuries in rats' eyes in vivo, such as corneal neovascularization, structural changes, cataracts, and inflammation. As a second application, we successfully performed multimodal imaging of tumors in vivo, visualizing melanomas without using labels and visualizing 4T1 mammary carcinomas using PEGylated gold nanorods. We strongly believe that the seamlessly integrated multimodal system can be used not only in ophthalmology and oncology but also in other healthcare applications with broad impact and interest.

Design of a Multichannel Pulser/Receiver and Optimized Damping Resistor for High-Frequency Transducer Applied to SAM System

Scanning acoustic microcopy (SAM) is widely used in biomedical and industrial applications in dermatology, ophthalmology, intravascular imaging, and small animal images, owing to SAM’s ability to photograph small structures with a good spatial resolution. One of the most important devices of this system is the pulser/receiver (P/R) (PRN-300, Ohlabs Corporation, Nam-gu Busan, Republic of Korea), which generates pulses to trigger a high-frequency transducer. This article presents the design of a pulse generator to excite high-frequency transducers with four channels. The characteristics of the pulses, such as time and frequency, can be reconfigured by using a high-speed field programmable gate array (FPGA). The configuration software was developed for communicating with the P/R device via a USB connector for easy, feasible pulse selection and real-time pulse management. Besides that, during the design and implementation of the hardware, we optimized the damping resistor value to reduce the overshoot and undershoot part of the signal, ensuring the best effect on the transducer signal. The test results show that unipolar pulses worked with transducers with frequencies over 100 MHz. The SAM systems can work simultaneously with multiple transducers, and the resulting images have different resolutions of regions.