Development of a Small-Footprint 50 MHz Linear Array: Fabrication and Micro-Ultrasound Imaging Demonstration.

Compact high-frequency arrays are of interest for clinical and preclinical applications in which a small-footprint or endoscopic device is needed to reach the target anatomy. However, the fabrication of compact arrays entails the connection of several dozens of small elements to the imaging system through a combination of flexible printed circuit boards at the array end and micro-coaxial cabling to the imaging system. The methods currently used, such as wire bonding, conductive adhesives, or a dry connection to a flexible circuit, considerably increase the array footprint. Here, we propose an interconnection method that uses vacuum-deposited metals, laser patterning, and electroplating to achieve a right-angle, compact, reliable connection between array elements and flexible-circuit traces. The array elements are thickened at the edges using patterned copper traces, which increases their cross-sectional area and facilitates the connection. We fabricated a 2.3 mm by 1.7 mm, 64-element linear array with elements at a 36 µm pitch connected to a 4 cm long flexible circuit, where the interconnect adds only 100 µm to each side of the array. Pulse-echo measurements yielded an average center frequency of 55 MHz and a -6 dB bandwidth of 41%. We measured an imaging resolution of 35 µm in the axial direction and 114 µm in the lateral direction and demonstrated the ex vivo imaging of porcine esophageal tissue and the in vivo imaging of avian embryonic vasculature.

Adaptation of a Clinical High-Frequency Transrectal Ultrasound System for Prostate Photoacoustic Imaging: Implementation and Pre-clinical Demonstration.

OBJECTIVE: High-frequency, high-resolution transrectal micro-ultrasound (micro-US: ≥15 MHz) imaging of the prostate is emerging as a beneficial tool for scoring disease risk and accurately targeting biopsies. Adding photoacoustic (PA) imaging to visualize abnormal vascularization and accumulation of contrast agents in tumors has potential for guiding focal therapies. In this work, we describe a new imaging platform that combines a transrectal micro-US system with transurethral light delivery for PA imaging. METHODS: A clinical transrectal micro-US system was adapted to acquire PA images synchronous to a tunable laser pulse. A transurethral side-firing optical fiber was developed for light delivery. A polyvinyl chloride (PVC)-plastisol phantom was developed and characterized to image PA contrast agents in wall-less channels. After resolution measurement in water, PA imaging was demonstrated in phantom channels with dyes and biodegradable nanoparticle contrast agents called porphysomes. In vivo imaging of a tumor model was performed, with porphysomes administered intravenously. RESULTS: Photoacoustic imaging data were acquired at 5 Hz, and image reconstruction was performed offline. PA image resolution at a 14-mm depth was 74 and 261 µm in the axial and lateral directions, respectively. The speed of sound in PVC-plastisol was 1383 m/s, and the attenuation was 4 dB/mm at 20 MHz. PA signal from porphysomes was spectrally unmixed from blood signals in the tumor, and a signal increase was observed 3 h after porphysome injection. CONCLUSION: A combined transrectal micro-US and PA imaging system was developed and characterized, and in vivo imaging demonstrated. High-resolution PA imaging may provide valuable additional information for diagnostic and therapeutic applications in the prostate.

Superharmonic and Microultrasound Imaging With Plane Wave Beamforming Techniques.

Superharmonic contrast imaging (SpHI) suppresses tissue clutter and allows high-contrast visualization of the vasculature. An array-based dual-frequency (DF) probe has been developed for SpHI, integrating a 21-MHz, 256-element microultrasound imaging array with a 2-MHz, 32-element array to take advantage of the broadband nonlinear responses from microbubble (MB) contrast agents. In this work, ultrafast imaging with plane waves was implemented for SpHI to increase the acquisition frame rate. Ultrafast imaging was also implemented for microultrasound B-mode imaging (HFPW B-mode) to enable high-resolution visualization of the tissue structure. Coherent compounding was demonstrated in vitro and in vivo in both imaging modes. Acquisition frame rates of 4.5 kHz and 187 Hz in HFPW B-mode imaging were achieved for imaging up to 21 mm with one and 25 angles, respectively, and 3.5 kHz and 396 Hz in the SpHI mode with one and nine coherently compounded angles, respectively. SpHI images showed suppression of tissue clutter prior to and after the introduction of MBs in vitro and in vivo. The nine-angle coherently compounded 2-D SpHI images of contrast-filled flow channel showed a contrast-to-tissue ratio (CTR) of 26.0 dB, a 2.5-dB improvement relative to images reconstructed from 0° steering. Consistent with in vitro imaging, the nine-angle compounded 2-D SpHI of a Lewis lung cancer tumor showed a 2.6-dB improvement in contrast enhancement, relative to 0° steering, and additionally revealed a region of nonviable tissue. The 3-D display of the volumetric SpHI data acquired from a xenograft mouse tumor using both 0° steering and nine-angle compounding allowed the visualization of the tumor vasculature. A small vessel visible in the compounded SpHI image, measuring around [Formula: see text], is not visualized in the 0° steering SpHI image, demonstrating the superiority of the latter in detecting fine structures within the tumor.

High-frequency quantitative ultrasound for the assessment of the acoustic properties of engineered tissues in vitro.

Acoustic properties of biomaterials and engineered tissues reflect their structure and cellularity. High-frequency ultrasound (US) can non-invasively characterize and monitor these properties with sub-millimetre resolution. We present an approach to estimate the speed of sound, acoustic impedance, and acoustic attenuation of cell-laden hydrogels that accounts for frequency-dependent effects of attenuation in coupling media, hydrogel thickness, and interfacial transmission/reflection coefficients of US waves, all of which can bias attenuation estimates. Cell-seeded fibrin hydrogel disks were raster-scanned using a 40 MHz US transducer. Thickness, speed of sound, acoustic impedance, and acoustic attenuation coefficients were determined from the difference in the time-of-flight and ratios of the magnitudes of US signals, interfacial transmission/reflection coefficients, and acoustic properties of the coupling media. With this approach, hydrogel thickness was accurately measured by US, with agreement to confocal microscopy (r2 = 0.97). Accurate thickness measurement enabled acoustic property measurements that were independent of hydrogel thickness, despite up to 60% reduction in thickness due to cell-mediated contraction. Notably, acoustic attenuation coefficients increased with increasing cell concentration (p < 0.001), reflecting hydrogel cellularity independent of contracted hydrogel thickness. This approach enables accurate measurement of the intrinsic acoustic properties of biomaterials and engineered tissues to provide new insights into their structure and cellularity. STATEMENT OF SIGNIFICANCE: High-frequency ultrasound can measure the acoustic properties of engineered tissues non-invasively and non-destructively with µm-scale resolution. Acoustic properties, including acoustic attenuation, are related to intrinsic material properties, such as scatterer density. We developed an analytical approach to estimate the acoustic properties of cell-laden hydrogels that accounts for the frequency-dependent effects of attenuation in coupling media, the reflection/transmission of ultrasound waves at the coupling interfaces, and the dependency of measurements on hydrogel thickness. Despite up to 60% reduction in hydrogel thickness due to cell-mediated contraction, our approach enabled measurements of acoustic properties that were substantially independent of thickness. Acoustic attenuation increased significantly with increasing cell concentration (p < 0.001), demonstrating the ability of acoustic attenuation to reflect intrinsic physical properties of engineered tissues.

Fine Pitch Flexible Printed Circuit Board Patterning for Miniaturized Endoscopic MicroUltrasound Arrays.

Microultrasound (micro-US) has become an invaluable tool for preclinical research and in emerging applications in clinical diagnosis and treatment guidance. Several such applications can benefit from arrays with a small footprint and endoscopic form factor. However, critical challenges arise in making electrical connections to array elements in such spatial constraints. In this work, we describe a method to pattern a high-density flexible circuit cabling on a copper-on polyimide film, using laser ablation of a polymer resist and wet etching, and then demonstrate a connection to a micro-US array. We investigate laser ablation process parameters and evaluate the ability to consistently pattern continuous copper traces. A minimum 30- [Formula: see text] pitch was achieved with 5- [Formula: see text]-wide electrode lines, and continuity of a 5-m-long trace is demonstrated. A flexible circuit with 30-mm-long traces with 30- [Formula: see text] line and 30- [Formula: see text] space before fan-out was fabricated to connect in an interleaved manner to a 32-element array with 30- [Formula: see text] element pitch. Metal deposition and laser ablation were used to connect and pattern the element electrodes to the copper traces of the flexible circuit. Electrical and acoustic measurements show good yield and consistent impedance across channels. Element pulse-echo tests demonstrated device functionality; the two-way pulse had 43-MHz center frequency and 40% fractional bandwidth (-6 dB). The proposed manufacturing methods facilitate the prototyping and fabrication of flexible endoscopic or small-footprint micro-US devices.

Acoustic Molecular Imaging Beyond the Diffraction Limit In Vivo.

Ultrasound molecular imaging (USMI) is a technique used to noninvasively estimate the distribution of molecular markers in vivo by imaging microbubble contrast agents (MCAs) that have been modified to target receptors of interest on the vascular endothelium. USMI is especially relevant for preclinical and clinical cancer research and has been used to predict tumor malignancy and response to treatment. In the last decade, methods that improve the resolution of contrast-enhanced ultrasound by an order of magnitude and allow researchers to noninvasively image individual capillaries have emerged. However, these approaches do not translate directly to molecular imaging. In this work, we demonstrate super-resolution visualization of biomarker expression in vivo using superharmonic ultrasound imaging (SpHI) with dual-frequency transducers, targeted contrast agents, and localization microscopy processing. We validate and optimize the proposed method in vitro using concurrent optical and ultrasound microscopy and a microvessel phantom. With the same technique, we perform a proof-of-concept experiment in vivo in a rat fibrosarcoma model and create maps of biomarker expression co-registered with images of microvasculature. From these images, we measure a resolution of 23 µm, a nearly fivefold improvement in resolution compared to previous diffraction-limited molecular imaging studies.

Implementation of a Novel 288-Element Dual-Frequency Array for Acoustic Angiography: In Vitro and In Vivo Characterization.

Acoustic angiography is a superharmonic contrast-enhanced ultrasound imaging method that produces high-resolution, 3-D maps of the microvasculature. Previous acoustic angiography studies have used twoelement, annular,mechanicallyactuated transducers(called "wobblers") to image microvasculature in preclinical tumor models with high contrast-to-tissue ratio and resolution, but these earlywobbler transducerscould not achieve the depth and sensitivity required for clinical acoustic angiography. In this work, we present a system for performing acoustic angiography with a novel dual-frequency(DF) transducer-a coaxially stacked DF array (DFA). We evaluate the DFA system bothin vitro andin vivo and demonstrate improvements in sensitivity and imaging depth up to 13.1 dB and 10 mm, respectively, compared with previous wobbler probes.

A novel, hands-free ultrasound patch for continuous monitoring of quantitative Doppler in the carotid artery.

Quantitative Doppler ultrasound of the carotid artery has been proposed as an instantaneous surrogate for monitoring rapid changes in left ventricular output. Tracking immediate changes in the arterial Doppler spectrogram has value in acute care settings such as the emergency department, operating room and critical care units. We report a novel, hands-free, continuous-wave Doppler ultrasound patch that adheres to the neck and tracks Doppler blood flow metrics in the common carotid artery using an automated algorithm. String and blood-mimicking test objects demonstrated that changes in velocity were accurately measured using both manually and automatically traced Doppler velocity waveforms. In a small usability study with 22 volunteer users (17 clinical, 5 lay), all users were able to locate the carotid Doppler signal on a volunteer subject, and, in a subsequent survey, agreed that the device was easy to use. To illustrate potential clinical applications of the device, the Doppler ultrasound patch was used on a healthy volunteer undergoing a passive leg raise (PLR) as well as on a congestive heart failure patient at resting baseline. The wearable carotid Doppler patch holds promise because of its ease-of-use, velocity measurement accuracy, and ability to continuously record Doppler spectrograms over many cardiac and respiratory cycles.

Characterization of an Array-Based Dual-Frequency Transducer for Superharmonic Contrast Imaging.

Superharmonic imaging with dual-frequency imaging systems uses conventional low-frequency ultrasound transducers on transmit, and high-frequency transducers on receive to detect higher order harmonic signals from microbubble contrast agents, enabling high-contrast imaging while suppressing clutter from background tissues. Current dual-frequency imaging systems for superharmonic imaging have been used for visualizing tumor microvasculature, with single-element transducers for each of the low- and high-frequency components. However, the useful field of view is limited by the fixed focus of single-element transducers, while image frame rates are limited by the mechanical translation of the transducers. In this article, we introduce an array-based dual-frequency transducer, with low-frequency and high-frequency arrays integrated within the probe head, to overcome the limitations of single-channel dual-frequency probes. The purpose of this study is to evaluate the line-by-line high-frequency imaging and superharmonic imaging capabilities of the array-based dual-frequency probe for acoustic angiography applications in vitro and in vivo. We report center frequencies of 1.86 MHz and 20.3 MHz with -6 dB bandwidths of 1.2 MHz (1.2-2.4 MHz) and 14.5 MHz (13.3-27.8 MHz) for the low- and high-frequency arrays, respectively. With the proposed beamforming schemes, excitation pressure was found to range from 336 to 458 kPa at its azimuthal foci. This was sufficient to induce nonlinear scattering from microbubble contrast agents. Specifically, in vitro contrast channel phantom imaging and in vivo xenograft mouse tumor imaging by this probe with superharmonic imaging showed contrast-to-tissue ratio improvements of 17.7 and 16.2 dB, respectively, compared to line-by-line micro-ultrasound B-mode imaging.

High-Frequency Array-Based Nanobubble Nonlinear Imaging in a Phantom and In Vivo.

There has been growing interest in nanobubbles (NBs) for vascular and extravascular ultrasound contrast imaging and therapeutic applications. Studies to date have generally utilized low frequencies (<12 MHz), high concentrations (>109 mL-1), and uncalibrated B-mode or contrast-mode on commercial systems without reporting investigations on NB signatures upon which the imaging protocols should be based. We recently demonstrated that low concentrations (106 mL-1) of porphyrin-lipid-encapsulated NBs scatter nonlinearly at low (2.5, 8 MHz) and high (12.5, 25, 30 MHz) frequencies in a pressure threshold-dependent manner that is advantageous for amplitude modulation (AM) imaging. Here, we implement pressure-calibrated AM at high frequency on a commercial preclinical array system to enhance sensitivity to nonlinear scattering of three phospholipid-based NB formulations. With this approach, improvements in contrast to tissue ratio relative to B-mode between 12.4 and 22.8 dB are demonstrated in a tissue-mimicking phantom, and between 6.7 and 14.8 dB in vivo.

High frequency ultrasound nonlinear scattering from porphyrin nanobubbles.

Emerging contrast imaging studies have highlighted the potential of nanobubbles for both intravascular and extravascular applications. Reports to date on nanobubbles have generally utilized low frequencies (<12 MHz), high concentrations (>109 mL-1), and B-mode or contrast-mode on preclinical and clinical systems. However, none of these studies directly examined nanobubble acoustic signatures systematically to implement nonlinear imaging schemes in a methodical manner based on nanobubble behaviour. Here, nanobubble nonlinear behaviour is investigated at high frequencies (12.5, 25, 30 MHz) and low concentration (106 mL-1) in a channel phantom, with different pulse types in single- and multi-pulse sequences to examine behaviour under conditions relevant to high frequency imaging. Porphyrin nanobubbles are demonstrated to initiate nonlinear scattering at high frequencies in a pressure-threshold dependent manner, as previously observed at low frequencies. This threshold behaviour was then utilized to demonstrate enhanced nanobubble imaging with pulse inversion, amplitude modulation, and a combination of the two, progressing towards the improved sensitivity and expanded utility of these ultrasound contrast agents.

Tetrazine-Derived Near-Infrared Dye as a Facile Reagent for Developing Targeted Photoacoustic Imaging Agents.

A new photoacoustic (PA) dye was developed as a simple-to-use reagent for creating targeted PA imaging agents. The lead molecule was prepared via an efficient two-step synthesis from an inexpensive commercially available starting material. With the dye's innate albumin-binding properties, the resulting tetrazine-derived dye is capable of localizing to tumor and exhibits a biological half-life of a few hours, allowing for an optimized distribution profile. The presence of tetrazine in turn makes it possible to link the albumin-binding optoacoustic signaling agent to a wide range of targeting molecules. To demonstrate the utility and ease of use of the platform, a novel PA probe for imaging calcium accretion was generated using a single-step bioorthogonal coupling reaction where high-resolution PA images of the knee joint in mice were obtained as early as 1 h post injection. Whole-body distribution was subsequently determined by labeling the probe with 99mTc and performing tissue counting following necropsy. These studies, along with tumor imaging and in vitro albumin binding studies, revealed that the core PA contrast agent can be imaged in vivo and can be easily linked to targeting molecules for organ-specific uptake.

Superharmonic Ultrasound for Motion-Independent Localization Microscopy: Applications to Microvascular Imaging From Low to High Flow Rates.

Recent advances in high frame rate biomedical ultrasound have led to the development of ultrasound localization microscopy (ULM), a method of imaging microbubble (MB) contrast agents beyond the diffraction limit of conventional coherent imaging techniques. By localizing and tracking the positions of thousands of individual MBs, ultrahigh resolution vascular maps are generated which can be further analyzed to study disease. Isolating bubble echoes from tissue signal is a key requirement for super-resolution imaging which relies on the spatiotemporal separability and localization of the bubble signals. To date, this has been accomplished either during acquisition using contrast imaging sequences or post-beamforming by applying a spatiotemporal filter to the B-mode images. Superharmonic imaging (SHI) is another contrast imaging method that separates bubbles from tissue based on their strongly nonlinear acoustic properties. This approach is highly sensitive, and, unlike spatiotemporal filters, it does not require decorrelation of contrast agent signals. Since this superharmonic method does not rely on bubble velocity, it can detect completely stationary and moving bubbles alike. In this work, we apply SHI to ULM and demonstrate an average improvement in SNR of 10.3-dB in vitro when compared with the standard singular value decomposition filter approach and an increase in SNR at low flow ( [Formula: see text]/frame) from 5 to 16.5 dB. Additionally, we apply this method to imaging a rodent kidney in vivo and measure vessels as small as [Formula: see text] in diameter after motion correction.

Tumor Contrast Imaging with Gas Vesicles by Circumventing the Reticuloendothelial System.

Gas vesicles (GVs) are nanosized structures (45-800 nm) and have been reported to produce non-linear contrast signals, making them an attractive agent for molecular targeting of tumors. One barrier to their use for pre-clinical oncology studies is rapid uptake into the reticuloendothelial system (RES) and consequent rapid decrease in contrast signal after infusion ends and low signal on reperfusion after a bubble burst sequence. The purpose of this study was to examine suppression of the RES and surface modification of GVs to prolong contrast circulation in tumors for ultrasound imaging. Ultrasound imaging to measure dynamics of contrast signal intensity in tumor models was carried out using a 21-MHz high-frequency array transducer with the Vevo 2100 ultrasound system. The non-linear contrast signal from intravenously injected GVs compared with peak enhancement was measured during contrast wash-out and on reperfusion after a contrast burst sequence. Disrupting the RES by saturating the macrophage population or chemically inhibiting the Kupffer cell population with gadolinium or Intralipid preserves 62%-88% of GVs' contrast enhancement relative to peak during the wash-out phase and 32%-56% on reperfusion compared with 38% and 14%, respectively, for no disruption of the RES, indicating longer circulation of GVs in the tumor. Additionally, coating the GVs with 2-, 5- or 10-kDa polyethylene glycol (PEG) chains resulted in >70% contrast signal retention in the tumors during wash-out and, for 5- or 10-kDa PEG chains, a return to >45% of peak contrast signal on reperfusion. These findings indicate that GVs can be used as a contrast agent for tumor imaging and that disruption of the RES improved recirculation and maintained contrast enhancement caused by GVs in the tumors.

In Vitro Superharmonic Contrast Imaging Using a Hybrid Dual-Frequency Probe.

Superharmonic imaging is an ultrasound contrast imaging technique that differentiates microbubble echoes from tissue through detection of higher-order bubble harmonics in a broad frequency range well above the excitation frequency. Application of superharmonic imaging in three dimensions allows specific visualization of the tissue microvasculature with high resolution and contrast, a technique referred to as acoustic angiography. Because of the need to transmit and receive across a bandwidth that spans up to the fifth harmonic of the fundamental and higher, this imaging approach requires imaging probes comprising dedicated transducers for transmit and receive. In this work, we report on a new dual-frequency probe including two 1.7-MHz rectangular transducers positioned one on each side of a 20-MHz 256-element array. Finite element modeling-based design, fabrication processes and assembly of the transducer are described, as is integration with a high-frequency ultrasound imaging platform. Dual-frequency single-plane-wave imaging was performed with a microbubble contrast agent in flow phantoms and compared with conventional high-frequency B-mode imaging, and resolution and contrast-to-tissue ratio were quantified. This work represents an intermediate but informative step toward the development of dual-frequency imaging probes based on array technology, specifically designed for clinical applications of acoustic angiography.

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.

High Resolution Microultrasound (µUS) Investigation of the Gastrointestinal (GI) Tract.

High resolution, microultrasound (µUS) scanning of the gastrointestinal (GI) tract has potential as an important transmural imaging modality to aid in diagnosis. Operating at higher frequencies than conventional clinical ultrasound instruments, µUS is capable of providing scanned images of the GI tract with higher resolution. To investigate the use of µUS for this application, a phantom which is cost effective, within ethical guidelines and, most importantly, similar in histology to the human GI tract is necessary. Therefore, a phantom utilizing porcine small bowel tissue has been developed for custom assembled µUS scanning systems. Two such systems, a stepping scanner and a continuous sweep scanner were utilized to repeatedly scan regions of prepared samples of porcine small bowel tissue. The porcine small bowel tissue phantom was perfused with degassed phosphate buffer saline (dPBS) solution through a cannula inserted in its mesenteric vessel to simulate in vivo conditions and achieve better µUS mucosal characterization. The µUS system scans a transducer across the tissue phantom to acquire RF echo data, which is then processed using MATLAB. A B-scan reconstruction produces 2D images with relative echo strength mapped to a color map of the user's choice. The phantom developed also allows for modifications such as the insertion of fiducial markers to detect tissue change over time and simultaneous perfusion and scanning, providing a platform for more detailed research and investigation into µUS scanning of the GI tract.

Implementation of a PMN-PT piezocrystal-based focused array with geodesic faceted structure.

The higher performance of relaxor-based piezocrystals compared with piezoceramics is now well established, notably including improved gain-bandwidth product, and these materials have been adopted widely for biomedical ultrasound imaging. However, their use in other applications, for example as a source of focused ultrasound for targeted drug delivery, is hindered in several ways. One of the issues, which we consider here, is in shaping the material into the spherical geometries used widely in focused ultrasound. Unlike isotropic unpoled piezoceramics that can be shaped into a monolithic bowl then poled through the thickness, the anisotropic structure of piezocrystals make it impossible to machine the bulk crystalline material into a bowl without sacrificing performance. Instead, we report a novel faceted array, inspired by the geodesic dome structure in architecture, which utilizes flat piezocrystal material and maximizes fill factor. Aided by 3D printing, a prototype with f#≈ 1.2, containing 96 individually addressable elements was manufactured using 1-3 connectivity PMN-PT piezocrystal-epoxy composite. The fabrication process is presented and the array was connected to a 32-channel controller to shape and steer the beam for preliminary performance demonstration. At an operating frequency of 1MHz, a focusing gain around 30 was achieved and the side lobe intensities were all at levels below -12dB compared to main beam. We conclude that, by taking advantage of contemporary fabrication techniques and driving instrumentation, the geodesic array configuration is suitable for focused ultrasound devices made with piezocrystal.

Dual Orientation 16-MHz Single-Element Ultrasound Needle Transducers for Image-Guided Neurosurgical Intervention.

Image-guided surgery is today considered to be of significant importance in neurosurgical applications. However, one of its major shortcomings is its reliance on preoperative image data, which does not account for brain deformations and displacements that occur during surgery. In this work, we propose to tackle this issue through the incorporation of an ultrasound device within the type of biopsy needles commonly used as an interventional tool to provide immediate feedback to neurosurgeons during surgical procedures. To identify the most appropriate path to access a targeted tissue site, single-element transducers that look either forward or sideways have been designed and fabricated. Micromolded 1-3 piezocomposites were adopted as the active materials for feasibility tests and epoxy lenses have been applied to focus the ultrasound beam. Electrical impedance analysis, pulse-echo testing, and wire phantom scanning have been carried out, demonstrating the functionality of the needle transducers at [Formula: see text]. The capabilities of these transducers for intraoperative image guidance were demonstrated by imaging within soft-embalmed cadaveric human brain and fresh porcine brain.

Screen-printed ultrasonic 2-D matrix array transducers for microparticle manipulation.

This paper reports the development of a two-dimensional thick film lead zirconate titanate (PZT) ultrasonic transducer array, operating at frequency approximately 7.5MHz, to demonstrate the potential of this fabrication technique for microparticle manipulation. All layers of the array are screen-printed then sintered on an alumina substrate without any subsequent patterning processes. The thickness of the thick film PZT is 139±2µm, the element pitch of the array is 2.3mm, and the dimension of each individual PZT element is 2×2mm(2) with top electrode 1.7×1.7mm(2). The measured relative dielectric constant of the PZT is 2250±100 and the dielectric loss is 0.09±0.005 at 10kHz. Finite element analysis was used to predict the behaviour of the array and to optimise its configuration. Electrical impedance spectroscopy and laser vibrometry were used to characterise the array experimentally. The measured surface motion of a single element is on the order of tens of nanometres with a 10Vpeak continuous sinusoidal excitation. Particle manipulation experiments have been demonstrated with the array by manipulating Ø10µm polystyrene microspheres in degassed water. The simplified array fabrication process and the bulk production capability of screen-printing suggest potential for the commercialisation of multilayer planar resonant devices for ultrasonic particle manipulation.