Colas Q,Bantignies C,Perroteau M,Porcher N,Vassal S,Guerif B,Kim T,Bosch JG,de Jong N,Verweij MD,Pertijs MA,Ferin G,Flesch M
Three-dimensional ultrasound has initially been used to address volumetric imaging for diagnostic purposes and represents the leading-edge technological orientation in both transducer and IC (integrated circuit) architecture and design. However, new applications are coming up like biomarker measurem
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ents, preoperative navigation, real time surgery guidance or therapeutic procedures where 3D ultrasound modalities are key but their design objectives may need to be thought outside 3D echocardiography and radiology technological trade-offs. For those new applications, system architectures would need less complexity and imaging performances enabling easier hardware reconfigurability tailored to application-oriented imaging. This paper presents an ongoing development where a large matrix transducer has been assembled with multiple ASIC dies in a reconfigurable way. The transducer has a central frequency of 8MHz, a square pitch of 150µm× 150µm capable to fully image the upper carotid window thanks to a large aperture of 80×240 elements, resulting in a transducer active footprint of 12×36 square millimeters.
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Hoang T,Rosinski B,Felix N
Wireless power transfer (WPT) is a promising way to power active implantable medical devices (AIMDs) which are increasingly used in modern life to monitor and/or treat diseases such as cardiovascular diseases which are the cause of about 1/3 of global deaths according to the WHO. In the last decade,
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among WPT technologies like optical, radio frequency or inductive coupling, acoustic power transfer (APT) has received great interest thank to its advantages in terms of efficiency, miniaturization, deep propagation, and electromagnetic compatibility. Designing an efficient implantable ultrasound (US) receiver requires appropriate material selection considerations. This study presents for the first time a benchmark of piezoelectric materials and their important parameters in the aim of optimizing the performance of US receiver for wireless battery charging in subcutaneous implantable device. Simulation and experimental results reveal that hard ceramics with high mechanical quality factor are the most suitable for making an efficient US receiver. APT measurement demonstrates that the US receiver provided a maximum of 3.7 mA charging current at a depth of 20 mm through silicone medium from an ultrasound beam with an acoustic intensity of 81 mW/cm 2 .
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Legros M,Rouffaud R,Colin L,Gross D,Certon D,Escoffre JM
In this work, a novel ultrasound probe dedicated to image-guided therapy of the skin cancer is presented. The dual-mode probe was designed to perform high-resolution imaging, and to deliver simultaneously significant output pressure for therapeutic low-frequency applications. A 20 MHz ultrasound arr
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ay was stacked on a 1 MHz nominal frequency 2D-array, offering the ability to transmit a large variety of radiation field pattern with a high acoustic output for therapeutic ultrasound sequences.
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Wodnicki R,Bendjador H,Kang H,Foiret J,Notard C,Zhou Q,Ferrara KW
We have been developing highly-integrated and modular large aperture multi-row 1.75D linear arrays interfaced to a configurable ultrasound system (Verasonics Vantage 32LE) using custom ASIC multiplexing electronics with the goal to improve detection of liver cancer deep in the body. The array consis
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ts of multiple rows which are capable of multiplexing an aperture in elevation for realization of synthetic focusing and imaging in both azimuthal and elevational planes. The large array addresses 1,024 acoustic elements (42 mm×16 mm aperture with 650μm azi.×1000 μm elev. element pitch) with 64 elements in azimuth and 16 rows in elevation. Each of the columns are interfaced directly to a single respective imaging system channel. Rows are selected using commands sent to a local FPGA which controls the ASICs during imaging. Beamforming for individual rows in azimuth is accomplished by the configurable imaging system using plane wave imaging in azimuth and either SRA or STRA synthetic aperture imaging performed to create images in the elevation dimension. Imaging in elevation was performed at Fc =2.5 MHz and achieved 1.3 mm and 0.8 mm resolution at a depth of 20 mm for SRA and STRA modes respectively. We are currently integrating the probe acoustic array and electronics into a handheld form factor for future use in human imaging.
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Benchemoul M,Lejeune A,Porcher N,Montauban E,Ferin G,Gehin C,Bertrand,Massot,Vince P,Flesch M
Cardiovascular diseases (CVD) are considered as the main cause of death representing more than 30% of worldwide casualties according to the World Health Organization [1]. The pulse wave velocity (PWV) is a relevant indicator of CVD [2] at an early stage but it requires specialized clinical tools for
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its monitoring. The versatility of ultrasound imaging thanks to the introduction of ultrafast imaging and recent progress in electronics and signal processing allow the measurement and the monitoring of this biomarker. The proposed hardware solution is a high-frequency ultrasound linear probe dedicated to superficial arteries imaging, PWV and arterial stiffness assessment. The probe allows simultaneous multiplane imaging thanks to three acoustic apertures adopting a H-topology: one 128-element acoustic aperture is placed at the center of the probe and two orthogonal 64-element acoustic apertures are placed on each side of the probe. This arrangement enables both longitudinal imaging of a small artery and cross-sectional imaging from either side.
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Benchemoul M,Mateo T,Savery D,Gehin C,Massot B,Ferin G,Vince P,Flesch M
Cardiovascular diseases (CVD) are considered as the main cause of death representing more than 30% of worldwide casualties according to the World Health Organization [1]. The pulse wave velocity (PWV) is a relevant indicator of CVD [2] at an early stage since it directly reflects the age and stiffne
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ss of the arterial network. A PWV measurement method using a high-frequency (15 MHz) ultrasound probe with a H-topology made for vascular imaging is presented in this paper. The probe includes a longitudinal 128-element linear array at the center of the probe and two orthogonal 64-element linear arrays on each side of the probe. This solution makes the probe very well suited to the anatomy of smaller arteries, enabling both longitudinal and cross-sectional simultaneous imaging of the artery of interest. High frame-rate (HFR) plane wave imaging (10 000 frames per second) is employed for a precise PWV measurement which is performed in-vivo on a healthy volunteer. The long-term objective of this work is to develop an innovative device using a dedicated ultrasonic probe and integrating a miniaturized electronic system. The system would be able to automatically drive the probe, collect data and calculate the PWV in ambulatory situations, on-demand or during periodical routine check-ups. The device would be used at the wrist above the ulnar artery to measure the local PWV.
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Wodnicki R,Kang H,Zhang J,Foiret J,Notard C,Ratsimandresy L,Auclair P,Zhou Q,Ferrara KW
Hepatocellular carcinoma is difficult to diagnose reliably using ultrasound in patients with thick abdominal walls. An important consideration for improving diagnosis in these patients is increased contrast to noise resolution (CNR) which is directly dependent on elevation focus and can be improved
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by using a large electronically scanned elevational aperture. Here we present recent work integrating ASIC electronics modules with a large area 64 × 16 element 1.75D acoustic array module. The pitch of the acoustic array is 650 µm in azimuth and 1000 µm in elevation, with a 2.4 MHz center frequency. The total size of the aperture is 42 mm × 16 mm. The acoustic response with the ASIC modules benefitted from an improvement in normalized sensitivity of + 12dB, and an increase in the Fractional Bandwidth (FBW) of 3% (0.85 to 0.88). The ASICs and modules provide a framework for academic-industry partnership for development of extended aperture probes with arbitrary geometries.
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Mateo T,Senegond N,Meynier C,Gross D,Vince P,Tan M,Kang E,Pertijs M
In this work, we report the acoustical characterization of a 9 French (Fr) CMUT-based 1D catheter tip (2.5×12.8 mm 2 - 64 elements - 7.5 MHz) embedding a 64 channels analog transceiver ASIC (180 nm HV BCD technology) dedicated to Intra-cardiac Echocardiography. To this end, a Through-Silicon-Via pr
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ocess has been integrated in the CMUT process flow to ensure suitable vertical integration level needed to accommodate with the catheter's form factor. Good overall functioning of essential ASIC functionalities with the CMUT, i.e. transmit, beamforming, and receive, is first reported, starting from elementary characterization up to imaging. Additionally, a comparison with a custom discrete solution based on Commercial Off-The-Shelf components (COTS) to provide suitable CMUT preamplification in receive is performed. Using the same CMUT chip either with the ASIC, either with the COTS, allowed to quantify the benefit brought by the ASIC compared to a more straightforward but less integrated solution. Main results highlight that CMUT-on-ASIC allows to recover a much wider bandwidth (BW), increasing by 3 MHz the -6dB upper limit, and therefore getting closer the theoretical BW of the CMUT itself. Moreover, lower element crosstalk is measured on CMUT-on-ASIC device, showing that the ASIC decreases the electrical coupling compared to the COTS. Finally, noise equivalent pressure measurements in comparison with simulations in realistic ICE configuration promise much higher receive sensitivity with the ASIC solution, hence, confirming its great interest for the CMUT technology compared to less integrated solution, especially for catheter application.
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Yosra D,Certon D,Meulon FV,Calle S,Hoang T,Ferin G,Rosinski B
The development of Implantable Medical Devices (IMDs) to monitor the function of certain organs in the human body and patient health have received great interest in recent years. However, these devices need a reliable supply of power for operation. As a solution to remote power transfer, ultrasound
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appear to be a promising and competing approach compared to classical RF-based technics. The main restriction is to place the ultrasonic source directly in contact with the skin. This study investigates the possibility of contactless ultrasonic power transmission to IMDs, by using airborne ultrasonic sources. Three different airborne ultrasound transducers (between 40 kHz and 200 kHz) were tested. After emission in air and transmission at an air/water interface, the transmitted pressure in water (simulating human tissue) is investigated.
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Kang E,Tan M,An JS,Chang Y,Vince P,Senegond N,Mateo T,Meynier C,Pertijs M
Miniature ultrasound probes, such as the intra-cardiac echography (ICE) probe shown in Fig. 23.6.1, increasingly employ in-probe ASICs to interface with the elements of an ultrasound transducer array to improve signal quality and reduce cable count [1]-[4]. For each transducer element, such an ASIC
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contains a pulser that drives the element to generate a pressure wave, a low-noise amplifier (LNA) that amplifies the resulting echo signal, and a time-gain compensation (TGC) circuit that compensates for the time-varying echo-signal amplitude due to propagation attenuation of the acoustic wave. Without TGC, the first echoes, from shallow tissue, are much larger than later echoes from deeper tissue. The TGC circuit corrects for this, ideally by providing a gain that increases exponentially with time, thus reducing the dynamic range (DR) by as much as 40dB and strongly relaxing the requirements of subsequent blocks. In conventional ultrasound systems, TGC is typically performed after the LNA, implying that a power-hungry LNA is required that can handle the full DR of the echo signal [5], [6]. In recent in-probe ASICs, programmable-gain LNAs have been employed that provide a step-wise TGC approximation [1]-[3]. While this saves power, the associated gain-switching transients lead to imaging artefacts. In this paper, we present an LNA with a built-in continuous TGC function that mitigates this problem. The LNA is a transimpedance amplifier (TIA) optimized to amplify the signal current of a capacitive micro-machined ultrasound transducer (CMUT). We demonstrate its integration into a 64-channel ASIC for a CMUT-based ICE probe.
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Sauvage J,Poree J,Rabut C,Ferin G,Flesch M,Rosinski B,Nguyen-Dinh A,Tanter M,Pernot M,Deffieux T
Functional ultrasound imaging (fUS) recently emerged as a promising neuroimaging modality to image and monitor brain activity based on cerebral blood volume response (CBV) and neurovascular coupling. fUS offers very good spatial and temporal resolutions compared to fMRI gold standard as well as simp
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licity and portability. It was recently extended to 4D fUS imaging in preclinical settings although this approach remains limited and complex. Indeed 4D fUS requires a 2D matrix probe and specific hardware able to drive the N 2 elements of the probe with thousands of electronic channels. Several under-sampling approaches are currently investigated to limit the channel count and spread ultrasound 4D modalities. Among them, the Row Column Addressing (RCA) approach combined with ultrafast imaging is a compelling alternative using only N + N channels. We present a large field of view RCA probe prototype of 128 + 128 channels and 15 MHz central frequency adapted for preclinical imaging. Based on the Orthogonal Plane Wave compounding scheme, we were able to perform 4D vascular brain acquisitions at high volume rate. Doppler volumes of the whole rat brain were obtained in vivo at high rates (23 dB CNR at 156 Hz and 19 dB CNR at 313 Hz). Visual and whiskers stimulations were performed and the corresponding CBV increases were reconstructed in 3D with successful functional activation detected in the superior colliculus and somato-sensorial cortex respectively. This proof of concept study demonstrates for the first time the use of a low-channel count RCA array for in vivo 4D fUS imaging in the whole rat brain.
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Tan M,Kang E,An JS,Chang Y,Vince P,Mateo T,Senegond N,Pertijs MA
This article presents a fully integrated 64-channel programmable ultrasound transmit beamformer for catheter-based ultrasound probes, designed to interface with a capacitive micro-machined ultrasound transducer (CMUT) array. The chip is equipped with programmable high-voltage (HV) pulsers that can g
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enerate ±30-V return-to-zero (RZ) and non-RZ pulses. The pulsers employ a compact back-to-back isolating HV switch topology that employs HV floating-gate drivers with only one HV MOS transistor each. Further die-size reduction is achieved by using the RZ switches also as the transmit/receive (T/R) needed to pass received echo signals to low-voltage receive circuitry. On-chip digital logic clocked at 200 MHz allows the pulse timing to be programmed with a resolution of 5 ns, while supporting pulses of 1 cycle up to 63 cycles. The chip has been implemented in 0.18-μm HV Bipolar-CMOS-DMOS (BCD) technology and occupies an area of 1.8 mm × 16.5 mm, suitable for integration into an 8-F catheter. Each pulser with embedded T/R switch and digital logic occupies only 0.167 mm2. The pulser successfully drives an 18-pF transducer capacitance at pulse frequencies up to 9 MHz. The T/R switch has a measured ON-resistance of ~180 Ω. The acoustic results obtained in combination with a 7.5-MHz 64-element CMUT array demonstrate the ability to generate steered and focused acoustic beams.
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Matéo T,Dumoux MC,Montauban E,Ferin G,Nguyen-Dinh A
Increasing use of energetic modes in modern ultrasonography has made efficient thermal management mandatory in medical transducers design. In this work, efficiency of different thermal conduction paths (central, peripheral, both), as well as different heat ways out (probe nose, whole probe body hous
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ing, cable braid shield) are investigated. Starting from a typical acoustic design for a 2,8 MHz phased array, 6 mock-ups are derived, using an acoustical stack either optimized for acoustical or thermal performances. Basically, each mock-up explores a particular thermal path, using passive solutions such as thermal fin, highly conductive backing (135 W/m/K), layers (85 W/m/K), resin (2.9W/m/K), etc. Thermal performances are then assessed in air, following a measurement protocol based on IEC60601-2-37. A heating burst is sent during 10 mins. at high PRF, while an IR camera records the temperature progress at the surface of the transducer. Owing to acoustic performances differences between both stacks, driving voltage is tuned to allow comparison either at a fixed MI or a same active power. IR frames are then processed to extract, for each mock-up, the hot spot profile during the heating stage. Further analysis of its dynamic provides insight on the impact of the different thermal solutions investigated.
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Aminot A,Shirkovskiy P,Dorme C,Legros M,Dufait R,Fink M,Ing RK
Non-contact ultrasound applications are raising more and more interests. However, very few applications have been reported, for now in medical applications. In this work, compact airborne piezotransducers have been designed, built and characterized for a novel medical application: contactless cornea
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l imaging. The emission transducer is cylindrical with a 5.5 mm diameter and the reception transducer is a 2D array of 4×16 elements. A specific emission-reception electronic is also designed for these transducers to drive their high electric impedances that are larger than kiloOhms. The measured parameters - directivity, sensitivity and frequency bandwidth - of both transducers respond well to the needs of corneal imaging application.
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Mateo T,Dumoux MC,Montauban E,Ferin G,Nguyen-Dinh A
Increasing use of energetic modes in modern ultrasonography has made efficient thermal management mandatory in medical transducers design. In this work, efficiency of different thermal conduction paths (central, peripheral, both), as well as different heat ways out (probe nose, whole probe body hous
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ing, cable braid shield) are investigated. Starting from a typical acoustic design for a 2,8 MHz phased array, 6 mock-ups are derived, using an acoustical stack either optimized for acoustical or thermal performances. Basically, each mock-up explores a particular thermal path, using passive solutions such as thermal fin, highly conductive backing (135 W/m/K), layers (85 W/m/K), resin (2.9W/m/K), etc. Thermal performances are then assessed in air, following a measurement protocol based on IEC60601-2-37. A heating burst is sent during 10 mins at high PRF, while an IR camera records the temperature progress at the surface of the transducer. IR frame are then processed to extract, for each mock-up, the hot spot profile during the heating stage. Further analyze of its dynamic provides insight on the impact of the different thermal solutions here investigated.
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Hery M,Senegond N,Certon D
This work is an extension of a model previously developed by our group to simulate the electroacoustic response of capacitive micromachined ultrasonic transducer (CMUT)-based linear arrays acoustically loaded by a fluid medium. The goal is to introduce the viscoelasticity effects of the propagation
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medium into the modeling. These effects are mainly due to the passivation layer used to protect the transducer, i.e., a silicon polymer, a few hundred micrometers thick. The passivation layer is also required to ensure good acoustic coupling between the transducer front face and human skin. The theoretical approach relies on the determination of a new boundary matrix to simulate the acoustic coupling between the CMUT array and the viscoelastic medium. The complete numerical implementation of a 3-D Green's function for a viscoelastic half-space is hence described. In order to reduce computing time, an optimization was carried out through vectorization and parallelization methods. A comparison is then performed with the analytical solutions, from the literature, obtained for elastic half-space. An experimental validation of shear viscosity effects is performed through electrical impedance measurements of the CMUT linear arrays loaded by oils of varying viscosity. A very good agreement is obtained, showing that the model correctly takes the shear viscosity effects on the mechanical response of the CMUT into account, i.e., a shift in the resonance frequency and a diminution in the mechanical quality factor are observed.
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Tan M,Kang E,An JS,Chang Y,Vince P,Senegond N,Pertijs MA
This letter presents a compact programmable high-voltage (HV) pulser for ultrasound imaging, designed for driving capacitive micromachined ultrasonic transducers (CMUTs) in miniature ultrasound probes. To enable bipolar return-to-zero (RZ) pulsing and embedded transmit/receive switching, a compact b
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ack-to-back isolating HV switch is proposed that employs HV 'boating-gate drivers with only one HV MOS transistor each. The pulser can be digitally programmed to generate bipolar pulses with and without RZ, with a peak-to-peak swing up to 60 V, as well as negative and positive unipolar pulses. It can generate bursts of up to 63 pulses, with a maximum pulse frequency of 9 MHz for an 18-pF transducer capacitance. Realized in TSMC 0.18-μm HV BCD technology, the pulser occupies only 0.167 mm 2 . Electrical characterization results of the pulser, as well as acoustic results obtained in the combination with a 7.5-MHz CMUT transducer, are presented.
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Ferin G,Dumoux MC,Flesch M,Montauban E,Lejeune A,Rosinski B,Mateo T,Poree J,Sauvage J,Dcffieux T,Pernot M,Tanter M,Nguyen-Dinh A
Matrix transducers have for long been the gold standard in volumetric imaging, and in particular for echocardiography. However, their inner constitution (N 2 elements) accounts for highly dense and individual interconnection of thousands of elements. There are several ways of reducing cable count su
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ch as using a micro beamformer or reducing the number of active elements over a wide aperture with a sparse array and also Row Column Addressed (RCA) matrices, which are made of two independent electrode arrays patterned perpendicularly one to each other (2N elements). The latest have recently drawn probes manufacturers attention as there is no need to embed a specific electronic system as for driving a micro beamformer. However, RCA matrices in their raw constitution are not suitable for volumetric echocardiography as a diverging field of view is required and that they only allow for a front axial projection of volume reconstruction. Furthermore, RCA architecture suffers from a lack of true electrical ground and would require dedicated electronic. As to answer this dual issue, a “stack” (λ/4) architecture is proposed (patent pending), where the two independent piezoelectric arrays are stacked together with internal common ground. Moreover, instead of using a diverging lens [1] that would account for decreased sensitivity, we suggest a smooth mechanical deformation process achieved through relevant tools and a soft single crystal-based 1-3 piezocomposite materials.
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Meynier C,Dumoux MC,Bantignies C,Ferin G,Nguyen-Dinh A
In this paper, a FEM model for a 3MHz 1.25D ultrasonic imaging probe (designed for echocardiography) is presented. The transducer design features quarter-wavelength concept (backside danping), single-crystal active material, and air-kerfed elements. The results of the FEM model are benchmarked with
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experimental data, in terms of impedance, angular aperture, frequency response and axial pressure.
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Hery M,Mateo T,Gross D,Senegond N,Boulme A,Meynier C,Certon D
he response of CMUT -based linear arrays. The method is applied to the design of linear arrays centered at 10 MHz. Two configurations, with two different spectral signatures (sensitive or broadband), were fabricated, measured and compared. Experimental data agree very well with the expected performa
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nces. The method is hence validated but experimental results pointed out the importance of the acoustic windows on the final performances of the probe.
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Sauvage J,Flesch M,Férin G,Nguyen-Dinh A,Porée J,Tanter M,Pernot M,Deffieux T
Four-dimensional (4D) Ultrafast ultrasound imaging was recently proposed to image and quantify blood flow with high sensitivity in 3D as well as anatomical, mechanical or functional information. In 4D Ultrafast imaging, coherent compounding of tilted planes waves emitted by a 2D matrix array were us
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ed to image the medium at high volume rate. 4D ultrafast imaging, however, requires a high channel count (>1000) to drive those probes. Alternative approaches have been proposed and investigated to efficiently reduce the density of elements, such as sparse or under-sampled arrays while maintaining a decent image quality and high volume rate. The row–columns configuration presents the advantage of keeping a large active surface with a low amount of elements and a simple geometry. In this study, we investigate the row and column addressed (RCA) approach with the orthogonal plane wave (OPW) compounding strategy using real hardware limitations. We designed and built a large 7 MHz 128 + 128 probe dedicated to vascular imaging and connected to a 256-channel scanner to implement the OPW imaging scheme. Using this strategy, we demonstrate that 4D ultrafast Power Doppler imaging of a large volume of up to depth, both in vitro on flow phantoms and in vivo on the carotid artery of a healthy volunteer at a volume rate of 834 Hz.
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Gross D,Legros M,Vince P,Certon D
Capacitive Micromachined Ultrasonic Transducer (CMUT) technology, which has been widely studied in the field of medical imaging, possesses strong design flexibility due to its manufacturing process. Many applications could benefit from this unique feature, especially those that require different ope
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rating ultrasonic frequencies. This article reports on the characterization of the therapeutic low-frequency field provided by an ultrasound-guided focused ultrasound CMUT probe that is connected to a custom ultrasonic scanner for hyperthermia applications. The study begins by mapping the focused ultrasonic beam in the vicinity of the focal spot and a parametric analysis providing the maximum peak-to-peak (PTP) pressure delivered by the probe under different acoustic conditions. The measured maximum PTP pressure at the targeted operating frequency of 1 MHz is 3 MPa, with a maximum of 3.6 MPa at 1.25 MHz. Based on an in vitro setup found in the literature, the temperature elevation at the focal point was measured, showing results in agreement with the targeted applications (max. ΔT = 7.5°C). The article concludes with a reliability study considering the delivered pressure and the self-heating of the CMUT probe: the results show the good stability of the pressure amplitude over 1.8 × 109 cycles at a duty cycle of 40%, with a moderate internal heating of 3°C.
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Brusseau E,Bernard A,Basset O,Meynier C,Ferin G,Nguyen-Dinh A
Quasi-static ultrasound elastography produces strain images of biological tissues subjected to compression. Processing 2-D radiofrequency ultrasound data can be a limitation for this application, since information like out-of-plane motion is inaccessible. In this study, a 5×128-element array transd
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ucer - specifically developed for elastography - is used. This prototype acquires series of three adjacent imaging planes over time and therefore makes it possible to compute 2-D elastograms of the central plane, with consideration of out-of-plane motion. Results from phantom experiments are presented and compared with those from 2-D processing.
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Gross D,Boulme A,Senegond N,Bawiec C,N'Djin WA,Certon D
Even though the CMUT technology is currently experiencing an exciting era in the field of ultrasonic imaging, few studies have assessed the real interest of this technology for therapeutic purposes compared to the state-of-the-art technology. Moreover, CMUT transducers could benefit from their low m
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echanical losses to produce long burst emission without the need of a bulky external cooling device. In addition to classical acoustic considerations, the output intensity is strongly influenced by the electroacoustic efficiency of the whole system. This latter takes into account the transducer itself, but also the losses in the electronic conditioning circuitry. The proposed study is focused on the analysis of CMUT intrinsic power efficiency to better assess the maximum expected performances and the potential improvements.
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Flesch M,Pernot M,Provost J,Ferin G,Nguyen-Dinh A,Tanter M,Deffieux T
4D ultrafast ultrasound imaging was recently shown using a 2D matrix (i.e. fully populated) connected to a 1024-channel ultrafast ultrasound scanner. In this study, we investigate the row-column addressing (RCA) matrix approach, which allows a reduction of independent channels from N × N
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to N + N, with a dedicated beamforming strategy for ultrafast ultrasound imaging based on the coherent compounding of orthogonal plane wave (OPW). OPW is based on coherent compounding of plane wave transmissions in one direction with receive beamforming along the orthogonal direction and its orthogonal companion sequence. Such coherent recombination of complementary orthogonal sequences leads to the virtual transmit focusing in both directions which results into a final isotropic point spread function (PSF).
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N'Djin WA,Gerold B,Vion-Bailly J,Canney MS,Nguyen-Dinh A,Carpentier A,Chapelon JY
Capacitive micromachined ultrasound transducers (CMUTs) exhibit several potential advantages over conventional piezo technologies for use in therapeutic ultrasound (US) devices, including ease of miniaturization and integration with electronics, broad bandwidth ( several megahertz), and compatibilit
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y with magnetic resonance imaging (MRI). In this paper, the electroacoustic performance of CMUTs designed for interstitial high-intensity contact US (HICU) applications was evaluated and the feasibility of generating US-induced heating and thermal destruction of biological tissues was studied. One-dimensional CMUT linear arrays as well as a prism-shaped 2-D array composed of multiple 1-D linear arrays mounted on a cylindrical catheter were fabricated. The electromechanical and acoustic characteristics of the CMUTs were first studied at low intensity. Then, the acoustic output during continuous wave (CW) driving was studied while varying the bias voltage (V DC ) and driving voltage (V AC ). US heating was performed in tissue-mimicking gel phantoms under infrared (IR) or MRthermometry monitoring. Acoustic intensities compatible with thermal ablation were obtained by driving the CMUTs in the collapse-snapback operation mode (I ac = 10-30 W·cm -2 ). Hysteresis in the acoustic output was observed with varying V DC . IR-and MR-thermometry monitoring showed directional US-induced heating patterns in tissue-mimicking phantoms (frequency: 6- 8 MHz and exposure time: 60-240 s) extending over 1.5-cm depth from the CMUT surface. Irreversible thermal damage was produced in turkey breast tissue samples (AT max 40 °C). Multidirectional US-induced heating was also achieved in 3-D with the CMUT catheter. These studies demonstrate that CMUTs can be integrated into HICU devices and be used for heating and destruction of tissue under MR guidance.
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N'Djin WA,Canney M,Meynier C,Chavrier F,Lafon C,Nguyen-Dinh A,Chapelon JY,Carpentier A
Interstitial therapeutic ultrasound devices are a promising technology for performing thermal ablation in a wide variety of organs. In this study, the use of Capacitive Micromachined Ultrasound Transducers (CMUTs) for interstitial heating applications was investigated. CMUTs exhibit potential advant
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ages for use in therapeutic ultrasound applications in comparison to standard piezo ultrasound transducer technologies as they have good characteristics in terms of miniaturization (cell size: few dozens of microns), bandwidth (several MHz) and high electro-acoustic efficiency. Two designs of CMUT arrays were studied: (1) a 1D 128-element planar-CMUT array originally dedicated to abdominal ultrasound imaging purposes (5 MHz, element size: 0.3 × 8.0 mm2); (2) a 12-element linear-array, 32.4-mm long and 0.8-mm wide, developed specifically for minimally-invasive interstitial therapeutic applications (6 MHz, element size: 2.7 × 0.8 mm2). Simulations were performed to evaluate the ability to generate thermal lesions in soft tissues with: (1) 1 single linear array, (2) a combination of multiple linear arrays positioned on a cylindrical catheter. Experimental investigations performed with the CMUT imaging array showed the ability to generate surface acoustic intensities (Iac) up to 20 W·cm−2 and to generate intense centimetric thermal lesions in in-vitro turkey breast tissues. At 6 MHz, a single element was able to generate in water a maximum peak pressure of >0.5 MPa. In simulations, the ability to use various power levels and frequencies on independent elements, as well as combinations of multiple linear-arrays offered sufficient flexibility to achieve a wide variety of thermal ablation patterns in 3D. Simulated ablation volumes could be controlled to cover accurately non-symmetrical volumes of brain metastases. In conclusion, CMUT arrays show interesting characteristics, which may open new perspectives of spatial control for conformal interstitial thermal therapy with miniaturized multi-element therapeutic ultrasound catheters.
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Flesch M,Deffieux T,Provost J,Férin G,Nguyen-Dinh A,Pernot M,Tanter M
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Gross D,Coutier C,Legros M,Bouakaz A,Certon D
Ultrasound-mediated targeted therapy represents a promising strategy in the arsenal of modern therapy. Capacitive micromachined ultrasonic transducer (cMUT) technology could overcome some difficulties encountered by traditional piezoelectric transducers. In this study, we report on the design, fabri
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cation, and characterization of an ultrasound-guided focused ultrasound (USgFUS) cMUT probe dedicated to preclinical evaluation of targeted therapy (hyperthermia, thermosensitive liposomes activation, and sonoporation) at low frequency (1 MHz) with simultaneous ultrasonic imaging and guidance (15 to 20 MHz). The probe embeds two types of cMUT arrays to perform the modalities of targeted therapy and imaging respectively. The wafer-bonding process flow employed for the manufacturing of the cMUTs is reported. One of its main features is the possibility of implementing two different gap heights on the same wafer. All the design and characterization steps of the devices are described and discussed, starting from the array design up to the first in vitro measurements: optical (microscopy) and electrical (impedance) measurements, arrays’ electroacoustic responses, focused pressure field mapping (maximum peak-to-peak pressure = 2.5 MPa), and the first B-scan image of a wire-target phantom.
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Kwiecinski W,Provost J,Dubois R,Sacher F,Haïssaguerre M,Legros M,Nguyen-Dinh A,Dufait R,Tanter M,Pernot M
Atrial fibrillation is associated with increased risk of stroke and heart failure. Currently it can be treated with minimally invasive radio-frequency catheter ablation. However, the lack of monitoring and assessment of the transmural extent of the lesion currently limits the success rate of this te
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chnique. In this study we have developed a novel dual-mode intracardiac echocardiography catheter capable of performing ultrasound imaging and high-intensity focused ultrasound ablation. Using the same device we demonstrate in vivo the feasibility of intracardiac shear-wave elastography to evaluate thermal ablation as well as the feasibility of creating transmural and linear lesions (up to 10-mm wide) in the atrial wall.
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Ferin G,Muralidharan Y,Mesbah N,Chatain P,Bantignies C,Khanh HL,Flesch E,Nguyen-DInh A
Ultrasound technologies are of great interest for aeronautical structure inspection. Mainly deployed through Phased Array (PA) ultrasonic transducer, ultrasound inspection is currently used as a complementary tool for the local examination of the structure to determine geometry, damage or compositio
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n of invisible flaws like cracks, delamination and corrosion. This approach cannot be easily automated since the access to the area of interest often requires to pass through the complex aeronautical structure. Moreover this approach relies on a high degree of human interaction, as the user often decides the spatial inspection sampling according to his intuition and experience of the structure composition and vulnerability. Structure Health Monitoring, namely SHM, overcomes these limitations by enabling rapid, automated, remote, and real-time monitoring of the structure to reduce operational costs and increase lifetime of structures. This inspection strategy gains its strength from the use of a large amount of individual embedded sensors with embedded intelligence (sensing, signal processing, communicating and storing relevant data in non-volatile memories) organized in dense network, a Neural Network. We present in this paper the developments of a novel autonomous wireless acoustic sensor node, including: a flat flexural acoustic sensor capable of working in transmit and receive, a custom vibrational piezoelectric energy harvesting device (PEH) charging a 0.5 Farad buffer supercapacitance through a commercial rectifying IC, an ARM based cortex M3 microprocessor driving digitization, signal processing, data storage and two ways RF communication. The main objective was to create a versatile hardware platform that can be embedded within the structure to monitor, and capable of hosting different acoustic inspection strategies.
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Warshavski O,Meynier C,Sénégond N,Chatain P,Rebling J,Razansky D,Felix N,Nguyen-Dinh A
In photoacoustic imaging, the angular reception performance of ultrasonic transducers is a critical parameter to be considered for system designers. The quantitative comparison between cMUT and PZT emphasizes the difference between the transducer requirements and specifications between conventional
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ultrasound and photoacoustic imaging. In this present work, we show significant benefits of cMUT based array transducers over conventional PZT arrays for the improvement of quality in photoacoustic imaging systems.
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Gross D,Perroteau M,Certon D,Coutier C,Legros M
In this paper, the development of wafer-bonded cMUTs arrays, which will be implemented on a dual-mode probe dedicated to liposomes activation and high frequency imaging, is presented. The process flow is briefly described, and optical and electrical characterizations are reported. Then, experimental
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electro-acoustic tests confirming the expected performances of each array are presented and discussed.
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Certon D,Legros M,Gross D,Vince P,Gens F,Gregoire JM,Coutier C,Novell A,Bouakaz A
This study reports on the development and the first experimental assessment of a custom ultrasound pre-clinical platform developed for diagnosis and targeted therapy. Moreover, a specific dual-mode probe developed for our application is based on cMUT technology. The platform combines two operating m
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odes: high frequency imaging in the 15−20 MHz frequency range and low frequency focused ultrasound at 1 MHz for local therapy.
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Kwiecinski W,Provost J,Dubois R,Sacher F,Haïssaguerre M,Legros M,Nguyen-Dinh A,Dufait R,Tanter M,Pernot M
Radio frequency catheter ablation (RFCA) is a well-established clinical procedure for the treatment of atrial fibrillation (AF) but suffers from a low single-procedure success rate. Recurrence of AF is most likely attributable to discontinuous or nontransmural ablation lesions. Yet, despite this urg
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ent clinical need, there is no clinically available imaging modality that can reliably map the lesion transmural extent in real time. In this study, the authors demonstrated the feasibility of shear-wave elastography (SWE) to map quantitatively the stiffness of RFCA-induced thermal lesions in cardiac tissues in vitro and in vivo using an intracardiac transducer array.
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Boulmé A,Ngo S,Minonzio JG,Legros M,Talmant M,Laugier P,Certon D
A wide range of ultrasound methods has been proposed to assess the mechanical strength of bone. The axial transmission technique, which consists of measuring guided elastic modes through the cortical shell of long bones such as the radius or tibia, has recently emerged as one of the most promising a
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pproaches of all bone exploration methods. Determination of dispersion curves of guided waves is therefore of prime interest because they provide a large set of input data required to perform inverse process, and hence to evaluate bone properties (elastic and geometric). The cortical thickness of long bones ranges from approximately 1 to 7 mm, resulting in wide inter-individual variability in the guided wave response. This variability can be overcome by using a single probe able to operate with a tunable central frequency, typically within the 100 kHz to 2 MHz frequency range. However, there are certain limitations in the design of low-frequency arrays using traditional PZT technology; these limitations have triggered active research to find alternative solutions. Capacitive micromachined ultrasonic transducers (cMUTs) have the potential to overcome these limitations and to improve axial transmission measurement significantly. The objective of this study was to design and construct a new cMUT-based axial transmission probe and to validate the approach. We report all the steps followed to construct such a prototype, from the description of the fabrication of the cMUT (based on a surface micromachining process) through probe packaging. The fabricated device was carefully characterized using both electrical and optical measurements to check the homogeneity of the device, first from cMUT to cMUT and then from element to element. Finally, axial transmission measurements carried out with the prototype cMUT probe are shown and compared with results obtained with a PZT-based array.
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Bantignies C,Filoux E,Mauchamp P,Dufait R,Thi MP,Rouffaud R,Gregoire JM,Levassort F
This work presents the fabrication of a 30 MHz, linear-array transducer based on a KN, 1–3 piezocomposite. Performances of the transducer were characterized and compared to a PZT-based linear array with similar structure. The composites were designed to minimize lateral modes of vibration which ca
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n severely degrade imaging performances. Fabrication steps were optimized to achieve a 40 MHz resonant frequency in air with a composite thickness of 69 µm. The measured thickness coupling factor was around 50%. A 128-element, linear array was then fabricated with 100 µm pitch and 1.5 mm elevation aperture. The structure of the transducer (backing, matching layers, and electric components) was optimized to deliver good fractional bandwidth and sensitivity. The final probe was integrated in a prototype, real-time, 128-channel scanner to acquire high-resolution images of the human skin in vivo. Results showed that, compared to PZT ceramics, KN single crystals provide low density and high acoustic velocity, both highly desirable for the manufacturing of HF transducers. The central frequency of the linear-array transducer was 30 MHz despite the KN composite being 20% thicker than equivalent PZT-based composites, and the relative bandwidth was about 50%. High-resolution images of the human skin were acquired and detailed features could be visualized.
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Meynier C,Yanamer Y,Canney M,Nguyen-Dinh A,Carpentier A,Chapelon JY
In this paper, multi-element arrays based on cMUT and piezoelectric technologies, using the same geometry, have been realized. The first part of the paper is focused on comparing both in terms of imaging performances. The CMUT is shown to be lower in sensivity but better in terms of bandwidth and re
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solution. The second part of the paper investigates the ability of the CMUT array for HIFU applications. The dual imaging-HIFU capability of the cMUT array is demonstrated. This is a new feature of the CMUT technology, as piezoelectric transducers are designed with a trade-off between bandwidth and transduction efficiency.
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Nguyen AD,Wang D,Meynier C,Tyholdt F,Vogl A,Tofteberg H,Ostbo NP,Flesch E
Capacitive ultrasonic tranducers, cMUTs rely on the electrostatic field between the membrane and a back plate for sensing andactuation. This is an excellent solution for small amplitudes. But the movement of the membrane is physically limited by the bottom plate (risk of collapse). Furthermore, pull
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-in and linearity considerations restrict the available range to about one percent of thegap. Piezoelectric micromachined ultrasonic transducers, pMUTs, on the other hand have no such restrictions. The excitation is basedon lateral contraction of a thin film of Lead Zirconate Titanate, PZT, deposited on top of the membrane. Then there is no need for abackplate, and the linear range is greatly increased. Therefore, pMUTs are ideally suited for applications demanding large excitationamplitude, such as high intensity focused ultrasound, HIFU. In this work, we present pMUTs designed for HIFU operation around 1MHz.
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Certon D,Sénégond N,Gross D,Legros M,Boulmé A,Roman B,Teston F,Férin G
This paper aims to develop an integrated dual mode ultrasonic transducers (based on cMUTs technology) for applications of targeted drug delivery dedicated to small animal experiments. Two functions are designed on the same transducer: one for high frequency imaging and the other for thermal activati
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on of liposomes. Tests and performances evaluation are reported.
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Bantignies C,Mauchamp P,Dufait R,Levassort F,Mateo T,Grégoire JM,Ossant F
Evolution of high resolution ultrasonic imaging is widely dependent on the development of efficient high frequency piezoelectric transducers. Nowadays, efforts are focused on the fabrication of linear arrays in the 40–50 MHz frequency range for dermatology, ophthalmology and small animals imaging.
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At these frequencies, technological aspects are predominant at several stages of the array fabrication due to typical dimensions of the constitutive elements (few tens of micrometers). Moreover, the development of the imaging system and associated beamforming specifically adapted is of primary interest to optimize the use of the corresponding array and consequently image quality.
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Chatain P,Voisin D,Legros M,Férin G,Dufait R
This paper presents an integrated electronic preamplifier design based on discrete components and evaluates its impact on image performances. The electronic, located close to the transducer, incorporates all useful functions to ensure compatible direct connection with most ultrasound scanners availa
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ble on the market today. People who has worked on this subject know that numerous challenges and problems have to be overcome: high voltage bypass, preamplifier protection cells, miniaturization, power dissipation, electronic stability and many other constraints. We will discuss different unavoidable tradeoffs, starting with electrical performances and then with practical aspects. Our electronic solution has been evaluated with different probe configurations, namely a 5 MHz Phased Array and a 9.5 MHz Linear Array probe. Images have been acquired and analysis of signal to noise ratio (SNR) performed to quantify the gain in image quality.
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Bantignies C,Mauchamp P,Ferin G,Michau S,Dufait R
Lead-based piezoelectric single crystals such as PZN-PT and PMN-PT have been first developed for under water applications by the U.S. Navy. Their outstanding piezoelectric properties (d33 as high as 2000 pC/N and k33 > 90%) make them valuable for high-end ultrasound transducers. Thus, they have been
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successfully used and commercialized in medical field mainly for cardiac imaging (2-5 MHz) but manufacturing such a probe is critical since single crystal structures are more sensitive to thermal and mechanical stresses induced by standard micromachining process. We propose in this paper to manufacture a high frequency ultrasound probe (15-20 MHz) based on very thin 1-3 single crystal composite materials (<70 ¿m thick) using low-stressing machining process and exhibiting improved electroacoustical performances. This paper presents the acoustical design, fabrication and evaluation of an ultrasound array based on single crystal piezocomposite. The array specifications were a 3 mm elevation, 100 ¿m pitch, 20 MHz center frequency. We demonstrate the feasibility to produce a PMN-PT single crystal probe with suitable performances for high resolution imaging. A complete electro-acoustical characterization has been done: bandwidth, directivity and pressure performances are then discussed and compared to classical PZT probes with the same specifications. Performances are compared to those obtained with state-of-the-art piezocomposite transducers, achieving competitive bandwidth and an improvement of +6 dB in sensitivity.
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Novell A,Legros M,Felix N,Bouakaz A
Capacitive micromachined ultrasonic transducers (CMUTs) present advantages such as wide frequency bandwidth, which could be further developed for nonlinear imaging. However, the driving electrostatic force induces a nonlinear behavior of the CMUT, thus generating undesirable harmonic components in t
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he generated acoustic signal. Consequently, the use of CMUT for harmonic imaging (with or without contrast agents) becomes challenging. This paper suggests 2 compensation approaches, linear and nonlinear methods, to cancel unwanted nonlinear components. Furthermore, nonlinear responses from contrast agent were evaluated using CMUT in transmit before and after compensation. The results were compared with those obtained using a PZT transducer in transmit. Results showed that CMUT nonlinear behavior is highly influenced by the excitation to bias voltage ratio. Measurements of output pressure very close to the CMUT surface allow the estimation of optimal parameters for each compensation approach. Both methods showed a harmonic reduction higher than 20 dB when one element or several elements are excited. In addition, the study demonstrates that nonlinear approach seems to be more efficient because it is shown to be less sensitive to interelement variability and further avoids fundamental component deterioration. The results from contrast agent measurements showed that the responses obtained using CMUT elements in transmit with compensation were similar to those from PZT transducer excitation. This experimental study demonstrates the opportunity to use CMUT with traditional harmonic contrast imaging techniques.
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Novell A,Bouakaz A,Legros M,Félix N
Advantages of capacitive micromachined ultrasonic transducers (CMUTs) such as wide frequency bandwidth could be used in nonlinear contrast imaging. However, the driving electrostatic force induces a nonlinear behavior of the CMUT generating thus undesirable harmonic components. Consequently, the use
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of CMUT for harmonic imaging, with or without contrast agents becomes challenging. To insure their exploitation for nonlinear imaging, a linear and a nonlinear method that compensate the CMUT nonlinear behavior are presented. Optimal parameters of cancellation components were estimated using a needle hydrophone positioned at 5 mm from the source. Alternatively, a wire (perfect reflector) was used and the reflected signal was measured using a single element 5-MHz transducer positioned perpendicularly. A fundamental excitation signal of 2.5 MHz Gaussian pulse was transmitted. The harmonic generation from a 1/2000 diluted solution of Sonovue microbubbles was measured with and without compensation. Compensation methods allow a harmonic reduction of approximately 20 dB when one element or 32 interconnected elements are excited. Second harmonic bubbles responses to CMUT compensated excitations are similar to bubbles echoes from PZT excitation. Results demonstrate the need for compensation methods in nonlinear imaging and the opportunity to use CMUT with traditional harmonic contrast imaging techniques.
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Jeanne E,Meynier C,Teston F,Certon D,Felix N,Roy M,Alquier D
For MEMS technology, reliability is of major concern. The implementation of a protection and passivation layer, that may easily enhance reliability of capacitive Micromachined Ultrasonic Transducers (cMUTs) must be done without degrading device performance. In this work, realization, simulation and
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characterization of passivated cMUT are presented. Two materials, SiNx and Parylene C, were selected with regard to their mechanical and physical properties as well as their compatibility with device processing. Particular attention was paid on layer deposition temperature to avoid a structural modification of the top aluminium electrode and, hence, a membrane bulge. The characterization results are in good agreement with the simulations. The SiN passivation layer clearly impact device performance while Parylene C effectiveness is clearly pointed out even through ageing characterizations. If SiNx layer can be used for passivation with particular precautions, Parylene is definitely an interesting material for cMUT passivation and protection.
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Legros M,Ferin G,Ratsimandresy L,Dufait R
Probes are well‐known to be a capital element for ultrasound image quality. During design, many parameters can be tuned on the acoustic stack to optimise the electrical, electroacoustical and acoustical performance measurements. But the effects on image quality of these performances are not so wel
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l identified. To overcome such a limitation, we developed a quantitative method for image quality assessment. A set of algorithms was developed to assess in vitro images. The goal of this investigation is to link the electroacoustical, acoustical performances and transducer parameters to the imaging performance. Ultrasound test objects were used to quantify the ultrasound images. The acquisition was carried out on a commercial scanner and imaging parameters were set constant in order to benchmark the probes in the same environment. From B‐mode images, key parameters such as axial and lateral resolutions, contrast, statistic or metric parameters, and signal to noise ratio are established. Data from transducers, exhibiting different trade‐offs on their performances (bandwidth, bandwidth shape, center frequency, elementary directivity) were characterized. Using the algorithms developed, all identified image properties were analysed with regard to these performances. The impact of each electroacoustical parameter on image quality have been identified and discussed.
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Teston F,Meynier C,Jeanne E,Felix N,Certon D
A procedure for an electrical impedance characterization standard in air of CMUTs was reported. The electromechanical coupling factor was calculated by the low and high frequency capacity and the resonance and antiresonance frequencies measurements. The CMUT will be able to analyze and compared in t
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erms of effective spring and mass with 1D model. The 1D model described the general behavior of the CMUT quite well, as long as first resonance/antiresonance mode and tensions below collapse were concerned
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Devallencourt C,Grimaud F,Michau S,Felix N
Both medical and industrial fields require ultrasound transducers able to withstand high temperature (>100degC) and harsh environment (high pressure, chemical resistance). Such probes can be used as sterilizable equipment by autoclave for the medical applications and can perform in-situ characteriza
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tion of materials and in-service inspection in non-destructive testing (NDT) applications. This article will focus on the development of specific 1-3 piezocomposite configurations to address these applications in the 5-8 MHz frequency range (single element and array transducers). Adequate piezocomposite configurations are integrated into complete transducer. The electro-acoustical performances will be reported after more from 20 to 85 sterilization cycles. For NDT applications, the transducers will be characterized at high temperatures up to 110degC
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Ferin G,Certon D,Felix N,Patat F
We report the development of two methods for determining the effective electroacoustic tensor of 1–3 piezocomposite material, one experimental and one theoretical based on homogenization techniques. The main aim was to compare and validate the results provided by these approaches. The slowness sur
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faces of bulk wave were computed in the large wavelength domain and were fitted to obtain the effective properties of the composite. Model predictions are discussed and compared with the Smith’s model. The experimental method is an inversion technique comparing measurement of transmission coefficient through the piezocomposite plate with the simulated coefficient. The accuracy and stability of the minimization procedure is discussed. Experimental results obtained from two piezocomposite test plates are presented and compared with theory.
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Teston F,Certon D,Patat F,Felix N
Capacitive micromachined transducers are competitive candidates for high performance ultrasonic imaging arrays in a wide frequency range. Furthermore, technology offers several degrees of freedom for the design and optimization for such devices. First, at elementary cell scale: the geometrical param
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eters and mechanical properties of the different layers must be considered in order to adjust electromechanical coupling coefficient, collapse voltage, resonance frequency and capacitance. On the other hand, for array elements, the size and layout of cells are essential for the radiated acoustic field. Through a parametric study, the purpose of this paper is to compare the performances of square and rectangular shapes to commonly used circular and hexagonal shapes.
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Cladé O,Tranquart F,Palanchon P,Bleuzen A,Diot P,Dinet D,Dufait R
Applying endoscopic ultrasound to image the part external bronchi is of great interest and complementary with other imaging methods. In continuation of our previous work [1], this article presents design and acoustic testing of a set of catheters for endobronchial imaging supplemented by the results
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of the clinical study carried out with this probe. The transducer is a ultrasound network of 64 elements included in a catheter of 7 Fr (outer diameter of 2.3 mm) in order to be used in an existing bronchofiberscope. The grating has a pitch of 200 µm, a 1.5mm elevation and operates at a center frequency of 10 MHz. Piezoelectric material is based on technology piezo-composite 1-3 and the front layer is selected for act as both an adaptation layer and a layer barrier. The probe is interfaced to a commercial ultrasound system. It was used in 25 patients without any disadvantage for the patient (in terms of discomfort and duration limited to 10 minutes at maximum) or for clinicians (ease of use, visualization perfect location of the area of interest). The only limitation encountered concerns the presence of air bubbles on the bronchial walls which could limit the visualization of structures. This made it possible to characterize thoracic tumors (hypoechoic tissues) with possible adjacent lymph nodes (minimum size 3 mm) that were not described on the scanner. This made it possible to clearly identify certain underlying vessels to be spared during biopsy. That helps identify certain areas of tumors that appeared vascularized to guide the biopsy site. In conclusion, this probe specific is of great interest to better image the structures bronchial, describe the extension of the tumors as well as possible sentinel lymph nodes for a more complete initial diagnosis and biopsy guidance. This will be used to improve diagnosis and biopsy safety.
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Devallencourt C,Michau S,Bantignies C,Felix N
In non-destructive testing (NDT) applications, ultrasound transducer arrays capable of withstanding high temperatures and harsh environment (high pressure, chemical resistance) are required to perform the in-situ characterisation of materials, process monitoring and in-service inspection.
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Patat F,Teston F,Felix N,Certon D
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Michau S,Mauchamp P,Dufait R
The range of applications demanding the development of high frequency ultrasound imaging is very broad, from dermatology and ophthalmology to intravascular and small animals imaging, to improve the resolution of the images over a small penetration depth. However the manufacture of such imaging syste
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ms remains very challenging from both transducer manufacture (small dimensions of the elements, thin layers materials properties control) and associated electronic system perspectives. This article extends the current state of the art limited at 20 MHz for fully operational array devices and presents the acoustical design, manufacture and evaluation of a 128 elements 30 MHz ultrasound array based on the 1-3 piezocomposite technology, with a 100 /spl mu/m pitch and a 2 mm elevation aperture. Electro-acoustical characterisation of the full array is reported (in terms of bandwidth, pulse duration and homogeneity performance) as well as electrical characterisation (impedance and cross-coupling measurements).
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Michau S,Mauchamp P,Dufait R
Lead-based piezoelectric single crystals such as Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PZN-PT) and Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/-PbTiO/sub 3/ (PMN-PT) have been extensively studied during the last years as their outstanding piezoelectric properties (d/sub 33/ as high as 2000pC/N and
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k/sub 33/ > 90%) make them valuable for high-end ultrasound transducers. Nevertheless the specific nature of these materials, as compared with standard piezoceramics, requires to develop new transducer micro-machining and manufacturing processes to enhance the final properties of the transducers and to improve both sensitivity and bandwidth of these probes. This paper presents the acoustical design, fabrication and evaluation of a 64 elements ultrasound phased array for transoesophagial probe based on single crystal materials. The achieved phased array is a 5MHz configuration with a circular aperture. The whole transducer is included within diameter 10mm and 2mm height. Acoustical design and final results will show the improvements achieved with single crystals for this configuration by comparing these results to those obtained on standard piezoceramic phased array. Electro-acoustic characterisation is performed on the whole array and homogeneity performances will also be presented.
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Clade O,Felix N,Lacaze E
Recent advances in ultrasound medical imaging such as contrast agent, harmonic or sonar type imaging require ultrasound arrays with higher electro-acoustical and acoustical performances than the standard state of the art. Higher bandwidth, higher sensitivity, better resolution and improved beam char
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acteristics are necessary to improve image quality. This paper presents two different configurations of array transducers: a 3.5 MHz center frequency curved linear array for general purpose, abdominal and obstetric imaging and a 7 MHz center frequency linear array for small parts and peripheral vascular imaging. Both arrays include optimized 1-3 piezocomposite material based on high dielectric permittivity piezoceramic. These arrays that use new acoustic matching design exhibit a higher bandwidth with a +15% to 25% gain compared to standard ones with high resolution resulting in a wide operating frequency range. Complete electroacoustic and acoustic evaluations of both arrays are presented in this paper. To characterize and evaluate the electroacoustic performances, we propose to set a figure of merit.
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Michau S,Ratsimandresy L,Auclair P
Multi-elements ultrasound probes are now used in the industrial Non Destructive Testing to replace single element probes in targeted applications to improve quality, reproducibility and speed of control. The complexity of the parts to be controlled requires the development of specific ultrasound pro
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bes, from complex geometries linear arrays (concave or conical shapes) to 2D matrix arrays. This poster presents the acoustical design and manufacture of a 2D conical ultrasound array for fastener hole inspection. This complex probe includes 504 rectangular elements, with dimensions 0.3 mm/spl times/ 0.4 mm at 10 MHz center frequency, that are laid out on a conical surface. The poster reviews also the electro-acoustic characterisation performed on the full array, including frequency, bandwidth and homogeneity performances. This conical 2D-array is finally integrated in a probe housing, interconnected and interfaced to an ultrasound system.
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Lacaze E,Michau S,Mauchamp P
Over the last decade, ultrasound imaging has been successfully demonstrated at 20 MHz and above using single elements transducer. High frequency arrays are only commercially available below 20 MHz and arrays with higher frequencies are still at the research stage. However, a 20 MHz center frequency
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exhibits a very interesting trade-off between sensitivity or penetration and expected image resolution. This paper presents the acoustical design, fabrication and evaluation of a 128 elements ultrasound array based on piezo-composite technology, with a 210 /spl mu/m pitch and a 3 mm elevation aperture. Electro-acoustic characterization is performed on the full array and an average center frequency of 20 MHz is achieved as well as state of the art homogeneity characteristics. Bandwidth, insertion loss results, directivity measurement and cross coupling performance are disclosed. The transducer array is subsequently integrated in a probe housing, interconnected and interfaced to an ultrasound system. Finally, images covering various applications are presented and discussed from a clinical perspective.
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Felix N,Ratsimandresy L,Dufait R
Nowadays, advanced ultrasound imaging such as contrast agent imaging, harmonic imaging, coded excitation or pulse inversion techniques require from ultrasound arrays higher performances than the standard state of the art. Then, higher bandwidth, higher resolution and better sensitivity have to be re
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ached in order to improve image quality. In order to overtake standard performances, we use multilayer stack of passive materials with a volume controlled impedance gradient as acoustic front matching adaptation with 1-3 piezocomposite to develop both single element transducers and high density arrays exhibiting very high fractional bandwidth. The 3.5 MHz high density array manufactured with innovative matching design presents outstanding performances as compared to state of the art: 90% to 95% bandwidth distribution on all array elements, a minimized -1.2 dB sensitivity loss and an excellent -20 dB pulse duration equal to 2.3 /spl lambda/. We have reported results on a 3.5 MHz high density array, but this high bandwidth design could also be applied to higher pitch configurations or higher frequency design.
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Certon D, Felix N, Lacaze E, Teston F, Patat F
Plate waves inside the piezoelectric layer are much involved in the element cross-coupling in transducer arrays for medical imaging. In this work, such waves are analyzed in 1-3 piezocomposite materials on the basis of conventional guided modes formalism in which the piezocomposite is considered as
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a homogeneous medium. Cross-coupling measurements have been made on two different transducer arrays using a network analyzer and a laser interferometric probe. It is shown how the analysis in terms of symmetrical Lamb waves gives an interesting qualitative interpretation, explaining most of the cross-coupling amplitude variations with frequency. Results show that the 0th and 3rd symmetrical Lamb waves are mainly involved in coupling inside composite plates. The S/sub 0/ mode is responsible for the inter-element coupling, whereas the S/sub 3/ mode widens the effective width of the excited element.
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Nguyen-Dinh A,Ratsimandresy L,Mauchamp P,Dufait R,Flesch A,Lethiecq M
A 20 MHz high density linear array transducer is presented in this paper, This array has been developed using an optimized ceramic-polymer composite material. The electro-mechanical behaviour of this composite, especially designed for high frequency applications, is characterised and the results are
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compared to theoretical predictions. To support this project, a new method of transducer simulation has been implemented. This simulation software takes into account the elementary boundary phenomena and allows prediction of inter-element coupling modes in the array. The model also yields realistic computed impulse responses of transducers, A miniature test device and water tank have been constructed to perform elementary acoustic beam pattern measurements. It is equipped with highly accurate motion controls and a specific needle-shaped target has been developed. The smallest displacement available in the three main axes of this system is 10 microns. The manufacturing of the array transducer has involved high precision dicing and micro interconnection techniques. The flexibility of the material provides us with the possibility of curving and focusing the array transducer. Performance of this experimental array are discussed and compared to the theoretical predictions. The results demonstrate that such array transducers will allow high quality near field imaging. This work presents the efforts to extend the well known advantages of composite piezoelectric transducers to previously unattainable frequencies.
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Lethiecq M,Feuillard G,Ratsimandresy L,Nguyen-Dinh A,Pardo L,Ricote J,Andersen B,Millar C
New fine grain ceramics have been developed for high frequency applications (i.e. 15 to 50 MHz). Modified lead titanate (MPT) and lead zirconate titanate (PZT) ceramics are prepared by either hydrothermal synthesis or hot isostatic pressing. Their fabrication is described, as well as results of micr
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ostructure analysis, which includes pore size and grain size distributions. The thickness mode piezoelectric, elastic and dielectric constants are measured and used as inputs for the design of 20 MHz linear array transducers with 32 elements of less than 100 μm width. The manufactured arrays are characterized in pulse echo operation and their centre frequency and bandwidth are compared to theoretical predictions. Finally, the radiation pattern of an element is measured and the effect of inter-element coupling is discussed. Performances are compared to those of PVDF-based transducers in view of intravascular imaging applications. The bandwidth is slightly lower but the sensitivity is much higher than those of PVDF devices. This is explained on the one hand by higher coupling coefficients and on the other by lower electrical input impedances due to higher dielectric-constants.
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