Three-dimensional echocardiography: technical aspects and imaging modalities

Real-time three-dimensional echocardiography (RT3DE) is increasingly available in the veterinary field due to continuous reduction in costs and improve-ment of equipment. Much like its motion-mode and bi-dimensional counterparts, acquisition and analysis of RT3DE images and datasets is greatly improved by a thor-ough understanding of the technological aspects, basic physic principles, and knowledge of available modalities with their advantages and drawbacks. In this re-view, the authors aim to describe how the currently available RT3DE technology has evolved, explain technical aspects of the equipment, and illustrate the most com-monly available modalities for image acquisition and visualization.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

3-D Coherent Multi-Transducer Ultrasound Imaging with Sparse Spiral Arrays

Coherent multi-transducer ultrasound (CoMTUS) creates an extended effective aperture through the coherent combination of multiple arrays, which results in images with enhanced resolution, extended field-of-view, and higher sensitivity. The subwavelength localization accuracy of the multiple transducers required to coherently beamform the data is achieved by using the echoes backscattered from targeted points. In this study, CoMTUS is implemented and demonstrated for the first time in 3-D imaging using a pair of 256-element 2-D sparse spiral arrays, which keep the channel-count low and limit the amount of data to be processed. The imaging performance of the method was investigated using both simulations and phantom tests. The feasibility of free-hand operation is also experimentally demonstrated. Results show that, in comparison to a single dense array system using the same total number of active elements, the proposed CoMTUS system improves spatial resolution (up to 10 times) in the direction where both arrays are aligned, contrast-to-noise-ratio (CNR, up to 30%), and generalized CNR (up to 11%). Overall, CoMTUS shows narrower main lobe and higher contrast-to-noise-ratio, which results in an increased dynamic range and better target detectability.Comment: 10 pages, 6 figure

Front-end receiver for miniaturised ultrasound imaging

Point of care ultrasonography has been the focus of extensive research over the past few decades. Miniaturised, wireless systems have been envisaged for new application areas, such as capsule endoscopy, implantable ultrasound and wearable ultrasound. The hardware constraints of such small-scale systems are severe, and tradeoffs between power consumption, size, data bandwidth and cost must be carefully balanced. To address these challenges, two synthetic aperture receiver architectures are proposed and compared. The architectures target highly miniaturised, low cost, B-mode ultrasound imaging systems. The first architecture utilises quadrature (I/Q) sampling to minimise the signal bandwidth and computational load. Synthetic aperture beamforming is carried out using a single-channel, pipelined protocol in order to minimise system complexity and power consumption. A digital beamformer dynamically apodises and focuses the data by interpolating and applying complex phase rotations to the I/Q samples. The beamformer is implemented on a Spartan-6 FPGA and consumes 296mW for a frame rate of 7Hz. The second architecture employs compressive sensing within the finite rate of innovation (FRI) framework to further reduce the data bandwidth. Signals are sampled below the Nyquist frequency, and then transmitted to a digital back-end processor, which reconstructs I/Q components non-linearly, and then carries out synthetic aperture beamforming. Both architectures were tested in hardware using a single-channel analogue front-end (AFE) that was designed and fabricated in AMS 0.35μm CMOS. The AFE demodulates RF ultrasound signals sequentially into I/Q components, and comprises a low-noise preamplifier, mixer, programmable gain amplifier (PGA) and lowpass filter. A variable gain low noise preamplifier topology is used to enable quasi-exponential time-gain control (TGC). The PGA enables digital selection of three gain values (15dB, 22dB and 25.5dB). The bandwidth of the lowpass filter is also selectable between 1.85MHz, 510kHz and 195kHz to allow for testing of both architectural frameworks. The entire AFE consumes 7.8 mW and occupies an area of 1.5×1.5 mm. In addition to the AFE, this thesis also presents the design of a pseudodifferential, log-domain multiplier-filter or “multer” which demodulates low-RF signals in the current-domain. This circuit targets high impedance transducers such as capacitive micromachined ultrasound transducers (CMUTs) and offers a 20dB improvement in dynamic range over the voltage-mode AFE. The bandwidth is also electronically tunable. The circuit was implemented in 0.35μm BiCMOS and was simulated in Cadence; however, no fabrication results were obtained for this circuit. B-mode images were obtained for both architectures. The quadrature SAB method yields a higher image SNR and 9% lower root mean squared error with respect to the RF-beamformed reference image than the compressive SAB method. Thus, while both architectures achieve a significant reduction in sampling rate, system complexity and area, the quadrature SAB method achieves better image quality. Future work may involve the addition of multiple receiver channels and the development of an integrated system-on-chip.Open Acces

A 125 ?m-Pitch-Matched Transceiver ASIC With Micro-Beamforming ADC and Multi-Level Signaling for 3-D Transfontanelle Ultrasonography

This article presents a pitch-matched transceiver application-specific integrated circuit (ASIC) for a wearable ultrasound device intended for transfontanelle ultrasonography, which includes element-level 20-V unipolar pulsers with transmit (TX) beamforming, and receive (RX) circuitry that combines eightfold multiplexing, four-channel micro-beamforming (&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu$&lt;/tex-math&gt; &lt;/inline-formula&gt;BF), and subgroup-level digitization to achieve an initial 32-fold channel-count reduction. The &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu$&lt;/tex-math&gt; &lt;/inline-formula&gt;BF is based on passive boxcar integration, merged with a 10-bit 40 MS/s SAR ADC in the charge domain, thus obviating the need for explicit anti-alias filtering (AAF) and power-hungry ADC drivers. A compact and low-power reference generator employs an area-efficient MOS capacitor as a reservoir to quickly set a reference for the ADC in the charge domain. A low-power multi-level data link, based on 16-level pulse-amplitude modulation, concatenates the outputs of four ADCs, providing an overall 128-fold channel-count reduction. A prototype transceiver ASIC was fabricated in a 180-nm BCD technology, and interfaces with a 2-D PZT transducer array of 16 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\times$&lt;/tex-math&gt; &lt;/inline-formula&gt; 16 elements with a pitch of 125 &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu$&lt;/tex-math&gt; &lt;/inline-formula&gt;m and a center frequency of 9 MHz. The ASIC consumes 1.83 mW/element. The data link achieves an aggregate 3.84 Gb/s data rate with 3.3 pJ/bit energy efficiency. The ASIC&amp;#x2019;s functionality has been demonstrated through electrical, acoustic, and imaging experiments.</p

Biomedical Imaging and Analysis In the Age of Big Data and Deep Learning

International audienc

Studio e simulazione di sistemi di micro-beamforming per ecografia 2D/3D con sonda CMUT

LAUREA MAGISTRALELo studio su cui verte questo lavoro di tesi, svolto presso la STMicroelectronics Srl, è inserito nell'ambito del progetto europeo DeNeCor, per il quale uno dei risultati attesi è quello di realizzare un sistema di neuronavigazione a ultrasuoni, minimamente invasivo e basato su trasduttori capacitivi, Capacitive Micromachined Ultrasonic Transducer (CMUT), di ultima generazione, la cui sonda deve essere miniaturizzata il più possibile. Obiettivo della tesi è realizzare uno studio orientato a diminuire l’area dell’Application Specific Integrated Circuit (ASIC) del modulo elettroacustico, costituito dal trasduttore e dall’elettronica di front-end, grazie ad un’implementazione di sistema. In letteratura analisi tridimensionali real time, in cui l’oggetto di studio è una matrice bidimensionale, sono rare e l’analisi di sistema su cui si focalizza il lavoro di tesi riguarda la fase di ricezione del segnale. La catena di ricezione è composta dal CMUT, realizzato grazie a processi di micro-fabbricazione, che permettono di ottenere la precisione e l'automazione proprie della micro-elettronica, che possono essere direttamente integrati nel processo CMOS, al fine di ridurre di un fattore 10 le capacità parassite tra il dispositivo e l'ASIC rispetto ad un trasduttore capacitivo. Ciò implica che il trasduttore è caratterizzato da una dissipazione termica 10 volte minore e tale caratteristica risulta fondamentale per le specifiche che caratterizzano il progetto DeNeCor. Quindi, il blocco di amplificazione è stato analizzato in riferimento ad un particolare circuito, chiamato Variable-Gain-Low-Noise-Amplifier, sviluppato presso l'Università di Pavia, che permette sia un'amplificazione a guadagno fisso sia la compensazione dell'attenuazione tissutale. In ambiente Matlab® è stato sviluppato il modello che simula le quattro fasi che caratterizzano l'amplificatore oggetto di studio, cui è sottoposto ciascuno dei campioni del segnale d'ingresso: la variazione della fase di amplificazione esponenziale è funzione della profondità da cui proviene l'eco. Ciascuno dei segnali amplificati è sottoposto ad un rifasatore, il cui scopo è di riallineare nel tempo tutti i segnali ricevuti da profondità differenti attraverso ritardi adeguati, ad un sommatore, al fine di ridurre il numero di cavi coassiali che connettono la sonda alla macchina principale e l'area dell'ASIC, e ad un Analog to Digital Converter (ADC) che costituiscono la funzione di micro-beamforming in ricezione. L'implementazione digitale dei ritardi è fondamentale per determinare il numero di bit necessario per rappresentarli e stimare l'ampiezza del registro, che implica un costo in termini di area. Tra le differenti architetture presenti in letteratura, proposte al fine di realizzare il rifasatore, questo lavoro di tesi valuta il Frequency Independent Phase Shifter. L'analisi di sensibilità, relativa al CMUT ha confermato l'adeguatezza dell'approssimazione, secondo il modello di Mason, del comportamento del trasduttore e le grandezze geometriche che influiscono maggiormente sul valore dell'impedenza meccanica specifica e sulla funzione di trasferimento in ricezione, sono il raggio e lo spessore della membrana del CMUT. Il VGLNA su cui si basa il modello sviluppato risulta adeguato alle applicazioni necessarie al progetto DeNeCor e i risultati ottenuti grazie al modello sviluppato in Matlab® sono stati paragonati con le simulazioni realizzate grazie ad ELDO presso l’Università degli studi di Pavia: lo script implementato si rivela adeguato alla descrizione del comportamento del VGLNA. L'analisi dei ritardi ha stabilito che un array di trasduttori circolare è migliore rispetto alla geometria quadrata e l'analisi del Frequency Independent Phase Shifter ha determinato l'inaccettabilità della stessa alle specifiche del progetto DeNeCor poiché anche piccole variazioni del valore nominale della capacità e della regolazione delle correnti di bias comportano uno scorretto rifasamento dei segnali ricevuti.The project described in this thesis, developed at STMicroelectronics Srl, is involved in the European project DeNeCor, as one of the expected results is to develop an ultrasound neuronavigation system, minimally invasive and based on new generation Capacitive Micromachined Ultrasonic Transducer (CMUT), where the probe has to be the most miniaturized as possible. Target of the thesis is to achieve a study aimed at decreasing the Application Specific Integrated Circuit (ASIC) area of the electroacoustic module, composed of the transducer and the front-end electronics, thanks to a system implementation. In literature tridimensional real time analysis, where the object of study is a bidimensional matrix, are uncommon and the system analysis on which the thesis is focused, concerns the reception of the ultrasound signal. The reception chain is composed of CMUT, made thanks to a micro-fabrication process, which allows precision and automation proper of micro-electronics, that can be directly integrated in CMOS process, in order to reduce 10 times the parasitic capacities between the device and ASIC compared with piezoelectric transducer. This means that the transducer is characterized by thermal dissipation 10 times lower and this feature is fundamental according to DeNeCor constraints. Then, the amplification block in the reception stage has been analyzed concerning a particular circuit, called Variable-Gain-Low-Noise-Amplifier, developed at the University of Pavia, that firstly allows a fixed gain amplification of the signal and then compensates the tissue attenuation. In Matlab® environment, the model which simulates the four steps that characterize the specific amplifier and that are repeated for each sample of the signal, has been developed: the variation of the exponential amplification stage is related to the depth from where the signal comes from. Each of the amplified signals is then passed through a phase shifter, aiming at realigning in time all the received signals from different depths through different delays , a summator, in order to reduce the number of coaxial cables from the probe to the processor and the area of the ASIC, and an Analog to Digital Converter (ADC) that constitute the micro-beamforming function during reception. Digital implementation of delays is fundamental as it determines the bit number needed to represent them and esteems the amplitude of the memory register, that implies a cost in terms of area. Among the different architectures reported in literature, proposed in order to realized the phase shifter, this thesis evaluates the Frequency Independent Phase Shifter. The sensitivity analysis related to CMUT has confirmed the suitability of the approximation, according to Mason model, of the transducer behavior and that the geometric parameters which mostly influence the value of the specific mechanical impedance and the reception transfer function, are the radius and the thickness of the membrane. The model of the VGLNA fits the applications needed by DeNeCor and the results obtained thanks to the model developed in Matlab® have been compared to ELDO simulations made at the University of Pavia: the implemented script is suitable to represent the behavior of the VGLNA. Delays analysis establishes that a circular array is better than a square one and the analysis of the Frequency Independent Phase Shifter has determined its unacceptableness according to the constraints of DeNeCor project as little variations from the nominal value of the capacity and the regulation of the bias currents mean an incorrect alignment of the received signals