Pulse-Encoded Ultrasound Imagine of the Vitreous With an Annular Array

The vitreous body is nearly transparent both optically and ultrasonically. Conventional 10- to 12-MHz diagnostic ultrasound can detect vitreous inhomogeneities at high gain settings, but has limited resolution and sensitivity, especially outside the fixed focal zone near the retina. To improve visualization of faint intravitreal fluid/gel interfaces, the authors fabricated a spherically curved 20-MHz five-element annular array ultrasound transducer, implemented a synthetic-focusing algorithm to extend the depth-of-field, and used a pulse-encoding strategy to increase sensitivity. The authors evaluated a human subject with a recent posterior vitreous detachment and compared the annular array with conventional 10-MHz ultrasound and spectral-domain optical coherence tomography. With synthetic focusing and chirp pulse-encoding, the array allowed visualization of the formed and fluid components of the vitreous with improved sensitivity and resolution compared with the conventional B-scan. Although optical coherence tomography allowed assessment of the posterior vitreoretinal interface, the ultrasound array allowed evaluation of the entire vitreous body

Correspondence - Characterization of the effective performance of a high-frequency annular-array-based imaging system using anechoic-pipe phantoms

A resolution integral (RI) method based on anechoic-pipe, tissue-mimicking phantoms was used to compare the detection capabilities of high-frequency imaging systems based on a single-element transducer, a state-of-the-art, 256-element linear array or a 5-element annular array. All transducers had a central frequency of 40 MHz with similar conventionally measured axial and lateral resolutions (about 50 and 85 μm, respectively). Using the RI metric, the annular array achieved the highest performance (RI = 60), followed by the linear array (47) and the single-element transducer (24). Results showed that the RI metric could be used to efficiently quantify the effective transducer performance and compare the image quality of different systems

Non-Planar Pad-Printed Think-Film Focused High-Frequency Ultrasonic Transducers for Imaging and Therapeutic Applications

Pad-printed thick-film transducers have been shown to be an interesting alternative to lapped bulk piezoceramics, because the film is deposited with the required thickness, size, and geometry, thus avoiding any subsequent machining to achieve geometrical focusing. Their electromechanical properties are close to those of bulk ceramics with similar composition despite having a higher porosity. In this paper, padprinted high-frequency transducers based on a low-loss piezoceramic composition are designed and fabricated. High-porosity ceramic cylinders with a spherical top surface are used as the backing substrate. The transducers are characterized in view of imaging applications and their imaging capabilities are evaluated with phantoms containing spherical inclusions and in different biological tissues. In addition, the transducers are evaluated for their capability to produce high-acoustic intensities at frequencies around 20 MHz. High-intensity measurements, obtained with a calibrated hydrophone, show that transducer performance is promising for applications that would require the same device to be used for imaging and for therapy. Nevertheless, the transducer design can be improved, and simulation studies are performed to find a better compromise between low-power and high-power performance. The size, geometry, and constitutive materials of optimized configurations are proposed and their feasibility is discussed

Modélisation par une méthode pseudospectrale : différences-finies et fabrication de transducteurs ultrasonores pour l'imagerie médicale haute résolution

L'imagerie ultrasonore haute résolution est aujourd'hui indispensable à l'établissement de nombreux diagnostics médicaux. Elle est basée sur l'utilisation de transducteurs piézoélectriques haute fréquence (HF) qui sont fabriqués à l'aide de matériaux et de techniques adaptés. L'optimisation de leurs performances nécessite en général l'utilisation de plusieurs modèles numériques pour simuler à la fois la vibration du résonateur et son rayonnement. Ce travail de thèse présente un nouvel algorithme basé sur un couplage pseudospectral / différences-finies, permettant de modéliser la génération et la propagation des ondes acoustiques dans un transducteur et son environnement avec un seul modèle. Cet algorithme hybride a été utilisé pour simuler le fonctionnement de différents transducteurs fabriqués au cours de cette thèse. Les résultats ont été validés de façons théorique et expérimentale, et ils ont permis d'étudier les influences de différents paramètres sur les performances des transducteurs fabriquésHigh resolution ultrasonic imaging has become an essential tool to assist physicians for various medical diagnoses. This technique relies on the ability of piezoelectric transducers to generate a high frequency (HF) acoustic field into the scanned media. Such transducers are obtained using particular materials and fabrication processes.They are optimized through modeling of their electromechanical behaviour and acoustic radiation pattern, which usually requires the use of several models. A new algorithm has been developped and is presented in this report, which is based on the coupling of pseudospectral and finite-diffrence methods to simulate both the generation and the propagation of acoustic waves in the transducer and the surrounding media, using a single model. This hybrid algorithm has been used to simulate various transducers and the results were accordingly compared to theory and experiments. It has also been used to study the influence of various parameters on the performance of several single-element and array transducer devices

Modélisation par une méthode pseudospectrale (différences-finies et fabrication de transducteurs ultrasonores pour l'imagerie médicale haute résolution)

TOURS-BU Médecine (372612103) / SudocSudocFranceF

Fabrication and Characterization of Annular-Array, High-Frequency, Ultrasonic Transducers Based on PZT Thick Film

International audienceIn this work, low temperature deposition of ceramics, in combination with micromachining techniques have been used to fabricate a kerfed, annular–array, high–frequency, micro ultrasonic transducer (with seven elements). This transducer was based on PZT thick film and operated in thickness mode. The 27 μm thick PZT film was fabricated using a low temperature (720 ºC) composite sol-gel ceramic (sol + ceramic powder) deposition technique. Chemical wet etching was used to pattern the PZT thick film to produce the annular array ultrasonic transducer with a kerf of 90 μm between rings. A 67 MHz resonance frequency in air was obtained. Pulse-echo responses were measured in water,showing that this device was able to operate in water medium. The resonance frequency and pulse-echo response have shown the frequency response presented additional resonance mode, which were due to the lateral modes induced by the small width-to-height ratios, especially for peripheral rings. A hybrid finite-difference (FD) and pseudospectral time-domain (PSTD) method (FD-PSTD) was used to simulate the acoustic field characteristics of two types of annular devices. One has no physical separation of the rings while the other has 90 μm kerf between each ring. The results show that the kerfed annular-array device has higher sensitivity than the kerfless one

Optimised Properties of High Frequency Transducers Based on Curved Piezoelectric Thick Films Obtained by Pad Printing Process

International audienceA high frequency transducer for medical imaging (25 MHz) was fabricated using a pad printing process to deposit a curved lead zirconate titanate (PZT) thick film on electroded backing (porous PZT). This piezoelectric thick film was characterised, and a thickness coupling factor (47%) comparable with that of a bulk ceramic with similar composition was measured. This transducer was successfully modelled with a numerical tool previously published and specifically adapted to curved shapes. The experimental axial and lateral resolutions are 40 and 230 μm respectively. Moreover, the sensitivity is sufficiently high to consider this transducer to be integrated in an echographic system for high frequency imaging such as skin

Caractérisation et modélisation de transducteurs haute fréquence utilisant les technologies de films épais piézoélectriques

National audienceLévolution de limagerie médicale haute résolution est fortement liée aux développements et à lamélioration des transducteurs ultrasonores haute fréquence. Aujourdhui, les technologies de films épais piézoélectriques (correspondant à des épaisseurs de quelques dizaines de micromètres) permettent de délivrer des performances électromécaniques comparables à celles des céramiques massives standard. Ces films épais sont intégrés dans des structures multi-couches, en utilisant différentes méthodes de dépôt, ce qui simplifie le procédé de fabrication des transducteurs. Toujours dans lobjectif de minimiser les étapes de fabrication des transducteurs, un substrat en PZT poreux est directement utilisé comme backing. A des fréquences de fonctionnement autour de 30 MHz et au-delà, la caractérisation et la modélisation de ces transducteurs restent délicates car la précision requise en termes de résolution spatiale est élevée (de lordre de quelques micromètres). Dans ce cadre, deux transducteurs haute fréquence, un plan et un incurvé (respectivement basés sur des films épais piézoélectriques déposés par sérigraphie et tamponnage), avec une fréquence centrale à 30 MHz, ont été fabriqués. Ils ont ensuite été modélisés par une méthode numérique hybride (FD-PSTD) [1] adaptée pour les configurations axisymétriques. Cet algorithme couple les méthodes par différences-finies et pseudospectrale permettant de modéliser la génération et la propagation des ondes acoustiques dans un transducteur et son environnement. Les résultats théoriques ont été comparés avec les déplacements expérimentaux mesurés à la surface des transducteurs (par interférométrie LASER) et les caractéristiques du champ de pression rayonné (mesures effectuées avec un hydrophone haute-fréquence). Les comparaisons satisfaisantes entre ces résultats ont permis détudier linfluence de certains paramètres de fabrication (comme les propriétés des électrodes) dans le but doptimiser les performances des transducteurs. [1] E. Filoux et al. , Modeling of Piezoelectric Transducers with Combined Pseudospectral and Finite-Difference Methods, Journal of the Acoustical Society of America, Vol. 123(6), pp. 4165-4173, 200