Number Of Transducer Elements Research Articles

Concentric-ring arrays for forward-viewing ultrasound imaging.

Current ultrasound (US)-image-guided needle insertions often require an expertized technique for clinicians because the performance of tasks in a three-dimensional space using two-dimensional images requires operators to cognitively maintain the spatial relationships between the US probe, the needle, and the lesion. This work presents forward-viewing US imaging with a ring array configuration to enable needle interventions without requiring the registration between tools and targets. The center-open ring array configuration allows the needle to be inserted from the center of the visualized US image, providing simple and intuitive guidance. To establish the feasibility of the ring array configuration, the design parameters causing the image quality, including the radius of the center hole and the number of ring layers and transducer elements, were investigated. Experimental results showed successful visualization, even with a hole in the transducer elements, and the target visibility was improved by increasing the number of ring layers and the number of transducer elements in each ring layer. Reducing the hole radius improved the region's image quality at a shallow depth. Forward-viewing US imaging with a ring array configuration has the potential to be a viable alternative to conventional US image-guided needle insertion methods.

Large-Pitch Synthetic Transmit Aperture Imaging: A Feasibility Study.

A 3-D or large-aperture 2-D synthetic transmit aperture (STA) ultrasound imaging system with a fully sampled array usually leads to high hardware complexity and cost since each element in the array is individually controlled. To reduce the hardware complexity, we propose a large-pitch method for STA (LPSTA) imaging integrated with a spatial response function (SRF) in the image reconstruction to improve image quality. To achieve this, we decreased the total number of measurement channels M (the product of the number of transmissions IT and the number of the receive channels in each transmission IR ). We combined L adjacent elements in transmission and K adjacent elements in receive into subapertures (SAPs), where L and K were coprime (no common factors) integers to suppress the grating lobes. We denoted it as an ( N/L, N /K ) system, where N is the number of transducer elements. In this article, first, we derived the beam pattern of the LPSTA using a far-field approximation. We demonstrated that the coprime selection and SRF can significantly reduce the grating lobes level (GLL) by using a beam pattern analysis. We also found that the LPSTA can have a similar beam pattern as that of a full array when the target is located along the steering direction. Second, the imaging performance of LPSTA was evaluated and validated with Field II simulations and experiments. The simulation results demonstrated that the proposed LPSTA with ( N /3, N /5) can achieve on average ~25% improvement in lateral resolution, ~24.6% and ~42.3% improvement in contrast-to-noise ratio (CNR) and contrast ratio (CR), respectively, over B-mode with a large-pitch receiver with ( N , N /5). LPSTA achieved comparable image contrast to the standard STA with the full array ( N , N ) at the cost of a reduced field of view. The experiment results were consistent with the simulation results. Finally, in addition to reducing the system (hardware) complexity, the LPSTA was more computationally efficient than the standard STA with a full array. The proposed method may help in realizing clinical applications of real-time 2-D or 3-D ultrasound imaging using large arrays.

Effect of frequency characteristic of excitation pulse on lateral spatial resolution in coded ultrasound imaging

Recently, portable ultrasonic diagnostic equipment has frequently been used in clinical situations. The use of portable ultrasonic diagnostic equipment expands various diagnosis areas, such as remote medical diagnosis, and emergent diagnosis at disaster. It is expected that portable ultrasonic diagnostic equipment will be used more frequently in the future. To make ultrasonic diagnostic equipment portable, the number of transducer elements in an ultrasonic probe should be reduced significantly. Therefore, the transmit–receive sensitivity of the ultrasonic probe is degraded. For the improvement of the signal-to-noise ratio (SNR) of the received ultrasonic echo, coded excitation was introduced in ultrasonic imaging. Owing to pulse compression applied to the received echo signal, its SNR significantly improved without the degradation of the range spatial resolution. However, the lateral spatial resolution in coded ultrasound imaging has not been investigated in previous studies. The present study showed that the lateral resolution in coded ultrasound imaging using a typical code, 5-bit Barker code, was worse than that using a conventional short pulse. Such degradation was discussed in terms of the frequency characteristics of the impulse response of the ultrasonic transducer and the excitation pulse. Also, the Gaussian phase coherence factor was introduced as one of the methods to overcome such degradation in lateral spatial resolution.

Realistic deformable 3D numeric phantom for transcutaneous ultrasound

Introduction Numerical phantoms are important tools to design, calibrate and evaluate several methods in various image-processing applications, such as echocardiography and mammography. We present a framework for creating ultrasound numerical deformable phantoms based on Finite Element Method (FEM), Linear Isomorphism and Field II. The proposed method considers that the scatterers map is a property of the tissue; therefore, the scatterers should move according to the tissue strain. Methods First, a volume representing the target tissue is loaded. Second, parameter values, such as Young’s Modulus, scatterers density, attenuation and scattering amplitudes are inserted for each different regions of the phantom. Then, other parameters related to the ultrasound equipment, such as ultrasound frequency and number of transducer elements, are also defined in order to perform the ultrasound acquisition using Field II. Third, the size and position of the transducer and the pressures that are applied against the tissue are defined. Subsequently, FEM is executed and deformation is computed. Next, 3D linear isomorphism is performed to displace the scatterers according to the deformation. Finally, Field II is carried out to generate the non-deformed and deformed ultrasound data. Results The framework is evaluated by comparing strain values obtained the numerical simulation and from the physical phantom from CIRS. The mean difference between both phantoms is lesser than 10%. Conclusion The acoustic and deformation outcomes are similar to those obtained using a physical phantom. This framework led to a tool, which is available online and free of charges for educational and research purposes.

Sparse Arrays and Image Compounding Techniques for Non-Destructive Testing Using Guided Acoustic Waves

Piezoelectric array transducers applications are becoming usual in the ultrasonic non-destructive testing area. However, the number of elements can increase the system complexity, due to the necessity of multichannel circuitry and to the large amount of data to be processed. Synthetic aperture techniques, where one or few transmission and reception channels are necessary, and the data are post-processed, can be used to reduce the system complexity. Another possibility is to use sparse arrays instead of a full-populated array. In sparse arrays, there is a smaller number of elements and the interelement spacing is larger than half wavelength. In this work, results of ultrasonic inspection of an aluminum plate with artificial defects using guided acoustic waves and sparse arrays are presented. Synthetic aperture techniques are used to obtain a set of images that are then processed with an image compounding technique, which was previously evaluated only with full-populated arrays, in order to increase the resolution and contrast of the images. The results with sparse arrays are equivalent to the ones obtained with full-populated arrays in terms of resolution. Although there is an 8 dB contrast reduction when using sparse arrays, defect detection is preserved and there is the advantage of a reduction in the number of transducer elements and data volume.

Ultrasound time-reversal MUSIC imaging with diffraction and attenuation compensation

Time-reversal imaging with multiple signal classification (TR-MUSIC) is an algorithm for imaging point-like scatterers embedded in a homogeneous and non-attenuative medium. We generalize this algorithm to account for the attenuation in the medium and the diffraction effects caused by the finite size of the transducer elements. The generalized algorithm yields higher-resolution images than those obtained with the original TR-MUSIC algorithm. We evaluate the axial and lateral resolutions of the images obtained with the generalized algorithm when noise corrupts the recorded signals and show that the axial resolution is degraded more than the lateral resolution. The TR-MUSIC algorithm is valid only when the number of point-like targets in the imaging plane is fewer than the number of transducer elements used to interrogate the medium. We remedy this shortcoming by dividing the imaging plane into subregions and applying the TR-MUSIC algorithm to the windowed backscattered signals corresponding to each subregion. The images of all subregions are then combined to form the total image. Imaging results of numerical and phantom data show that when the number of scatterers within each subregion is much smaller than the number of transducer elements, the windowing method yields super-resolution images with accurate scatterer localization. We use computer simulations and tissue-mimicking phantom data acquired with a real-time synthetic-aperture ultrasound system to illustrate the algorithms presented in the paper.

50 kHz 체장어군탐지기용 분할 빔 음향 변환기의 개발

An improved split-beam transducer for a 50 kHz fish-sizing echo sounder was developed. The main objective of this study was to minimize the side lobe level in the beam pattern and the distance between acoustic centers for adjacent transducer quadrants in the geometrical arrangement of array elements while maintaining a given number of transducer elements and beam width. To achieve these goals, a 32-element planar array transducer (<TEX>$6{\times}6$</TEX> array with one element in each corner missing) was designed using the Dolph-Chebyshev shading function to suppress side lobes in the array beam pattern and fabricated by arranging the inter-element spacing to be substantially equal to half the wavelength using the transducer element of 0.4 times the wavelength in diameter. The performance characteristics of this split-beam transducer were evaluated in the experimental water tank of <TEX>$5m{\times}5m{\times}6m$</TEX> (length<TEX>${\times}$</TEX>height<TEX>${\times}$</TEX>width). In this study, the design goal of the beam width and side lobe level for transmitting a beam pattern was initially set at <TEX>$21^{\circ}$</TEX> and -30 dB, respectively. However, the measured beam width at 3 dB was <TEX>$21^{\circ}$</TEX> in both directions with side lobe levels of -24.7 dB in the horizontal plane and -25.6 dB in the vertical plane. The averaged beam width at -3 dB of the receiving beam patterns for four receiving quadrants was <TEX>$31.4^{\circ}$</TEX>. The transmitting voltage response was 161.5 dB (re <TEX>$1{\mu}Pa$</TEX>/V at 1 m) at 50.23 kHz with a bandwidth of 2.16 kHz, and the averaged receiving sensitivity for four receiving quadrants was -178.13 dB (re 1 V/<TEX>${\mu}Pa$</TEX>) at 49.8 kHz with a bandwidth of 2.64 kHz.

Enhancing Controllability and Observability in Underactuated and Undersensed Systems Through Switching: Application to Vibration Control

Many dynamical systems use transducers that can function both as actuators and sensors. It is possible to continuously switch the functionality of the transducer elements in such systems and effectively use each element both as an actuator and a sensor. This provides the scope for significantly reducing the number of transducer elements required for complete controllability and observability of the system and hence reduce the hardware required for controlled system operation. In this paper we advocate underactuation and undersensing in dynamical systems with the objective of reducing cost, weight, and system complexity. To this end, we first illustrate the role of switching in enhancing controllability and observability in underactuated and undersensed linear time-invariant systems and determine the switching requirement for observer-based control designs. For a proof of principle, we consider the problem of vibration suppression in a flexible beam instrumented with piezoelectric transducers. Using simulation and experiments, we demonstrate feasibility of switching the piezoelectric elements between actuator and sensor modalities and establish the merit of introducing underactuation and undersensing deliberately.

Method of reduction of the number of driving system channels for phased-array transducers using isolation transformers.

Phased-array technology offers an incredible advantage to therapeutic ultrasound due to the ability to electronically steer foci, create multiple foci, or to create an enlarged focal region by using phase cancellation. However, to take advantage of this flexibility, the phased-arrays generally consist of many elements. Each of these elements requires its own radio-frequency generator with independent amplitude and phase control, resulting in a large, complex, and expensive driving system. A method is presented here where in certain cases the number of amplifier channels can be reduced to a fraction of the number of transducer elements, thereby simplifying the driving system and reducing the overall system complexity and cost, by using isolation transformers to produce 180 degrees phase shifts.

Coarse-fine ultrasound transducer array for medical imaging

The ultrasound transducer array defines an average row spacing along the elevation for receiving transducer elements that differs from an average row spacing along the elevation for transmitting transducer elements. In one embodiment a relatively "coarse" row spacing is used for reception and a relatively "fine" row spacing is used for transmission. The differing spacings lead to different transmit-elevation and receive-elevation beam-patterns. In one configuration the number of transducer elements, and correspondingly the number of ultrasound processing channels, is reduced. In an alternative configuration the beam-pattern "footprint" is increased without increasing the number of transducer elements or processing channels. The array includes dedicated transmit-only elements and/or dedicated receive-only elements, together with coincident, time-shared transmit/receive elements. The coarse-fine spacings enable improved elevational focus without substantially increasing side lobe levels in a focal plane and far field portion of a resulting beam-pattern.

Method and apparatus for controlling transducer multiplexing in ultrasound imaging system

A method and apparatus for controlling multiplexing of a transducer having more elements than the imaging system has receive channels. The active aperture is shifted in increments of a predetermined number of transducer elements, e.g., eight. While the active aperture is maintained constant for a predetermined number of vectors, the phase center of the vectors in the group is shifted so that offset is minimized. In the case wherein the active aperture is successively shifted by eight elements, the offset is varied between +4 and -4 during the interval between shifts of the active aperture.

Synthetic aperture ultrasound imaging system

An acoustical imaging system for producing high resolution medical images provides a method and apparatus for obtaining accurate velocity characterizations of samples within the human body, and for obtaining high resolution images of the samples by utilizing the velocity characterizations of the samples within the human body. The acoustical imaging system also provides a method and apparatus for efficient use of switching channels whereby for a transducer array having a plurality of transducer elements, a set of receiver channels which number less than the number of transducer elements in the array are assigned to a selected portion of the plurality of transducers in the array, wherein for any predetermined set of transducers symmetrically located about a selected transducer, the predetermined set equal in number to the number of receiver channels in the system, each receiver channel in the set of receiver channels is only assigned to one transducer in said predetermined sampling set.

Analysis of acoustic radiation patterns of array transducers using the TLM method

The paper describes the application of the TLM numerical method for the analysis of acoustic wave propagation. It presents a general scattering algorithm for modelling homogeneous and inhomogeneous mediums where both the density and compressibility of the propagation space are varied. The method is used to obtain the acoustic radiation patterns of discrete transducer arrays. The effect of the spacing and the number of transducer elements on the radiation pattern are demonstrated by numerical results obtained using a two-dimensional TLM mesh. The results also show the effect of array shading on the radiation pattern. Beam steering by delayed excitation of the transducer elements is also demonstrated here. In addition the paper presents two simple techniques for detecting the direction of wave propagation in the TLM mesh.