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Non-standard scan modes, based on the transmission of plane and diverging waves, are the key to enable high frame rate and volumetric imaging modalities and are promising in the implementation of novel system architectures for ultra-integrated (high channel count) scanners. So far, capacitive micromachined ultrasonic transducer (CMUT) arrays have been benchmarked against standard piezoelectric transducers only in standard modalities. In this work, a 256-element CMUT probe and a state-of-the art single crystal composite piezoelectric probe, sharing the same array geometry and bandwidth, are compared in plane wave (PW) imaging mode. The CMUT probe provided, on average, improved signal power (+9 dB) and contrast (+3 dB) for all PW aperture angles. Also, compared to the piezoelectric probe, the CMUT one offered comparable axial resolution, but slightly worse (10%) lateral resolution.

International audience; 2-D sparse arrays may push the development of lowcost 3-D systems, not needing to control thousands of elements by expensive application-specific integrated circuits. However, there is still some concern about their suitability in applications, such as Doppler investigation, which inherently involve poor signal-tonoise ratios (SNRs). In this paper, a novel real-time 3-D pulsed-wave Doppler system, based on a 256-element 2-D spiral array, is presented. Coded transmission and matched filtering were implemented to improve the system SNR. Standard sonograms as well as multigate spectral Doppler (MSD) profiles, along lines that can be arbitrarily located in different planes, are presented. The performance of the system was assessed quantitatively on experimental data obtained from a straight tube flow phantom. An SNR increase of 11.4 dB was measured by transmitting linear chirps instead of standard sinusoidal bursts. For a qualitative assessment of the system performance in more realistic conditions, an anthropomorphic phantom of the carotid arteries was used. Finally, real-time B-mode and MSD images were obtained from healthy volunteers.

The 2-D sparse arrays, in which a few hundreds of elements are distributed on the probe surface according to an optimization procedure, represent an alternative to full 2-D arrays, including thousands of elements usually organized in a grid. Sparse arrays have already been used in B-mode imaging tests, but their application to Doppler investigations has not been reported yet. Since the sparsity of the elements influences the acoustic field, a corresponding influence on the mean frequency (Fm), bandwidth (BW), and signal-to-noise ratio (SNR) of the Doppler spectra is expected. This article aims to assess, by simulations and experiments, to what extent the use of a sparse rather than a full gridded 2-D array has an impact on spectral Doppler measurements. Parabolic flows were investigated by a 3 MHz, 1024-element gridded array and by a sparse array; the latter was obtained by properly selecting a subgroup of 256 elements from the full array. Simulations show that the mean Doppler frequency does not change between the sparse and the full array while there are significant differences on the BW (average reduction of 17.2% for the sparse array, due to different apertures of the two probes) and on the signal power (Ps) (22 dB, due to the different number of active elements). These results are confirmed by flow phantom experiments, which also highlight that the most critical difference between sparse and full gridded array in Doppler measurements is in terms of SNR (-16.8 dB). ispartof: IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL vol:67 issue:2 pages:278-285 ispartof: location:United States status: published

Sparse arrays represent an alternative to full-gridded arrays in 2-D probes realization. Sparse arrays have been used in B-mode imaging tests, but not in spectral Doppler measurements yet. In this paper, we have investigated, by mean of simulations and experiments, how the use of a sparse array instead of a full-gridded 2-D array impacts on spectral Doppler measurements. A 3 MHz, 1024-element gridded array and a sparse array obtained by properly selecting 256 elements from the full array, have been used to interrogate a parabolic flow. Simulations and experiments highlight that the mean Doppler frequency does not change by using the sparse array instead of the full one. Significant differences appear for the bandwidth (17.2% average bandwidth reduction for the sparse array), and for the signal power (22 dB). Possible explanations of this behavior are discussed. Furthermore, it is shown that the empty lines in the 2-D array impact on the Doppler spectra, leading to sidelobes when steering in the direction perpendicular to such lines.

International audience; The use of 2-D array probes to perform 3-D ul-trasound imaging is still investigated in many domains. The extension from 2-D to 3-D imaging causes problems because of the need to control a very large number of elements on the probe. It might be overcome by using 2-D sparse array. This problem has been recently shown that sparse 2-D arrays can be used for 3-D fast ultrasound imaging based on the transmission of Diverging Waves (DW). The aim of this work is to experimentally analyze how the distribution of a given number (25) of Virtual Sources (VS) over a predefined area affects the images obtained with one fully populated probe and two sparse array probes, respectively. In order to do that, gridded and spiral distributions of virtual sources have been implemented. The results show that with the spiral distribution there is a general improvement of the contrast despite of a degradation on both lateral and axial resolutions.

Biplane modality is frequently used in medical ultrasound imaging applications. Crossed array configurations, in which two orthogonal 1-D arrays co-exist on the same area, are particularly suitable for biplane imaging. However, the imaging performance is limited by the absence of focusing capability in the arrays respective elevation directions. In this paper, we present a novel 120+120-element 7 MHz crisscross Capacitive Micromachined Ultrasonic Transducer (CMUT) probe in which the orthogonal arrays are both provided with Fresnel elevation focusing capability. The CMUT probe includes low-noise amplifiers and high-voltage switches, which allow fast switching (

This work shows the feasibility of performing ultrafast 3D ultrasound imaging by producing diverging waves (DW) with 2D sparse arrays. The 3D volumes were experimentally acquired by individually driving the 1024 elements of a full 32×32 matrix array. The volumes obtained with different sparse configurations were compared to those obtained with two references arrays: the full 32×32 array and a dense array of 716 elements where obtained by de-activating the corner elements of the full array. The comparison criteria were the lateral resolution using the full width at half maximum (FWHM) and the contrast to noise ratio (CNR), measured on the images obtained by scanning a grayscale phantom. The results show that ultrafast 3D ultrasound imaging can be performed with a reduced number of channels using 2D sparse arrays. However, there is still space to find the optimal 2D sparse array configurations to best transmit 3D DWs and potential improvements on image quality may be achieved with dedicated optimization e.g. cost function to homogenize DW wave front.