This paper describes a unique crossed electrode array for real-time volume ultrasound imaging. By placing orthogonal linear array electrode patterns on the opposite sides of a hemispherically shaped composite transducer substrate, a 2-D array can be fabricated using a small fraction of the elements required for a traditional 2-D array. The performance of the array is investigated using a computer simulation of the radiation pattern. We show that by using a 288-element crossed electrode pattern it is possible to collect large field of view volume images (60° x 60° sector) at real-time frame rates (>20 volume images/s), with image contrast and resolution comparable to what can be obtained using a conventional 128-element linear phased array.

Real-Time Volume Imaging Using a Crossed Electrode Array

Abstract The SOLARIS synchrotron located in Krakow, Poland, is a third-generation light source operating at medium electron energy. The first synchrotron light was observed in 2015, and the consequent development of infrastructure lead to the first users’ experiments at soft X-ray energies in 2018. Presently, SOLARIS expands its operation towards hard X-rays with continuous developments of the beamlines and concurrent infrastructure. In the following, we will summarize the SOLARIS synchrotron design, and describe the beamlines and research infrastructure together with the main performance parameters, upgrade, and development plans. 

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SOLARIS National Synchrotron Radiation Centre in Krakow, Poland

Synthetic aperture (SA) ultrasound imaging, despite its notable advantages, suffers from hardware complexity, especially for an array with excessive number of elements. This paper proposes a method to reduce the number of measurement channels in SA ultrasound imaging while maintaining image quality. Specifically, this work presents a method based on beam steering in the intra-sub-aperture (SAP) beamforming level to improve image quality in coprime sparse array imaging. Simulation and experimental results validated the effectiveness of the proposed method in improving resolution and field of view. The proposed method can be applied to a 2D matrix array for 3D ultrasound imaging.

Field of View and Resolution Improvement in Coprime Sparse Synthetic Aperture Ultrasound Imaging

Synthetic aperture (SA) ultrasound imaging, despite its notable advantages, suffers from hardware complexity, especially for an array with excessive number of elements. This paper proposes a method to reduce the number of measurement channels in SA ultrasound imaging while maintaining image quality. Specifically, this work presents a method based on beam steering in the intra-sub-aperture (SAP) beamforming level to improve image quality in coprime sparse array imaging. Simulation and experimental results validated the effectiveness of the proposed method in improving resolution and field of view. The proposed method can be applied to a 2D matrix array for 3D ultrasound imaging. 

This paper focuses on dealing with aliasing artifacts in millimeter-wave imaging systems. To address the challenges and complexities of designing multi-static arrays, sparse arrangements are utilized in practical imaging systems. Depending on the arrangement of antennas, such arrays may present severe aliasing artifacts. Some techniques have already been introduced to tackle such artifacts and enhance the image quality. These techniques may either distort the target image by causing some loss in parts of the image, impose high computational/system costs or suffer from the lack of generalizability. One of these techniques uses non-uniform arrays. Such arrays are designed by optimizing the point spread function (PSF). The PSF is a suitable representative of the system&#x2019;s performance provided that the system is shift-invariant. Since non-uniform arrays are shift-variant, these techniques are unreliable, especially in the case of off-center targets. As a consequence, there are no frameworks to design non-uniform arrays on a reliable basis to suppress aliasing artifacts in the whole region of interest (ROI). To address this issue, based on the k-space analysis of aliasing in multi-static arrays and non-uniform Fourier transform concept, we propose a small random displacement to be applied to antennas&#x2019; location in sparse periodic arrays. This displacement prevents the aliasing components from coherently accumulating. Nevertheless, due to the imposed non-uniformity, it is impossible to use FFT-based algorithms in this case. A subsequent resampling or the use of non-uniform FFT can address this problem. The provided simulations and experimental measurements show that the proposed method can efficiently lower the peak level of aliasing artifacts by around 3dB compared to sparse periodic arrays. So, the proposed method can be used as an effective way to suppress aliasing artifacts in real-time multi-static millimeter-wave imaging systems. 

Aliasing Artifacts Suppression in MIMO Millimeter-Wave Imaging Systems Based on K-Space Analysis

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 ${I}_{T}$ and the number of the receive channels in each transmission ${I}_{R}$ ). 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.

Large-Pitch Synthetic Transmit Aperture Imaging: A Feasibility Study

The invention generally relates to the field of synthetic aperture imaging. In particular, the invention relates to systems and methods for generating synthetic transmit aperture (“STA”) signals and processing synthetic aperture imaging (“SAI”) signals for improved signal-to-noise ratio (“SNR”) and spatial resolution. This generally relates to a method to improve the signal-noise-ratio (SNR) of array signals by both encoding the transmission from multiple array elements with waveform modifications and time delays and encoding the receivers into output channels and decoding the measured signals at the selected output channels to estimate the equivalent received signals of a receiver as if only one transmitting element were fired individually in each transmission event. SAI techniques are subsequently applied to the equivalent SAI signals to obtain improved images.

Synthetic Aperture Imaging Methods And Systems

X-ray computed tomography (CT) is an invaluable technique for generating three-dimensional (3D) images of inert or living specimens. X-ray CT is used in many scientific, industrial, and societal fields. Compared to conventional 2D X-ray imaging, CT requires longer acquisition times because up to several thousand projections are required for reconstructing a single high-resolution 3D volume. Plenoptic imaging—an emerging technology in visible light field photography—highlights the potential of capturing quasi-3D information with a single exposure. Here, we show the first demonstration of a flexible plenoptic microscope operating with hard X-rays; it is used to computationally reconstruct images at different depths along the optical axis. The experimental results are consistent with the expected axial refocusing, precision, and spatial resolution. Thus, this proof-of-concept experiment opens the horizons to quasi-3D X-ray imaging, without sample rotation, with spatial resolution of a few hundred nanometres.

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Flexible Plenoptic X-ray Microscopy

Various spatial compounding techniques have been proposed to improve contrast to noise ratio (CNR) of targets in ultrasound imaging by incoherently averaging sub-aperture images. However, spatial compounding (SC) sacrificed lateral resolution due to the decreased width of the selected sub-aperture. This paper presents the application of combining the SC and modified coherence factor (CF) techniques to single transmission plane wave imaging. The spatial resolution and contrast to noise ratio (CNR) of the tested phantoms were improved in the proposed method, compared to the conventional delay-and-sum technique.

Application of coherence factor and spatial compounding to single transmission plane wave imaging

A linear ultrasound array system usually has a larger pitch and is less costly than a phased array system, but loses the ability to fully steer the ultrasound beam. In this paper, we propose a system whose hardware is similar to a large-pitch linear array system, but whose ability to steer the beam is similar to a phased array system. The motivation is to reduce the total number of measurement channels M (the product of the number of transmissions, nT, and the number of the receive channels in each transmission, nR), while maintaining reasonable image quality. We combined adjacent elements (with proper delays introduced) into groups that would be used in both the transmit and receive processes of synthetic transmit aperture imaging. After the M channels of RF data were acquired, a pseudo-inversion was applied to estimate the equivalent signal in traditional STA to reconstruct a STA image. Even with the similar M, different choices of nT and nR will produce different image quality. The images produced with M=N2/15 in the selected regions of interest (ROI) were demonstrated to be comparable with a full phased array, where N is the number of the array elements. The disadvantage of the proposed system is that its field of view in one delay-configuration is smaller than a standard full phased array. However, by adjusting the delay for each element within each group, the beam can be steered to cover the same field of view as the standard fully-filled phased array. The LPSSTA system might be useful for 3D ultrasound imaging.

Ying Li

Papers

Large-Pitch Synthetic Transmit Aperture Imaging: A Feasibility Study

Synthetic Aperture Imaging Methods And Systems

Flexible Plenoptic X-ray Microscopy

Application of coherence factor and spatial compounding to single transmission plane wave imaging

Large-pitch steerable synthetic transmit aperture imaging (LPSSTA)