Blood-flow Volume Estimation by a 2-D Sparse Array.

Objective: The assessment of blood-flow volume (BFV) is clinically relevant for the diagnosis and monitoring of cardiovascular dysfunctions and the prevention of subsequent secondary diseases. Non-invasive BFV measurement based on ultrasound methods are appealing for lower cost, real-time operation, and equipment portability. Recently, complex ultrasound research scanners with 1024 channels controlling the elements of a 2-D matrix array probe, have been demonstrated suitable for off-line accurate BFV estimates.

Specific Filtered Delay Multiply and Sum beamforming for coherent multi-transducer ultrasound imaging.

Coherent multi-transducer ultrasound (CoMTUS) imaging enables the use of multiple arrays as one large effective aperture yielding images with enlarged field-of-view, improved resolution, and higher signal-to-noise ratio. However, creating a large but discontinuous effective aperture increases the grating and sidelobe levels, and generates cross-talk artifacts between arrays. These additional challenges can degrade the contrast of the images obtained through the classic Delay and Sum (DAS) beamforming algorithm.

Multi-probe Vector Velocity Estimation in Deep and Large Regions of Interest: a Simulation Study.

Objective: The current vector velocity measurement techniques are typically limited by probe apertures, which restrict their use to superficial vessels. This work introduces a high frame rate method based on the use of multiple array probes transmitting defocused beams and shows that such a method permits accurate and precise measurements of blood velocities in deep and large regions/volumes of interest.

Methods: Multiple probes are positioned to investigate a common region of interest and activated in a sequence.

An Innovative Ultrasound Research Platform Integrating an Open Scanner and a 3072-Element Dense Array.

High-end 4-D ultrasound (US) imaging systems typically use probes based on 2-D arrays containing thousands of transducers. Application specific integrated circuits (ASICs), embedded in the probe, manage the numerous transducers, significantly reducing the number of channels needed for the associated scanner. Unfortunately, the closed architecture of these high-end systems prevents research activities, such as the experimental testing of new imaging methods.

On the Impact of Microbeamformers in 3-D High Frame Rate Ultrasound Imaging: A Simulation Study.

Background And Objective: three-dimensional ultrasound imaging is based on two-dimensional (2-D) arrays controlled by application-specific integrated circuits, which implement the so-called microbeamformer (µB) to reduce the channel count. µBs are designed for line-by-line scan sequences based on focused beams (FBs), providing low frame rates. On the other hand, high frame rate (HFR) imaging techniques using defocused beams are increasingly attractive for reconstructing detailed tissue and blood motion information.

A Heterogeneous Ultrasound Open Scanner for the Real-Time Implementation of Computationally Demanding Imaging Methods.

Ultrasound (US) open scanners have recently boosted the development and validation of novel imaging techniques. They are usually split into hardware- or software-oriented systems, depending on whether they process the echo data using embedded field programmable gate arrays (FPGAs)/digital signal processors (DSPs) or a graphics processing unit (GPU) on a host personal computer (PC). The goal of this work was to realize a high-performance heterogeneous open scanner capable of leveraging the strengths of both hardware- and software-oriented systems.

A Deep Learning Approach for Beamforming and Contrast Enhancement of Ultrasound Images in Monostatic Synthetic Aperture Imaging: A Proof-of-Concept.

In this study, we demonstrate that a deep neural network (DNN) can be trained to reconstruct high-contrast images, resembling those produced by the multistatic Synthetic Aperture (SA) method using a 128-element array, leveraging pre-beamforming radiofrequency (RF) signals acquired through the monostatic SA approach. : A U-net was trained using 27200 pairs of RF signals, simulated considering a monostatic SA architecture, with their corresponding delay-and-sum beamformed target images in a multistatic 128-element SA configuration. The contrast was assessed on 500 simulated test images of anechoic/hyperechoic targets.

Interaction of macro- and microvascular function underlies brachial artery flow-mediated dilation in humans.

Brachial artery flow-mediated dilation (BAFMD) is induced by hyperemic wall shear rate (WSR) following forearm ischemia. In older adults, there appears to be a reduced brachial hyperemic WSR and altered stimulus-response relationship compared with young adults. However, it is unclear if an altered forearm microvascular response to ischemia influences brachial hyperemic WSR in older adults.

3-D Coherent Multitransducer Ultrasound Imaging With Sparse Spiral Arrays.

Coherent multitransducer 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.

Lung Ultrasound Artifacts Interpreted as Pathology Footprints.

Background: The original observation that lung ultrasound provides information regarding the physical state of the organ, rather than the anatomical details related to the disease, has reinforced the idea that the observed acoustic signs represent artifacts. However, the definition of artifact does not appear adequate since pulmonary ultrasound signs have shown valuable diagnostic accuracy, which has been usefully exploited by physicians in numerous pathologies.

Method: A specific method has been used over the years to analyze lung ultrasound data and to convert artefactual information into anatomical information.

Sparse 2-D PZT-on-PCB Arrays With Density Tapering.

Two-dimensional (2-D) arrays offer volumetric imaging capabilities without the need for probe translation or rotation. A sparse array with elements seeded in a tapering spiral pattern enables one-to-one connection to an ultrasound machine, thus allowing flexible transmission and reception strategies. To test the concept of sparse spiral array imaging, we have designed, realized, and characterized two prototype probes designed at 2.

Unfocused Field Analysis of a Density-Tapered Spiral Array for High-Volume-Rate 3-D Ultrasound Imaging.

Spiral array transducers with a sparse 2-D aperture have demonstrated their potential in realizing 3-D ultrasound imaging with reduced data rates. Nevertheless, their feasibility in high-volume-rate imaging based on unfocused transmissions has yet to be established. From a metrology standpoint, it is essential to characterize the acoustic field of unfocused transmissions from spiral arrays not only to assess their safety but also to identify the root cause of imaging irregularities due to the array's sparse aperture.

High-Frame-Rate Speckle Tracking for Echocardiographic Stress Testing.

Stress echocardiography helps to diagnose cardiac diseases that cannot easily be detected or do not even manifest at rest. In clinical practice, assessment of the stress test is usually performed visually and, therefore, in a qualitative and subjective way. Although speckle tracking echocardiography (STE) has been proposed for the quantification of function during stress, its time resolution is inadequate at high heart rates.

Design, Implementation, and Medical Applications of 2-D Ultrasound Sparse Arrays.

An ultrasound sparse array consists of a sparse distribution of elements over a 2-D aperture. Such an array is typically characterized by a limited number of elements, which in most cases is compatible with the channel number of the available scanners. Sparse arrays represent an attractive alternative to full 2-D arrays that may require the control of thousands of elements through expensive application-specific integrated circuits (ASICs).

Spatial Coherence Beamforming With Multi-Line Transmission to Enhance the Contrast of Coherent Structures in Ultrasound Images Degraded by Acoustic Clutter.

This work demonstrates that the combination of multi-line transmission (MLT) and short-lag spatial coherence (SLSC) imaging improves the contrast of highly coherent structures within soft tissues when compared to both traditional SLSC imaging and conventional delay and sum (DAS) beamforming. Experimental tests with small (i.e.

High Frame Rate Volumetric Imaging of Microbubbles Using a Sparse Array and Spatial Coherence Beamforming.

Volumetric ultrasound imaging of blood flow with microbubbles enables a more complete visualization of the microvasculature. Sparse arrays are ideal candidates to perform volumetric imaging at reduced manufacturing complexity and cable count. However, due to the small number of transducer elements, sparse arrays often come with high clutter levels, especially when wide beams are transmitted to increase the frame rate.

Architecture for an Ultrasound Advanced Open Platform With an Arbitrary Number of Independent Channels.

Ultrasound open platforms are programmable and flexible tools for the development and test of novel methods. In most cases, they embed the electronics for the independent control of (maximum) 256 probe elements. However, a higher number of channels is needed for the control of 2-D array probes.

On the Depth-Dependent Accuracy of Plane-Wave-Based Vector Velocity Measurements With Linear Arrays.

High-frame-rate vector Doppler methods are used to measure blood velocities over large 2-D regions, but their accuracy is often estimated over a short range of depths. This article thoroughly examines the dependence of velocity measurement accuracy on the target position. Simulations were carried out on flat and parabolic flow profiles, for different Doppler angles, and considering a 2-D vector flow imaging (2-D VFI) method based on plane wave transmission and speckle tracking.

Impact of Aperture, Depth, and Acoustic Clutter on the Performance of Coherent Multi-Transducer Ultrasound Imaging.

Transducers with a larger aperture size are desirable in ultrasound imaging to improve resolution and image quality. A coherent multi-transducer ultrasound imaging system (CoMTUS) enables an extended effective aperture through the coherent combination of multiple transducers. In this study, the discontinuous extended aperture created by CoMTUS and its performance for deep imaging and through layered media are investigated by both simulations and experiments.

Real-Time 3-D Spectral Doppler Analysis With a Sparse Spiral Array.

2-D sparse arrays may push the development of low-cost 3-D systems, not needing to control thousands of elements by expensive application-specific integrated circuits (ASICs). However, there is still some concern about their suitability in applications, such as Doppler investigation, which inherently involve poor signal-to-noise ratios (SNRs). In this article, a novel real-time 3-D pulsed-wave (PW) Doppler system, based on a 256-element 2-D spiral array, is presented.

In Vivo Comparison of Multiline Transmission and Diverging Wave Imaging for High-Frame-Rate Speckle-Tracking Echocardiography.

High-frame-rate (HFR) speckle-tracking echocardiography (STE) assesses myocardial function by quantifying motion and deformation at high temporal resolution. Among the proposed HFR techniques, multiline transmission (MLT) and diverging wave (DW) imaging have been used in this context both being characterized by specific advantages and disadvantages. Therefore, in this article, we directly contrast both approaches in an in vivo setting while operating at the same frame rate (FR).

A Novel 2-D Speckle Tracking Method for High-Frame-Rate Echocardiography.

Speckle tracking echocardiography (STE) is a clinical tool to noninvasively assess regional myocardial function through the quantification of regional motion and deformation. Even if the time resolution of STE can be improved by high-frame-rate (HFR) imaging, dedicated HFR STE algorithms have to be developed to detect very small interframe motions. Therefore, in this article, we propose a novel 2-D STE method, purposely developed for HFR echocardiography.

High-Frame-Rate Color Doppler Echocardiography: A Quantitative Comparison of Different Approaches.

Ultrasound color Doppler imaging (CDI) provides a map of the axial blood flow velocities in a 2-D/3-D region of interest. While CDI is clinically effective for a qualitative analysis of abnormal blood flows, e.g.

A Comparison of Coherence-Based Beamforming Techniques in High-Frame-Rate Ultrasound Imaging With Multi-Line Transmission.

One of the current challenges in ultrasound imaging is achieving higher frame rates, particularly in cardiac applications, where tracking the heart motion and other rapid events can provide potential valuable diagnostic information. The main drawback of ultrasound high-frame-rate strategies is that usually they partly sacrifice image quality in order to speed up the acquisition time. In particular, multi-line transmission (MLT), which consists in transmitting multiple ultrasound beams simultaneously in different directions, has been proven able to improve frame rates in echocardiography, unfortunately generating artifacts due to inter-beam crosstalk interferences.