546 research outputs found
VLSI Circuits for adaptive digital beamforming in ultrasound imaging
Cataloged from PDF version of article.For phased-array ultrasound imaging, alternative
beamforming techniques and their VLSI circuits are studied
to form a fully digital receive frontad hardware. In order
to increase the timiig accuracy in beamforming, a computationally
efficient interpolation scheme to increase the sampling
rate is examined. For adaptive beamforming, a phase aberration
correction method with very low computational complexity is
described. Image quality performance of the method is examined
by processing the non-aberrated and aberrated phased-array
experimental data sets of an ultrasound resolution phantom. A
digital beamforming scheme based on receive focusing at the
raster focal points is examined. The sector images of the resolution
phantom, reconstructed from the phased-array experimental
data by beamforming at the radial and raster focal points, are
presented for comparison of the image resolution performances
of the two beamforming schemes. VLSI circuits and their implementations
for the proposed techniques are presented
Photoacoustic guided ultrasound wavefront shaping for targeted acousto-optic imaging
To overcome speed of sound aberrations that negatively impact the acoustic focus in acousto-optic imaging, received photoacoustic signals are used to guide the formation of ultrasound wavefronts to compensate for acoustic inhomogeneities. Photoacoustic point sources composed of gold and superparamagnetic iron oxide nanoparticles are used to generate acoustic waves that acoustically probe the medium as they propagate to the detector. By utilizing cross-correlation techniques with the received photoacoustic signal, transmitted ultrasound wavefronts compensate for the aberration, allowing for optimized and configurable ultrasound transmission to targeted locations. It is demonstrated that utilizing a portable commercially available ultrasound system using customized software, photoacoustic guided ultrasound wavefront shaping for targeted acousto-optic imaging is robust in the presence of large, highly attenuating acoustic aberration
Three-Dimensional Ultrasound Matrix Imaging
Matrix imaging paves the way towards a next revolution in wave physics. Based
on the response matrix recorded between a set of sensors, it enables an
optimized compensation of aberration phenomena and multiple scattering events
that usually drastically hinder the focusing process in heterogeneous media.
Although it gave rise to spectacular results in optical microscopy or seismic
imaging, the success of matrix imaging has been so far relatively limited with
ultrasonic waves because wave control is generally only performed with a linear
array of transducers. In this paper, we extend ultrasound matrix imaging to a
3D geometry. Switching from a 1D to a 2D probe enables a much sharper
estimation of the transmission matrix that links each transducer and each
medium voxel. Here, we first present an experimental proof of concept on a
tissue-mimicking phantom through ex-vivo tissues and then, show the potential
of 3D matrix imaging for transcranial applications.Comment: 60 pages, 14 figure
Reflection matrix approach for quantitative imaging of scattering media
We present a physically intuitive matrix approach for wave imaging and
characterization in scattering media. The experimental proof-of-concept is
performed with ultrasonic waves, but this approach can be applied to any field
of wave physics for which multi-element technology is available. The concept is
that focused beamforming enables the synthesis, in transmit and receive, of an
array of virtual transducers which map the entire medium to be imaged. The
inter-element responses of this virtual array form a focused reflection matrix
from which spatial maps of various characteristics of the propagating wave can
be retrieved. Here we demonstrate: (i) a local focusing criterion that enables
the image quality and the wave velocity to be evaluated everywhere inside the
medium, including in random speckle, and (ii) an highly resolved spatial
mapping of the prevalence of multiple scattering, which constitutes a new and
unique contrast for ultrasonic imaging. The approach is demonstrated for a
controllable phantom system, and for in vivo imaging of the human abdomen. More
generally, this matrix approach opens an original and powerful route for
quantitative imaging in wave physics.Comment: 18 pages, 6 figure
Ultrasonic Imaging of Static Objects Through a Scattering Layer Using the Harmonic Phase Conjugation Approach
The main goal of this study is to develop a new image reconstruction approach for the ultrasonic detection of foreign objects inside the human brain through a simplified skull model. The proposed solution is based on the Harmonic Phase Conjugation technique. A source of ultrasound (transducer), small reflecting and scattering objects, a simplified skull layer, and a linear array of ultrasonic receivers are the main components of the test setup. The algorithm starts with the forward propagation step, when the phase and amplitude distributions of the ultrasonic field from the source transducer are recorded with an array of receivers. These distributions are also calculated in presence of a skull layer and small reflecting objects. The recorded phase and amplitude information is then used in the back propagation step, when the phase-conjugated scattered field is numerically propagated through the same medium in the reverse direction. As this field naturally focuses at the locations of the reflecting objects, their image can be reconstructed. After testing the algorithm using a numerical model, a set of laboratory experiments was conducted to verify the accuracy of the developed simulation. The results of these tests are presented, and the main advantages and drawbacks of the approach are discussed
A phase aberration correction method for ultrasound imaging
Cataloged from PDF version of article.A computationally efficient method for phase aberration
correction in ultrasound imaging is presented. The method
is based on time delay estimation via minimization of the sum of
absolute differences between radio frequency samples of adjacent
array elements. Effects of averaging estimated aberration patterns
over scan angles, and truncation to a single bit wordlength
are examined. Phase distortions due to near-field inhomogeneities
are simulated using silicone rubber aberrators. Performance of
the method is tested using experimental data. Simulation studies
addressing different factors affecting efficiency of the method,
such as the number of iterations, window length, and the number
of scan angles used for averaging, are presented. Images of a
standard resolution phantom are reconstructed and used for
qualitative testing
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