1,098 research outputs found
Correction of concentrated and distributed aberrations in medical ultrasound imaging
A method is presented for iterative correction of wave fields aberrated in a plane located at an arbitrary distance from an array transducer. The signals received from the transducer are processed by an inverse extrapolator in such a way that the output yields the transducer signals as if the transducer had been located directly at the position of the aberrator. For subsequent transmission cycles, the same inverse extrapolator is applied to delta pulses at time instants incorporating the time-reversed estimated aberration profile. The method can be applied to scattering and absorptive media, i.e. in medical conditions. The compensation of distributed aberration is also developed. It is shown that correction algorithms intended for concentrated aberrations can be used to reduce effects due to distributed aberrations; our conclusions with respect to the position of the equivalent concentrated aberrator differ from results reported in the literature. The method is demonstrated on realistic simulations of solid lesions, and cysts (voids) disturbed by intervening aberrating medi
Forward model for quantitative pulse-echo speed-of-sound imaging
Computed ultrasound tomography in echo mode (CUTE) allows determining the
spatial distribution of speed-of-sound (SoS) inside tissue using handheld
pulse-echo ultrasound (US). This technique is based on measuring the changing
phase of beamformed echoes obtained under varying transmit (Tx) and/or receive
(Rx) steering angles. The SoS is reconstructed by inverting a forward model
describing how the spatial distribution of SoS is related to the spatial
distribution of the echo phase shift. CUTE holds promise as a novel diagnostic
modality that complements conventional US in a single, real-time handheld
system. Here we demonstrate that, in order to obtain robust quantitative
results, the forward model must contain two features that were not taken into
account so far: a) the phase shift must be detected between pairs of Tx and Rx
angles that are centred around a set of common mid-angles, and b) it must
account for an additional phase shift induced by the error of the reconstructed
position of echoes. In a phantom study mimicking liver imaging, this new model
leads to a substantially improved quantitative SoS reconstruction compared to
the model that has been used so far. The importance of the new model as a
prerequisite for an accurate diagnosis is corroborated in preliminary volunteer
results
Full modelling of high-intensity focused ultrasound and thermal heating in the kidney using realistic patient models
Objective: High-intensity focused ultrasound (HIFU) therapy can be used for
non-invasive treatment of kidney (renal) cancer, but the clinical outcomes have
been variable. In this study, the efficacy of renal HIFU therapy was studied
using nonlinear acoustic and thermal simulations in three patients. Methods:
The acoustic simulations were conducted with and without refraction in order to
investigate its effect on the shape, size and pressure distribution at the
focus. The values for the attenuation, sound speed, perfusion and thermal
conductivity of the kidney were varied over the reported ranges to determine
the effect of variability on heating. Furthermore, the phase aberration was
studied in order to quantify the underlying phase shifts using a second order
polynomial function. Results: The ultrasound field intensity was found to drop
on average 11.1 dB with refraction and 6.4 dB without refraction. Reflection at
tissue interfaces was found to result in a loss less than 0.1 dB. Focal point
splitting due to refraction significantly reduced the heating efficacy.
Perfusion did not have a large effect on heating during short sonication
durations. Small changes in temperature were seen with varying attenuation and
thermal conductivity, but no visible changes were present with sound speed
variations. The aberration study revealed an underlying trend in the spatial
distribution of the phase shifts. Conclusion: The results show that the
efficacy of HIFU therapy in the kidney could be improved with aberration
correction. Significance: A method is proposed by which patient specific
pre-treatment calculations could be used to overcome the aberration and
therefore make ultrasound treatment possible.Comment: Journal paper, IEEE Transactions on Biomedical Engineering (2018
Phase Aberration Correction: A Deep Learning-Based Aberration to Aberration Approach
One of the primary sources of suboptimal image quality in ultrasound imaging
is phase aberration. It is caused by spatial changes in sound speed over a
heterogeneous medium, which disturbs the transmitted waves and prevents
coherent summation of echo signals. Obtaining non-aberrated ground truths in
real-world scenarios can be extremely challenging, if not impossible. This
challenge hinders training of deep learning-based techniques' performance due
to the presence of domain shift between simulated and experimental data. Here,
for the first time, we propose a deep learning-based method that does not
require ground truth to correct the phase aberration problem, and as such, can
be directly trained on real data. We train a network wherein both the input and
target output are randomly aberrated radio frequency (RF) data. Moreover, we
demonstrate that a conventional loss function such as mean square error is
inadequate for training such a network to achieve optimal performance. Instead,
we propose an adaptive mixed loss function that employs both B-mode and RF
data, resulting in more efficient convergence and enhanced performance.
Finally, we publicly release our dataset, including 161,701 single plane-wave
images (RF data). This dataset serves to mitigate the data scarcity problem in
the development of deep learning-based techniques for phase aberration
correction.Comment: arXiv admin note: text overlap with arXiv:2303.0574
Ultrasound Matrix Imaging. I. The focused reflection matrix and the F-factor
This is the first article in a series of two dealing with a matrix approach
\alex{for} aberration quantification and correction in ultrasound imaging.
Advanced synthetic beamforming relies on a double focusing operation at
transmission and reception on each point of the medium. Ultrasound matrix
imaging (UMI) consists in decoupling the location of these transmitted and
received focal spots. The response between those virtual transducers form the
so-called focused reflection matrix that actually contains much more
information than a raw ultrasound image. In this paper, a time-frequency
analysis of this matrix is performed, which highlights the single and multiple
scattering contributions as well as the impact of aberrations in the
monochromatic and broadband regimes. Interestingly, this analysis enables the
measurement of the incoherent input-output point spread function at any pixel
of this image. A focusing criterion can then be built, and its evolution used
to quantify the amount of aberration throughout the ultrasound image. In
contrast to the standard coherence factor used in the literature, this new
indicator is robust to multiple scattering and electronic noise, thereby
providing a highly contrasted map of the focusing quality. As a
proof-of-concept, UMI is applied here to the in-vivo study of a human calf, but
it can be extended to any kind of ultrasound diagnosis or non-destructive
evaluation.Comment: 14 pages, 3 figure
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