37 research outputs found
Logical Inference for Model-Based Reconstruction of Ultrasonic Nonlinearity
Quantifying the constitutive nonlinearity parameter β in fluids is of key interest for understanding ultrasonic propagation and its wide implications in medical and industrial applications. However, current methods for ultrasonically measuring it show large limitations in that the signal is only valid at a reduced and unjustified spatial range away from the transducer. This is not consistent with the fact that β should be constant everywhere in the fluid and independently of the ultrasonic experimental setup. To overcome this, the nonlinear wave propagation equations are rigorously derived and the ensuing differential equation is numerically solved. As a second contribution, the experimental and model information sources are treated under the information theory context to probabilistically reconstruct β, providing not only its value, but also the degree of confidence on it given both sources of data. This method is satisfactorily validated testing the repeatability of β in water varying distances, energies, frequencies, and transducer setups, yielding values compatible with β= 3.5.The authors acknowledge the Spanish Ministerio de Economia y Competitividad for Projects DPI2010-17065 and DPI2014-51870-R and Junta de AndalucĂa for Projects P11-CTS-8089 and GGI3000IDIB
Experimental Configuration to Determine the Nonlinear Parameter β in PMMA and CFRP with the Finite Amplitude Method
Parameters to measure nonlinearity in polymethylmethacrylate (PMMA) and carbon fiber
reinforced polymer (CFRP) materials have been determined with nonlinear ultrasound (NLUS). The
nonlinear parameter b has been determined using the variation of the Finite Amplitude Method
(FAM) with harmonic generation. Using this as a reference, the first contribution of this work consists
of deducting the experimental configuration necessary to measure this nonlinear parameter in a
correct and feasible way. Excitation level, frequency of the wave generated, number of cycles analysed
and the distances transducer-specimen and specimen-hydrophone have been determined in both
materials. The second contribution is a semi-analytical model that allows to obtain the nonlinear
parameter in materials by removing water contribution and considering geometric and viscous
attenuation, using the data obtained in an immersion tank. Finally, an application of this model has
been carried out in PMMA in order to determinate the nonlinear parameter in this material. From
the results, we confirm that the configuration determined in this paper to obtain the parameter β
decreases the noise in the measurements.This research was funded by the Ministry of Education DPI2017-83859-R
Wave Propagation in a Fractional Viscoelastic Tissue Model: Application to Transluminal Procedures
In this article, a wave propagation model is presented as the first step in the development
of a new type of transluminal procedure for performing elastography. Elastography is a medical
imaging modality for mapping the elastic properties of soft tissue. The wave propagation model is
based on a Kelvin Voigt Fractional Derivative (KVFD) viscoelastic wave equation, and is numerically
solved using a Finite Difference Time Domain (FDTD) method. Fractional rheological models, such as
the KVFD, are particularly well suited to model the viscoelastic response of soft tissue in elastography.
The transluminal procedure is based on the transmission and detection of shear waves through the
luminal wall. Shear waves travelling through the tissue are perturbed after encountering areas of
altered elasticity. These perturbations carry information of medical interest that can be extracted by
solving the inverse problem. Scattering from prostate tumours is used as an example application to
test the model. In silico results demonstrate that shear waves are satisfactorily transmitted through the
luminal wall and that echoes, coming from reflected energy at the edges of an area of altered elasticity,
which are feasibly detectable by using the transluminal approach. The model here presented provides
a useful tool to establish the feasibility of transluminal procedures based on wave propagation and
its interaction with the mechanical properties of the tissue outside the lumen.University College London, United KingdomTalentia scholarship (grant C2012H-75146405T-1)
from the regional government of Andalusia, Spainthe Ministry of Education and Science, Spain,
grants DPI2017-83859-R, EQC2018-004508-P and UNGR15-CE3664Andalusia, Spain, grants SOMM17/6109/UGR, B-TEP-026-UGR18, IE2017-5537 and P18-RT-165
Reverse Time Migration and Genetic Algorithms combined for reconstruction in transluminal shear wave elastography: An in silico case study
A new reconstruction approach that combines Reverse Time Migration (RTM) and Genetic Algorithms
(GAs) is proposed for solving the inverse problem associated with transluminal shear wave elastography.
The transurethral identification of the first thermal lesion generated by transrectal High Intensity Focused
Ultrasound (HIFU) for the treatment of prostate cancer, was used to preliminarily test in silico the combined
reconstruction method. The RTM method was optimised by comparing reconstruction images from several
cross-correlation techniques, including a new proposed one, and different device configurations in terms of
the number and arrangement of emitters and receivers of the conceptual transurethral probe. The best results
were obtained for the new proposed cross-correlation method and a device configuration with 3 emitters and
32 receivers. The RTM reconstructions did not completely contour the shape of the HIFU lesion, however, as
planned for the combined approach, the areas in the RTM images with high level of correlation were used
to narrow down the search space in the GA-based technique. The GA-based technique was set to find the
location of the HIFU lesion and the increment in stiffness and viscosity due to thermal damage. Overall, the
combined approach achieves lower level of error in the reconstructed values, and in a shorter computational
time, compared to the GA-based technique alone. The lowest errors were accomplished for the location of HIFU
lesion, followed by the contrast ratio of stiffness between thermally treated tissue and non-treated normal
tissue. The homologous ratio of viscosity obtained higher level of error. Further investigation considering
diverse scenarios to be reconstructed and with experimental data is required to fully evaluate the feasibility
of the combined approach.Talentia scholarship C2012H-
75146405T-1 from the regional government of AndalusiaMinistry of Science
and Innovation, grants PID2020-115372RB-I00 and PDC2021-
120945-I00Regional government of Andalusia, grants
B-TEP-026-UGR18 and P18-RT-1653University of Granada
PPJIA2022-2
Experimental evidence of shear waves in fractional viscoelastic rheological models
The authors want to acknowledge the Fluids Mechanics Research Group from University of Jaen for the use of their facilities and support, Miguel Riveiro for his assistance in the signal generation, and Lydia Fernandez for her collaboration in the phantom fabrication. The first author was supported by a Talentia scholarship (Grant C2012H-75146405T-1) from the regional government of Andalusia, Spain, for the two first years of his PhD programme at University College London, United Kingdom. The other 2 years of his PhD programme he was supported by the Mechanical Engineering Department of University College London, United Kingdom. Other minor financial support was provided by the Ministry of Education and Science, Spain, Grants DPI2017-83859-R, EQC2018-004508-P, UNGR15-CE3664, PID2020-115372RB-I00 and PDC2021-120945-I00, and by the regional government of Andalusia, Spain, grants SOMM17/6109/UGR, B-TEP-026-UGR18, IE2017-5537 and P18-RT-1653.Fractional viscoelastic rheological models, such as the Kelvin Voigt Fractional Derivative model,
have been proposed in the literature for modelling shear wave propagation in soft tissue. In this
article, our previously developed wave propagation model for transluminal propagation based on
a Kelvin Voigt Fractional Derivative wave equation is experimentally validated. The transluminal
procedure uses the transmission and detection of shear waves through the luminal wall. The model
was compared against high-speed camera observations in translucent elastography phantoms with
similar viscoelastic properties to prostate tissue. An ad hoc cross-correlation procedure was used to
reconstruct the angular displacement from the high-speed camera observations. Rheometry and
shear wave elastography were used for characterising the shear wave velocity dispersion curve for
the phantoms. Fractional viscoelastic properties were derived after fitting the dispersion curve to its
analytical expression. Propagation features and amplitude spectra from simulations and high-speed
camera observations were compared. The obtained results indicate that the model replicates the
experimental observations with acceptable accuracy. The model presented here provides a useful tool
to model transluminal procedures based on wave propagation and its interaction with the mechanical
properties of the tissue outside the lumen.Talentia scholarship from the regional government of Andalusia, Spain C2012H-75146405T-1Mechanical Engineering Department of University College London, United KingdomSpanish Government DPI2017-83859-R
EQC2018-004508-P
UNGR15-CE3664
PID2020-115372RB-I00
PDC2021-120945-I00Junta de Andalucia SOMM17/6109/UGR
B-TEP-026-UGR18
IE2017-5537
P18-RT-165
Logical Inference Framework for Experimental Design of Mechanical Characterization Procedures
Optimizing an experimental design is a complex task when a model is required for indirect
reconstruction of physical parameters from the sensor readings. In this work, a formulation is
proposed to unify the probabilistic reconstruction of mechanical parameters and an optimization
problem. An information-theoretic framework combined with a new metric of information density
is formulated providing several comparative advantages: (i) a straightforward way to extend
the formulation to incorporate additional concurrent models, as well as new unknowns such as
experimental design parameters in a probabilistic way; (ii) the model causality required by Bayes’
theorem is overridden, allowing generalization of contingent models; and (iii) a simpler formulation
that avoids the characteristic complex denominator of Bayes’ theorem when reconstructing model
parameters. The first step allows the solving of multiple-model reconstructions. Further extensions
could be easily extracted, such as robust model reconstruction, or adding alternative dimensions to
the problem to accommodate future needs.This research was supported by the Ministry of Education DPI2014-51870-R, DPI2017-85359-R and
UNGR15-CE-3664, Ministry of Health DTS15/00093 and PI16/00339, and Junta de AndalucĂa PIN-0030-2017 and
PI-0107-2017 projects, and university of Granada PP2017-PIP2019
A Preliminary Study on the Safety of Elastography during Pregnancy: Hypoacusia, Anthropometry, and Apgar Score in Newborns
Transient or acoustic radiation force elastography (ARFE) is becoming the most extended
technology to assess cervical effacement, additionally to the Bishop test and conventional ultrasound.
However, a debate on the fetal safety has been opened due to the high intensity focused beam emitted
to produce shear waves. This work is aimed at providing preliminary data to assess clinical effects of
fetal exposure. A follow-up study in newborns of 42 women exposed to ARFE during pregnancy
was carried out to explore neonatal hypoacusia, Apgar test, and anthropometry. No hypoacusia
cases attributable to ARFE were observed. The Apgar test at five minutes scored normally in all the
newborns. Comparisons between anthropometric measurements showed no significant statistically
differences. The results preclude to state the harmfulness nor the safety of ARFE. However, given
the concern on the high level of energy and the potential risk of harmful bioeffects, larger studies
are recommended.Ministry of Education
DPI2017-85359-R
UNGR15-CE-3664
PI16/00339Carlos III Feder fundJunta de AndalucĂa
PIN-0030-2017
PI-0107-2017Spanish Government
TEC2014-57394-PMNat Scientific Unit of Excellence
UCE.PP2017.0
Braiding Thermoplastic and Glass Fibers in Composite Dental Post Improves Their Mechanical Compatibility, In Vitro Experiment
Mechanical compatibility with the human dentin is a considerable issue when fabricating
dental fiber posts. To this purpose, this study introduces a new method of fabricating compatible dental posts using braiding techniques of thermoplastic fibers (matrix) with glass fibers (reinforcement).
Fifty fiber-reinforced composite (FRC) posts of thermoplastic yarns polypropylene (PP) braided with
continuous filaments glass fibers (GFs) for reinforcement, varying in fiber volume fraction (FVF), and
core types are fabricated and tested. Posts are performed using a braiding machine, and braids are
placed in an aluminum mold. The filled mold is playced inside an oven at the melting temperature
of the polypropylene to produce the final post’s shape. An ultrasonic test is conducted to measure
the shear modulus and Young’s modulus of FRC post specimens by measuring the velocities of
both the P-wave and S-wave. In order to ensure the accuracy of the measurements, each sample is
measured three times, and then the means and standard deviations of each sample are calculated
before analyzing the test results using the means of two steps, namely, clustering and comparing the
P and R² values of each cluster, which revealed that FVF, fiber mass, and core type of the specimen
had a significant effect on the resulted Young’s and shear modulus. The results indicate that the
proposed method can fabricate competitive dental posts with regard to different fabricating variables.
The samples show Young’s modulus ranges of from 10.08 GPa to 31.83 GPa. The following tested
hypothesis is supported: the braiding technique of thermoplastic fibers with glass fibers will improve
the mechanical compatibility of the resulting posts (ex vivo).Ministry of Science and Innovation, Spain grant numbers
DPI2017-83859-R, PID2019-106947RA-C22(FEDER) EQC2018-004508-PMinistry of Health,
Spain, grant number PI16/00339Junta de AndalucĂa IE2017-5537 and PI-0107-201Erasmus
Experimental Evidence of Generation and Reception by a Transluminal Axisymmetric Shear Wave Elastography Prototype
Experimental evidence on testing a non-ultrasonic-based probe for a new approach in
transluminal elastography was presented. The proposed modality generated shear waves by inducing
oscillatory rotation on the lumen wall. Detection of the propagated waves was achieved at a set of
receivers in mechanical contact with the lumen wall. The excitation element of the probe was an
electromagnetic rotational actuator whilst the sensing element was comprised by a uniform anglewise
arrangement of four piezoelectric receivers. The prototype was tested in two soft-tissue-mimicking
phantoms that contained lumenlike conduits and stiffer inclusions. The shear wave speed of the
different components of the phantoms was characterized using shear wave elastography. These values
were used to estimate the time-of-flight of the expected reflections. Ultrafast ultrasound imaging,
based on Loupas’ algorithm, was used to estimate the displacement field in transversal planes to the
lumenlike conduit and to compare against the readouts from the transluminal transmission–reception
tests. Experimental observations between ultrafast imaging and the transluminal probe were in good
agreement, and reflections due to the stiffer inclusions were detected by the transluminal probe. The
obtained experimental evidence provided proof-of-concept for the transluminal elastography probe
and encouraged further exploration of clinical applications.Ministry of Education grant numbers EQC2018-004508-
P, DPI2017-83859-R, and UNGR15-CE-3664Ministry of Health grant numbers DTS15/00093 and
PI16/00339, and Junta de AndalucĂa grant numbers, PI-0107-2017 and PIN-0030-2017, and B-TEP-026-
UGR18, IE2017-5537, P18-RT-1653 (Junta de AndalucĂa)ConsejerĂa de EconomĂa, Conocimiento,
Empresas y UniversidadEuropean Regional Development Fund (ERDF) SOMM17/6109/UG