1,232 research outputs found
Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study
Quantitative, non-invasive and local measurements of arterial mechanical
properties could be highly beneficial for early diagnosis of cardiovascular
disease and follow up of treatment. Arterial shear wave elastography (SWE)
and wave velocity dispersion analysis have previously been applied to
measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D)
vary with age and pathology and may influence the shear wave propagation.
Nevertheless, the effect of arterial geometry in SWE has not yet been
systematically investigated. In this study the influence of geometry on the
estimated mechanical properties of plates (h = 0.5–3 mm) and hollow
cylinders (h = 1, 2 and 3 mm, D = 6 mm) was assessed by experiments in
phantoms and by finite element method simulations. In addition, simulations
in hollow cylinders with wall thickness difficult to achieve in phantoms
were performed (h = 0.5–1.3 mm, D = 5–8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency
range 200–1000 Hz and showed good agreement (R2 = 0.80 ± 0.07 for plates
and R2 = 0.82 ± 0.04 for hollow cylinders). Wall thickness had a larger effect
than diameter on the dispersion curves, which did not have major effects above
400 Hz. An underestimation of 0.1–0.2 mm in wall thickness introduces an
error 4–9 kPa in hollow cylinders with shear modulus of 21–26 kPa. Therefore,
wall thickness should correctly be measured in arterial SWE applications for
accurate mechanical properties estimation
Contactless Remote Induction of Shear Waves in Soft Tissues Using a Transcranial Magnetic Stimulation Device
This study presents the first observation of shear wave induced remotely
within soft tissues. It was performed through the combination of a transcranial
magnetic stimulation device and a permanent magnet. A physical model based on
Maxwell and Navier equations was developed. Experiments were performed on a
cryogel phantom and a chicken breast sample. Using an ultrafast ultrasound
scanner, shear waves of respective amplitude of 5 and 0.5 micrometers were
observed. Experimental and numerical results were in good agreement. This study
constitutes the framework of an alternative shear wave elastography method
Kelvin–Voigt Parameters Reconstruction of Cervical Tissue-Mimicking Phantoms Using Torsional Wave Elastography
The reconstruction of viscous properties of soft tissues, and more specifically, of cervical
tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the
viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography
(TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP)
approach, is presented and experimentally validated against Shear Wave Elastography (SWE).
The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom
that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were
fabricated at different proportion to test the new reconstruction technique. The PIP approach was used
for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements
obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain
(FDTD) KV wave propagation model. Additionally, SWE tests were realized in order to characterize
the viscoelastic properties of each batch of gelatine. Finally, validation was carried out by comparing
the KV parameters inferred from the PIP with those reconstructed from the shear wave dispersion
curve obtained from the SWE measurements. In order to test the degree of agreement between
both techniques, a Student’s T-test and a Pearson’s correlation study were performed. The results
indicate that the proposed method is able to reconstruct the KV viscoelastic properties of the cervical
tissue, for both the epithelial and connective layers, as well as the thickness of the first layer with
acceptable accuracy.This research was supported by the Ministry of Education, DPI2017-83859-R, DPI2014-51870-R, and
UNGR15-CE-3664, Ministry of Health DTS15/00093, and Junta de AndalucĂa PI16/00339, PI-0107-2017, and
PIN-0030-2017 projects
Feasibility of optical coherence elastography measurements of shear wave propagation in homogeneous tissue equivalent phantoms
In this work, we explored the potential of measuring shear wave propagation using optical coherence elastography (OCE) based on a swept-source optical coherence tomography (OCT) system. Shear waves were generated using a 20 MHz piezoelectric transducer (circular element 8.5 mm diameter) transmitting sine-wave bursts of 400 ÎĽs, synchronized with the OCT swept source wavelength sweep. The acoustic radiation force (ARF) was applied to two gelatin phantoms (differing in gelatin concentration by weight, 8% vs. 14%). Differential OCT phase maps, measured with and without the ARF, demonstrate microscopic displacement generated by shear wave propagation in these phantoms of different stiffness. We present preliminary results of OCT derived shear wave propagation velocity and modulus, and compare these results to rheometer measurements. The results demonstrate the feasibility of shear wave OCE (SW-OCE) for high-resolution microscopic homogeneous tissue mechanical property characterization
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
Dual-Probe Shear Wave Elastography in a Transversely Isotropic Phantom
This project aimed to evaluate the possibility of obtaining a full mechanical characterization of a transversely isotropic (TI) phantom with dual-probe SWE. A TI phantom was developed and mechanical tests were performed to verify its anisotropy. Moreover, multiple wave propagation modes calculated with dual-probe SWE showed a good agreement with the theoretical curves and indicated the possibility of measuring all the elasticity constants needed to fully characterize a TI tissueope
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
Performance Study of a Torsional Wave Sensor and Cervical Tissue Characterization
A novel torsional wave sensor designed to characterize mechanical properties of soft tissues is presented in this work. Elastography is a widely used technique since the 1990s to map tissue stiffness. Moreover, quantitative elastography uses the velocity of shear waves to achieve the shear stiffness. This technique exhibits significant limitations caused by the difficulty of the separation between longitudinal and shear waves and the pressure applied while measuring. To overcome these drawbacks, the proposed torsional wave sensor can isolate a pure shear wave, avoiding the possibility of multiple wave interference. It comprises a rotational actuator disk and a piezoceramic receiver ring circumferentially aligned. Both allow the transmission of shear waves that interact with the tissue before being received. Experimental tests are performed using tissue mimicking phantoms and cervical tissues. One contribution is a sensor sensitivity study that has been conducted to evaluate the robustness of the new proposed torsional wave elastography (TWE) technique. The variables object of the study are both the applied pressure and the angle of incidence sensor–phantom. The other contribution consists of a cervical tissue characterization. To this end, three rheological models have fit the experimental data and a static independent testing method has been performed. The proposed methodology permits the reconstruction of the mechanical constants from the propagated shear wave, providing a proof of principle and warranting further studies to confirm the validity of the results.This research was supported by the Ministry of Education DPI2014-51870-R, DPI2010-17065 and UNGR15-CE-3664, Ministry of Health DTS15/00093 and PI16/00339, and Junta de AndalucĂa P11-CTS-8089 projects. Modesto T. LĂłpez-LĂłpez acknowledges financial support by the project FIS2013-41821-R (Ministry of Economy and Competitiveness, co-funded by the ERDF, European Union). We acknowledge the collaboration of the members of the Anatomical Pathology Unit of the University Hospital Complex of Granada. Finally, Antonio Callejas is grateful to the University of Granada for the award of an PhD fellowship
Viscoelastic Biomarkers of Ex Vivo Liver Samples via TorsionalWave Elastography
We thank the Department of Electronics and Computer Technology of the University of Granada for assistance with the electronic system of the torsional wave sensor.The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of soft tissue in order to quantify the tissue condition and to be able to track its consistency. Torsional Wave Elastography (TWE) is an emerging technique proposed for interrogating soft tissue mechanical viscoelastic constants. Torsional waves are a particular configuration of shear waves, which propagate asymmetrically in-depth and are radially transmitted by a disc and received by a ring. This configuration is shown to be particularly efficient in minimizing spurious p-waves components and is sensitive to mechanical constants, especially in cylinder-shaped organs. The objective of this work was to validate (TWE) technique against Shear Wave Elasticity Imaging (SWEI) technique through the determination of shear wave velocity, shear moduli, and viscosity of ex vivo chicken liver samples and tissue mimicking hydrogel phantoms. The results of shear moduli for ex vivo liver tissue vary 1.69–4.0kPa using TWE technique and 1.32–4.48kPa using SWEI technique for a range of frequencies from 200 to 800Hz. Kelvin–Voigt viscoelastic parameters reported values of ÎĽ = 1.51kPa and η = 0.54Pa·s using TWE and ÎĽ = 1.02kPa and η = 0.63Pa·s using SWEI. Preliminary results show that the proposed technique successfully allows reconstructing shear wave velocity, shear moduli, and viscosity mechanical biomarkers from the propagated torsional wave, establishing a proof of principle and warranting further studies.This research was funded by the Ministry of Education grant numbers DPI2017-83859-R, DPI2014-51870-R, and UNGR15-CE-3664; Ministry of Health grant numbers DTS15/00093 and PI16/00339 Carlos III Instituto de Salud y Fondos Feder; and Junta de AndalucĂa grant numbers, PI-0107-2017 and PIN-0030-2017. Juan de la Cierva IncorporaciĂłn IJC2018-037167-I
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