590 research outputs found
Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography
Corneal collagen crosslinking (CXL) is commonly used to prevent or treat
keratoconus. Although changes in corneal stiffness induced by CXL surgery can
be monitored with non-contact dynamic optical coherence elastography (OCE) by
tracking mechanical wave propagation, depth dependent changes are still unclear
if the cornea is not crosslinked through the whole depth. Here,
phase-decorrelation measurements on optical coherence tomography (OCT)
structural images are combined with acoustic micro-tapping (AT) OCE to
explore possible reconstruction of depth-dependent stiffness within crosslinked
corneas in an ex vivo human cornea sample. Experimental OCT images are analyzed
to define the penetration depth of CXL into the cornea. In a representative ex
vivo human cornea sample, crosslinking depth varied from in the
periphery to in the cornea center and exhibited a sharp
in-depth transition between crosslinked and untreated areas. This information
was used in an analytical two-layer guided wave propagation model to quantify
the stiffness of the treated layer. We also discuss how the elastic moduli of
partially CXL-treated cornea layers reflect the effective engineering stiffness
of the entire cornea to properly quantify corneal deformation.Comment: Submitted to Biomedical Optics Express on June 13th 2023, Manuscript
ID: 497970 - Under Review. Manuscript, 10 pages / 6 figures / 2 tables.
Supplementary, 7 pages / 4 figure
Imaging of Shear Waves Induced by Lorentz Force in Soft Tissues
This study presents the first observation of elastic shear waves generated in
soft solids using a dynamic electromagnetic field. The first and second
experiments of this 5 study showed that Lorentz force can induce a displacement
in a soft phantom and that this displacement was detectable by an ultrasound
scanner using speckle-tracking algorithms. For a 100 mT magnetic field and a 10
ms, 100 mA peak-to-peak electrical burst, the displacement reached a magnitude
of 1 um. In the third experiment, we showed that Lorentz force can induce shear
waves in a phantom. A physical model 10 using electromagnetic and elasticity
equations was proposed. Computer simulations were in good agreement with
experimental results. The shear waves induced by Lorentz force were used in the
last experiment to estimate the elasticity of a swine liver sample
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Towards the identification of spatially resolved mechanical properties in tissues and materials: State of the art, current challenges and opportunities in the field of flow measurements
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This work is focused on optical methods that provide tomographic reconstructions of the structure
of materials and tissues. Phase information can also be used to measure 3-D displacement and strain fields
with interferometric sensitivity. Different approaches are presented, including recent developments in phase
contrast wavelength scanning interferometry and a combination of optical coherence tomography and digital
volume correlation to estimate elastic properties of synthetic phantoms and porcine corneas. Inversion
algorithms based on finite elements and the Virtual Fields Method (VFM) are used to extract mechanical
properties from the knowledge of the applied loads, geometry and measured deformation fields. Current
efforts into extending these methods into single shot techniques have the potential of expanding the range of
applications to study dynamic events such as micro-flows in engineering and biological systems in which
scattering particles are transported in a flow, e.g. tribology, microfluidic devices, cell migration or multiphase
flows
Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography
Collagen crosslinking of the cornea (CXL) is commonly employed to prevent or
treat keratoconus. Although the change of corneal stiffness induced by CXL
surgery can be monitored with non-contact dynamic Optical Coherence
Elastography (OCE) by tracking mechanical wave propagation, the depth
dependence of this change is still unclear if the cornea is not crosslinked
through the whole depth. Here we propose to combine phase-decorrelation
measurement applied to OCT structural images and acoustic micro-tapping
(AT) OCE to explore possible depth reconstruction of stiffness within
crosslinked corneas in an ex vivo human cornea sample. The analysis of
experimental OCT images is used to define the penetration depth of CXL into the
cornea, which varies from 100 in the periphery to 150
in the central area and exhibits a sharp transition between areas. This
information was used in a two-layer analytical model to quantify the stiffness
of the treated layer. We also discuss how the elastic moduli of partially
CXL-treated cornea layers reconstructed from OCE measurements reflect the
effective mechanical stiffness of the entire cornea to properly quantify
surgical outcome.Comment: Main: 10 Pages, 6 Figures Supplemental: 12 Pages, 3 Figure
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