Ultrasound contrast agents : dynamics of coated bubbles

Overvelde, Maria Levina Joanna

doi:10.3990/1.9789036530064

Cited by 8 publications

(21 citation statements)

References 136 publications

(425 reference statements)

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“…A comparison of the response of a functionalized bubble in the unbounded fluid with the response of an adherent bubble resulted in a decrease of over 50% of the frequency of maximum response for the adherent microbubble. The frequency of maximum response of a phospholipid-coated bubble floating up against an OptiCell wall was observed to decrease by only 20%, which is in excellent agreement with previously obtained results for bubble-wall interactions (Overvelde 2010a). This finding may prove useful for developing imaging protocols to discriminate between adherent and freely circulating bubbles.…”

Section: Discussionsupporting

confidence: 87%

“…1C). The results of a BG-6437 bubble at the wall and in free space were compared to confirm the influence of the boundary as discussed by Garbin et al (2007) and Overvelde (2010a). In the previous three experiments, the bubbles were injected in an uncoated OptiCell.…”

Section: Methodsmentioning

confidence: 91%

“…The much larger decrease of the frequency of maximum response for a bubble adherent to a wall can be interpreted as a much larger decrease in k=m. On the other hand, the OptiCell wall is compliant and cannot simply be modeled by a rigid wall model with an identical bubble oscillating in phase (Allen et al 2003;Overvelde 2010a). In particular, longitudinal modes of oscillations can be excited in a thin compliant wall.…”

Section: Discussionmentioning

confidence: 97%

“…With A 1 .0:15, the frequency of maximum response is hardly affected by the initial properties of the coating (Overvelde 2010a) and only the influence of the neighboring wall and adherence to the wall is investigated. We observe no influence of the targeting ligands on the dynamics of bubbles away from the wall, hence, no influence of the preparation protocol is expected on the behavior of the bubbles.…”

Section: Discussionmentioning

confidence: 99%

See 3 more Smart Citations

Dynamics of Coated Microbubbles Adherent to a Wall

Overvelde¹,

Garbin²,

Dollet³

et al. 2011

Ultrasound in Medicine & Biology

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Section: Discussionsupporting

confidence: 87%

Section: Methodsmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamics of Coated Microbubbles Adherent to a Wall

Overvelde¹,

Garbin²,

Dollet³

et al. 2011

Ultrasound in Medicine & Biology

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“…scattering cross section, and the radial time series, i.e., resonance frequency and radial excursion from equilibrium as a function of amplitude or phase of the oscillation. [4][5][6][7] In this fashion, a number of dynamic phenomena that were reported experimentally in association with pulsating contrast agents have been studied, such as the nonlinear reduction of resonance frequency 4,8 and the abrupt onset of radial vibrations as the sound amplitude increases, 4,9 the compression only and expansion only effects, 4,6,7,10,11 and the rich harmonic content of certain contrast agents at large amplitudes. 4,6,12 All the above effects can be recovered within the scope of radial symmetry, with the exception of compression only behavior that is most likely associated with a deformed bubble interface 7, 10 and the harmonic content that is enriched in the presence of shape modes 13, 14 buckling 14 and break-up.…”

Section: Introductionmentioning

confidence: 99%

Simulations of insonated contrast agents: Saturation and transient break-up

Tsigklifis

Pelekasis

2013

Physics of Fluids

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Under insonation contrast agents are known to perform nonlinear pulsations and deform statically, in the form of buckling, or dynamically via parametric mode excitation, and often exhibit jetting and break-up like bubbles without coating. Boundary element simulations are performed in the context of axisymmetry in order to establish the nonlinear evolution of these patterns. The viscoelastic stresses that develop on the coating form the dominant force balance tangentially to the shell-liquid interface, whereas the dynamic overpressure across the shell balances viscoelastic stresses in the normal direction. Strain softening and strain hardening behavior is studied in the presence of shape instabilities for various initial conditions. Simulations recover the pattern of static buckling, subharmonic/harmonic excitation, and dynamic buckling predicted by linear stability. Preferential mode excitation during compression is obtained supercritically for strain softening phospholipid shells while the shell regains its sphericity at expansion. It is a result of energy transfer between the emerging unstable modes and the radial mode, eventually leading to saturated oscillations of shape modes accompanied by asymmetric radial pulsations in favor of compression. Strain softening shells are more prone to sustain saturated pulsations due to the mechanical behavior of the shell. As the sound amplitude increases and before the onset of dynamic buckling, both types of shells exhibit transient break-up via unbalanced growth of a number of unstable shape modes. The effect of pre-stress in lowering the amplitude threshold for shape mode excitation is captured numerically and compared against the predictions of linear stability analysis. The amplitude interval for which sustained shape oscillations are obtained is extended, in the presence of pre-stress, by switching from a strain softening constitutive law to a strain hardening one once the shell curvature increases beyond a certain level. This type of mechanical behavior models the formation of lipid bilayer structures on the shell beyond a certain level of bending, as a result of a lipid monolayer folding transition. In this context a compression only type behavior is obtained in the simulations, which is accompanied by preferential shape deformation during compression at relatively small sound amplitudes in a manner that bears significance on the interpretation of available experimental observations exhibiting similar dynamic behavior.

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Dynamic simulation of a coated microbubble in an unbounded flow: response to a step change in pressure

Vlachomitrou

Pelekasis

2017

J. Fluid Mech.

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A numerical method is developed to study the dynamic behaviour of an encapsulated bubble when the viscous forces of the surrounding liquid are accounted for. The continuity and Navier–Stokes equations are solved for the liquid, whereas the coating is described as a viscoelastic shell with bending resistance. The Galerkin Finite Element Methodology is employed for the spatial discretization of the flow domain surrounding the bubble, with the standard staggered grid arrangement that uses biquadratic and bilinear Lagrangian basis functions for the velocity and pressure in the liquid, respectively, coupled with a superparametric scheme with $B$-cubic splines as basis functions pertaining to the location of the interface. The spine method and the elliptic mesh generation technique are used for updating the mesh points in the interior of the flow domain as the shape of the interface evolves with time, with the latter being distinctly superior in capturing severely distorted shapes. The stabilizing effect of the liquid viscosity is demonstrated, as it alters the amplitude of the disturbance for which a bubble deforms and/or collapses. For a step change in the far-field pressure the dynamic evolution of the microbubble is captured until a static equilibrium is achieved. Static shapes that are significantly compressed are captured in the post-buckling regime, leading to symmetric or asymmetric shapes, depending on the relative dilatation to bending stiffness ratio. As the external overpressure increases, shapes corresponding to all the solution families that were captured evolve to exhibit contact as the two poles approach each other. Shell viscosity prevents jet formation by relaxing compressive stresses and bending moments around the indentation generated at the poles due to shell buckling. This behaviour is conjectured to be the inception process leading to static shapes with contact regions.

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Ultrasound contrast agents : dynamics of coated bubbles

Cited by 8 publications

References 136 publications

Dynamics of Coated Microbubbles Adherent to a Wall

Dynamics of Coated Microbubbles Adherent to a Wall

Simulations of insonated contrast agents: Saturation and transient break-up

Dynamic simulation of a coated microbubble in an unbounded flow: response to a step change in pressure

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