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Assessment of the Viscoelastic and Oscillation Properties of a Nano-engineered Multimodality Contrast Agent
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
KTH, School of Technology and Health (STH), Medical Engineering, Medical Imaging.
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2014 (English)In: Ultrasound in Medicine and Biology, ISSN 0301-5629, Vol. 40, no 10, 2476-2487 p.Article in journal (Refereed) Published
Abstract [en]

Combinations of microbubbles (MBs) and superparamagnetic iron oxide nanoparticles (SPIONs) are used to fabricate dual contrast agents for ultrasound and MRI. This study examines the viscoelastic and oscillation characteristics of two MB types that are manufactured with SPIONs and either anchored chemically on the surface (MBs-chem) or physically embedded (MBs-phys) into a polymer shell. A linearized Church model was employed to simultaneously fit attenuation coefficients and phase velocity spectra that were acquired experimentally. The model predicted lower viscoelastic modulus values, undamped resonance frequencies and total damping ratios for MBs-chem. MBs-chem had a resonance frequency of approximately 13 MHz and a damping ratio of approximately 0.9; thus, MBs-chem can potentially be used as a conventional ultrasound contrast agent with the combined functionality of MRI detection. In contrast, MBs-phys had a resonance frequency and damping of 28 MHz and 1.2, respectively, and requires further modification of clinically available contrast pulse sequences to be visualized.

Place, publisher, year, edition, pages
2014. Vol. 40, no 10, 2476-2487 p.
Keyword [en]
Ultrasound contrast agent, Magnetic microbubbles, Fe3O4 nanoparticles, Harmonic oscillation, Viscoelastic properties
National Category
Medical Engineering
URN: urn:nbn:se:kth:diva-155796DOI: 10.1016/j.ultrasmedbio.2014.05.018ISI: 000343144400017ScopusID: 2-s2.0-84926200070OAI: diva2:763727
EU, FP7, Seventh Framework Programme, FP7-NMP-2009-LARGE-3

QC 20141117

Available from: 2014-11-17 Created: 2014-11-13 Last updated: 2015-08-26Bibliographically approved
In thesis
1. Nano-Engineered Contrast Agents: Toward Multimodal Imaging and Acoustophoresis
Open this publication in new window or tab >>Nano-Engineered Contrast Agents: Toward Multimodal Imaging and Acoustophoresis
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diagnostic ultrasound (US) is safer, quicker and cheaper than other diagnostic imaging modalities. Over the past two decades, the applications of US imaging has been widened due to the development of injectable, compressible and encapsulated microbubbles (MBs) that provide an opportunity to improve conventional echocardiographic imaging, blood flow assessment and molecular imaging. The encapsulating material is manufactured by different biocompatible materials such as proteins, lipids or polymers. In current research, researchers modify the encapsulated shell with the help of advanced molecular chemistry techniques to load them with dyes (for fluorescent imaging), nanoparticles and radioisotopes (for multimodal imaging) or functional ligands or therapeutic gases (for local drug delivery). The echogenicity and the radial oscillation of MBs is the result of their compressibility, which undoubtedly varies with the encapsulated shell characteristics such as rigidity or elasticity.

In this thesis, we present acoustic properties of novel type of polyvinyl alcohol (PVA)-shelled microbubble (PVA-MB) that was further modified with superparamagnetic iron oxide nanoparticles (SPIONs) to work as a dual-modal contrast agent for magnetic resonance (MR) imaging along with US imaging. Apparently, the shell modification changes their mechanical characteristics, which affects their acoustic properties. The overall objective of the thesis is to investigate the acoustic properties of modified and unmodified PVA-MBs at different ultrasound parameters.

The acoustic and mechanical characterization of SPIONs modified PVA-MBs revealed that the acoustical response depends on the SPION inclusion strategy. However they retain the same structural characteristics after the modification. The modified MBs with SPIONs included on the surface of the PVA shell exhibit a soft-shelled behavior and produce a higher echogenicity than the MBs with the SPIONs inside the PVA shell. The fracturing mechanism of the unmodified PVA-MBs was identified to be different from the other fracturing mechanisms of conventional MBs. With the interaction of high-pressure bursts, the air gas core is squeezed out through small punctures in the PVA shell. During the fracturing, the PVA-MBs exhibit asymmetric (other modes) oscillations, resulting in sub- and ultra-harmonic generation. Exploiting the US imaging at the other modes of the oscillation of the PVA-MBs would provide an opportunity to visualize very low concentrations of (down to single) PVA-MBs. We further introduced the PVA-MBs along with particles mimicking red blood cells in an acoustic standing-wave field to observe the acoustic radiation force effect. We observed that the compressible PVA-MBs drawn toward pressure antinode while the solid blood phantoms moved toward the pressure node. This acoustic separation method (acoustophoresis) could be an efficient tool for studying the bioclearance of the PVA-MBs in the body, either by collecting blood samples (in-vitro) or by using the extracorporeal medical procedure (ex-vivo) at different organs.

Overall, this work contributes significant feedback for chemists (to optimize the nanoparticle inclusion) and imaging groups (to develop new imaging sequences), and the positive findings pave new paths and provide triggers to engage in further research. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. x, 53 p.
TRITA-STH : report, ISSN 1653-3836 ; 2015:5
Nano-engineered microbubbles, SPION nanoparticles, Acoustic characterization of MBs, Fracturing mechanism of MBs, Opto-acoustics, Acoustophoresis
National Category
Medical Laboratory and Measurements Technologies Medical Image Processing Nano Technology Signal Processing Polymer Technologies
Research subject
Physics; Järnvägsgruppen - Ljud och vibrationer; Technology and Health
urn:nbn:se:kth:diva-172397 (URN)978-91-7595-648-0 (ISBN)
Public defence
2015-09-22, 3221, Alfred Nobels Álle 8, Hudding, 09:00 (English)
EU, FP7, Seventh Framework Programme, 245572

QC 20150827

Available from: 2015-08-26 Created: 2015-08-20 Last updated: 2015-08-27Bibliographically approved

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Kothapalli, Veeravenkata S.Brodin, Lars- ÅkeGrishenkov, Dmitry
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