Tuning Viscoelasticity with Minor Changes in Speed of Sound in an Ultrasound Phantom Material

Research output: Contribution to journalArticle

Abstract

The acoustic properties of ultrasound phantom materials have always been important, but with new applications interrogating tissue mechanical properties, viscoelasticity has also become an interesting feature to consider. Along with Young's modulus, the viscous component of tissue is affected by certain diseases and can therefore be used as a biomarker. Furthermore, viscoelasticity varies between tissue types and individuals, and therefore it would be useful with a phantom material that reflects this physiological range. Here we describe a gel for ultrasound imaging with a range of mechanical properties given by mixing different ratios of two oil-based gels, clear ballistic and styrene-ethylene/butylene-styrene (SEBS). The gels were mixed in five different proportions, ranging from 0-100% of either gel. For each of the gel compositions, we measured time of flight to determine speed of sound, narrowband ultrasound transmission for attenuation, stress-relaxation for viscoelasticity, mass and volume. Analysis of the stress-relaxation data using the generalized Maxwell model suggests that the material can be described by five parameters, E0, E1, E2, η1 and η2, and that each of these parameters decreases as more SEBS is incorporated into the mixed material. Instantaneous Young's modulus (the sum of E0, E1 and E2 in our model) ranges between 49 and 117 kPa for the different ratios, similar to values reported for cancerous tissue. Despite the large span of obtainable mechanical properties, speed of sound is relatively constant regardless of composition, with mean value estimates (± 95 % CI) between 1438 ± 9 and 1455 ± 3 m/s for pure and mixed gels. This was attributed to a variation in density and Poisson's ratio, following from the relation linking them to speed of sound and elasticity. Furthermore, both speed of sound and attenuation were within a suitable range for ultrasound phantoms. Combining this ballistic gel with SEBS copolymer in oil allows for control of mechanical properties, both elastic and viscous as evaluated by the material model. Furthermore, it does so without compromising ease of use, longevity and safety of the pre-made gel.

Details

Authors
Organisations
External organisations
  • University of São Paulo
  • Lund University
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Medical Biotechnology

Keywords

  • Phantom, Longevity, Young's Modulus, Tunable, Clear ballistic, Styrene–ethylene/butylene–styrene, SEBS, Ultrasound, Generalized Maxwell model
Original languageEnglish
Pages (from-to)2070-2078
Number of pages8
JournalUltrasound in Medicine and Biology
Volume46
Issue number8
Early online date2020 May 15
Publication statusPublished - 2020 Aug
Publication categoryResearch
Peer-reviewedYes