Feasibility of micro-elastography for tissue surrounding phase-change microbubbles using bubble wavelet transform

Pathological states of soft tissue are usually correlated with changes in its mechanical properties. Currently, several sonoelastographic methods have been developed to evaluate the elastic properties. However, applicability of sonoelastography for small targets such as tissues surrounding tumor angiogenesis, is limited because of poor resolution and difficulty in producing detectable strain by external induction or internal physiological fluctuations. We propose to explore the possibility of quantifying the viscoelastic properties of soft tissues through phase-change microbubble (PCMB) dynamic in tissue and bubble wavelet transform detection method. A mother wavelet named “PCMB wavelet” was constructed according to the modified Yang-Church equation, and also expected to obtain a high correlation with echoes backscattered from the PCMBs. A transparent homogeneous tissue-mimicking polyacrylamide phantom containing nanoparticles of perfluoropentane was built. The comparison of contrast-to-tissue ratio among the images processed by continuous wavelet transform with “PCMB wavelet” of different shear elasticity and viscosity revealed the viscoelastic properties of the phantoms. The values of shear elasticity and viscosity of different kinds of phantoms were compared. This technique demonstrated the possibility to quantify the viscoelastic properties.