Carneiro, Antônio Adilton Oliveira

Abstract Tissue-mimicking phantoms play a crucial role in evaluating new imaging modalities, simulating clinical scenarios, and ensuring the quality and reliability of imaging systems. Styrene–ethylene/butylene–styrene (SEBS) is an extremely stable and versatile material that has been recently used in ultrasound, elastography, and photoacoustic imaging across diverse applications. Despite its extensive use, a systematic viscoelastic characterization of different SEBS-based formulations reported in the literature, particularly using shear wave elastography (SWE), remains limited. To address this gap, this study investigates the viscoelastic properties of tissue-mimicking phantoms composed of SEBS, glycerol dispersions in SEBS gels, and mixtures of SEBS with low-density polyethylene (LDPE) in mineral oil, using gelatin phantoms as a reference for comparison. Viscoelastic parameters were estimated from shear wave velocity and attenuation dispersion curves using a Kelvin–Voigt model, based on SWE measurements with acoustic radiation force (ARF) excitation, shear plane-wave excitation, and complementary mechanical testing. SEBS-based phantoms exhibited broad, composition-dependent viscoelastic tunability. Increasing SEBS or LDPE content led to stiffer and more viscous responses, while glycerol primarily modulated viscosity and, at higher concentrations, also affected stiffness. Consistent and concordant values were obtained using both ARF and plane wave SWE techniques. The resulting stiffness (2–22 kPa) and viscosity (0.01–1.24 Pa⋅s) overlaps with the mechanical properties of several biological soft tissues, supporting use of these phantoms for SWE validation.

Shear wave dispersion ultrasound vibrometry (SDUV) has been introduced to use the dispersive nature of shear wave speed to locally estimate the material properties or tissue. Shear waves were created using a mechanical shaker and pulsed radiation force. Using the information from the phase one can estimate the shear velocity. A theoretical Voigt model allows us to find, at different frequencies (100–400 Hz), the viscosity and shear elasticity of the polymer gel dosimeter. The aim of this work was to perform the SDUV and mechanical vibrometry techniques to study the viscoelastic properties of absorbed dose phantoms. The experiments were performed using five phantoms of different absorbed doses varying 10 up to 50 Gy, while a nonirradiated phantom was kept as a control. The SDUV technique was performed using a pulsed radiation force to vibrate the gel provide by a confocal transducer with a focal depth of 70 mm, nominal frequency of 3 MHz. For the mechanical vibrometry and SDUV experiments, shear wave motion measurements were made with a commercial ultrasound machine with a research using a 10 MHz linear array transducer. The quantitative elasticity and viscosity results for these two experiments were compared.

This work introduces a new method based on acoustic radiation force and magnetic measurement for interrogating the mechanical properties of fluid and biological tissues. In this method, ultrasound radiation is used to exert a low-frequency (in kHz range) force on a rigid magnetized target immersed in a viscoelastic medium. In response, the target vibrates in a pattern determined by viscoelastic properties of medium. We report the relation between the magnetic field signal and the incident ultrasonic pressure field in terms of the mechanical parameters of the medium. Simulations were conducted to demonstrate a simple approach based on using amplitude-modulated ultrasound to generate a dynamic acoustic radiation force on a magnetic target. The magnetic field generated by vibration of this target is then obtained and used to estimate the radiation-force-induced displacement as a function of time. It was observed that the intensity of the dynamic component of the magnetic field caused by the acoustic excitation is high enough to be registered by a conventional magnetic sensor. This proposed methodology presents a powerful tool for evaluation of acoustic radiation force as well as the mechanical properties of soft material.