Bilayer aberration-inducing gel phantom for high intensity focused ultrasound applications

Abstract

Aberrations induced by soft tissue inhomogeneities often complicate high-intensity focused ultrasound (HIFU) therapies. In this work, a bilayer phantom made from polyvinyl alcohol hydrogel and ballistic gel was built to mimic alternating layers of water-based and lipid tissues characteristic of an abdominal body wall and to reproducibly distort HIFU fields. The density, sound speed, and attenuation coefficient of each material were measured using a homogeneous gel layer. A surface with random topographical features was designed as an interface between gel layers using a 2D Fourier spectrum approach and replicating different spatial scales of tissue inhomogeneities. Distortion of the field of a 256-element 1.5 MHz HIFU array by the phantom was characterized through hydrophone measurements for linear and nonlinear beam focusing and compared to the corresponding distortion induced by an ex vivo porcine body wall of the same thickness. Both spatial shift and widening of the focal lobe were observed, as well as dramatic reduction in focal pressures caused by aberrations. The results suggest that the phantom produced levels of aberration that are similar to a real body wall and can serve as a research tool for studying HIFU effects as well as for developing algorithms for aberration correction.

Demystifying Regulating Active Rectifiers for Energy Harvesting Systems: A Tutorial Assisted by Verilog-A Models

“…It is worth noting that the mentioned gel allows to mimic the acoustic impedance of human tissues and the distance, d, between the transmitting and receiving device is assumed equal to 1.0 cm. Moreover, the tissue attenuation is estimated around 2 dB/cm•MHz [48], yielding an expected attenuation of about 4-5 dB. The experimental results in Fig.…”

Fluidic Ultrasound Generation for Non‐Destructive Testing

“…The sound velocity of this material is comparable to that in various tissues [64] and has been used for the fabrication of ultrasound phantoms. [65][66][67] The fourth material is cast polyamide PA6, a polymer that is often used as a reference case for ultrasonic testing. [68][69][70] Table 1 provides a summary of the specimens investigated.…”

“…Polyamide 6 206, 262, 312 Single block with the dimensions 206 mm × 262 mm × 312 mm 2635…2653 [ 68,75] 2645 Ballistic gel 145, 415 Single block with the dimensions 145 mm × 145 mm × 415 mm 1424…1470 [ 66,67,76] 1450 The actual velocity is calculated to be 156000 ms -1 . c) Peak-to-peak ratio (P2P) of the cross-correlation output.…”