Synchronous Temperature Variation Monitoring During Ultrasound Imaging and/or Treatment Pulse Application: A Phantom Study

Abstract

Ultrasound attenuation through soft tissues can produce an acoustic radiation force (ARF) and heating. The ARF-induced displacements and temperature evaluations can reveal tissue properties and provide insights into focused ultrasound (FUS) bio-effects. In this study, we describe an interleaving pulse sequence tested in a tissue-mimicking phantom that alternates FUS and plane-wave imaging pulses at a 1 kHz frame rate. The FUS is amplitude modulated, enabling the simultaneous evaluation of tissue-mimicking phantom displacement using harmonic motion imaging (HMI) and temperature rise using thermal strain imaging (TSI). The parameters were varied with a spatial peak temporal average acoustic intensity (<inline-formula> <tex-math notation= LaTeX >$I_{spta}$ </tex-math></inline-formula>) ranging from 1.5 to 311 W.cm⁻², mechanical index (MI) from 0.43 to 4.0, and total energy (<inline-formula> <tex-math notation= LaTeX >$E$ </tex-math></inline-formula>) from 0.24 to 83 J.cm⁻². The HMI and TSI processing could estimate displacement and temperature independently for temperatures below 1.80°C and displacements up to <inline-formula> <tex-math notation= LaTeX >$\\sim -117 \\mu {\\text{m}}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation= LaTeX >$I_{spta} < 311 \\text{ W.cm}^{-2}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation= LaTeX >$MI < 4.0$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation= LaTeX >$E < 83 \\text{ J.cm}^{-2}$ </tex-math></inline-formula>) indicated by a steady-state tissue-mimicking phantom displacement throughout the sonication and a comparable temperature estimation with simulations in the absence of tissue-mimicking phantom motion. The TSI estimations presented a mean error of ±0.03°C versus thermocouple estimations with a mean error of ±0.24°C. The results presented herein indicate that HMI can operate at diagnostictemperature levels (i.e., <1°C) even when exceeding diagnostic acoustic intensity levels (<inline-formula> <tex-math notation= LaTeX >$720 \\text{ mW.cm}^{-2} < I_{spta} < 207 \\text{ W.cm}^{-2}$ </tex-math></inline-formula>). In addition, the combined HMI and TSI can potentially be used for simultaneous evaluation of safety during tissue elasticity imaging as well as FUS mechanism involved in novel ultrasound applications such as ultrasound neuromodulation and tumor ablation.