Radiation-force-based estimation of acoustic attenuation using harmonic motion imaging

Abstract

Tissue characterization such as attenuation estimation remains challenging but important. Attenuation represents the energy loss during wave propagation through biological tissues, thus affects both therapeutic and diagnostic ultrasound applications. In this study, a novel attenuation estimation approach was developed using radiation-force-based method of Harmonic Motion Imaging (HMI). The HMI set-up comprised of a forcing transducer (fcenter = 4.7 MHz, AM frequency = 25 Hz) in conjunction with a confocal pulse-echo transducer (fcenter = 7.5 MHz), with the former inducing tissue displacement and the latter simultaneously acquiring RF signals. Tissue displacements were estimated from the RF signals using a 1-D cross-correlation method (window size: 1 mm; overlap: 90%). 2D displacement images were obtained through raster-scan (10 × 10 mm2). A linear regression model was applied to the displacements at different depths for calculating attenuation. Gel phantoms with known attenuation (n = 5) (CIRS Inc.) and in vitro canine livers (n = 3) were tested. Results demonstrated that attenuations obtained from the phantoms showed good correlation (R2 ≈ 99%) with the independently obtained values (0.28–1.45 dB/cm/MHz) (13 ± 8% underestimated), while those from the canine liver were 0.32 ± 0.03 dB/cm/MHz, within the normal range reported in the literature (0.28–1.01 dB/cm/MHz) (Duck, Academic Press 1990). Future studies will entail attenuation measurements in pathological tissues and HIFU monitoring.