Broadband Ultrasonic Attenuation Estimation and Compensation With Passive Acoustic Mapping.

Michael D Gray,Constantin C Coussios

doi:10.1109/tuffc.2018.2866171

Abstract

Several active and passive techniques have been developed to detect, localize, and quantify cavitation activity during therapeutic ultrasound procedures. Much of the prior cavitation monitoring research has been conducted using lossless in vitro systems or small animal models in which path attenuation effects were minimal. However, the performance of these techniques may be substantially degraded by attenuation between the internal therapeutic target and the external monitoring system. As a further step toward clinical application of passive acoustic mapping (PAM), this paper presents methods for attenuation estimation and compensation based on broadband cavitation data measured with a linear ultrasound array. Soft tissue phantom experiment results are used to illustrate: 1) the impact of realistic attenuation on PAM; 2) the possibility of estimating attenuation from cavitation data; 3) cavitation source energy estimation following attenuation compensation; and 4) the impact of sound speed uncertainty on PAM-related processing. Cavitation-based estimates of attenuation were within 1.5%-6.2% of the values found from conventional through-transmission measurements. Tissue phantom attenuation reduced the PAM energy estimate by an order of magnitude, but array data compensation using the cavitation-based attenuation spectrum enabled recovery of the PAM energy estimate to within 2.9%-5.9% of the values computed in the absence of the phantom. Sound speed uncertainties were found to modestly impact attenuation-compensated PAM energies, inducing errors no larger than 28% for a 40-m/s path-averaged speed error. Together, the results indicate the potential to significantly enhance the quantitative capabilities of PAM for ensuring therapeutic safety and efficacy.

Highlights

T HE field of therapeutic ultrasound is achieving clinical translation for applications ranging from neuromodulation [1] to ultrasound-mediated drug delivery across the blood–brain barrier [2] or to solid tumors [3], [4]
The results of this study quantified the impact of attenuation on passive acoustic mapping (PAM)-based estimates of cavitation energy, showing that order of magnitude effects are possible in propagation paths as short as 4 cm
Correction of both diffraction and attenuation effects will be essential for quantitative comparison of PAM data from different patients with different target depths or if monitored with different arrays

Summary

Introduction

T HE field of therapeutic ultrasound is achieving clinical translation for applications ranging from neuromodulation [1] to ultrasound-mediated drug delivery across the blood–brain barrier [2] or to solid tumors [3], [4]. To reduce risk and improve treatment efficacy, several passive [5]–[10] and active [11]–[13] acoustic monitoring techniques have been developed, allowing localization and quantification of nonlinear acoustic emissions (including cavitation) from both targeted and off-target regions. Much of the passive acoustic mapping (PAM) algorithmic development. Manuscript received July 7, 2018; accepted August 15, 2018. Date of publication August 20, 2018; date of current version November 7, 2018.

Methods

Results

Discussion

Conclusion