Investigation of the repeatability and reproducibility of hydrophone measurements of medical ultrasound fields

Eleanor Martin,Bradley Treeby

doi:10.1121/1.5093306

Abstract

Accurate measurements of acoustic pressure are required for characterisation of ultrasonic transducers and for experimental validation of models of ultrasound propagation. Errors in measured pressure can arise from a variety of sources, including variations in the properties of the source and measurement equipment, calibration uncertainty, and processing of measured data. In this study, the repeatability of measurements made with four probe and membrane hydrophones was examined. The pressures measured by these hydrophones in three different ultrasound fields, with both linear and nonlinear, pulsed and steady state driving conditions, were compared to assess the reproducibility of measurements. The coefficient of variation of the focal peak positive pressure was less than 2% for all hydrophones across five repeated measurements. When comparing hydrophones, pressures measured in a spherically focused 1.1 MHz field were within 7% for all except 1 case, and within 10% for a broadband 5 MHz pulse from a diagnostic linear array. Larger differences of up to 55% were observed between measurements of a tightly focused 3.3 MHz field, which were reduced for some hydrophones by the application of spatial averaging corrections. Overall, the major source of these differences was spatial averaging and uncertainty in the complex frequency response of the hydrophones.

Highlights

Accurate measurements of acoustic pressure are essential for characterisation of ultrasonic sources and for experimental validation of models of ultrasound propagation
If models of ultrasound propagation are to be used for treatment planning for applications such as transcranial ultrasonic neuromodulation,3 their accuracy must be validated to ensure that the amplitude and spatial distribution of acoustic pressure can be accurately known at the target location, ensuring that treatments are safe and effective
It has been shown that repeatable measurements can be made with a variety of hydrophones in a 1.1 MHz spherically focused ultrasound field with a beam width of 3 mm

Summary

Introduction

Accurate measurements of acoustic pressure are essential for characterisation of ultrasonic sources and for experimental validation of models of ultrasound propagation. For example, if models of ultrasound propagation are to be used for treatment planning for applications such as transcranial ultrasonic neuromodulation, their accuracy must be validated to ensure that the amplitude and spatial distribution of acoustic pressure can be accurately known at the target location, ensuring that treatments are safe and effective. If models of ultrasound propagation are to be used for treatment planning for applications such as transcranial ultrasonic neuromodulation, their accuracy must be validated to ensure that the amplitude and spatial distribution of acoustic pressure can be accurately known at the target location, ensuring that treatments are safe and effective. To begin this process of validation, an ultrasonic source is experimentally characterised, using acoustic holography for example, and supplied as an input to a computational model. Factors contributing to errors and uncertainty in the measured pressure are explored

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