Laser-induced ultrasound transmitters for large-volume ultrasound tomography

D Thompson,J.R Nagel,D.B Gasteau,S Manohar

doi:10.1016/j.pacs.2021.100312

Abstract

We present a protocol for the design, fabrication and characterisation of laser-induced ultrasound transmitters with a specific, user-defined frequency response for the purpose of ultrasound tomography of large-volume biomedical samples. Using an analytic solution to the photoacoustic equation and measurements of the optical and acoustic properties of the materials used in the transmitters, we arrive at a required mixture of carbon black and polydimethylsiloxane to achieve the desired frequency response. After an in-depth explanation of the fabrication and characterisation approaches we show the performance of the fabricated transmitter, which has a centre frequency of 0.9 MHz, 200% bandwidth and 45.8∘ opening angle, multi-kPa pressures over a large depth range in water.

Highlights

Laser-induced ultrasound (LIUS) for biomedical imaging applications has been an emerging field of study for the last two decades [1,2,3]
A LIUS transmitter, is an engineered optically absorbing object with a specific set of optical and mechanical properties to generate a desired ultrasound field depending on the ultrasound imaging application at hand
One method to efficiently illuminate such an array of LIUS transmitters sequentially could be through the use of a fibre-optic multiplexer based on a matrix of fibre inputs, selectively illuminated by a laser via galvanometer mirrors and a scanning lens, as we have presented in previous work [8]

Summary

Introduction

Laser-induced ultrasound (LIUS) for biomedical imaging applications has been an emerging field of study for the last two decades [1,2,3]. LIUS is preferred for minimally-invasive imaging applications e.g. interstitial imaging [6,7] owing to the ease with which transmitters can be miniaturised by coating the tip of an optical fibre to create an active element. Another advantage of using LIUS is the ability to avoid interelement crosstalk when independently exciting many closely spaced ultrasound sources [8,9,10,11], a feature of interest considering the current trend towards miniaturisation of ultrasound multi-element arrays. The potentially very broadband frequency response of LIUS transmitters [12,13] promises advances in the fields of acoustic microscopy and mesoscopy

Methods

Results

Conclusion