Photoacoustics meets ultrasound: micro-Doppler photoacoustic effect and detection by ultrasound

TL;DR

This paper introduces the micro-Doppler photoacoustic effect, a novel interaction between photoacoustic waves and ultrasound, enabling sensitive detection of photoacoustic vibrations in scattering media.

Contribution

It reports the first experimental observation and modeling of the micro-Doppler photoacoustic effect resulting from simultaneous laser and ultrasound excitation.

Findings

Experimental observation of the micro-Doppler photoacoustic effect

Modeling of the frequency modulation mechanism

Potential for improved deep tissue imaging

Abstract

In recent years, photoacoustics has attracted intensive research for both anatomical and functional biomedical imaging. However, the physical interaction between photoacoustic generated endogenous waves and an exogenous ultrasound wave is a largely unexplored area. Here, we report the initial results about the interaction of photoacoustic and external ultrasound waves leading to a micro-Doppler photoacoustic (mDPA) effect, which is experimentally observed and consistently modelled. It is based on a simultaneous excitation on the target with a pulsed laser and continuous wave (CW) ultrasound. The thermoelastically induced expansion will modulate the CW ultrasound and leads to transient Doppler frequency shift. The reported mDPA effect can be described as frequency modulation of the intense CW ultrasound carrier through photoacoustic vibrations. This technique may open the possibility to sensitively detect the photoacoustic vibration in deep optically and acoustically scattering medium, avoiding acoustic distortion that exists in state-of-the-art pulsed photoacoustic imaging systems.