Photoacoustic clutter reduction by inversion of a linear scatter model using plane wave ultrasound measurements.

Hans-Martin Schwab,Martin F Beckmann,Georg Schmitz

doi:10.1364/boe.7.001468

Abstract

Photoacoustic imaging aims to visualize light absorption properties of biological tissue by receiving a sound wave that is generated inside the observed object as a result of the photoacoustic effect. In clinical applications, the strong light absorption in human skin is a major problem. When high amplitude photoacoustic waves that originate from skin absorption propagate into the tissue, they are reflected back by acoustical scatterers and the reflections contribute to the received signal. The artifacts associated with these reflected waves are referred to as clutter or skin echo and limit the applicability of photoacoustic imaging for medical applications severely. This study seeks to exploit the acoustic tissue information gained by plane wave ultrasound measurements with a linear array in order to correct for reflections in the photoacoustic image. By deriving a theory for clutter waves in k-space and a matching inversion approach, photoacoustic measurements compensated for clutter are shown to be recovered.

Highlights

In medical photoacoustic (PA) imaging, the observed tissue is illuminated by short light pulses, and the evolving sound waves, generated by photoacoustic energy conversion, are detected with conventional ultrasound transducers
Known as skin-echo, is a distortion of the received PA signal that originates in strong light absorption at the tissue surface, generating high amplitude waves that propagate into the tissue and are reflected by acoustical heterogeneities
Due to the high fluence at the irradiation area on the skin surface and the strong absorption of melanin in human skin, the amplitudes of the reflected clutter waves can overcome the amplitudes of the waves carrying the desired signal information

Summary

Introduction

In medical photoacoustic (PA) imaging, the observed tissue is illuminated by short light pulses, and the evolving sound waves, generated by photoacoustic energy conversion, are detected with conventional ultrasound transducers. The fact that reflected waves are shifted twice as much as direct PA waves during a tissue displacement induced by radiation force is exploited in [10] These approaches, based on decorrelation, have been shown to reduce the clutter artifacts effectively, but require additional mechanical setups or well-trained clinicians. The idea to exploit ultrasound measurements to retrieve information about the scattering behavior for clutter reduction has been assessed by Singh et al in [13]. This approach uses focused ultrasound that is emitted onto high intensities in the PA image to identify clutter artifacts. The proposed method has been implemented for both simulated and experimental measurement data and the capabilities of the method are presented below

Theory

PA wave reflection in the frequency domain

Inversion

Simulation

Experiment

Discussion and conclusions