Electromagnetic-Acoustic (EMA) imaging of stiffness and dielectric properties in gels

Abstract

Here we present a novel multi-modal imaging method, electromagnetic- acoustics (EMA) that combines acoustic radiation force and electromagnetic scattering. Experiments were carried out in gels using a focused megahertz ultrasound source, amplitude modulated at 160 Hz, to create an oscillating radiation force resulting in vibration of the gel in the focal region. At the same time a 434 MHz EM signal was transmitted into the gel and the backscattered EM signal recorded. The tissue that was in motion resulted in a Doppler shift of the EM signal which manifested itself as frequency modulation of the EM wave. The modulated component was detected by means of a demodulator and lock-in amplifier and the amplitude of the modulated signal we call the EMA signal. By steering the ultrasound beam trough the sample an EMA image can be created which has spatial resolution of the ultrasound but is sensitive to shear and dielectric properties. We show that the EMA signal is sensitive to changes in elasticity in a gel and conductivity in a sheep kidney. EMA may have utility in biomedical imaging by detecting diseases which have contrast in dielectric properties without the cost and complexity of an magnetic resonance imaging system. © 2013 Acoustical Society of America.