Mechanism of contrast-enhancement in ultrasound-modulated laser feedback imaging with ultrasonicmicrobubble contrast agent

Abstract

Ultrasound-modulated optical imaging technology is a new type of biological tissue optical detection technology, and sensitive to the change of scattering coefficient and absorption coefficient of biological tissue. This technology is a non-ionizing and non-invasive pathological detection method, which has great potential application in early detection of cancer. However, ultrasound-modulated optical imaging technology is insufficient in signal-to-noise ratio (SNR) and imaging contrast. Frequency-shifted laser feedback technology with microchip laser is a new type of highly sensitive interference technology, whose gain coefficient for weak optical signal can reach 10<sup>6</sup>. This technology can greatly improve the SNR of imaging. Combined with the high sensitive laser feedback technology, the ultrasound-modulated laser feedback technology is proposed. The SNR of this technology is better than that of the traditional ultrasound-modulated optical imaging technology. The increase in SNR can achieve greater depth of detection in biological tissue imaging, but there is no significant improvement in imaging contrast. In order to improve the contrast of biological tissue imaging and achieve high resolution imaging of thick biological tissue, we use ultrasound microbubble contrast agent in ultrasound-modulated laser feedback imaging technology. We establish a Monte Carlo photon transport model with microbubbles in order to study the mechanism of contrast enhancement in ultrasound-modulated laser feedback imaging with microbubbles. Finally, we establish an experimental system to verify the correctness of the simulation results. Experimental and simulation results show that in the transparent solution, the ultrasonic microbubble contrast agent can enhance the ultrasound-modulated laser feedback signal and generate harmonic modulation, which can improve the imaging contrast by detecting the enhancement of the fundamental and harmonic signals of the feedback. In the scattering medium, the ultrasonic microbubble contrast agent can significantly attenuate the ultrasound modulated laser feedback signal, and the imaging contrast can be improved by detecting the attenuation of the fundamental and harmonic signal.