Dual-mode Ultrasound: Magnetoacoustics for Biological Tissue Imaging and Ultrasound Mediated Neuromodulation

Abstract

Ultrasound is a type of mechanical energies that have been widely employed in clinical diagnosis and therapeutic use. The overall goal of this dissertation is to further develop ultrasound-based imaging modality in assisting cancer diagnosis and explore the transcranial focused ultrasound (tFUS) in brain stimulation. In this dissertation, I firstly summarize my research on detecting cancer by harnessing a passive-mode ultrasound generated by magnetoacoustics. Probing the electrical conductivity of in vivo tissues, a high-frequency magnetoacoustic tomography with magnetic induction (hfMAT-MI) imaging system has been developed for cancer imaging with 1-mm spatial resolution. With the aid of magnetic nanoparticles (MNPs), the magnetoacoustic tomography is further enhanced in the imaging contrast and thus used to reconstruct the in vivo biodistribution of MNPs noninvasively. By reversing the imaging model, I secondly introduce my studies of transmitting active-mode pulsed ultrasound in a transcranial way and electrically sensing global and local brain responses to the deposited low-intensity ultrasound energy. In this second research topic, non-invasive electroencephalography (EEG)-based source imaging (ESI) is used to map the whole brain dynamics, which allows to better understand the effects of tFUS stimulation with high spatiotemporal resolutions. Furthermore, towards a mechanistic investigation, intracranial electrophysiological recordings from in vivo brains receiving low-intensity tFUS uncover an intrinsic cell-type specificity of neurons in responding to levels of ultrasound pulse repetition frequencies. Potential confounding factors, i.e. auditory side effects and somatosensation are also studied to thus identify the direct neuronal effects induced by the tFUS in vivo.