Theses Doctoral

A System for Monitoring Focused Ultrasound-Mediated Neuromodulation in the Central Nervous System

Aurup, Christian

Focused ultrasound (FUS) can modulate activity in the central nervous system of animals, however the mechanism of action is not yet fully understood. FUS is a promising technique for clinical use in treating both physiological and psychological pathology of the nervous system. FUS can noninvasively penetrate the skull deep into the brain and modulate brain targets with millimeter-scale resolution. FUS is less invasive than deep brain stimulation (DBS) and can target deeper structures with greater resolution than transcranial magnetic stimulation (TMS). Functional ultrasound imaging (fUSI) is an emerging modality for monitoring stimulus-evoked brain activity. However, the thick skull of large animals poses a significant obstacle for the noninvasive translation of the technique to nonhuman primates and humans. In this dissertation, FUS is performed in mice and nonhuman primates and an fUSI technique is developed for transcranially imaging FUS-evoked responses in both species.

The first aim of this dissertation established a procedure for performing high-resolution FUS in mice in vivo. FUS-evoked motor responses were evaluated using four-limb electromyography (EMG). A detailed quantitative analysis of several EMG characteristics demonstrated that observed motor responses exhibited brain target-specific differences. FUS in the brain was also shown to modulate cardiorespiratory activity. However, simulations conceded that intracranial reverberations may activate brain structures outside acoustic foci, suggesting that direct detection of brain activity is preferable to responses like EMG and cardiorespiratory activity.

The second aim of this dissertation developed an fUSI system for monitoring FUS-evoked responses in mice in vivo. fUSI was validated using electrical peripheral nerve stimulation to elicit somatosensory-evoked responses, a well-characterized approach in established techniques like functional magnetic resonance imaging (fMRI). fUSI was later integrated into an ultrasoundbased optogenetic stimulation procedure. Lastly, a dual FUS-fUSI transducer system for performing neuromodulation and functional activity monitoring was developed and successfully demonstrated in mice in vivo. The final aim of this dissertation was to adapt the FUS-fUSI procedure developed in mice for use in nonhuman primates. Two approaches were developed and tested in vivo. The first approach employed a low-frequency ultrasound array for both neuromodulation and activity monitoring. The second approach implemented a dual FUS-fUSI transducer system similar to that used in mice. Preliminary evidence indicated that the adapted dual transducer system can successfully perform fully noninvasive neuromodulation and functional activity monitoring transcranially in nonhuman primates in vivo.

The findings presented in this dissertation provide a framework for performing fully noninvasive ultrasound-mediated neuromodulation and functional activity monitoring in non human primates and describes a road map for further translating the technique for clinical use in human subjects. A fully noninvasive FUS-fUSI technique can provide an invaluable tool for clinicians to treat diseases of the nervous system not indicated for invasive procedures, opening the door to a wide range of therapeutic applications.


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More About This Work

Academic Units
Biomedical Engineering
Thesis Advisors
Konofagou, Elisa E.
Ph.D., Columbia University
Published Here
February 8, 2023