Poster Z19 - Effect of the addition of coupled electric fields in Transcranial magnetoacoustic coupled stimulation on neuronal firing thresholds

Friday, October 25, 2024

3:30 PM - 4:30 PM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

ZL

Zhipeng Liu

Professor
Chinese Academy of Medical Sciences & Peking Union Medical College, Institute of Biomedical Engineering, United States

Co-Author(s)

Ren Ma, Dr (he/him/his)

Associate Researcher
Institute of Biomedical Engineering, Chinese Academy of Medical Sciences
Tianjin, United States
Xin Wang

Associate Researcher
Institute of Biomedical Engineering, Chinese Academy of Medical Sciences, United States
Xiaoqing Zhou

Associate Researcher
Institute of Biomedical Engineering, Chinese Academy of Medical Sciences, United States
Tao Yin, MA

Professor
Institute of Biomedical Engineering, Chinese Academy of Medical Sciences, United States

Primary Investigator(s)

Ruxin Tan, Doctor of Engineering (she/her/hers)

Doctor
Chinese academy of medical science, institute of biomedical engineering, United States

Introduction: Transcranial magnetoacoustic electrical stimulation (TMAS) is a novel neuromodulation technique that uses focused ultrasound in a static magnetic field to target brain regions. It is based on the principle that focused ultrasound drives the vibration of conductive particles in biological tissues, and the vibrating conductive particles are subjected to the Lorentz force in a static magnetic field, forming an electric field perpendicular to the direction of ultrasound and the direction of the magnetic field. TMAS is not just purely electrical stimulation, but composite field stimulation. In order to make TMAS a safe and effective neuromodulation technique, it is important to clarify the basic mechanisms by which ultrasound and coupled electric fields interact with neural tissues at the cellular scale, how these mechanisms change in neural structures, and the optimal ultrasound parameters required to achieve the desired modulation effect. A simulation and computational model for the joint action of ultrasound and coupled electric fields in TMAS is developed, in which the effects of ultrasound and coupled electric fields in TMAS to modulate neuronal electrical activity at the cellular scale are explored.

Materials and

Methods: The simulation of ultrasound action on neurons is mainly based on the cavitation mechanism. The Neuronal Intramembrane Cavitation Excitation (NICE) model assumes that ultrasound induces cavitation of specific nanoscale phospholipid structures within the plasma membrane, also known as bilayer sonic pores.
The action of ultrasound through specific calcium-selective mechanosensitive ion channels was experimentally confirmed. Ultrasound causes a gradual accumulation of calcium ions, which in turn is amplified by calcium-gated and voltage-gated channels, producing a discharge response.
The coupled electric field in TMAS is converted into a current coupled into the model. The speed of vibration of the charged particles is determined by the ultrasonic sound pressure.
v=p/ρc（1.1）
where v is the vibrational velocity of the charged particle, p is the ultrasonic sound pressure,  is the density of biological tissue, and c is the speed of sound. A moving charged particle in a static magnetic field is subjected to a Lorentz force F
F=qv×B（1.2）
The current density in a tissue with a conductivity of  is
(J=/ρc Bp（1.3）

Here the base frequency of ultrasound is set to be 1MHz and the magnetic field strength to be 0.3 T. The duty cycle interval is 0-100% in steps of 0.01% and the ultrasound intensity interval is 10kPa-103kPa. the discharge frequency is simulated and calculated at repetition frequencies of 10Hz, 100Hz, and 1KHz, respectively.

Results, Conclusions, and Discussions: Results
The cumulative dose of ultrasound can determine the amplitude as well as the duration of depolarization when ultrasound is applied. The duty cycle-ultrasound intensity excitation threshold curves of TMAS show the same duty cycle and ultrasound intensity dependence in the RS neuron model. At low duty cycles, the ultrasound intensity required for TMAS excitation discharge was high; as the duty cycle gradually increased, the required ultrasound intensity gradually decreased. The ultrasonic intensity threshold tends to stabilize at a duty cycle greater than 50%. The figure shows that under the same ultrasound parameters, the curve of TMAS shifts to the left compared with TUS, indicating that the increase of the coupled electric field significantly reduces the ultrasound dose threshold for triggering the spiking pulse.
Conclusion
The duty cycle dependence of the discharge threshold of the TMAS in the RS neuron model confirms the important role of the ultrasonic field in the TMAS, not only as a physical field that generates a coupled electric field. And the effect of the ultrasonic field is cumulative. Meanwhile, the response curves of TMAS all showed a significant leftward shift compared to TUS, indicating that the addition of coupled electric field in TMAS can significantly reduce the issuance threshold to the need of ultrasound dose.
Discussion
The simulation model used in this paper not only includes the effect of ultrasound mechanical forces on membrane capacitance in TMAS, but furthermore takes into account the effect of ultrasound on calcium ions. The effects of ultrasound-only TUS and TMAS including ultrasound field and coupled electric field on neurons were compared, and the parameter spaces of TUS and TMAS were explored more intensively by titration. The incorporation of coupled electric fields in TMAS was found to significantly reduce the threshold of discharging to the requirement of ultrasound dose. It is shown that the combination of coupled electric and ultrasound fields in TMAS has the potential to improve safety and dynamic range and energy efficiency.

Acknowledgements (Optional):