Research And Application Of Magnetic Resonance Compatible Array Ultrasound System For Noninvasive Transcranial Neuromodulation

With the development of modern medical technology,non-invasive treatment is developing rapidly.Low intensity focused ultrasound(LIFU)is a new type of neuromodulation technology that can penetrate the complete skull and target deeper brain structures so that Stimulation of neurons produces excitatory or inhibitory effects,thereby regulating the brain's nerve function.However,when transcranial nerve stimulation is performed,due to the uneven thickness of the skull,reflection,refraction and absorption occur when the ultrasound passes through the skull,causing the position of the ultrasound focus to deviate from the target point.In recent years,magnetic resonance imaging(MRI)combined with the application of ultrasound phased array technology,ultrasound can be accurately focused in the brain.Phased array technology adjusts the launch delay time of each channel to compensate for distortion caused by factors such as skull thickness and density non-uniformity.The guidance ofMRI can improve the safety and accuracy of ultrasound treatment.Now LIFU has gradually shown great application prospects in the treatment of intracranial cranial neurological diseases and the opening of the blood-brain barrier.This thesis relies on the national major scientific research equipment development project "Development of Deep Brain Stimulation and Neuromodulation Instruments Based on Ultrasonic Radiation Force",which proposes an MRI compatible ultrasound array system that can be flexibly configured to support 256,1024 or even 10,000 channels Introduce the 1024 channel ultrasonic array system.The main research work of the subject is as shown follows:1.Based on the application of noninvasive transcranial neuromodulation,this thesis designs a 1024-channel ultrasound array system and completes the hardware structure design of each functional module,including FPGA as the digital control core for the realization of ultrasound beam synthesis.Then,the excitation pulse transmission circuit achieves the power amplification of the transducer excitation electrical signal,and adds an echo receiving circuit for the detection system working state.2.Large-scale array ultrasound systems need to cascade multiple subsystems to work at the same time,clock synchronization between each excitation subsystem is very important.Therefore,this thesis proposes a clock synchronization method based on optical fiber.The optical fiber not only supports clock synchronization between various subsystems,but also supports data loading and command transfer.The transmission path is bidirectional.Both clock and data can be sent and received at the same time,and the error accuracy can reach nanoseconds.Meantime,it has good magnetic compatibility based on the optical fiber clock solution.In addition,it also solves the problem of magnetic resonance compatibility through electromagnetic shielding and filtering.An aluminum alloy grounding shield is added to the entire hardware component to filter the power module and some key signals and magnetic resonance compatibility is performed.The test verified the magnetic compatibility of the system.3.In order to verify the output performance of the ultrasound system,the focusing performance of the system was tested in terms of acoustic performance,and single-focus and multi-focus focusing experiments were carried out in a uniform medium.In addition,the acoustic field distribution is measured quantitatively by using the hydrophone acoustic field scanning equipment,including the sound field distribution of a single probe,the linear adjustable sound field energy,and the cross acoustic field distribution of two vertical combined probes.4.Designed and carried out MRI-guided primate neuromodulation experiments,explored the stimulation of different regions of the brain under specific ultrasound stimulation parameters,applied MRI-based acoustic radiation force imaging(ARFI)to monkeys in the 3T MRI system,and acquired A functional magnetic resonance image(fMRI)was used to verify the focus position of the ultrasound target and the functional response of the brain to stimulation.The preliminary experiment will lay the foundation for the application of ultrasonic nerve control system in clinic.