Research On Ultrasonic Field Visualization Technology Based On Shadowgraph

Transcranial phase array focused ultrasound is an emerging technology for the treatment of brain diseases,which has the advantages of non-invasive safety and deep penetration site.Phase distortion and energy attenuation occur after ultrasound passes through the porous,fluid-filled,and complex skull,which in turn affects the therapeutic effect,so phase correction of transcranial phase array focused ultrasound is essential.Existing hydrophone phase correction methods have disadvantages such as measurement elements interfering with the original sound field distribution,long scanning time,single measurement direction and limited measurement angle.By recording the deflection displacement of light in the sound field,shadowgraph ultrasonic field visualization technology can dynamically and real-time display the propagation and energy distribution of sound waves in space.It has the advantage of fast full-field recording of the real spatial distribution of sound waves without interference to the original sound field.Therefore,this paper records the ultrasound transcranial focusing process based on the shadowgraph ultrasound field visualization technique,realizes the rapid,full-field and dynamic visualization of complex acoustic fields,and performs accurate correction of transcranial phase array focusing ultrasound,which provides a rapid and accurate dynamic phase correction method for realizing transcranial focusing ultrasound therapy.The main research is as follows.(1)Based on the relationship between geometrical optics,medium refractive index and acoustic pressure,the relationship between light intensity and acoustic pressure under acoustic pressure perturbation was derived to provide a theoretical basis for acoustic wave spatial position localization;meanwhile,sensitivity and resolution analysis of direct shadowgraph,parallel light shadowgraph and focused shadowgraph systems were conducted to compare the advantages and disadvantages of each system,and the focused shadowgraph was preferentially selected as the optical imaging system for this paper in consideration with the required imaging range.(2)A focused shadowgraph ultrasound field visualization system was built,mainly including the optical imaging system and the synchronous time delay control system.The main components of the visualization system(light source,camera and imaging lens)are selected and analyzed to ensure that the performance parameters of the light source and camera meet the requirements of the focused shadowgraph system for capturing transient ultrasound field images and have good imaging quality.(3)The acoustic visualization experiment of single array focusing transducer was conducted,and the pixel curves of the focused acoustic field shadowgraph photo were compared with the measurement results of the hydrophone method,and the two were in good agreement,which verified the feasibility and accuracy of this system for acoustic field visualization.Secondly,the real-time visualization and analysis of transcranial phase array focused ultrasound process was realized by adjusting the time difference between the laser and ultrasound excitation signal for dynamic filming of the sound field.The shadow method ultrasound field visualization technology has the potential to develop into a three-dimensional sound field dynamic visualization technology through multi-angle sound field recording,using the advantage of spatial location sound pressure measurement without directional and angular restrictions to achieve accurate measurement of real sound pressure at any spatial location in complex three-dimensional sound fields.(4)A phase correction experiment of transcranial phase array focused ultrasound based on the focused shadowgraph ultrasound field visualization system was conducted,and the delay data of each array element after correction were obtained.Next,to evaluate the correction effect,the transcranial focused sound fields before and after correction were visualized using the focused shadowgraph system,and the sound pressure measurements of the transcranial focused sound fields before and after correction were performed with a fiber optic hydrophone.The results shows that the corrected sound fields were symmetrically distributed and the maximum peak sound pressure of the focal spot was increased by 27 k Pa,which confirmed that the transcranial phase array focused ultrasound phase correction method based on the shadowgraph ultrasound field visualization technique can effectively improve the transcranial ultrasound focusing effect and provide a new idea for achieving accurate ultrasound focusing.