Simulation Research Of MACT-MI Based On Relaxation Effect

The research of magnetic nanoparticles in medicine is emerging as a booming trend.Because of the excellent biodegradability,micro-size effect,and magnetic properties of magnetic particles,scholars at home and abroad have extensively conducted research on magnetic tumor thermotherapy,stem cell labeling,gene delivery,targeted drug release,and disease diagnosis in recent years.However,these technologies must be supported by imaging techniques for their ultimate realization in real human applications,and with the rapid development of nanomedicine,these applications have put forward higher requirements on magnetic particle imaging technology.Classical magnetic particle imaging(MPI)imaging devices can achieve resolutions of 1-5 mm,and direct feed-through electromagnetic interference between both the drive and detection coils can degrade the resolution of reconstructed images;therefore,how to improve the resolution of imaging has been one of the main research questions in this field.Magneto-acoustic concentration tomography of magnetic nanoparticles with magnetic induction(MACT-MI)is a innovative magnetic particle imaging method proposed by our group in 2020,which uses ultrasonic reception instead of coil reception for MPI imaging to overcome the problem of electromagnetic interference between the drive coil and the detection coil,with greatly enhanced anti-interference capability.In the research of other medical imaging such as magnetic resonance(MRI)and MPI,the relaxation process of magnetic nanoparticles affects the resolution and contrast of imaging,and using the relaxation effect can enhance the signal intensity generated by the magnetization response,effectively improving the accuracy of image reconstruction.In view of this,in this paper,based on the previous work of the group,the research work of MACT-MI based on the relaxation effect of magnetic nanoparticles was carried out to further improve the resolution of MACT-MI.Firstly,the forward imaging theory of MACT-MI was studied in detail from the relaxation effect of magnetic nanoparticles,and the electromagnetic and acoustic coupling model of MACT-MI based on the relaxation effect was proposed.Furthermore,the relaxation effect was used to enhance the MACT-MI magnetoacoustic signals,including the gradient magnetic field design in the imaging system,the influence of magnetic particle size and fluid media environmental parameters on the sound pressure signals.Whale optimization algorithm was used to optimize the current and structure parameters of the multi-coil group to provide a more uniform ideal gradient magnetic field for MACT-MI imaging.Comsol Multiphysics was used to build a biological tissue simulation model embedded with MNPs.The magnetic intensity distribution and magnetic force distribution of MNPs were compared under two cases with or without considering the relaxation process,and the effects of particle size and fluid environment on the magneto-acoustic signal intensity were further investigated.Finally,the inverse problem reconstruction algorithm based on moment method was used to reconstruct the concentration distribution image of MACT-MI magnetic nanoparticles under relaxation effect.The results show that the magnetization intensity distribution and magnetic nanoparticle concentration distribution of magnetic nanoparticles in MACT-MI can be well presented by using the relaxation process within the same excitation conditions and environmental parameters,without the limitation of excitation frequency and particle superparamagnetism.Meanwhile,the optimal particle size for imaging can be obtained by the relaxation effect to enhance the MACT-MI magnetoacoustic signal amplitude.In the case of the same average particle size,the magnetic nanoparticle particle size distribution is not uniform and the standard deviation is too large to weaken the magnetic and acoustic pressure amplitude.The results of the study can provide a theoretical basis for achieving high-precision reconstruction of magnetic nanoparticle concentration and promoting the practical clinical application of MACT-MI.The paper has 53 Figures,5 Tables,and 65 References.