Research On High-sensitivity Two-dimensional Magnetic Particle Imaging System

Magnetic particle imaging(MPI),as a new generation of medical imaging system,uses the nonlinear magnetization curve of superparamagnetic nanoparticles to image the concentration distribution of superparamagnetic nanoparticles with high sensitivity,resolution and imaging speed.The MPI system realizes spatial positioning and dynamic imaging through gradient fields,moving devices,excitation fields,and detection devices.As a medical imaging system,important parameters include detection sensitivity and spatial resolution.Among them,the detection sensitivity is mainly determined by the properties of magnetic nanoparticles,the size of the gradient field and the sensitivity of the detection device,and the spatial resolution is determined by the gradient field and the excitation field.Compared with PET,SPECT,etc.,it has significant advantages such as fast imaging speed,no harmful radiation,and tracer safety.At present,Philips and the University of California,Berkeley,etc.have launched animal-grade MPI products,both of which are small enclosed imaging spaces.The detected object needs to be completely placed in a closed detection space,which is difficult to achieve for applications such as dynamic disease monitoring and intraoperative radiation-free imaging.And the excitation strength beyond the safe limit also makes the current MPI technology unable to enter clinical application.In order to solve these problems,an open magnetic particle imaging device is proposed,which has a large imaging space,and the intensity is only limited by the gradient field and not by the excitation field.The DC gradient field strength and linear range can be increased while maintaining low excitation field strength.Due to the nonlinear magnetization characteristics of the magnetized response of magnetic nanoparticles,the received signal includes a higher harmonic signal in addition to the fundamental frequency signal.After separating the fundamental frequency signal,the harmonic signal is detected and the image is reconstructed to obtain the spatial distribution information of the magnetic nanoparticles,that is,the MPI signal.Through the research and analysis of the system,including gradient field,excitation field and detection device.The results show that the open scanning space is not only conducive to improving the spatial resolution and sensitivity,but also facilitates the optimization of the later scanning space.At the same time,the influence of the position relationship between the DC field and the AC field is analyzed,and the influence of different parameters on the gradient field and the relationship between gradient field size and spatial resolution and sensitivity are analyzed.In addition,the detection device also affects the sensitivity,for effectively improving the sensitivity of the detection device,the analysis of wire material,size parameters and other angles to improve its sensitivity.Improving the imaging experiment,it was found that its spatial resolution and detection sensitivity were effectively improved,and the original spatial resolution of 10 mm and the detection sensitivity of 10 ug iron have been reached.According to the repeated experiment of the system,it is proved that the system has a certain stability,and the technical indicators of the MPI system are also preliminarily realized.