Numerical Computation Methods for Evaluating the Electromagnetic Safety of Magnetic Resonance Imaging System

In recent years, with the development of magnetic resonance imaging (MRI) technology, increasingly attention has been paid to electromagnetic safety of MRI. To summarize the researches in recent years, we introduce the biological effects and safety standards of three different kinds of electromagnetic fields (static magnetic field, gradient field, and radio frequency field) produced by MRI equipment firstly. On the basis of this, the numerical computing methods used for evaluating the electromagnetic safety of MRI are emphatically introduced, in which the human numerical model and numerical algorithm are studied in detail and evaluated for both accuracy and efficiency. The results of research show that when the electromagnetic fields generated by MRI exceed a certain limit, they will create significant biological effects, leading to the discomfort reaction of body. The current body voxel model has high resolution and can reflect the real human body to some extent. However, the general model limits the full advantages of high field MRI equipment, and developing a specific voxel model is an inevitable trend. The existing numerical algorithms used to evaluate the MRI electromagnetic safety include finite element method, moment method, and time domain finite difference method, as well as quasi-static approximation methods and mixed numerical calculation methods. These methods can accurately predict the electromagnetic field value in human tissue up to a point, but can not take into account accuracy and efficiency simultaneously, still need to further improved. The existing safety standards are not yet complete and should add relevant safety standards about open MRI, PET/MRI, LINAC/MRI and other new MRI system. The results can provide references for MRI designers, help to complement the existing MRI safety standards, then to simultaneously improve system performance and ensure electromagnetic safety.