Abstract

Background: In Magnetic Resonance Imaging, inhomogeneity of the static magnetic field lead to perturbations in the resulting images, called artifacts. Artifact generated by the magnetic metal is a significant problem of medical equipment used in the nuclear magnetic environment. Our goal is to present a method, assuming the field disturbances are known, to construct the resulting images based on the actual principle of MRI by means of simulation, and then, to study the relation between artifact’s size and the shape, magnetic susceptibility of material for the shape optimization and material selection of medical equipment at the start of the product development cycle.

Methods: A mathematical model of the MRI process is developed. The way the images are distorted in intensity and shape is explained and an algorithm to simulate magnetic susceptibility artifacts is deduced.

Then, we have studied the impact of length, shape of chamfer, and magnetic susceptibility on the artifact.

Results: The results of simulation have been confirmed to be consistent with the experiment, which means that MRI artifact caused by magnetic metal can be simulated by theoretical simulation. By modifying the parameters in this model, we have found that the artifact gets smaller as the magnetic susceptibility becomes smaller, as the size of chamfer gets greater, as the shape of chamfer gets smoother. The study in this paper has a great significance for the design of medical equipment and can predict MRI artifact of medical equipment before it will be produced.

Conclusion: With the increase of material’s permeability, the stronger the sample internal magnetic field will be, and the stronger the external magnetic field disturbance will be; in addition, short samples have weak magnetic conductivity to disturb magnetic field, therefore, as the length or permeability of the cylinder gets greater, the artifact size gets greater. In addition, chamfer size can influence the artifact size as mentioned above, but the effect will get smaller as the distance from the chamfer is greater. The shape of longitudinal section does affect the artifact size, and the relation between them is that the smoother boundary produces smaller artifact; the cause of the phenomenon can be explained that the magnetic charge in the sample surface is not stable, because the repulsion between same magnetic charge is easy to distribute on the boundary of sample and cause the disturbance of magnetic field. In summary, small size, low permeability and smooth boundary can make a contribution to the reduction of the artifact. Moreover, the affecting factors and calculation model of MRI artifact can provide proposed indicators to the design of MRI-compatible surgical robot and medical equipment.

Keywords: MRI, simulation, magnetic perturbations, artifact size, static magnetic field, chamfer.

Graphical Abstract