Title:The Simulation and Experimental Comparison of Parameter Factors Impact on MRI Artifact
Volume: 13
Author(s): Siyuan Li, Shan Jiang*, Zhiyong Yang and Zhengxing Wu
Affiliation:
- Centre for Advanced Mechanisms and Robotics, School of Mechanical Engineering, Tianjin University, Tianjin 300072, Tianjin,China
Keywords:
MRI, simulation, magnetic perturbations, artifact size, static magnetic field, chamfer.
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.
