MAGNETIC FIELD CONTROL USING LOCAL ELEMENTS FOR MRI

Abstract

Homogeneity of the magnetic field is an important criterion of the MRI scanner that affects the quality of its images. The homogeneous field is prone to a distortion when a patient is placed inside the scanner. One way to compensate the distortion is to shim the field using integrated RF-shim coil that has been proved its ability to improve the distorted field and receive an excellent RF signal at the same time. In their studies, the researchers modified an existing RF coil instead of designing the coil from scratch. This study aims to determine the shape of the DC conductor that could perform the shimming process better. Using COMSOL software, an environment to study the performance of the designed coil was modelled which includes: the main magnet in the MRI scanner that generates uniform 3-Tesla static magnetic field in the middle region and a phantom that can induce inhomogeneities in that region. The shapes of the DC conductor that was under investigation are the circular and square loops. 12.5% of the magnetic field produced by the Helmholtz coils that were used to model the main magnet was uniform and found in the centre of the system, and the simulation solution was less than the empirical solution by 6.7%. The phantom succeeded in distorting the direction and the magnitude of the magnetic flux density near its boundary. The designed coils performed well in compensating for the distortion locally along the y-axis. The circular shape showed better result by compensating 77.5% for the distortion while the square shape corrected 66.2% of it.