Effects of Non-symmetrical Current Distribution Controlled by Capacitor Placement in Loop Coils at 300 MHz MRI

Abstract

In this work, we present a study on the effects of the non-symmetric electrical design of radiofrequency (RF) coils for magnetic resonance imaging (MRI) operating at ultra-high frequency (UHF). A typical loop coil used in MRI consists of symmetrically distributed capacitors along the coil; this design is able to produce uniform current distributions inside the coil. However, in UHF conditions, the magnetic flux density (|B1|) field produced by this setup may exhibit field distortion, requiring a method of controlling the field distribution and improving the field intensity of the circular loop coil. The control mechanism investigated in this study is based on the position of the tuning capacitor in the circular coil. We performed comparisons against a reference coil that is based on a circular coil with four symmetrically distributed tuning capacitors. We performed electromagnetic (EM) simulations and MRI at 7 T to determine the effects of variations in the position of the capacitor and confirmed that unbalanced current distributions were created.