In this paper, we present a study on the effects of varying the position of a single tuning capacitor in a circular loop coil as a mechanism to control and produce non-symmetric current distribution, such that could be used for magnetic resonance imaging (MRI) operating at ultra-high frequency (UHF). This study aims to demonstrate that the position of the tuning capacitor of a circular loop could improve the coupling between adjacent coils, used to optimize transmission field uniformity or intensity, improve signal-to-noise ratio (SNR) or specific absorption rate (SAR). 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, the capacitor position was varied from 15° to 345°, in steps of 15°. We performed electromagnetic (EM) simulations, fabricated the coils, and performed MRI experiments at 7T, with each of the coils with capacitor position from 15° to 345° to determine the effects on field intensity, coupling between adjacent coils, SAR, and applications for field uniformity optimization. For the case of free space, a coil with capacitor position at 15° showed higher field intensity compared to the reference coil; while an improved decoupling was achieved when a coil had the capacitor placed at 180° and the other coil at 90°; in a similar matter, we discuss the results for SAR, field uniformity and an application with an array coil for the spinal cord.

Rectangular coaxial slot arrays (RCSAs) are antennas designed to ensure superior field penetration depth with a high signal-to-noise ratio (S/N) in the deeper imaging region of ultra-high magnetic resonance imaging (MRI). The RCSA consists of a transmission line of λ/4 length surrounded by a dielectric material, and a ground plate that resembles a rectangular coaxial line. We extended this antenna to eight elements. The simulation indicates that a single RCSA has a B þ 1 -field distribution similar to that of the generally used dipole antenna for traveling RF waves. However, the B þ 1 -component of the RCSA in an array configuration was stronger in the deep brain region of the human brain model and its specific absorption rate was lower compared to the dipole and monopole antenna arrays. The proposed RSCA array can be adapted to acquire MR signals with high sensitivity in a deeper imaging region in an ultra-high field MRI scanner.

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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.