Π (Pi)-matching technique for RF coil of MRI systems

Abstract

Radio frequency (RF) coils are an essential part of hardware in Magnetic Resonance Imaging (MRI) systems and are used to excite the magnetized protons inside the human body and receive the Nuclear Magnetic Resonance (NMR) signals from anatomy. These RF coils based on microstrip transmission line resonator, the TEM coil, that has been widely used for high field MRI and most coils use the L-matching network consisting of two capacitors, Cm (matching capacitor) in series and Ct (tuning capacitor) in parallel with a signal line. If the loading condition changes, e.g. repositioned the patient, these capacitances should be adjusted to match the impedances with 50 Ω coaxial cable. The series capacitor connection to the main signal line, however, causes problems such as transmission loss and significant coupling between adjacent components when additional circuitry such as capacitor arrays is implemented. In this study, a Π-matching network with two parallel capacitors and microstrip line acting as an inductor is proposed to overcome the transmission losses caused by capacitors at high power and coupling issues for the implementation of the automatic tuning unit for RF coil with capacitor arrays.