Design and Implementation of Multi-Channel Multipurpose RF Coil for Low Tesla MRI

Abstract

Magnetic Resonance Imaging (MRI) is a non-ionizing imaging modality that provides excellent soft tissue contrast that is not possible from x-ray or CT-scan. A typical MRI system comprises a Magnet, RF System, Gradient System and an Image Reconstruction System, out of which the main component is the Magnet. Majority of MRI systems in Pakistan are based on Permanent Magnets, which typically correspond to low magnetic fields. The significant benefit of a permanent magnet is its use in open magnet MRIs that is friendly for claustrophobic patients in contrast to bore magnet MRIs. RF Coils are another important and regularly used part of MRI scanner as the data acquisition majorly relies on them. The RF system of the MRI scanner consists of a Transmit and Receiver system. The former has hardware like RF power amplifier and Transmit coil whereas the receive section has pre-amplifiers and receive coils. This thesis focuses on design and implementation of a dual-channel multipurpose MRI receiver coil. The acquisition of the signal relies on the receiver coil because the net magnetic flux originating from the relaxing energy is being captured by the receiver coil. And then this magnetic flux can be detected and digitized in the form of induced voltage after performing amplification (using a preamplifier). The sensitivity of the detection is directly related to the efficiency of the receiver coil. The main objective of this research is to develop indigenous capability of design and manufacturing of MRI receiver coils for permanent magnet MRI scanner at domestic level to reduce import burden of MRI components in Pakistan. Therefore, the thesis focuses on studying the operation of receive coils for low tesla or permanent magnet MRI systems, followed by the design and implementation of an independent dual channel multipurpose coil suitable for integration with a commercial MRI scanner. Initially the 3D model of the coil is being designed on CST software followed by PCB layout in Altium Designer. The matching circuitry is carried out in Advance Design System (ADS) to achieve the resonance frequency at 14.6 𝑀𝐻𝑧. After successful fabrication, the design is tested on the 0.35T Siemens Magnetom C! MRI system, which shows excellent results in image quality. The required signal-to-noise ratio (SNR) value must be higher than 56 dB and the value obtained for the designed coil is 73 dB which is higher than the currently used Siemens RF coils and improves image quality.