Thin Film Detector for Internal MRI

Thin film detectors that combine a flexible microcoil with a flexible transmission line are presented, for in vivo magnetic resonance imaging of the human bile duct. The thin-film format allows integration on a catheter, which may then be delivered into the duct with the help of a guidewire using a non-magnetic side opening endoscope. The high filling factor obtained using this approach provides very high Signal-to-Noise Ratio (SNR) and image quality, but the overall procedure is much less invasive than surgical intrabiliary MRI. In this thesis, two models are proposed. The first has a multi-turn spiral with integrated tuning and matching capacitors as a detector coil, and a photonic bandgap structure with a periodically patterned ground plane as a transmission line. Commercial electromagnetic modelling software (AWR Microwave Office) is used to perform a detailed analysis of a complete detector system. Coil and cable are both modelled using Axiem, a method of moments solver. Analysis of the reflection and transmission coefficient is used to extract parameters such as characteristic impedance and propagation loss. Parameters are chosen for operation at 63.8 MHz (1H MRI at 1.5T) with a 50 Ω system impedance. Because the first design was implemented without considering MR-safety, a second-generation system was developed. This design uses a figure-of-eight shaped coil used as a detector and also as the resonant element in a magneto-inductive transmission line. As a result, coupling to both the B1 and E fields of the transmitter is prevented. AWR Microwave Office is, again, used to perform a detailed design. Additional electrical parameters such as coupling coefficient, and mutual inductance of the cable are measured and extracted. Mismatch impedance is solved using transformer matching. Analytic models of both designs are also developed and compared with simulation data and to experimental data from prototypes fabricated using copper-clad Kapton.Open Acces