Microengineered needle micro-coils for magnetic resonance spectroscopy

A process for batch fabrication of low-cost needle-shaped micro-coils for magnetic resonance (MR) spectroscopy is demonstrated. The conductors are embedded inside a cross-section designed to avoid the signal cancellation effects that can occur with completely immersed detectors. Simple models are developed for the sensitivity of an immersed coil and for the electrical performance of coils on silicon substrates. Conductors are fabricated on oxidized Si by electroplating metals inside a deep photoresist mould, and then capped with a thick layer of plastic. Through-wafer deep reactive ion etching is used to define needle shapes. At 63.8 MHz frequency, Q-factors obtained on Si are comparable to those on glass, and resonators based on single-turn coils have Q-factors of approximate to 14. Total immersion H-1 MR imaging and spectroscopy are demonstrated in a 1.5 T magnetic field using tomato fruits. Q-factors are raised at higher frequencies (to > 30 at 255 MHz) using thick polymer isolation, and hybrid integration of additional circuitry is demonstrated

Microcoils on structured silicon substrates for magnetic resonance detection

The design and performance of a silicon-based RF detector coil for use in magnetic resonance (MR) spectroscopy applications is described. The coil is fabricated using microelectromechanical systems (MEMS) technology by deep reactive ion etching (DRIE) of an oxidized silicon substrate carrying electroplated conductors. The DRIE step simultaneously forms a sample trough and creates a trepan cut around the coil so that it may be detached from the substrate by cleaving short sections of sprue. A single-turn coil with Q-factor similar to 16 at 63.6 MHz is demonstrated and MR spectroscopy experiments are described. An accurate numerical model based on the time-domain finite integration technique is used to investigate the effect on the Q-factor of deliberately structuring the substrate to limit the volume of silicon exposed to RF energy. The model is compared with known analytic approximations, and good agreement is obtained