Microengineered needle micro-coils for magnetic resonance spectroscopy

Abstract

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.