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A novel 3-dimensional laser-lathe process for manufacturing magnetic resonance microcoils is presented. The process has been used to print coils on a variety of materials, including glass and Teflon. The dimensions of these coils can be varied easily to allow any number of different coil designs, including solenoids and saddle coils. In our fabrication process, capillary tubes sputter-coated with a thin titanium-copper multilayer are plated with a positive electrodeposited photoresist. The resist is exposed with a computer-controlled laser-lathe apparatus consisting of an argon-ion laser, an acousto-optic modulator, a movable aperture, a lead screw stage and a spindle stage. After exposure and development, copper is electrolytically deposited through the resist mask. Following copper deposition the resist mask is removed and the sputtered copper and titanium are etched away, leaving a microcoil firmly adhered to the capillary. The resistivity of the laser-lathe copper windings is 7.6% higher than the resistivity of hand-wound coils (1.85 μΩ-cm for laser-lathe copper compared with 1.72 μΩ-cm for bulk annealed copper). For laser-lathe and hand-wound microcoils of similar size and geometry, the coil quality factor, Q, of the laser patterned coils would be 7.6% lower than the hand-wound coils. Examples of 13C NMR spectra obtained using laser-lathe coils are shown, and a relative improvement of 68 in the NMR sensitivity is calculated for a laser-lathe microcoil compared with a conventional 5 mm NMR sample tube. |
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