Micron-scale magnetic resonance imaging of both liquids and solids

Abstract

We describe and demonstrate a novel apparatus for magnetic resonance imaging (MRI), suitable for imaging of both liquid and solid samples with micron-scale isotropic resolution. The apparatus includes a solenoidal radio-frequency microcoil with 170μm inner diameter and a set of planar gradient coils, all wound by hand and supported on a series of stacked sapphire plates. The design ensures efficient heat dissipation during gradient pulses and also facilitates disassembly, sample changes, and reassembly. To demonstrate liquid state 1H MRI, we present an image of polystyrene beads within CuSO4-doped water, contained within a capillary tube with 100μm inner diameter, with 5.0μm isotropic resolution. To demonstrate solid state 1H MRI, we present an image of NH4Cl particles within the capillary tube, with 8.0μm isotropic resolution. High-resolution solid state MRI is enabled by frequency-switched Lee–Goldburg decoupling, with an effective rotating frame field amplitude of 289kHz. At room temperature, pulsed gradients of 4T/m (i.e., 170Hz/μm for 1H MRI) are achievable in all three directions with currents of 10A or less. The apparatus is contained within a variable-temperature liquid helium cryostat, which will allow future efforts to obtain MRI images at low temperatures with signal enhancement by dynamic nuclear polarization.