Micron-scale magnetic resonance imaging of both liquids and solids

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 170 mu m 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 H-1 MRI, we present an image of polystyrene beads within CuSO4-doped water, contained within a capillary tube with 100 mu m inner diameter, with 5.0 mu m isotropic resolution. To demonstrate solid state H-1 MRI, we present an image of NH4Cl particles within the capillary tube, with 8.0 mu m isotropic resolution. High-resolution solid state MRI is enabled by frequency-switched Lee-Goldburg decoupling, with an effective rotating frame field amplitude of 289 kHz. At room temperature, pulsed gradients of 4 T/m (i.e., 170 Hz/mu m for H-1 MRI) are achievable in all three directions with currents of 10 A 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. Published by Elsevier Inc.