Practical design of a 4 Tesla double-tuned RF surface coil for interleaved 1H and 23Na MRI of rat brain

MRI is proving to be a very useful tool for sodium quantification in animal models of stroke, ischemia, and cancer. In this work, we present the practical design of a dual-frequency RF surface coil that provides (1)H and (23)Na images of the rat head at 4 T. The dual-frequency RF surface coil comprised of a large loop tuned to the (1)H frequency and a smaller co-planar loop tuned to the (23)Na frequency. The mutual coupling between the two loops was eliminated by the use of a trap circuit inserted in the smaller coil. This independent-loop design was versatile since it enabled a separate optimisation of the sensitivity and RF field distributions of the two coils. To allow for an easy extension of this simple double-tuned coil design to other frequencies (nuclei) and dimensions, we describe in detail the practical aspects of the workbench design and MRI testing using a phantom that mimics in vivo conditions. A comparison between our independent-loop, double-tuned coil and a single-tuned (23)Na coil of equal size obtained with a phantom matching in vivo conditions, showed a reduction of the (23)Na sensitivity (about 28 %) because of signal losses in the trap inductance. Typical congruent (1)H and (23)Na rat brain images showing good SNR ((23)Na: brain 7, ventricular cerebrospinal fluid 11) and spatial resolution ((23)Na: 1.25 x 1.25 x 5mm(3)) are also reported. The in vivo SNR values obtained with this coil were comparable to, if not better than, other contemporary designs in the literature.     

Electrospinning of ultra-thin polymer fibers

The electrospinning technique was used to spin ultra-thin fibers from several polymer/solvent systems. The diameter of the electrospun fibers ranged from 16 nm to 2 μm. The morphology of these fibers was investigated with an atomic force microscope (AFM) and an optical microscope. Polyethylene oxide) (PEO) dissolved in water or chloroform was studied in greater detail. PEO fibers spun from aqueous solution show a “beads on a string” morphology. An AFM study showed that the surface of these fibers is highly ordered. The “beads on a string” morphology can be avoided if PEO is spun from solution in chloroform; the resulting fibers show a lamellar morphology. Polyvinylalcohol (PVA) dissolved in water and cellulose acetate dissolved in acetone were additional polymer/solvent systems which were investigated. Furthermore, the electrospinning process was studied: different experimental lay-outs were tested, electrostatic fields were simulated, and voltage - current characteristics of the electrospinning process were recorded.     

High-pressure Synthesis,Structure, IR Spectroscopy,and Theoretical Calculations of the New Silver Tetraborate Ag2B4O7 with a Unique Crystal Structure

Ag₂B₄O₇ is synthesized at high-pressure/high-temperature conditions of 11 GPa and 1073 K in a multianvil device. It crystallizes in the monoclinic centrosymmetric space group P2₁/c (no. 14) with four formula units per unit cell (Z=4). The cell parameters are a=787.53(3), b=651.63(2), c=943.88(3) pm, β=107.911(2)°, and V=460.90(3) ų. Ag₂B₄O₇ crystallizes in a unique crystal structure that consists of complex anionic borate layers with Ag⁺ ions in between. Additionally, the silver cations show argentophilic interactions. The compound was analysed via single-crystal and powder diffraction as well as infrared spectroscopy. Furthermore, theoretical calculations at HSEsol level were conducted.     

Synthesis and Crystal Structure of the Zinc Borate Zn3B4O9

The new zinc borate Zn₃B₄O₉ was synthesized at high-pressure/high-temperature conditions of 10 GPa and 1173 K in a Walker-type multianvil pressure device. It crystallizes in the space group P (no. 2) with a=5.5028(2) Å, b=6.7150(3) Å, c=7.8887(3) Å, α=83.99(1)°, β=73.38(1)°, γ=74.75(1)°, V=269.35(2) ų, and two formula units (Z=2) per unit cell. The structure was confirmed via single-crystal X-ray diffraction. Zn₃B₄O₉ can be synthesized phase pure, which is shown with a Rietveld refinement. IR-spectroscopic data of a powder sample were collected.