title: Design and construction of an actively frequency-switchable RF coil for field-dependent Magnetisation Transfer Contrast MRI with fast field-cycling.
abstract: Magnetisation Transfer Contrast (MTC) is an important MR contrast-generating mechanism to characterise the MR-invisible macromolecular protons using an off-resonance pre-saturation RF irradiation pulse (or MT pulse). MTC MRI is normally implemented at a fixed magnetic field; however, it may be useful to evaluate changes of the MT effect as a function of external magnetic field strength (B₀). In order to conduct field-dependent MTC experiments with a single MR system, two techniques are crucially needed. B₀ should be able to be switched between levels during irradiation of the MT pulse. At the same time, the resonance frequency of the RF coil (f₀) should also be able to be shifted to the corresponding value. Switching B₀ is attained by the fast field-cycling technique, while in order to switch f₀, a specially designed multi-tunable RF coil is required. Here, we designed and constructed an actively frequency-switchable RF coil for frequencies at and below 2.5 MHz. The design employed PIN diodes, and enabled switching f₀ between five different values, with excellent impedance matching (approximately -37 dB S₁₁ reflection) and Q-factor of about 100 at each configuration.
authors.affiliation: Aberdeen Biomedical Imaging Centre, Biomedical Physics, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK.
authors.forename: Chang-Hoon
authors.initials: CH
authors.lastname: Choi
authors.forename: James M S
authors.initials: JM
authors.lastname: Hutchison
authors.forename: David J
authors.initials: DJ
authors.lastname: Lurie
mesh_terms: D004574:Electromagnetic Fields; D004581:Electronics; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D019047:Phantoms, Imaging; D011522:Protons; D011846:Radio Waves
chemical_list: D011522:Protons