Description:
Slotted Waveguide Array RF Coil for Ultra-High-Field MRI
Problem to be Solved:
Current magnetic resonance imaging (MRI) technology utilizes a relatively low static magnetic field (B0 ≤ 3T). Ultra-high field (B0 ≥ 7) imagers increase sensitivity and functionality of MRI overall, but come with their own set of challenges. At higher magnetic fields, the radio frequency (RF) wavelength decreases, creating a mix of near and far field behavior leading to highly non-uniform magnetic fields. Recent research in this field has either been unsuccessful at mitigating this factor (ex: TEM body coil) or suffer from intolerably low RF power efficiency (twisting bird cage, traveling-wave coil).
Abstract:
Investigators at Colorado State University have designed a novel method and apparatus for the excitation of RF magnetic fields in ultra-high field (UHF) MRI systems utilizing a slotted waveguide array (featured below in the left figure). Each element in the circular array is itself a slotted waveguide antenna filled with a low-loss high-permittivity dielectric (right figure), which in turn is a linear array of slots in a waveguide wall, and each slot is a radiator itself. Dielectric lenses can be added on each slotted waveguide wall to further improve the efficiency of the exciter. Potential applications include research, pre-clinical, and clinical MRI/NMR systems.
Advantages:
• Provides RF magnetic field B1+ with: (1) high field-uniformity, (2) high efficiency, (3) excellent circular polarization, (4) negligible axial z-component, (5) arbitrary large field of view, and (6) exceptional possibilities for field-optimizations via RF shimming.
• RF efficiency ≥ 2.3 µT/√W in the human head
• Each waveguide antenna can be near perfectly decoupled from all other elements in the array
• Allows for multichannel excitation with highly decoupled channels to facilitate parallel imaging and RF shimming by different feeding patterns in order to achieve optimal B1+ field distribution within the imaged subjects
• Universal / Not limited to any particular field strength or any particular frequency
• Slotted waveguide array coils can be used as body, head, limb, torso, or partial body coils
