title: Design of a parallel transmit head coil at 7T with magnetic wall distributed filters.
abstract: Ultra-high field magnetic resonance imaging (MRI) scanners ( ≥ 7T) require radio-frequency (RF) coils to operate in the range of the electromagnetic spectrum where the effective wavelength in the tissue approaches the patient dimensions. Multi-channel transmit arrays, driven in parallel, have been developed to increase the transmit field (B1(+)) uniformity in this wavelength regime. However, the closely packed array elements interact through mutual coupling. This paper expands on the ability of a distributed planar filter (the "magnetic wall") to decouple individual elements in an entire array. A transmit RF coil suitable for neuroimaging at 7T was constructed. The transmit coil, composed of 10 individual surface coil elements, was decoupled with magnetic walls. A separate receive coil array was used for signal reception. The hardware and imaging performance of the transmit coil was validated with electromagnetic simulation, bench-top measurements, and in vivo MRI experiments. Analysis and measurements confirmed that the magnetic wall decoupling method provides high isolation between transmit channels, while minimally affecting the B1(+) field profiles. Electromagnetic simulations confirmed that the decoupling method did not correlate to local specific absorption rate (SAR) "hot spots" or increase local-to-global SAR fractions in comparison to previously reported 7T multi-channel transmit arrays employing different decoupling methods.
authors.forename: Ian R O
authors.initials: IR
authors.lastname: Connell
authors.forename: Kyle M
authors.initials: KM
authors.lastname: Gilbert
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Abou-Khousa
authors.forename: Ravi S
authors.initials: RS
authors.lastname: Menon
mesh_terms: D004574:Electromagnetic Fields; D004867:Equipment Design; D006257:Head / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D011846:Radio Waves; D015203:Reproducibility of Results