title: Improving whole brain structural MRI at 4.7 Tesla using 4 irregularly shaped receiver coils.
abstract: Both higher magnetic field strengths (> or =3 T) and multiple receiver "array coils" can provide increased signal-to-noise ratio (SNR) for MRI. This increase in SNR can be used to obtain images with higher resolution, enabling better visualisation of structures within the human brain. However, high field strength systems also suffer from increased B(1) non-uniformity and increased power deposition, reaching specific absorption rate (SAR) limits more quickly. For these problems to be mitigated, a careful choice of both the pulse sequence design and transmit RF coil is required. This paper describes the use of a prototype array coil consisting of 4 irregularly shaped coils within a standard configuration for neuroimaging at 4.7 T (a head transmit/receive volume coil to minimise SAR and a head gradient insert for maximum gradient performance). With a fast spin echo (FSE) pulse sequence optimised for 4.7 T, this provides dramatically increased quality and resolution over a large brain volume. Using the array coil, a SNR improvement relative to the volume coil of 1-1.5 times in central brain areas and 2-3 times in cortical regions was obtained. Array coil images with a resolution of 352 x 352 x 2000 mum had a SNR of 16.0 to 26.2 in central regions and 19.9 to 34.8 in cortical areas. Such images easily demonstrate cortical myeloarchitecture, while still covering most of the brain in a approximately 12 min scan.
authors.affiliation: Wellcome Trust High Field Laboratory, Department of Medical Physics and Bioengineering, University College London, 12 Queen Square, London, WC1N 6BG, UK. d.carmichael@medphys.ucl.ac.uk
authors.forename: David W
authors.initials: DW
authors.lastname: Carmichael
authors.forename: David L
authors.initials: DL
authors.lastname: Thomas
authors.forename: Enrico
authors.initials: E
authors.lastname: De Vita
authors.forename: Maria A
authors.initials: MA
authors.lastname: Fernández-Seara
authors.forename: Navjeet
authors.initials: N
authors.lastname: Chhina
authors.forename: Mark
authors.initials: M
authors.lastname: Cooper
authors.forename: Colin
authors.initials: C
authors.lastname: Sunderland
authors.forename: Chris
authors.initials: C
authors.lastname: Randell
authors.forename: Robert
authors.initials: R
authors.lastname: Turner
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Ordidge
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D003142:Communication; D004581:Electronics; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*