title: An Asymmetric Birdcage Coil for Small-animal MR Imaging at 7T.
abstract: The birdcage (BC) coil is currently being utilized for uniform radiofrequency (RF) transmit/receive (Tx/Rx) or Tx-only configuration in many magnetic resonance (MR) imaging applications, but insufficient magnetic flux (|B1|) density and their non-uniform distribution still exists in high-field (HF) environments. We demonstrate that the asymmetric birdcage (ABC) transmit/receive (Tx/Rx) volume coil, which is a modified standard birdcage (SBC) coil with the end ring split into two halves, is suitable for improving the |B1| sensitivity in 7T small-animal MR imaging. Cylindrical SBC and ABC coils with 35 mm diameter were constructed and bench tested for mouse body MR imaging at 300 MHz using a 7T scanner. To assess the ABC coil performance, computational electromagnetic (EM) simulation and 7T MR experiment were performed by using a cylindrical phantom and in vivo mouse body and quantitatively compared with the SBC coil in terms of |B1| distribution, RF transmit (|B1+|) field, and signal-to-noise ratio (SNR). The bench measurements of the two BC coils are similar, yielding a quality value (Q-value) of 74.42 for the SBC coil and 77.06 for the ABC coil. The computational calculation results clearly show that the proposed ABC coil offers superior |B1| field and |B1+| field sensitivity in the central axial slice compared with the SBC coil. There was also high SNR and uniformly distributed flip angle (FA) under the loaded condition of mouse body in the 7T experiment. Although ABC geometry allows a further increase in the |B1| field and |B1+| field sensitivity in only the central axial slice, the geometrical modification of the SBC coil can make a high performance RF coil feasible in the central axial slice and also make target imaging possible in the diagonal direction.
authors.affiliation: Center for Molecular and Cellular Imaging, Samsung Biomedical Research Institute.
authors.forename: Kyoung-Nam
authors.initials: KN
authors.lastname: Kim
authors.affiliation: Center for Molecular and Cellular Imaging, Samsung Biomedical Research Institute.
authors.forename: Sang-Doc
authors.initials: SD
authors.lastname: Han
authors.affiliation: Center for Molecular and Cellular Imaging, Samsung Biomedical Research Institute.
authors.forename: Jeung-Hoon
authors.initials: JH
authors.lastname: Seo
authors.affiliation: Department of Health Sciences and Technology, Samsung Advanced Institute for Health Science and Technology, Sungkyunkwan University.
authors.forename: Phil
authors.initials: P
authors.lastname: Heo
authors.affiliation: Center for Molecular and Cellular Imaging, Samsung Biomedical Research Institute.
authors.forename: Dongkyeom
authors.initials: D
authors.lastname: Yoo
authors.affiliation: Center for Molecular and Cellular Imaging, Samsung Biomedical Research Institute.
authors.forename: Geun Ho
authors.initials: GH
authors.lastname: Im
authors.affiliation: Department of Health Sciences and Technology, Samsung Advanced Institute for Health Science and Technology, Sungkyunkwan University.|Department of Radiology, Samsung Medical Center, Sungkyunkwan University School of Medicine.
authors.forename: Jung Hee
authors.initials: JH
authors.lastname: Lee
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004867:Equipment Design; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D051379:Mice; D019047:Phantoms, Imaging; D011846:Radio Waves; D059629:Signal-To-Noise Ratio
keywords: 7T; Asymmetric birdcage coil; magnetic resonance imaging; radiofrequency coil; signal-to-noise ratio; |B1| field