title: B1 transmit phase gradient coil for single-axis TRASE RF encoding.
abstract: OBJECTIVE
  TRASE (Transmit Array Spatial Encoding) MRI uses RF transmit phase gradients instead of B0 field gradients for k-space traversal and high-resolution MR image formation. Transmit coil performance is a key determinant of TRASE image quality. The purpose of this work is to design an optimized RF transmit phase gradient array for spatial encoding in a transverse direction (x- or y- axis) for a 0.2T vertical B0 field MRI system, using a single transmitter channel. This requires the generation of two transmit B1 RF fields with uniform amplitude and positive and negative linear phase gradients respectively over the imaging volume.
  
  
  METHODS
  A two-element array consisting of a double Maxwell-type coil and a Helmholtz-type coil was designed using 3D field simulations. The phase gradient polarity is set by the relative phase of the RF signals driving the simultaneously energized elements.
  
  
  RESULTS
  Field mapping and 1D TRASE imaging experiments confirmed that the constructed coil produced the fields and operated as designed. A substantially larger imaging volume relative to that obtainable from a non-optimized Maxwell-Helmholtz design was achieved.
  
  
  CONCLUSIONS
  The Maxwell (sine)-Helmholtz (cosine) approach has proven successful for a horizontal phase gradient coil. A similar approach may be useful for other phase-gradient coil designs.
authors.affiliation: National Research Council of Canada, Calgary, Alberta, Canada T3G 1Z5.
authors.forename: Qunli
authors.initials: Q
authors.lastname: Deng
authors.forename: Scott B
authors.initials: SB
authors.lastname: King
authors.forename: Vyacheslav
authors.initials: V
authors.lastname: Volotovskyy
authors.forename: Boguslaw
authors.initials: B
authors.lastname: Tomanek
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Sharp
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation*; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008280:Magnetics / Q000295:instrumentation*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014159:Transducers