title: Transmit and receive RF fields determination from a single low-tip-angle gradient-echo scan by scaling of SVD data.
abstract: OBJECTIVE
  A new method, called Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images (TRIPLET), is described which simultaneously maps the B1+ and B1- fields of a transmit/receive radiofrequency coil array. The input data are low-tip-angle gradient-echo images, which can be acquired in a relatively short scanning time.
  
  
  METHODS
  For each voxel in the field of view, a matrix can be assembled with the low-tip-angle gradient-echo image values of the radiofrequency coil array. Applying the singular value decomposition to those matrices, datasets are obtained which show a high resemblance with the true B1+ and B1- fields. These datasets are a voxel-wise scaled version of the true radiofrequency maps. The channel independent scaling parameters can be found by implicitly forcing the reconstructed fields to be solutions of the Maxwell equations. This is achieved by introducing a multipole expansion consisting of Bessel/Fourier functions.
  
  
  RESULTS
  Two FDTD simulated radiofrequency fields for two coil array combinations at 7 T and a measured, in vivo dataset at 7 T are investigated to illustrate the singular value decomposition analysis of the low-tip-angle gradient-echo images and to show how the B1+ and B1- fields can be reconstructed by Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images.
  
  
  CONCLUSIONS
  The Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images algorithm can convert the datasets from singular value decomposition analysis of low-tip-angle gradient-echo images to true B1+ and B1- fields.
authors.affiliation: Imaging Division, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sbrizzi
authors.forename: Alexander J E
authors.initials: AJ
authors.lastname: Raaijmakers
authors.forename: Hans
authors.initials: H
authors.lastname: Hoogduin
authors.forename: Jan J W
authors.initials: JJ
authors.lastname: Lagendijk
authors.forename: Peter R
authors.initials: PR
authors.lastname: Luijten
authors.forename: Cornelis A T
authors.initials: CA
authors.lastname: van den Berg
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D011846:Radio Waves; D013997:Time Factors
keywords: TRIPLET; parallel imaging; receive fields; shimming; transmit fields