Design and evaluation of an RF front-end for 9.4 T human MRI

G. Shajan, Jens Hoffmann, Juliane Budde, Gregor Adriany, Kamil Ugurbil, Rolf Pohmann

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

At the field strength of 9.4 T, the highest field currently available for human MRI, the wavelength of the MR signals is significantly shorter than the size of the examined structures. Even more than at 7 T, constructive and destructive interferences cause strong inhomogeneities of the B1 field produced by a volume coil, causing shading over large parts of the image. Specialized radio frequency hardware and B1 management methods are required to obtain high-quality images that take full advantage of the high field strength. Here, the design and characteristics of a radio frequency front-end especially developed for proton imaging at 9.4 T are presented. In addition to a 16-channel transceiver array coil, capable of volume transmit mode and independent signal reception, it consists of custom built low noise preamplifiers and TR switches. Destructive interference patterns were eliminated, in virtually the entire brain, using a simple in situ radio frequency phase shimming technique. After mapping the Ba1+ profile of each transmit channel, a numerical algorithm was used to calculate the appropriate transmit phase offsets needed to obtain a homogeneous excitation field over a user defined region. Between two and three phase settings are necessary to obtain homogeneous images over the entire brain.

Original languageEnglish (US)
Pages (from-to)594-602
Number of pages9
JournalMagnetic resonance in medicine
Volume66
Issue number2
DOIs
StatePublished - Aug 2011

Keywords

  • 9.4 T human brain MRI
  • microstrip transmission line
  • transceiver array

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