High-Field Transmit Field Mapping

The radio frequency (RF) transmit field (B1+), plays an essential role in MR signal generation. This comprises signal excitation, signal refocusing and / or appropriate magnetization preparation. However, with the trend to higher main field strengths in MR, the effective RF wavelengths approaches body and transmit coil dimensions, thus wave propagations effects begin compromising RF homogeneity, image contrast and in worst cases SNR and image quality. To mitigate these effects parallel transmit technology (using RF shimming or transmit SENSE), special RF pulse designs or dedicated image processing can be used. All of them benefit from the profound knowledge of the corresponding B1+ fields of the involved transmit antennas, making efficient B1+ mapping approaches mandatory. Therefore, the DREAM (Dual Refocusing Echo Acquisition Method), which is one of the fastest RF transmit field-mapping techniques known, has been further developed, finding many applications in high field mapping in MR imaging and spectroscopy. The intrinsically low RF power level of DREAM makes it to the method of choice to explore and evaluate new transmit concepts especially at high fields.

Example developments and applications:









Tutorial:

Börnert P. Modeling, Mapping, & Application of RF Transmit Fields. Tutorial ISMRM, Montreal, May 9, 2011.

7 Tesla development and applications:

  1. Nehrke K, Versluis MJ, Webb A, Börnert P. Volumetric B(1) (+) Mapping of the Brain at 7T using DREAM. Magn Reson Med. 2014 Jan;71(1):246-56.
  2. Brink WM, Börnert P, Nehrke K, Webb AG. Ventricular B1 (+) perturbation at 7?T - real effect or measurement artifact? NMR Biomed. 2014 Jun;27(6):617-20.

3 Tesla development and applications:

  1. Nehrke K, Börnert P. DREAM-a novel approach for robust, ultrafast, multislice B1+ mapping. Magn Reson Med. 2012 Nov;68(5):1517-26.
  2. Sprinkart AM, Nehrke K, Träber F, Block W, Gieseke J, Schmitz G, Willinek WA, Schild H, Börnert P. Ultrafast volumetric B1 + mapping for improved radiofrequency shimming in 3 tesla body MRI. J Magn Reson Imaging. 2014 Oct;40(4):857-63.
  3. Nehrke K, Sprinkart AM, Börnert P. An in vivo comparison of the DREAM sequence with current RF shim technology. MAGMA. 2015 Apr;28(2):185-94.
  4. Hooijmans MT, Dzyubachyk O, Nehrke K, Koken P, Versluis MJ, Kan HE, Börnert P. Fast multistation water/fat imaging at 3T using DREAM-based RF shimming. J Magn Reson Imaging. 2015 Jul;42(1):217-23. 
  5. Brink WM, Versluis MJ, Peeters JM, Börnert P, Webb AG. Passive radiofrequency shimming in the thighs at 3 Tesla using high permittivity materials and body coil receive uniformity correction. Magn Reson Med. Magn Reson Med. 2016 Dec;76(6):1951-1956. doi: 10.1002/mrm.26070.


The project started in 2012 (active)