posters 5th Asia-Pacific NMR Symposium 2013

High Imaging Acceleration with a Rotating Radiofrequency Coil Array at 7T (#170)

Mingyan Li 1 , Jin Jin 1 , Feng Liu 1 , Adnan Trakic 1 , Ewald Weber 1 , Stuart Crozier 1
  1. School of Information Technology and Electrical Engineering, the University of Queensland, St Lucia/Brisbane, QLD, Australia

Introduction: To provide excellent parallel imaging performance without using a large number of coils in an array, we propose to strategically combine the rotating radiofrequency coil (RRFC) 1,2 with phased-array coils (PACs). In this approach, considerably more sensitivity profiles can be employed for sensitivity encoding (SENSE)3,4, thereby achieving higher reduction factor without increasing the number of coil elements.

Method: Fig.1 illustrates a prototype of rotating radiofrequency coil array (RRFCA) for MR neuroimaging that consists of 4 identical elements evenly distributed around the subject. After loading with a cylindrical homogeneous phantom (εr = 78, σ = 0.53), the mutual coupling between any two channels were under -23 dB without the employment of additional decoupling techniques. Electromagnetic modelling was performed with FEKO (EMSS, SA). The steady-state circularly-polarized RF magnetic field (B1) was calculated according to 5 with MATLAB (Mathworks, MA). Assume that the coil array steps through various azimuthal angles θ during sampling. By carefully choosing θ, sensitivity encoding ability of RRFCA can be optimised as 6,7:


where gx,y(θ) was the g-factor calculation at voxel (x, y) in a image with size N× N.


Results: Fig. 2 shows that, at all reduction factors, the RRFCA had the best imaging acceleration capability demonstrated by lowset max g-factor and most uniform g-map when compared to two conventional arrays. Fig. 3 (a) and (c) were the phantom images reconstructed by RRFCA and 8-element PACs, respectively. (b) and (d) correspond to the error maps of (a) and (c). The root-mean-standard-deviation and artefact power of RRFCA reconstructed images were improved 13.3% and 24% respectively, compared to stationary 8-element PACs.

Conclusion: This preliminary study showed obvious advantages of RRFCA in imaging acceleration and artefact suppression when compared to traditional stationary phased-array coils with same and doubled number of channels.

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  2. A.Trakic, et al, J of Magn Reson,vol 201,2009.
  3. K. Pruessmann , et al, Magn Reson in Med, vol 42, 1999.
  4. K. Pruessmann , et al, Magn Reson in Med, vol 46, 2001.
  5. D. Hoult, Concepts in Magnetic Resonance, vol. 12, 2000.
  6. M. Li et al,ISMRM, SLC, 2013.
  7. M. Li, et al, IEEE EMBC San Diego, 2012.