High Permittivity Dielectric Pads

The generation of a high quality MR image is extremely challenging when imaging body parts that are large compared with the wavelength of the Radio-Frequency (RF) field. Constructive and destructive interference effects of the RF field can severely degrade the quality of an MR image reducing its use for interpretation and diagnostics . Interference effects may be particularly predominant for abdominal and cardiac imaging at 3T and neurological, abdominal, and cardiac imaging at 7T.

There are many approaches to address this issue including the use of transmit arrays and specially designed RF pulses. We have developed a complementary approach using high permittivity materials, often referred to as dielectric pads.

Example applications.

Imaging the inner ear of a patient at 7 Tesla, using asymmetrically-placed barium titanate pads to focus the B1+ field to the areas of interest.

  Inner ear imaging using dielectric pads at 7T

A comparison of using a commercial bulky pad with a much thinner barium titanate pad at 3 Tesla from the group in Utah.

Blood imaging of femoral arteries using dielectric pads at 3T 

Work at 3 Tesla shows that the global SAR is decreased with the use of high permittivity dielectric pads.

SAR reduction using dielectric pads at 3T 

Recent papers.

Electromagnetic modelling.

1.        J.van Gemert, W.M.Brink, A.G.Webb and R.F.Remis, An Efficient Pad Design Methodology for Dielectric Shimming in Magnetic Resonance Imaging, IEEE Trans.Med.Imag. in press, 2016.

2.        W.M.Brink, R.F.Remis, and A.G.Webb, A theoretical approach based on electromagnetic scattering for analysing dielectric shimming in high-field MRI, Magn.Reson.Med., 75:2185-94, 2016.

3.        W. Brink and A. Webb, A forward model analysis of dielectric shimming in magnetic resonance imaging, ICEAA, 528–531, 2013. 

7 Tesla development and applications.

4.        MA van der Jagt, WM Brink, MJ Versluis, S.C.A Steens, JJ Briaire, AG Webb, JHM Frijns, BM Verbist Visualization of Human Inner Ear Anatomy with High Resolution Magnetic Resonance Imaging at 7 Tesla: first initial clinical assessment and application, AJNR, 36, 378-383, 2015.

5.        W.M.Brink, A.M.A.van der Jagt, M.J.Versluis, B.M.Verbist and A.G.Webb, Dielectric pads improve high resolution imaging of the inner ear at 7 Tesla, Inv.Radiol. 49(5):271-7, 2014.

6.        W.M. Teeuwisse, W.M.Brink, K.N.Haines and A.G.Webb. Simulations of high permittivity materials for 7 T neuroimaging and evaluation of a new barium titanate-based dielectric. Magn Reson Med. 67, 912-918, 2012.

7.        W.M.Teeuwisse, W.M.Brink and A.G.Webb, A quantitative assessment of the effects of high permittivity pads in 7 Tesla MRI of the brain, Magn.Reson.Med. 67, 1285-1293, 2012.

8.        K.Haines, N.B.Smith and A.G.Webb, New high dielectric constant materials for tailoring the B1+ distribution at high magnetic fields, J.Magn.Reson, 203, 323-327, 2010.

3 Tesla applications.

9.        J.Oudeman, B.F.Coolen, V.Mazzoli, Ma.Maas, C.Verhamme, W.Brink, A.G.Webb, G.J. Strijkers, A. J. Nederveen.Diffusion-prepared neurography of the brachial plexus with a large field-of-view at 3T, J.Magn.Reson.Imag, 43, 644-654, 2016.

10.    W.M.Brink, M.J. Versluis, J.M. Peeters, P. Börnert, A.G.Webb, Passive radiofrequency shimming in the thighs at 3 Tesla using high permittivity materials and body coil receive uniformity correction, Magn Reson Med. 2015 Dec 14. doi: 10.1002/mrm.26070.

11.    W.M.Brink, J.S. van den Brink, A.G.Webb. The effect of high-permittivity pads on SAR behaviour in RF-shimmed  cardiac imaging at 3 Tesla, J.Cardiovasc.Magn.Reson. 17, 82-90, 2015.

12.    W.M.Brink and A.G.Webb, Optimized high permittivity dielectric pads reduce specific absorption rate and improve B1 homogeneity and contrast-to-noise ratio for functional cardiac MRI at 3T, 71(4):1632-40, 2014.

13.    P.de Heer, W.Brink, B.J.de Kooij and A.G.Webb, Increasing signal homogeneity in abdominal imaging at 3 Tesla with high permittivity materials, Magn.Reson.Med., 68(4):1317-24, 2012.

Review articles.

14.    W.M.Brink, V.Gulani, and A.G.Webb. Clinical perspectives on multiple transmit MRI, J.Magn.Reson.Imag., 42, 855-869, 2015.

15.    A.G.Webb, Dielectric materials in magnetic resonance, Conc.Magn.Reson. 38A, 148-184, 2011.