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Oral 12
Abstract
Phase-gradient coil designs for 3D TRASE MRI at low field
Jesse Bellec b , Scott B. King c , <strong>and</strong> Christopher P. Bidinosti a,b ,
a Department of Physics, University of Winnipeg, Winnipeg, Canada
b Department of Physics <strong>and</strong> Astronomy, University of Manitoba, Winnipeg, Canada
c National Research Council of Canada, Winnipeg, Canada
Transmit Array Spatial Encoding (TRASE) is a new MR imaging technique that utilizes
B 1 phase-gradient fields to manage spatial encoding, rather than the st<strong>and</strong>ard B 0
magnitude-gradient fields [1]. The method offers a means to eliminate some of the
disadvantages associated with the generation of rapidly pulsed B 0 imaging gradients:
namely, equipment expense <strong>and</strong> power consumption, mechanical vibration <strong>and</strong> acoustic
noise, <strong>and</strong> nerve stimulation in patients. In a similar spirit, the on-going development of
low field NMR/MRI [2] is also strongly motivated by the increased functionality that can
be achieved through simplified, lightweight, <strong>and</strong> low-cost apparatus. As a result, low
field MRI appears to be an ideal application of TRASE worthy of investigation.
The main requirement for TRASE is the generation of B 1 fields that have uniform
magnitude <strong>and</strong> linearly varying phase over the volume of interest. For multi-dimensional
TRASE MRI, two phase-gradient coils are typically needed for each image encoding
direction [1]. We have previously explored the general design principles of phasegradient
coils using a target field method [3]. Based on this work we have developed an
array of current structures (resonators for higher frequencies; wire-wound coils for very
low frequencies) that generate all 6 phase-gradients needed for 3D imaging (Fig. 1 & 2).
Figure 1: A recent prototype array
with spiral, birdcage, <strong>and</strong> Maxwell
resonant structures. Such structures
have inherently low inductance <strong>and</strong>
cannot be tuned for very low
field/frequency operation.
y
y
z
x
z
x
Figure 2: Resonant structures (left) can be replaced with wire-wound equivalents (right)
for very low field/frequency operation.
References:
[1] JC Sharp <strong>and</strong> SB King, Magn. Reson. Med. 63, 151 (2010).
[2] B Blümich et al., Chem Phys Lett 477, 231 (2009); KP Pruessmann, Nature 455, 43
(2008); J Clarke et al., Annu Rev Biomed Eng 9, 389 (2007).
[3] J Bellec, C-Y Liu, SB King, <strong>and</strong> CP Bidinosti, Proc. Int. Soc. Magn. Reson. Med. 19,
723 (2011).
<strong>8th</strong> <strong>Conference</strong> on Fast Field Cycling NMR Relaxometry, Turin 23-25 May 2013