| dc.description.abstract | Phased array surface coils offer high SNR over a large field of view. Phased array
volume coils have high SNR at the surface and centre of the volume. Most array coil
designs typically employ a combination of geometrical and additional techniques, such
as isolating preamplifiers for element-to-element decoupling. The development of array
coils for small animal MRI is of increasing interest. However isolation preamplifiers are
expensive and not ubiquitous at the field strengths typically employed for small animal
work (4.7T, 9.4T, etc). In addition, isolating preamps complicates the designs of coils for
transmit SENSE since they do not decouple during transmitting. Therefore, this thesis
reexamines a "tried and true" method for decoupling coil elements. In this work five
different coils for mouse imaging at 200MHz are presented: a 16 leg trombone design
quadrature birdcage coil and four geometrically decoupled volume phased array coils.
The first mouse array coil is a two saddle quadrature coil with a circularly polarized
field. The second coil is a four channel transmit/receive volume array coil that is
decoupled purely geometrically, without the need for other forms of decoupling. The
third array coil is a modified 'open' configuration to facilitate the loading of animals.
The fourth coil presented is a 'tunable' decoupling coil, where the geometric decoupling between elements is 'tunable', in order to compensate for different loading conditions of
the coil.
Tunable decoupling between elements was achieved using two mechanisms, a
decoupling paddle for isolation of top to bottom elements, with a variable overlap
mechanism for decoupling diagonal elements. Bench measurements demonstrate good
decoupling (better than -20dB) of the coil elements and 'tunability' of both mechanisms.
Phantom images from all coils are presented. | en |
