  We present a magnet and high power electronics for Prepolarized Magnetic
Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system
designed for simultaneous visualization of hard and soft biological tissues.
PMRI boosts the signal-to-noise ratio (SNR) by means of a long and strong
magnetic pulse which must be rapidly switched off prior to the imaging pulse
sequence, in timescales shorter than the spin relaxation (or T1) time of the
sample. We have operated the prepolarizer at up to 0.5 T and demonstrated
enhanced magnetization, image SNR and tissue contrast with PMRI of tap water,
an ex vivo mouse brain and food samples. These have T1 times ranging from
hundreds of milli-seconds to single seconds, while the preliminary high-power
electronics setup employed in this work can switch off the prepolarization
field in tens of milli-seconds. In order to make this system suitable for
solid-state matter and hard tissues, which feature T1 times as short as 10 ms,
we are developing new electronics which can cut switching times to ~300 us.
This does not require changes in the prepolarizer module, opening the door to
the first experimental demonstration of PMRI on hard biological tissues.
