Investigation of NMR properties of gel volume change with magnetic resonance imaging
Yung, Kaung-Ti
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https://hdl.handle.net/2142/31247
Description
Title
Investigation of NMR properties of gel volume change with magnetic resonance imaging
Author(s)
Yung, Kaung-Ti
Issue Date
1999
Doctoral Committee Chair(s)
Lauterbur, Paul C.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
polyacrylamide gels
magnetic resonance imaging
Language
en
Abstract
Ferromagnetic or supetparamagnetic particles as MRI contrast agent
present many advantages for bringing about soft tissue contrast as
compared to single-ion complexes. Based on the dynamic frequency scale
1/τ and the magnetic frequency scale δω (perturber strength) of the
system the relaxation behavior is categorized into five diffusion regimes.
Two empirical models are proposed, one for the spin echo and the other
the gradient echo sequence, to account for the relaxation dependence of
such variables as sphere radius R, δω , and diffusion coefficient D in these
regimes. The models are verified with the results of our spectroscopic
measurements as well as simulations and experiments in the literature.
Through proper scaling of the sphere radius and the relaxation rate
normalized models are obtained, which maybe used to quantitatively
estimate l/T2 for various combinations of the variables. The models are
then extended to account for effects of sphere size change upon relaxation
rate of surrounding spins. The predicted l/T2 are close to simulation
points for small R but not for large R. Experimental approaches were used
to investigate NMR physical properties of the interior of gel network for
polyacrylamide gels. Longitudinal relaxation time T1, T2 , and D of proton
spins trapped within polymer network decrease as gels reduce in size
during the volume phase transition. The values fall shatply around acetone
concentration of 30% to 40%, at 50% the gels appear to complete the phase
transition. For gels in the contracted state T1 is one order and D and T2
less than two orders of magnitude smaller than when in the swollen state.
The internal component therefore contribute very little as compared to the
iii
external component to the total relaxation, making this situation resemble
to that of the impermeable polystyrene beads where our extended empirical
models seem to apply well.
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