th  - 1987 - 51st ENC Conference

WK3S
EXPERIMENTAL STUDY OF THE OPTIRIZED SELECTIVE RF PULSES
Jintong Haoo, T.H. hreci, K.E. Scott and E.R. Andrev
Departments of Radiology and Physics
Gsinesvllle, FL 32611
Selective rodiofrequency (rf) pulmes ore important in both NHR
spectroscopy end imaging. Because the magnetization equation of
motion is nonlineor, the design of the rf pulse shapes cspoble of
precisely affecting the magnetization in a veil-defined frequency
range is not s simple problem. Recently, the concept of optimal
control hob been introduced for the design of rf pulses amplitude
modulated as a function of time to provide frequency selectivity.
Several selective pulse shapes hsve been developed using these
tethods, hoverer, very few experimental results have been presented.
We have presented a detoiled description of the use of the conjugate
gradient method in the optics1 control problem to design a selective
180 degree inversion pulses (1). Using this method, we have found a
series of the 9e and the 180 degree rf pulse shapes that have very
high selectivity. We have performed experiments on I GE CS1-2
imager/spectrometer vhich confirm theoretical predictions from the
application of optimal control methods. Both our computer
simulations end experimental results are presented in this poster.
Also, we 8how that the frequency response of the magnetization
affected by a selective 180 degree inversion rf pulse is the game as
that for a selective refocusing pulse. Computer simulations for both
a sinc and optimal pulse are presented to demonstrate the principle
and experimental results for selective refocusing pulses ire
presented. Thus, I single optimal selective 180 degree rf pulse can
be used is either in inversion or refocusing pulse. In both
IituationI, its selectivity can be optiIlzed to fit the desired
frequency profile end we rill diicuII how to apply thlI procedure in
designing selective pulses to fit various selectivity criteria.
Optimal control methods can also be applied to the case of
selective 90 degree rf pulses. The degree of improvement possible is
not as great as for selective 180 degree pulses but significant
improvement is possible. Both experimental and computer simulation
results of the optimal selective 90 degree rf pulses will also
be presented in this poster. Thus, the optimal control sethod has
solved the problem of designing optimized rf pulse shapes for
frequency selective excitation.
This research is supported by grants from the National Znstitute of
Health {P41-RR-e2278) and the Veterans Administration Medical
Research Service.
1. Jintong Meo, T. H. Mareci, K. N. Scott and E. R. Andrev, J. MIgn.
ReIon. 70, 31e (1986)