th  - 1987 - 51st ENC Conference

WF68
The SWIFT Method for In Vlvo Localized Spectroscopy
W.M. Chew, L.-H. Chang, T.L.dames*
Department of Pharmaceutical Chemistry
University of California San Francisco
San Francisco, California g4143
Of paramount Importance in in v/vo MRS studies is the ability to
acqulre localized spectra from the region of interest and with maximum
signal to noise. Failure to localize can lead to false results and erroneous
conclusions. Spectra obtained using localization schemes that fail to
maxlmlze signal to noise (S/N) can require long acquisition times and thus
obscure the ability to detect physiological changes. The optimal strategy
during the localization process is to keep manipulation of the magnetization
from the region of Interest to a minimum, thereby minimizing the loss of
S/N that can occur due to finite T2's and Instrumental imperfections.
We present a method of localization using the SWIFT (Stored
Waveform Inverse Fourier Transform) excitation method (1). Unlike most
gradient localization methods (wlth one exception (2)), magnetization in the
region of Interest is not manipulated (volume selective nonexcitation during
the preparation period) thereby retaining full z magnetization, an important
signal to noise consideration. Magnetization outside the region of interest is
dephased and saturated using a combination of tailored SWIFT pulses and
magnetic field gradients; a "read-out" pulse then interrogates spins left on
the z axis from the region of interest.
(i) A.6. Marshal, A.T. Hsu, W.W. HunLer Jr., P. Schmalbrock, Prec. Soc. Me~. Res. Med. FirLh Annual
MeeLing, Montreal (1986).
(2) D.M. DoddrelI, J.M. Bulsing, GJ. 6allowiy, W~. Brooks. J. Field, M. Irving, H. Baddeley, d. Magn.
Res. 70(2), 31g (1986).