th  - 1987 - 51st ENC Conference

Thursday - AM
IMAGE GUIDED LOCALIZED NMR SPECTROSCOPY AT 1.5 T
Peter R. Luyten and Jan A. den Hollander
Philips Medical Systems, P.O. Box I0000, NL-5680 DA Best,
The Netherlands
We have explored localization techniques to obtain high
resolution spectra of human tissues in situ on a 1.5 T whole body
MR imager. These techniques use switched field gradients to
define one or more volumes of interest from which NMR spectra can
be obtained. By using gradients for volume selection the exact
coordinates of the selected volumes can easily be determined from
a standard NMR image.
For optimal results different nuclei may require different
pulse sequences, in order to meet the typical NMR characteristics
of each particular nucleus. To obtain localized IH spectra we
use a technique in which magnetization in the volume of interest
is retained along the z axis, wheras all signal outside this
volume is dephased in the xy plane. The advantage of this
technique is that it allows for localization in one single shot.
This can be used for shimming the volume of interest. When this
technique is combined with an appropriate phase cycling scheme a
very good suppression of unwanted signal from outside the volume
of intererest is achieved. The disadvantage is that the
technique relies on relatively long T2 values and small homo
nuclear J couplings. Therefore, localized 31P spectra have been
obtained by a different localization technique which avoids
transversal magnetization during the localization pulse sequence.
In stead, selected volumes are obtained by using selective
frequency modulated inversion pulses in combination with an
appropriate add-subtract scheme.
Both localization sequences can be easily combined with
established pulse sequences to measure relaxation rates or to
perform water suppression and spin editing techniques. Some
results that were obtained with these techniques and the
technical difficulties that may be encountered in these
experiments will be discussed.