th  - 1988 - 51st ENC Conference

8o I
HIGH RESOLUTION MR IMAGING AT 4.7T OF THE CENTRAL NERVOUS SYSTEM
IN RATS: Paul C. Wang, Alan Muraki, Sunder Rajan, Charles
Wambabe, Alessandro Guidotti, Mark Carvlin, Georgetown
University, Washington, DC 20007.
The rat is used commonly as an animal model in neurological
research. One of the inherent problems has been to discern
extremely small structures and detect pathological changes in the
rat's brain. High resolution in vivo nuclear magnetic resonance
images of the brain and spinal cord in rats were obtained using a
4.7 Tesla magnet with a 33 cm bore imaging system (Spectroscopy
Imaging System, Fremont, CA). Detailed anatomic structures are
revealed due to the high resolving capability (resolution: ]20 um
x 120 um, 4 averages). The slice thickness was 1.5 mm. A 2-
Gauss/cm gradient coil with a 2-inch diameter saddle shaped RF
coil was used. The RF coil was connected to the matching and
running circuit by means of a 50~ transmission cable. Standard
spin warp techniques with TR range from 0.3 sec to 3.0 sec and TE
range from 22 msec to 50 msec were utilized to obtain the TI and
T2 weighted images. Detailed microscopic structures such as the
basal ganglia, ventricular system, and olfactory bulb as well as
defining the gray matter from the white matter are clearly shown.
In vivo relaxation times of the brain tissue at 4.7 Tesla were
also measured.
81 J SODIUM IMAGING OF OCULAR TUMORS: Susan J. Kohler *,a, Nancy H. Kolodnyb, c,
and Swarna Balasubramaniam b, aBrigham and Womens Hospital, Boston MA 02115; bWellesley
College, Wellesley MA 02181; CMassachusetts Eye and Ear Infirmary, Boston MA 02114
Operating at field strengths of 1.5 and 1.9 T, we have developed 23Na magnetic resonance
imaging protocols which provide high resolution multi-echo sodium images in short times. Using
rapidly switchable gradients with minimum eddy currents we have implemented a multi-echo gradient
echo technique (J. Granot, J. Magn. Reson. 68, 575 (1986)) which produces acomplete three-
dimensional set of useable ocular images with 2x2x2mm voxels in four minutes by co-adding eight
echoes (TE=3.5ms). Alternatively, longer acquisition times may be used, and the echoes processed
individually to yield eight T2-weighted image sets. Since the echo time is only 3.5 ms, T2*'s may be
readily calculated.
Enucleated human and bovine eyes have been studied by these techniques. Conditions including
intraocular tumor, retinal detachment, and vitreous hemorrhage have been clearly visualized in these
systems. We have developed procedures to allow voxel by voxel calculations of T2 ° values from the
eight echoes generated from the gradient echo technique we employ. At 1.9 T the T2 ° value measured
from saline solutions is approximately 55 ms. The addition of increasing concentrations of
Tris3DyTTHA shift reagent shortens the T2* values as expected, reaching a value of 8.5 ms for a
solution containing 0.75 M NaCI and 0.05 M shift reagent. The measurement of T2* in the vitreous of
enucleated bovine eyes is more difficult due to increased noise, but preliminary results indicate T2*
values on the order of 50 ms.
Related studies of the "visibility" of sodium in the bovine vitreous have provided the
interesting and provocative result that the sodium in this environment has a visibility of
approximately 80%. This value is intermediate between the 100% visibility predicted for sodium in
an isotropic environment and the 40% visibility predicted for sodium in an anisotropic environment,
and is suggestive of two sodium pools within the vitreous.
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