th  - 1987 - 51st ENC Conference

WFIO
BULK MAGNETIC SUSCEPTIBILITY EFFECTS IN NA-23 NMR SPECTRA OF
COMPARTMENTALIZED SAMPLES CONTAINING NA + AND SHIFT REAGENTS
S
Simon C-K. Chu , James A. Balschi, & Charles S. Springer, Jr.
Department of Chemistry, State University of New York,
Stony Brook, New York 11794-3400
Since the Z3Na NMR signal is by far the second strongest
arising from tissue samples in pulsed experiments,
developments in 23Na NMR of living systems are occurring very
rapidly. 23Na MRI has become the second most common (e.g.,
Magn. Res. Med., 3, 296, 1986). Because of the isochronicJty
of Z3Na resonances from different compartments, we and
several other groups introduced paramagnetic shift reagents
(SRs) for use with Z3Na (and other cationic resonances)
in 1981-82, and we reported the nature of the spectra arising
from SR-perfused tissue in 1985 (BiophFs. J., 48, 159, 1985).
The first report of 23Na spectra from a living animal
infused wlth a SR has recently appeared (J. Magn. Res., 69,
523, 1986).
Different SRs cause hyperfine shifts of the Z3Na NMR
signal of different magnitudes and different signs. The
former is because of differing equilibrium quotients and
limiting shifts (dipolar) in the different SR-Na ÷ binding
equilibria. The latter is because of differing geometric
relationships between the Na ÷ binding site(s) and the
axes of the magnetic susceptibility tensor of the SR
molecular anion.
Since, in living systems, the distribution of the SR
will be restricted to certain tissue compartments (e.g.,
vascular only, interstitial only, vascular and interstitial),
bulk magnetic susceptibility (BMS) effects will be manifest
in the 23Na NMR spectrum. Both the magnitude and the
sign of the BMS shift depend on the shape of the compartment
and its orientation with respect to the static magnetic field
(B0). We have conducted a thorough comparison of the
relative sizes of the BMS and hyperfine shifts induced by
three different SRs in cylindrical compartments (simulating
either blood vessels or interstitial spaces) oriented either
parallel or perpendicular to the B0 field direction.
For the SRs chosen, both the magnitude and the sign of the
hyperfine shift also vary. Thus, the ratio of the BMS
contribution to the hyperfine contribution varies over a very
wide range (-0.92 to 0.75, in the samples chosen). These
contributions are, of course, algebraically additive in any
given spectrum. The local inhomogeneJties produced outside a
cylindrical vessel running perpendicular to B0 also
cause interesting inhomogeneous broadening patterns in the
resonances of nuclei restricted to the space outside the
vessel when that space is itself constrained.