MAGNETIC-SUSCEPTIBILITY MEASUREMENT OF INSOLUBLE SOLIDS BY NMR - MAGNETIC-SUSCEPTIBILITY OF BONE

Measurements of the volume magnetic susceptibility of solids using the classical Gouy balance approach are hampered by variations in apparen t density of the packed powder. In this paper a quantitative NMR measu rement of the volume magnetic susceptibility of powdered solids is des cribed and the volume susceptibility of bone is reported. The techniqu e is based on the measurement of changes in incremental linewidth (1/p i T-2') induced in a marker fluid whose susceptibility can be predicta bly modified by changing the composition, such as by addition of a sol uble diamagnetic compound. The spectroscopic linewidth of the marker f luid is determined by the susceptibility difference between the fluid and the suspended solid. Changes in the linewidth are accompanied by b ulk magnetic susceptibility induced frequency shifts in the fluid reso nance. Correlating the two dependencies allows measurement of the abso lute volume susceptibility of the solid. The susceptibility of bovine rib bone was found to be -0.90 +/- 0.02 x(-) 10(-6) (CGS) confirming p revious estimates which suggested bone to be more diamagnetic than the marrow constituents. Knowledge of the susceptibility of bone is relev ant in view of the growing interest in MRI osteodensitometric techniqu es.