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The variation of proton density in agarose gels used as NMR test substances through the use of glass beads.

If an entirely tissue-equivalent test substance, with respect to nuclear magnetic resonance imaging, is to be produced, then some method of varying the proton density must be found. Until now the only feasible method of varying the proton density was to use D2O; however, it is hoped that the technique described will provide an alternative method that will prove to be as reproducible as D2O but at a fraction of the cost. In order to produce the desired variation in proton density, without the inhibiting cost of using D2O, glass beads can be added to the agarose gel. These glass beads, obtained from Jencons (Scientific) Ltd., have a small average diameter, around 0.113 mm, and do not produce a signal detectable by NMR when excited at the proton excitation frequency. The addition of a variable quantity of glass beads is therefore able to change the effective proton density of the gel.