Concerning the preparation and use of substances with a magnetic susceptibility equal to the magnetic susceptibility of air.

In this work it is demonstrated that the susceptibility of diamagnetic substances, such as water and agarose gel, can easily be tuned to the susceptibility of air by the addition of a proper amount of strongly paramagnetic ions, in this case 16.6 +/- 0.1 mM holmium(III). The resultant air-equivalent substances are shown to allow the creation of objects that do not disturb the static magnetic field of the scanner and hence do not invoke susceptibility artifacts, regardless of the objects' shape, size, and orientation with respect to B(0), and regardless of the pulse sequence being used. The addition of the proper amount of holmium(III) to aqueous solutions and gels is further shown to exert a negligible influence on the chemical shift and to cause a moderate increase of the relaxation rates 1/T(1) and 1/T(2). The results indicate the potential of air-equivalent substances for many purposes, including construction of artifact-free test objects; experimental setups and accessory devices; investigation of systems that contain air cavities, gas bubbles, etc.; and monitoring of system-related and object-induced field disturbances. (c) 2006 Wiley-Liss, Inc.