Spatial resolution and sensitivity of magnetic susceptibility imaging

The use of a scanning susceptometer to image the 2-D distribution of magnetic susceptibility in thin samples is discussed. High-resolution magnetic field data recorded above complex shapes of plexiglass, scanned in a uniform applied field, are presented. Deconvolution of these data yielded magnetization distributions that were accurate images of the samples. It was found that the susceptibility of plexiglass is -9.0*10/sup -6/ (SI) and it was demonstrated that the present system is sensitive to susceptibility contrasts as small as 5*10/sup -7/ (SI), with a spatial resolution better than 1 mm. This performance is limited by the strength of the applied field, by the size and distance from the sample of the sensing coils, and by superconducting quantum interference device (SQUID) noise. It is estimated that one could increase spatial resolution by a factor of two, and sensitivity to susceptibility contrast by at least one order of magnitude by using an imaging susceptometer whose SQUIDs are integrally mounted within a superconducting magnet.<>