The use of an inhomogeneous applied field improves the spatial sensitivityprofile of an in vivo SQUID susceptometer

We present a SQUID susceptometer with a non-homogeneous magnetizing field w hich is null at the sensing coil and increases towards the patient position with a constant gradient plus a cubic term at large distances. Compared wi th the magnetizing fields of similar instruments described in the literatur e, our gradient field enhances the signal due to internal organs with respe ct to the signal due to superficial tissue. Preliminary measurements have b een performed on phantoms of known magnetic susceptibility. The advantage o f using a non-homogeneous field compared with a uniform field has been inve stigated in the case of a double-layer phantom.