Patent ID: 8812078

Claim:
An apparatus ( 100 ) for determining at least one electromagnetic quantity characterizing an electromagnetic property of an object, wherein said object contains magnetic particles, which apparatus comprises: selection means comprising a selection field signal generator unit ( 110 ) and selection field elements ( 116 ) for generating a magnetic selection field ( 50 ) having a pattern in space of a magnetic field strength such that a first sub-zone ( 52 ) having a low magnetic field strength and a second sub-zone ( 54 ) having a higher magnetic field strength are formed in a field of view ( 28 ); drive means comprising a drive field signal generator unit ( 130 ) and drive field coils ( 136 a , 136 b , 136 c ) for changing the position in space of the two sub-zones ( 52 , 54 ) in the field of view ( 28 ) by means of a magnetic drive field so that a magnetization of the magnetic particles contained in said object changes locally; receiving means comprising at least one signal receiving unit ( 140 ) and at least one receiving coil ( 148 ) for acquiring detection signals, which detection signals depend on the magnetization in the field of view ( 28 ), which magnetization is influenced by the change in the position in space of the first and second sub-zone ( 52 , 54 ); a reconstruction unit ( 152 ) for reconstructing a particle distribution quantity characterizing a spatial distribution of the magnetic particles within at least a portion of the object depending on the detection signals; and a control unit ( 150 ) for controlling the receiving unit for acquiring a first set of detection signals corresponding to a first drive field frequency and for acquiring a second set of detection signals corresponding to a second drive field frequency, wherein the first and the second drive field frequency differ from each other, and for controlling the reconstruction unit ( 152 ) for reconstructing a first particle distribution quantity depending on the first set of detection signals and for reconstructing a second particle distribution quantity depending on the second set of detection signals, wherein the reconstruction unit ( 152 ) contains a determination unit ( 160 ) for determining the electromagnetic quantity as a function of different distortion effects by the first and the second particle distribution quantity.