The present invention relates to an apparatus (100) for determining at least one electromagnetic quantity characterizing an electromagnetic property of an object, in particular a human body, wherein said object contains magnetic particles. The apparatus (100) applying the known principle of Magnetic Particle Imaging (MPI) comprises selection means for generating a magnetic selection field (50) having the known field pattern showing a field free point (FFP), drive means for changing the position in space of the FFP by means of a magnetic drive field, receiving means for acquiring detection signals depending on the magnetization of the magnetic particles within a field of view (28) and a reconstruction unit (152) for reconstructing a particle distribution quantity depending on the detection signals. The apparatus (100) further comprises a control unit (150) for controlling the receiving means for acquiring a first set of detection signals corresponding to a first drive field frequency and a second set of detection signals corresponding to a second drive field frequency, with both drive field frequencies differing from each other. The control unit (15) further controls the reconstruction unit (152) for reconstructing a first particle distribution quantity depending on the first set of detection signals and a second particle distribution quantity depending on the second set of detection signals. The apparatus (100) further comprises a determination unit (160) for determining the electromagnetic quantity depending on the first and second particle distribution quantity. The present invention further relates to a corresponding method as well as to a computer program.本発明は、磁性粒子を含む対象物、特に人体の電磁特性を特徴づける少なくとも一つの電磁量を決定するための装置１００に関する。磁性粒子撮像法（ＭＰＩ）の既知の原理を適用する装置１００は、フィールドフリーポイント（ＦＦＰ）を示す既知の磁場パターンを持つ選択磁場５０を生成するための選択手段と、駆動磁場によってＦＦＰの空間内の位置を変えるための駆動手段と、撮像領域２８内の磁性粒子の磁化に依存して検出信号を得るための受信手段と、検出信号に依存して粒子分布量を再構成するための再構成ユニット１５２とを有する。装置１００は、更に、第１の駆動磁場周波数に対応する検出信号の第１のセットと、第１の駆動磁場周波数とは異なる第２の駆動磁場周波数に
