Abstract: The invention relates to an arrangement and a method for determining the spatial distribution of magnetic particles in an examination area. Magnetic field means are used to generate a spatially inhomogeneous gradient magnetic field with at least one region with a low field strength, in which the magnetization of the particles is in a state of non-saturation, whereas they are in a state of saturation in the remaining region. By using change means to shift the area with a low field strength within the examination area, a change in the magnetization of the magnetic particles is brought about which can be detected from outside by detection means and contains information about the spatial distribution of the magnetic particles in the examination area The magnetic field means or the change means or the detection means or a combination of these means are arranged at least partially on a medical instrument.