The invention relates to an examination apparatus (100), a method and a computer program for tracking permanently magnetic beads (107) that are transported by a fluid flowing through a channel (106) of an object (105). The examination apparatus (100) comprises at least three magnetic field sensors (101, 102, 103) and an evaluation unit (104). With the magnetic field sensors, the magnetic field caused by the permanently magnetic beads (107) is detected. Due to shear forces acting in the fluid, the permanently magnetic beads (107) are rotating and the magnetic field caused by the beads (107) is temporally varying. This temporal variation of the magnetic field is used by the evaluation unit (104) for discriminating sub-signals related to single beads (107) from the overall signal generated by the magnetic field sensors. Furthermore, the evaluation unit determines positioning information of individual beads on the basis of the discriminated sub-signals.
