An apparatus (100) detects magnetic particles in a field of view (28). The apparatus includes selection and focus magnetic field coil pairs (12, 14), drive pairs (16), and detection coils (148). A computer is configured to receive background signals with the detection coils, controls current supplied to the drive coil pair to shift the field of view in space, and reconstruct detection signals from the detection coils into an image of the field of view (28). The computer selects one or more frequency components of the detection signals and/or weighted by use of a frequency component specific signal quality factor obtained from the background signal measurements. Only the selected and/or weighted frequency components are used for reconstruction of the image.
