System calibration unit for magnetic particle imaging: System matrix

Magnetic particle imaging (MPI) has the potential to deliver images at high time resolution and submillimetre spatial resolution. In order to reconstruct the images from the measured data one needs to obtain a so called system matrix. A system matrix can be measured by physically moving a voxel sized sample and measuring the signal at each position within the imaging volume of the scanner. A system calibration unit (SCU) provides a fast and efficient method to measure a system matrix. The physical movement of the sample can be replaced by the use of homogeneous focus fields. This resulted in time saving of a factor of 2-3. In this paper, the use of sensitive dedicated receive coils is described that provide a further improvement by up to an order of magnitude in sensitivity.