Experimental Validation of the Selection Field of a Rabbit-Sized FFL Scanner

Abstract

There are two different field topologies in magnetic particle imaging which enable the spatial encoding of the signal. Scanners using a field-free line (FFL) are promising regarding their sensitivity, because the low field volume is larger compared to a field-free point (FFP) and therefore, more particles contribute to the signal. A rabbit-sized FFL scanner with a bore diameter of 173 mm was presented in 2014.  After planning and assembling the scanner an experimental validation of the designated field topology of the selection field is presented. With a hall probe the field topologies of the z-gradient coil and the two quadrupoles forming together the selection field of the scanner were investigated. These magnetic field measurements show the expected field topologies: an FFP formed by the z-gradient coil and an FFL parallel to the bore of the scanner formed by each quadrupole. From these measurements the field gradients were calculated and approximated towards the designated currents. The results are in good agreement with the expected field gradients. In order to determine the best suitable frequency for rotating the FFL measurements were done on the power loss in the shielding taking place for higher frequencies. And the power transmission of the transformer, which is problematic for low frequencies. A rotation frequency of 20 Hz is chosen as it represents a compromise between transformer performance and power loss in the shielding.