(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: In Magnetic Particle Imaging (MPI), a selection field containing a field-free point (FFP) or a field-free line (FFL) is used to enable spatial selection of a particular region so to achieve spatial coding. Using FFL, instead of FFP, reduces acquisition time, improves sensitivity, and signal-to-noise ratio (SNR). In this study, FFL was formed by using multiple Halbach rings that generated a homogenous dipole magnetic field. A magnet system was designed using a nested Halbach array of three layers and their effects on FFL performance for each layer were investigated.
Methods: In this study, FFL was generated along the x-axis using a nested Halbach array of cylindrical magnets arranged in dipole form (k=2). Remanence (Br) value of NdFeB (neodymium-iron-boron) permanent magnets was taken as 1.42 T. Magnetic flux density and gradient field strength for each layer of this design were obtained from simulation using COMSOL Multiphysics software.
Results: As the number of layers increases, magnetic flux density, and gradient field strength increase on the y-axis. Gradients on the y-axis were obtained 4.2 T/m at one-layer design (i.e. the innermost layer), 6.9 T/m at two-layer, and 8.7 T/m at three-layer design. The gradient values were stable along 35 mm at one-layer design, 45 mm at two-layer, and 50 mm at three-layer design, and its homogeneity was above 95%. Thus, the three-layer design is superior to the stability and provides a better resolution since spatial resolution strongly depends on gradient field strength.
Conclusion: In this work, FFL was successfully formed using multiple Halbach rings consist of permanent magnets. We demonstrated that the multiple layers of Halbach magnet system have significant effects on FFL performance. A drive field generated by permanent magnets will be added to the system, and then, FFL performance based on different parameters will be analyzed in the near future.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Scientific and Technological Research Council of Turkey under Grant TUBITAK 115E776 & 115E777.
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