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Using Multiple Cylindrical Halbach Rings in Magnetic Particle Imaging

M Ergor1, A Olamat1, N Dogan2, A Bingolbali1*, (1) Yildiz Technical University, Istanbul, TR, (2) Gebze Technical University, Gebze-Kocaeli, TR


(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.

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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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