| Magnetic resonance imaging(MRI), which is based on the principles of nuclear magnetic resonance(NMR), is an imaging technique used to obtain anatomical, functional and pathological information of the inside of the human body. It is one of the non-invasion diagnostic techniques and a powerful tool for medical and molecular biology research.With the rapid development of technology, the pursuit of high-performance permanent magnet MRI system has become one of the current trends. In particular, for our country, permanent magnet MRI systems have become the main model for clinical diagnosis, and will continue to have enormous potential.Because human tissues contain a lot of adipose tissue, taking into account the special characteristics of fat, in order to clearly show lesions, increase contrast and reduce artifacts, fat suppression technique has emerged and become one of key techniques in MRI. Binomial water excitation technique is an effective fat-suppression technique, but in the low-field permanent magnet MRI system, it is protected by the main drift of the magnetic field, especially in 3D imaging scan. In this paper, the dynamic frequency drift correction algorithm is used to improve the effectiveness of fat suppression by binominal water excitation in low-field permanent magnet MRI system.Dynamic frequency drift correction algorithm is based on a 1D navigator. By comparing the phases of navigator signals acquired in the same time interval, phase differences are obtained, with which the variation of resonance frequency caused by field drift will be calculated. Initial phase of binominal combination pulse is corrected by this variation during scanning. The experimental results show that the method obviously improves the effectiveness of fat suppression by binominal water excitation in 3D imaging scan. In addition, the method will only slightly increase the scan time, and can be extended to other pulse sequences which are sensitive to the stability of the magnetic field.
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