Magnetic field homogeneity for magnetic resonance imaging system, theory, calculation and experiment

Investigators: I. Frollo, P. Andris, A. Krafčík, D. Gogola, T. Dermek

Magnetic resonance imaging requires a source of magnetic field of the highest homogeneity for the entire volume of the object under study. The aim of this result is the presentation of shim coil design methods, theoretical calculations and homogeneous tomograph homogeneity adjustment, based on three methods of measuring the static magnetic field.
Measurements were performed using: a Hall effect magnetometer, a point MR magnetometer and a Gradient-echo imaging method applied to test ring tubes. All measurements of the magnetic field were oriented at one point in the center of the circle and 12 measurement points on its circumference. The system of linear equations, determination of the target function and optimization of calculations are procedures that ensure optimal values ​​of currents of correction coils. The results of all three methods were compared and analyzed.
The proposed methods are suitable for regular testing and correction of inhomogeneities of magnetic field sources for MRI devices.
The developed mathematical tool can also be used on other physical objects whose parameters can be influenced by external sources of fields, signals or radiation.
The result is the product of several years of work by a scientific team. The individual results were continuously published in the attached publications.

Fig. 1 a) Imaging of selected correction coils of the whole-body NMR tomograph. b) Circular measuring module fitted with measuring capsules. c) Graphic display of magnetic field values in three planes (left, central, right), original values and corrected values.

 

Related projects:
• VEGA 2/0001/17 – Measurement and imaging methods based on magnetic resonance for materials and biomedical research.
• APVV-15-0029 – Research of comparative magnetic resonance imaging methods for the diagnosis of neurological and musculoskeletal diseases.

 

Result applicator:
• The result can be applied for regular testing and correction of inhomogeneities of magnetic field sources for MRI devices. The company showed interest: Wega-MS spol. Ltd. Moravany nad Váhom.

 

Publications:

  1. FROLLO, Ivan – ANDRIS, Peter – KRAFČÍK, Andrej – GOGOLA, Daniel – DERMEK, Tomáš. Magnetic field homogeneity adjustment for magnetic resonance imaging equipment. In IEEE Transactions on Magnetics, 2018, vol. 54, no. 5, p. 6500309. ISSN 0018-9464. (1.467-IF2017)
  2. FROLLO, Ivan – ANDRIS, Peter – KRAFČÍK, Andrej – GOGOLA, Daniel – DERMEK, Tomáš. Comparative magnetic field measurements for homogeneity adjustment of magnetic resonance imaging equipments. In MEASUREMENT 2017: Proceedings of the 11th International Conference on Measurement. Editors: J. Maňka, M. Tyšler, V. Witkovský, I. Frollo. – Bratislava, Slovakia: Institute of Measurement Science, Slovak Academy of Sciences, 2017, p. 259-262. ISBN 978-80-972629-0-7.
  3. ANDRIS, Peter – FROLLO, Ivan. Optimized measurement of magnetic field maps using nuclear magnetic resonance (NMR). In Measurement Science and Technology, 2011, vol. 22, no. 4, art. no. 045501. ISSN 0957-0233. (1.350-IF2010)