EM Modeling

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Objective: Electromagnetic modeling of magnet fields, switched gradient field and radiofrequency fields for MRI and NMR applications.
Fig 1. Calculated EF fields and thermal contours.

Numerical modeling of electromagnetic (EM) field propagation and losses is an important tool for understanding, designing and implementing new technologies and methods, safely and successfully for MRI applications. While EM modeling is used to simulate static magnetic fields (B0), and switched gradient magnetic fields (dB0/dt), most field calculations done at the CMRR are of the radiofrequency (RF) magnetic B1 fields generated and received by various RF coils to stimulate and receive the NMR signal response from the body for MRI. RF electric (E) fields, their losses in tissue (SAR) and consequential heating are also predicted through EM modeling. Dr. Vaughan and others have employed full-wave EM modeling by the finite element method (FEM) and by finite difference time domain (FDTD) since the early 1990s for RF coil design, RF pulse sequence design and RF safety applications (1-6).

1. J. T. Vaughan, J. G. Harrison, H. P. Hetherington, W. T. Evanochko, and G. M. Pohost, "Radiofrequency surface coil heating measurements in porcine muscle," in ISMRM 11th Annual Scientific Meeting and Exhibition, Berlin, Germany, 1992, p. 4026.
2. J. T. Vaughan, J. M. Vaughan, H. P. Hetherington, J. G. Harrison, P. J. Noa, and G. M. Pohost, "High frequency surface coils for clinical NMR imaging and spectroscopy," in ISMRM 12th Annual Scientific Meeting and Exhibition, New York City, NY, 1993, p. 1332.
3. J. T. Vaughan, H. P. Hetherington, J. O. Otu, J. W. Pan, and G. M. Pohost, "High frequency volume coils for clinical NMR imaging and spectroscopy," Magn Reson Med, vol. 32, pp. 206-18, Aug. 1994. PMID: 7968443
4. J. H. McDuffie, J. G. Harrison, G. M. Pohost, and J. T. Vaughan, "3D numerical modeling of high frequency volume coilds for clinical NMR," in ISMRM 3rd Scientific Meeting and Exhibition, Nice, France, 1995, p. 185.
5. J. G. Harrison and J. T. Vaughan, "Finite element modeling of head coils for high-frequency magnetic resonance imaging applications," in 12th Annual Review of Progress in Applied Computational Electromagnetics, Monterey, CA, 1996, pp. 1220-1226.
6. J. T. Vaughan, "Ultra high field MRI: high-frequency coils," in Ultra High Field Magnetic Resonance Imaging, P.-M. L. Robitaille and L. J. Berliner, Eds., ed New York City, NY: Springer Academic / Plenum Publishers, 2006, pp. 127-61.