Abstract
Computational methods such as the finite difference time domain (FDTD) play an important role in simulating radiofrequency (RF) coils used in magnetic resonance imaging (MRI). The choice of absorbing boundary conditions affects the final outcome of such studies. We have used FDTD to assess the Berenger's perfectly matched layer (PML) as an absorbing boundary condition for computation of the resonance patterns and electromagnetic fields of RF coils. We first experimentally constructed a high-pass birdcage head coil, measured its resonance pattern, and used it to acquire proton phantom MRI images. We then computed the resonance pattern and field of the coil using FDTD with a PML as an absorbing boundary condition. We assessed the accuracy and efficiency of PML by adjusting the parameters of the PML and comparing the calculated results with measured ones. The optimal PML parameters that produce accurate (comparable to the experimental findings) FDTD calculations are then provided for the birdcage head coil operating at 127.72 MHz, the Larmor frequency of at 3 Tesla (T).
Highlights
The dimensions and resolutions of a discretized domain for calculating electromagnetic fields can be restrained by the memory and computational capacity of the computer
We have explored the role of Berenger’s perfect matched layer (PML) as an absorbing boundary condition in the computational characterization of RF coils for magnetic resonance imaging (MRI) at 3 T
We presented a method that evaluates the accuracy and efficiency of the PML for computing the resonance patterns and B1 fields of RF coils using finite difference time domain (FDTD)
Summary
The dimensions and resolutions of a discretized domain for calculating electromagnetic fields can be restrained by the memory and computational capacity of the computer. Since its introduction to FDTD, PML has been extended by a number of researchers. Among these PMLs, Berenger’s PML [2, 3], anisotropic PML (APML) [4, 5], complex frequency shifted PML (CFS PML) [6], and higher-order PML [7, 8] represent the most usual types of PML. CFS PML is more efficient in annihilating the evanescent waves than are the regular PMLs [9], it sacrifices good absorption of the propagation waves at low frequencies [7]. Higherorder PML is a new attempt to combine the advantages of both regular PML and CFS PML [7, 8]
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