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Birdcage MRI Coil Simulation Example with SAR



Abstract:In this example, a birdcage-style MRI coil simulation is explained.To receive a good signal, RF coils used in magnetic resonance imaging (MRI) equipment are required to couple the energy from nuclei in precedence to a receiver. This example shows an RF coil simulation in MRI applications and Specific Abortion Ratio (SAR) analysis of a human head located inside a birdcage-style system and exposed to a 64MHz RF signal.

Figure 1 shows a high fidelity human head mesh inside a birdcage-style MRI system with RF coils.

Figure 1: Birdcage-style MRI Coil with Human Upper Body

Design Challenges

The RF coil must be responsive to frequencies within the general band of the Lamor frequency of interest. In human imaging, the wavelength is generally of the same order of magnitude as the sample. Often, a coil design known as the “birdcage” is used. This coil combines lumped capacitors with distributed inductance to form a volume resonator. If the resonance of the coil is designed well, it should increase the efficiency of the coil at the operating frequency (1). Finite difference time domain (FDTD) simulation technology is used to analyze the 64MHz RF coil performance to see the B field. Also, SAR analysis can be easily done with a built-in SAR function provided in EMPro FDTD.


Figure 2 shows the B-field at 64MHz.

Figure 2: B-field data at 64MHz

Figure 3 shows SAR data.

Figure 3: SAR data


FDTD EM simulation technology is the choice for RF coil simulation and SAR analysis for MRI applications. In this example, it is shown that FDTD simulation technology is very effective for analyzing those critical design factors.


(1) "Design of Medical Electronic Devices" by Reinaldo J. Perez

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