Dielectric Constant Characterization of Artificial Electromagnetic Materials for Ultra-high Field Magnetic Resonance Radio Frequency Field Manipulation

Magnetic resonance imaging (MRI) technology is the mainstream medical imaging technology today. The use of ultra-high static magnetic field strength (≥7T) can better improve the signal-to-noise ratio of imaging and bring clearer imaging quality. However, the inherent standing wave effect of the classic resonant cavity transmitting coil will cause B1+ field inhomogeneity and high SAR value. Studies have shown that high dielectric constant materials can effectively improve the standing wave effect, but there are problems such as difficulties in manufacturing and long-term stability. This paper proposes a method for measuring the dielectric constant of artificial electromagnetic materials based on the microstrip line resonance method, which improves the traditional method of using scattering parameters to obtain the dielectric constant of artificial electromagnetic materials in the induced near-field region, and can effectively reflect the artificial electromagnetic materials in the near-field region. By loading the artificial electromagnetic material on the 7T birdcage coil and comparing it with the birdcage coil without control material, its B1+ field has been doubled, compared with the artificial electromagnetic material B1+ field designed by the traditional measurement method. The artificial electromagnetic material structure designed by the microstrip line resonance method has a significant field regulation effect in improving the uniformity of the B1+ field in the induced near-field area through experimental verification, and has good clinical applicability.