A Design Method of Artificial Electromagnetic Materials for Ultra-High Field Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) technology is widely used in medical imaging. Using ultra-high field strength (7T) improves the signal-to-noise ratio and enhances imaging quality. However, the inherent standing wave effect of the traditional resonant cavity transmitting coil leads to inhomogeneity in the B$_{1}^{+}$ field. The artificial electromagnetic materials (AEM) with capabilities mimicking arbitrary dielectric constant are highly useful in field manipulation in MRI. For the equivalent dielectric constant of AEM, it is usually measured at radiation region, while the RF coil in MRI usually works at reactive region. Classic dielectric constant measurement of AEM at design stage may leads to inaccurate field manipulation compared to its dielectric pad counterpart. This paper proposes a novel method measuring the dielectric constant of AEM at reactive region, through using the microstrip line resonator. Its efficacy was verified through loading AEMs into the 7T MRI birdcage coil. The AEM structure designed using the microstrip line resonator method can better mimic the field manipulation effect of dielectric materials.