Using Additional Dielectric Material to Improve the RF Uniformity in Traveling-Wave MRI

In ultra high field, the wave behavior results in significant RF field inhomogeneities. To solve the high field RF problem, the traveling wave MRI, has been introduced to uniformly excite spins over a greater volume than that of the conventional volume RF coils. However, in large objects, such as the human head, the traveling wave method does not provide good RF uniformity due to the reflection and interference effects on account of largely difference of dielectric constants at boundaries between the tissues and the air. To eliminate the wave-impedance mismatch, we used additional dielectric material to fill the cavity around the head to mitigate the field inhomogeneities for human head imaging. The three-dimensional finite difference time domain numerical models at 300 MHz are used to theoretically validate the effectiveness of the approach.