Influence of a Dielectric Insert of High Permittivity on the Transmit Performance of a 300 MHz Multi-channel MRI Loop Array

摘要

Several recent reports have suggested that the transmit performance of a given MRI RF coil can be enhanced by incorporating suitable dielectric materials. To analyse this proposed approach more deeply, we investigated the effect of a dielectric material insert on loop array power balance, transmit performance and slice homogeneity. To obtain a useful database in a reasonable time, we varied only the insert permittivity, the load diameter, the separation between array and load, and the length of loop elements. For a range of parameter combinations, use of the insert increases the mean transmit RF field over the central transverse slice B_(1+S), and the homogeneity of this slice, but not the transmit performance, expressed as ratio of the mean RF field over the field of view to the square root of power deposited in the FOV, B_(1+~A) /P~(1/2)_l. An array with the insert cannot provide better B_(1+S) and homogeneity than an array without the insert in which the geometry is optimized for a given target region. We have found no general recipe for achieving the best array performance and homogeneity using the insert in an array with arbitrary geometry.