  In contrast to linearly polarized RF coil arrays, quadrature transceiver coil
arrays are capable of improving signal-to-noise ratio (SNR), spatial resolution
and parallel imaging performance. Owing to a reduced excitation power, low
specific absorption rate can be also obtained using quadrature RF coils.
However, due to the complex nature of their structure and their electromagnetic
proprieties, it is challenging to achieve sufficient electromagnetic decoupling
while designing multichannel quadrature RF coil arrays, particularly at
ultrahigh fields. In this work, we proposed a double cross magnetic wall
decoupling for quadrature transceiver RF arrays and implemented the decoupling
method on common-mode differential mode quadrature (CMDM) quadrature
transceiver arrays at ultrahigh field of 7T. The proposed magnetic decoupling
wall comprised of two intrinsic decoupled loops is used to reduce the mutual
coupling between all the multi-mode current present in the quadrature CMDM
array. The decoupling network has no physical connection with the CMDMs' coils
giving leverage over size adjustable RF arrays. In order to validate the
feasibility of the proposed cross magnetic decoupling wall, systematic studies
on the decoupling performance based on the impedance of two intrinsic loops are
numerically performed. A pair of quadrature transceiver CMDMs is constructed
along with the proposed decoupling network and their scattering matrix is
characterized using a network analyzer. The measured results show all the
current modes coupling are concurrently suppressed using the proposed cross
magnetic wall. Moreover, field distribution, and SNR intensity are numerically
obtained for a well-decoupled 8-channel quadrature knee-coil array.
