Eight channel transmit array volume coil using on-coil radiofrequency current sources.
BACKGROUND
At imaging frequencies associated with high-field MRI, the combined effects of increased load-coil interaction and shortened wavelength results in degradation of circular polarization and B1 field homogeneity in the imaging volume. Radio frequency (RF) shimming is known to mitigate the problem of B1 field inhomogeneity. Transmit arrays with well decoupled transmitting elements enable accurate B1 field pattern control using simple, non-iterative algorithms.


METHODS
An eight channel transmit array was constructed. Each channel consisted of a transmitting element driven by a dedicated on-coil RF current source. The coil current distributions of characteristic transverse electromagnetic (TEM) coil resonant modes were non-iteratively set up on each transmitting element and 3T MRI images of a mineral oil phantom were obtained.


RESULTS
B1 field patterns of several linear and quadrature TEM coil resonant modes that typically occur at different resonant frequencies were replicated at 128 MHz without having to retune the transmit array. The generated B1 field patterns agreed well with simulation in most cases.


CONCLUSIONS
Independent control of current amplitude and phase on each transmitting element was demonstrated. The transmit array with on-coil RF current sources enables B1 field shimming in a simple and predictable manner.
1 Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA ; 2 Department of Radiology, University of Wisconsin, Madison, WI 53705, USA ; 3 Applied Science Laboratory, GE Healthcare, Waukesha, WI 53188, USA ; 4 Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA ; 5 Department of Radiology, Texas A&M Health Sciences Center, Bryan, TX 77807, USA.
Krishna N
KN
Kurpad
1 Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA ; 2 Department of Radiology, University of Wisconsin, Madison, WI 53705, USA ; 3 Applied Science Laboratory, GE Healthcare, Waukesha, WI 53188, USA ; 4 Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA ; 5 Department of Radiology, Texas A&M Health Sciences Center, Bryan, TX 77807, USA.
Eddy B
EB
Boskamp
1 Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA ; 2 Department of Radiology, University of Wisconsin, Madison, WI 53705, USA ; 3 Applied Science Laboratory, GE Healthcare, Waukesha, WI 53188, USA ; 4 Department of Biomedical Engineering, Texas A&M University, College Station, TX 77843, USA ; 5 Department of Radiology, Texas A&M Health Sciences Center, Bryan, TX 77807, USA.
Steven M
SM
Wright
B1 field pattern control; High field MRI; current element; non-resonant structure; transmit phased array; volume coils