Comparison of RF body coils for MRI at 3  T: a simulation study using parallel transmission on various anatomical targets.
The performance of multichannel transmit coil layouts and parallel transmission (pTx) RF pulse design was evaluated with respect to transmit B1 (B1 (+)) homogeneity and specific absorption rate (SAR) at 3 T for a whole body coil. Five specific coils were modeled and compared: a 32-rung birdcage body coil (driven either in a fixed quadrature mode or a two-channel transmit mode), two single-ring stripline arrays (with either 8 or 16 elements), and two multi-ring stripline arrays (with two or three identical rings, stacked in the z axis and each comprising eight azimuthally distributed elements). Three anatomical targets were considered, each defined by a 3D volume representative of a meaningful region of interest (ROI) in routine clinical applications. For a given anatomical target, global or local SAR controlled pTx pulses were designed to homogenize RF excitation within the ROI. At the B1 (+) homogeneity achieved by the quadrature driven birdcage design, pTx pulses with multichannel transmit coils achieved up to about eightfold reduction in local and global SAR. When used for imaging head and cervical spine or imaging thoracic spine, the double-ring array outperformed all coils, including the single-ring arrays. While the advantage of the double-ring array became much less pronounced for pelvic imaging, with a substantially larger ROI, the pTx approach still provided significant gains over the quadrature birdcage coil. For all design scenarios, using the three-ring array did not necessarily improve the RF performance. Our results suggest that pTx pulses with multichannel transmit coils can reduce local and global SAR substantially for body coils while attaining improved B1 (+) homogeneity, particularly for a "z-stacked" double-ring design with coil elements arranged on two transaxial rings.
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Xiaoping
X
Wu
Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.
Xiaotong
X
Zhang
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Jinfeng
J
Tian
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Sebastian
S
Schmitter
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Brian
B
Hanna
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
John
J
Strupp
Siemens Healthcare, Erlangen, Germany.
Josef
J
Pfeuffer
Siemens Healthcare, Erlangen, Germany.
Michael
M
Hamm
Siemens Healthcare, Erlangen, Germany.
Dingxin
D
Wang
Siemens Healthcare, Erlangen, Germany.
Juergen
J
Nistler
Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.|Institute for Engineering in Medicine, University of Minnesota, Minneapolis, MN, USA.
Bin
B
He
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Thomas J
TJ
Vaughan
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Kamil
K
Ugurbil
University of Minnesota Medical School, Department of Radiology, Center for Magnetic Resonance Research, Minneapolis, MN, USA.
Pierre-Francois
PF
Van de Moortele
D000465:Algorithms; D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008962:Models, Theoretical; D012984:Software
RF array design; body MRI; high field MRI; parallel transmission