The fractionated dipole antenna: A new antenna for body imaging at 7 Tesla.
OBJECTIVE
Dipole antennas in ultrahigh field MRI have demonstrated advantages over more conventional designs. In this study, the fractionated dipole antenna is presented: a dipole where the legs are split into segments that are interconnected by capacitors or inductors.


METHODS
A parameter study has been performed on dipole antenna length using numerical simulations. A subsequent simulation study investigates the optimal intersegment capacitor/inductor value. The resulting optimal design has been constructed and compared to a previous design, the single-side adapted dipole (SSAD) by simulations and measurements. An array of eight elements has been constructed for prostate imaging on four subjects (body mass index 20-27.5) using 8 × 2 kW amplifiers.


RESULTS
For prostate imaging at 7T, lowest peak local specific-absorption rate (SAR) levels are achieved if the antenna is 30 cm or longer. A fractionated dipole antenna design with inductors between segments has been chosen to achieve even lower SAR levels and more homogeneous receive sensitivities.


CONCLUSIONS
With the new design, good quality prostate images are acquired. SAR levels are reduced by 41% to 63% in comparison to the SSAD. Coupling levels are moderate (average nearest neighbor: -14.6 dB) for each subject and prostate B1+ levels range from 12 to 18 μT.
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
Alexander J E
AJ
Raaijmakers
MR Coils B.V, Drunen, The Netherlands.
Michel
M
Italiaander
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
Ingmar J
IJ
Voogt
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
Peter R
PR
Luijten
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
Johannes M
JM
Hoogduin
Department of Radiology, UMC Utrecht, Utrecht, The Netherlands.
Dennis W J
DW
Klomp
Department of Radiotherapy, UMC Utrecht, Utrecht, The Netherlands.
Cornelis A T
CA
van den Berg
D000328:Adult; D003198:Computer Simulation; D004867:Equipment Design; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D011467:Prostate / Q000000981:diagnostic imaging; D059629:Signal-To-Noise Ratio; D055815:Young Adult
Body imaging; Dipole antenna; Prostate imaging; Transceive array; Ultrahigh field