Counteracting radio frequency inhomogeneity in the human brain at 7 Tesla using strongly modulating pulses.
We report flip angle and spoiled gradient echo measurements at 7 Tesla on human brains in three-dimensional imaging, using strongly modulating pulses to counteract the transmitted radiofrequency inhomogeneity problem. Compared with the standard square pulse results, three points of improvement are demonstrated, namely: (i) the removal of the bright center (typical at high fields when using a quadrature head coil), (ii) the substantial gain of signal in the regions of low B(1) intensity, and (iii) an increased 35% signal uniformity over the whole brain at the flip angle where maximum contrast between white and gray matter occurs. We also find by means of simulations that standard BIR-4 adiabatic pulses need several times more energy to reach a similar performance at the same field strength.
Boulant
N
N
CEA, DSV, I2BM, NeuroSpin, LRMN, Gif sur Yvette, France. nicolas.boulant@cea.fr
Mangin
J-F
JF
Amadon
A
A
D000465:Algorithms; D016880:Anisotropy; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity