title: Signal-domain optimization metrics for MPRAGE RF pulse design in parallel transmission at 7 tesla.
abstract: Standard radiofrequency pulse design strategies focus on minimizing the deviation of the flip angle from a target value, which is sufficient but not necessary for signal homogeneity. An alternative approach, based directly on the signal, here is proposed for the MPRAGE sequence, and is developed in the parallel transmission framework with the use of the kT-points parametrization.
  
  
  
  The flip angle-homogenizing and the proposed methods were investigated numerically under explicit power and specific absorption rate constraints and tested experimentally in vivo on a 7 T parallel transmission system enabling real time local specific absorption rate monitoring. Radiofrequency pulse performance was assessed by a careful analysis of the signal and contrast between white and gray matter.
  
  
  
  Despite a slight reduction of the flip angle uniformity, an improved signal and contrast homogeneity with a significant reduction of the specific absorption rate was achieved with the proposed metric in comparison with standard pulse designs.
  
  
  
  The proposed joint optimization of the inversion and excitation pulses enables significant reduction of the specific absorption rate in the MPRAGE sequence while preserving image quality. The work reported thus unveils a possible direction to increase the potential of ultra-high field MRI and parallel transmission. Magn Reson Med 76:1431-1442, 2016. © 2015 International Society for Magnetic Resonance in Medicine.
authors.affiliation: CEA, I2BM, Neurospin, UNIRS, Gif sur Yvette 91191 Cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Gras
authors.affiliation: CEA, I2BM, Neurospin, UNIRS, Gif sur Yvette 91191 Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Vignaud
authors.affiliation: Siemens Healthcare, Saint-Denis, France.
authors.forename: F
authors.initials: F
authors.lastname: Mauconduit
authors.affiliation: CEA, DSM, Irfu, SACM, Gif sur Yvette 91191 Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Luong
authors.affiliation: CEA, I2BM, Neurospin, UNIRS, Gif sur Yvette 91191 Cedex, France.
authors.forename: A
authors.initials: A
authors.lastname: Amadon
authors.affiliation: CEA, I2BM, Neurospin, UNIRS, Gif sur Yvette 91191 Cedex, France.
authors.forename: D
authors.initials: D
authors.lastname: Le Bihan
authors.affiliation: CEA, I2BM, Neurospin, UNIRS, Gif sur Yvette 91191 Cedex, France. nicolas.boulant@cea.fr.
authors.forename: N
authors.initials: N
authors.lastname: Boulant
mesh_terms: D000465:Algorithms; D001921:Brain / Q000033:anatomy & histology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011846:Radio Waves; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted
keywords: B1 inhomogeneity mitigation; MPRAGE; kT-points; parallel transmission; radiofrequency pulse design; specific absorption rate; ultra high field