title: Parallel transmit pulse design for patients with deep brain stimulation implants.
abstract: OBJECTIVE
  Specific absorption rate (SAR) amplification around active implantable medical devices during diagnostic MRI procedures poses a potential risk for patient safety. In this study, we present a parallel transmit (pTx) strategy that can be used to safely scan patients with deep brain stimulation (DBS) implants.
  
  
  METHODS
  We performed electromagnetic simulations at 3T using a uniform phantom and a multitissue realistic head model with a generic DBS implant. Our strategy is based on using implant-friendly modes, which are defined as the modes of an array that reduce the local SAR around the DBS lead tip. These modes are used in a spokes pulse design algorithm in order to produce highly uniform magnitude least-squares flip angle excitations.
  
  
  RESULTS
  Local SAR (1 g) at the lead tip is reduced below 0.1 W/kg compared with 31.2 W/kg, which is obtained by a simple quadrature birdcage excitation without any sort of SAR mitigation. For the multitissue realistic head model, peak 10 g local SAR and global SAR are obtained as 4.52 W/kg and 0.48 W/kg, respectively. A uniform axial flip angle is also obtained (NRMSE <3%).
  
  
  CONCLUSIONS
  Parallel transmit arrays can be used to generate implant-friendly modes and to reduce SAR around DBS implants while constraining peak local SAR and global SAR and maximizing flip angle homogeneity.
authors.affiliation: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA; Madrid-MIT M+ Vision Consortium, Madrid, Spain.
authors.forename: Yigitcan
authors.initials: Y
authors.lastname: Eryaman
authors.forename: Bastien
authors.initials: B
authors.lastname: Guerin
authors.forename: Can
authors.initials: C
authors.lastname: Akgun
authors.forename: Joaquin L
authors.initials: JL
authors.lastname: Herraiz
authors.forename: Adrian
authors.initials: A
authors.lastname: Martin
authors.forename: Angel
authors.initials: A
authors.lastname: Torrado-Carvajal
authors.forename: Norberto
authors.initials: N
authors.lastname: Malpica
authors.forename: Juan A
authors.initials: JA
authors.lastname: Hernandez-Tamames
authors.forename: Emanuele
authors.initials: E
authors.lastname: Schiavi
authors.forename: Elfar
authors.initials: E
authors.lastname: Adalsteinsson
authors.forename: Lawrence L
authors.initials: LL
authors.lastname: Wald
mesh_terms: D000465:Algorithms; D000075202:Contraindications; D046690:Deep Brain Stimulation / Q000295:instrumentation*; D004574:Electromagnetic Fields; D004869:Equipment Safety; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008670:Metals; D019047:Phantoms, Imaging
chemical_list: D008670:Metals
keywords: deep brain stimulation (DBS); electric field steering; excitation fidelity; global SAR; implant safety; local SAR; parallel transmit (pTx)