title: Dual-echo Z-shimmed proton resonance frequency-shift magnetic resonance thermometry near metallic ablation probes: Technique and temperature precision.
abstract: OBJECTIVE
  To improve the precision of proton resonance frequency-shift magnetic resonance thermometry near ablation probes by recovering near-probe image signals that are typically lost due to magnetic susceptibility-induced field distortions.
  
  
  METHODS
  A dual-echo gradient-recalled echo sequence was implemented, in which the first echo was under- or over-refocused in the slice dimension to recover image signal and temperature precision near a probe, and the second echo was fully refocused to obtain image signal everywhere else in the slice. A penalized maximum likelihood algorithm was implemented to estimate a single temperature map from both echoes. Agar phantom and ex vivo experiments with and without microwave heating at 3 T evaluated how much temperature precision was improved near a microwave ablator compared to a conventional single-echo scan as a function of slice and needle orientation in the magnet.
  
  
  RESULTS
  The number of near-probe voxels with temperature standard deviation σ>1°C was decreased by 51% in the phantom experiment, averaged across orientations, and by 31% in the pork. Temperature maps near the probe were more smoother and more complete in all orientations.
  
  
  CONCLUSIONS
  Dual-echo z-shimmed temperature imaging can recover image signal for more precise temperature mapping near metallic ablation probes. Magn Reson Med 78:2299-2306, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Biomedical Engineering, Tsinghua University, Beijing, China.
authors.forename: Yuxin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Megan E
authors.identifier: http://orcid.org/0000-0001-5474-8776
authors.initials: ME
authors.lastname: Poorman
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: Grissom
mesh_terms: D000362:Agar / Q000737:chemistry; D000465:Algorithms; D000818:Animals; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016013:Likelihood Functions; D008279:Magnetic Resonance Imaging; D008872:Microwaves; D018482:Muscle, Skeletal / Q000502:physiology; D019047:Phantoms, Imaging; D011522:Protons; D015203:Reproducibility of Results; D013552:Swine; D013696:Temperature; D013817:Thermography; D062125:Thermometry
chemical_list: D011522:Protons; D000362:Agar
keywords: ablation; interventional magnetic resonance imaging; magnetic resonance thermometry; microwave; z-shimming