Dual‐echo Z‐shimmed proton resonance frequency‐shift magnetic resonance thermometry near metallic ablation probes: Technique and temperature precision

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Abstract
Purpose: 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 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.Conclusion: 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.
Funding Information
  • National Institutes of Health (R21 NS091735, T32 EB021937)

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