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

摘要

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 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. 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.