Yuxin Zhang1, Megan E Poorman2,3, William A Grissom2,3. 1. Department of Biomedical Engineering, Tsinghua University, Beijing, China. 2. Vanderbilt University Institute of Imaging Science, Nashville, Tennessee, USA. 3. Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
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 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.
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.
Authors: Amanda K Funai; Jeffrey A Fessler; Desmond T B Yeo; Valur T Olafsson; Douglas C Noll Journal: IEEE Trans Med Imaging Date: 2008-10 Impact factor: 10.048
Authors: Hans Weber; Pejman Ghanouni; Aurea Pascal-Tenorio; Kim Butts Pauly; Brian A Hargreaves Journal: Magn Reson Med Date: 2017-12-07 Impact factor: 4.668