Gisela E Hagberg1,2, Korbinian Eckstein3,2, Elisa Tuzzi1,2, Jiazheng Zhou1,2, Simon Robinson4,3,5, Klaus Scheffler1,2. 1. Department for Biomedical Magnetic Resonance, University Hospital Tübingen, Tübingen, Germany. 2. High Field Magnetic Resonance Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany. 3. High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Vienna, Austria. 4. Department of Neurology, Medical University of Graz, Graz, Austria. 5. Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia.
Abstract
PURPOSE: To develop improved tissue masks for QSM. METHODS: Masks including voxels at the brain surface were automatically generated from the magnitude alone (MM) or combined with test functions from the first (PG) or second (PB) derivative of the sign of the wrapped phase. Phase images at 3T and 9.4T were simulated at different TEs and used to generate a mask, PItoh , with between-voxel phase differences less than π. MM, PG, and PB were compared with PItoh . QSM were generated from 3D multi-echo gradient-echo data acquired at 9.4T (21 subjects aged: 20-56y), and from the QSM2016 challenge 3T data using different masks, unwrapping, background removal, and dipole inversion algorithms. QSM contrast was quantified using age-based iron concentrations. RESULTS: Close to air cavities, phase wraps became denser with increasing field and echo time, yielding increased values of the test functions. Compared with PItoh , PB had the highest Dice coefficient, while PG had the lowest and MM the highest percentage of voxels outside PItoh. Artifacts observed in QSM at 9.4T with MM were mitigated by stronger background filters but yielded a reduced QSM contrast. With PB, QSM contrast was greater and artifacts diminished. Similar results were obtained with challenge data, evidencing larger effects of mask close to air cavities. CONCLUSION: Automatic, phase-based masking founded on the second derivative of the sign of the wrapped phase, including cortical voxels at the brain surface, was able to mitigate artifacts and restore QSM contrast across cortical and subcortical brain regions.
PURPOSE: To develop improved tissue masks for QSM. METHODS: Masks including voxels at the brain surface were automatically generated from the magnitude alone (MM) or combined with test functions from the first (PG) or second (PB) derivative of the sign of the wrapped phase. Phase images at 3T and 9.4T were simulated at different TEs and used to generate a mask, PItoh , with between-voxel phase differences less than π. MM, PG, and PB were compared with PItoh . QSM were generated from 3D multi-echo gradient-echo data acquired at 9.4T (21 subjects aged: 20-56y), and from the QSM2016 challenge 3T data using different masks, unwrapping, background removal, and dipole inversion algorithms. QSM contrast was quantified using age-based iron concentrations. RESULTS: Close to air cavities, phase wraps became denser with increasing field and echo time, yielding increased values of the test functions. Compared with PItoh , PB had the highest Dice coefficient, while PG had the lowest and MM the highest percentage of voxels outside PItoh. Artifacts observed in QSM at 9.4T with MM were mitigated by stronger background filters but yielded a reduced QSM contrast. With PB, QSM contrast was greater and artifacts diminished. Similar results were obtained with challenge data, evidencing larger effects of mask close to air cavities. CONCLUSION: Automatic, phase-based masking founded on the second derivative of the sign of the wrapped phase, including cortical voxels at the brain surface, was able to mitigate artifacts and restore QSM contrast across cortical and subcortical brain regions.
Authors: Christian Langkammer; Ferdinand Schweser; Karin Shmueli; Christian Kames; Xu Li; Li Guo; Carlos Milovic; Jinsuh Kim; Hongjiang Wei; Kristian Bredies; Sagar Buch; Yihao Guo; Zhe Liu; Jakob Meineke; Alexander Rauscher; José P Marques; Berkin Bilgic Journal: Magn Reson Med Date: 2017-07-31 Impact factor: 4.668
Authors: Barbara Dymerska; Korbinian Eckstein; Beata Bachrata; Bernard Siow; Siegfried Trattnig; Karin Shmueli; Simon Daniel Robinson Journal: Magn Reson Med Date: 2020-10-26 Impact factor: 4.668