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Model‐based super‐resolution reconstruction of T 2 maps
Author(s) -
Bano Wajiha,
Piredda Gian Franco,
Davies Mike,
Marshall Ian,
Golbabaee Mohammad,
Meuli Reto,
Kober Tobias,
Thiran JeanPhilippe,
Hilbert Tom
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27981
Subject(s) - imaging phantom , resolution (logic) , isotropy , high resolution , physics , acceleration , image resolution , data acquisition , nuclear magnetic resonance , algorithm , computer science , artificial intelligence , optics , remote sensing , geology , classical mechanics , operating system
Purpose High‐resolution isotropic T 2 mapping of the human brain with multi‐echo spin‐echo (MESE) acquisitions is challenging. When using a 2D sequence, the resolution is limited by the slice thickness. If used as a 3D acquisition, specific absorption rate limits are easily exceeded due to the high power deposition of nonselective refocusing pulses. A method to reconstruct 1‐mm 3 isotropic T 2 maps is proposed based on multiple 2D MESE acquisitions. Data were undersampled (10‐fold) to compensate for the prolonged scan time stemming from the super‐resolution acquisition. Theory and Methods The proposed method integrates a classical super‐resolution with an iterative model‐based approach to reconstruct quantitative maps from a set of undersampled low‐resolution data. The method was tested on numerical and multipurpose phantoms, and in vivo data. T 2 values were assessed with a region‐of‐interest analysis using a single‐slice spin‐echo and a fully sampled MESE acquisition in a phantom, and a MESE acquisition in healthy volunteers. Results Numerical simulations showed that the best trade‐off between acceleration and number of low‐resolution datasets is 10‐fold acceleration with 4 acquisitions (acquisition time = 18 min). The proposed approach showed improved resolution over low‐resolution images for both phantom and brain. Region‐of‐interest analysis of the phantom compartments revealed that at shorter T 2 , the proposed method was comparable with the fully sampled MESE. For the volunteer data, the T 2 values found in the brain structures were consistent across subjects (8.5‐13.1 ms standard deviation). Conclusion The proposed method addresses the inherent limitations associated with high‐resolution T 2 mapping and enables the reconstruction of 1 mm 3 isotropic relaxation maps with a 10 times faster acquisition.