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Artifact suppression in readout‐segmented consistent K‐t space EPSI ( RS‐COKE ) for fast 1 H spectroscopic imaging at 7 T
Author(s) -
Seginer Amir,
Keith Graeme A.,
Porter David A.,
Schmidt Rita
Publication year - 2022
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.29373
Subject(s) - artifact (error) , physics , chemistry , nuclear magnetic resonance , computer science , artificial intelligence
Purpose Fast proton ( 1 H) MRSI is an important diagnostic tool for clinical investigations, providing metabolic and spatial information. MRSI at 7 T benefits from increased SNR and improved separation of peaks but requires larger spectral widths. RS‐COKE (Readout‐Segmented Consistent K‐t space Epsi ) is an echo planar spectroscopic imaging ( Epsi ) variant capable to support the spectral width required for human brain metabolites spectra at 7 T. However, mismatches between readout segments lead to artifacts, particularly when subcutaneous lipid signals are not suppressed. In this study, these mismatches and their effects are analyzed and reduced. Methods The following corrections to the data were performed: i) frequency‐dependent phase corrections; ii) k‐space trajectory corrections, derived from short reference scans; and iii) smoothing of data at segment transitions to mitigate the effect of residual mismatches. The improvement was evaluated by performing single‐slice RS‐COKE on a head‐shaped phantom with a “lipid” layer and healthy subjects, using varying resolutions and durations ranging from 4.1 × 4.7 × 15 mm 3 in 5:46 min to 3.1 × 3.3 × 15 mm 3 in 13:07 min. Results Artifacts arising from the readout‐segmented acquisition were substantially reduced, thus providing high‐quality spectroscopic imaging in phantom and human scans. LCModel fitting of the human data resulted in a relative Cramer‐Rao lower bounds within 6% for NAA, Cr, and Cho images in the majority of the voxels. Conclusion Using the new reference scans and reconstruction steps, RS‐COKE was able to deliver fast 1 H MRSI at 7 T, overcoming the spectral width limitation of standard EPSI at this field strength.