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B 1 artifact reduction in abdominal DCE‐MRI using k T ‐points: First clinical assessment of dynamic RF shimming at 3T
Author(s) -
TomiTricot Raphaël,
Gras Vincent,
Mauconduit Franck,
Legou François,
Boulant Nicolas,
Gebhardt Matthias,
Ritter Dieter,
Kiefer Berthold,
Zerbib Pierre,
Rahmouni Alain,
Vignaud Alexandre,
Luciani Alain,
Amadon Alexis
Publication year - 2018
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.25908
Subject(s) - artifact (error) , reduction (mathematics) , nuclear medicine , computer science , dynamic contrast enhanced mri , physics , nuclear magnetic resonance , magnetic resonance imaging , medicine , radiology , biomedical engineering , mathematics , artificial intelligence , geometry
Background The excitation inhomogeneity artifact occurring at 3T in the abdomen can lead to dramatic loss of signal and contrast, thereby hampering diagnosis. Purpose To assess excitation homogeneity and image quality achieved by nonselective prototypical k T ‐points pulses, compared to tailored static RF shimming, in clinical routine on a commercial dual‐transmit scanner. Study Type Retrospective study with Institutional Review Board approval; informed consent was waived. Population Fifty consecutive patients referred for liver MRI at a single hospital. Field Strength/Sequence 3D breath‐hold dynamic contrast‐enhanced (DCE) MRI at 3T. Assessment Flip angle homogeneity was estimated via numerical simulation based on measured static and RF field maps. In all, 20 of the 50 patients underwent DCE‐MRI while a pulse designer was present. The effect of RF shimming and k T ‐point pulses could be compared by repeating the acquisition with each transmit scheme before injection and in the late phase. Signal homogeneity, T 1 contrast, enhancement quality, structure details, and global image quality were assessed on a 4‐level scale (0 to 3) by two radiologists. Statistical tests Means were compared using Wilcoxon signed‐rank tests. Results Normalized root mean square flip angle error was significantly reduced with k T ‐points compared to static RF shimming (8.5% ± 1.5% [mean ± standard deviation, SD] vs. 20.4% ± 9.8%; P < 0.0001). The worst case (heavy ascites) led to 13.0% (k T ‐points) vs. 54.9% (RF shimming). Global image quality was significantly higher for k T ‐points (2.3 ± 0.5 vs. 1.9 ± 0.6; P = 0.008). One subject's examination was judged unusable with RF shimming by one reader, none with k T ‐points. 85% of k T ‐points acquisitions were graded at least 2/3, and only 55% for static RF shimming. Data Conclusion K T ‐points reduce excitation inhomogeneity quantitatively and qualitatively, especially in patients with ascites and prone to B 1 shading. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:1562–1571.