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Probing chemical exchange using quantitative spin‐lock R 1ρ asymmetry imaging with adiabatic RF pulses
Author(s) -
Jiang Baiyan,
Jin Tao,
Blu Thierry,
Chen Weitian
Publication year - 2019
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.27868
Subject(s) - asymmetry , amplitude , adiabatic process , bloch equations , radio frequency , physics , nuclear magnetic resonance , pulse (music) , computational physics , materials science , optics , computer science , thermodynamics , telecommunications , quantum mechanics , detector
Purpose CEST is commonly used to probe the effects of chemical exchange. Although R 1ρ asymmetry quantification has also been described as a promising option for detecting the effects of chemical exchanges, the existing acquisition approaches are highly susceptible to B 1 RF and B 0 field inhomogeneities. To address this problem, we report a new R 1ρ asymmetry imaging approach, AC‐iTIP, which is based on the previously reported techniques of irradiation with toggling inversion preparation (iTIP) and adiabatic continuous wave constant amplitude spin‐lock RF pulses (ACCSL). We also derived the optimal spin‐lock RF pulse B 1 amplitude that yielded the greatest R 1ρ asymmetry. Methods Bloch‐McConnell simulations were used to verify the analytical formula derived for the optimal spin‐lock RF pulse B 1 amplitude. The performance of the AC‐iTIP approach was compared to that of the iTIP approach based on hard RF pulses and the R 1ρ ‐spectrum acquired using adiabatic RF pulses with the conventional fitting method. Comparisons were performed using Bloch‐McConnell simulations, phantom, and in vivo experiments at 3.0T. Results The analytical prediction of the optimal B 1 was validated. Compared to the other 2 approaches, the AC‐iTIP approach was more robust under the influences of B 1 RF and B 0 field inhomogeneities. A linear relationship was observed between the measured R 1ρ asymmetry and the metabolite concentration. Conclusion The AC‐iTIP approach could probe the chemical exchange effect more robustly than the existing R 1ρ asymmetry acquisition approaches. Therefore, AC‐iTIP is a promising technique for metabolite imaging based on the chemical exchange effect.