Chemical shift encoding (CSE) for sensitive fluorine-19 MRI of perfluorocarbons with complex spectra

Abstract

Purpose: To implement a fluorine-19 (19F) chemical shift encoding (CSE) approach for the sensitive imaging of molecules with multi-resonance spectra to remove their chemical shift displacement (CSD) artifacts, and to characterize its sensitivity versus established pulse sequences. Methods: The feasibility of CSE spoiled gradient echo (GRE) and balanced steady-state free precession (bSSFP) was first demonstrated in a phantom study. The dependence of the sensitivity of CSE-bSSFP on several pulse sequence parameters was then established, after which the occurrence of out-of-plane excitation was assessed for 2D and 3D techniques. Next, the sensitivity (in mm−3s−0.5) of both CSE techniques was compared to bSSFP ultrashort echo time (bSSFP-UTE) imaging and multi-chemical-shift-selective turbo spin echo (MCSS-TSE) in a second phantom study. Finally, the sensitivity of the CSE-bSSFP, bSSFP-UTE, and MCSS-TSE pulse sequences was compared in a preliminary in vivo mouse study. Results: Both CSE approaches were successfully implemented and resulted in negligible residual CSD artifacts, while large-volume 3D acquisitions should be considered to reduce problems related to out-of-plane excitation. CSE–bSSFP was shown to have a higher sensitivity than the bSSFP-UTE and MCSS-TSE pulse sequences (15.8 ± 1.3 vs. 11.7 ± 1.0 vs. 13.3 ± 0.9 mm−3s−0.5, respectively, P < 0.001), whereas CSE-GRE technique had a lower sensitivity (4.8 ± 1.1 mm−3s−0.5). Conclusion: CSE 19F MR imaging enables the unambiguous visualization of compounds with complex spectra, and provides high sensitivity both in vitro and in vivo. Magn Reson Med 79:2724–2730, 2018. © 2017 International Society for Magnetic Resonance in Medicine.