Quantitative ~(19)F MRI of perfluoro-15-crown-5-ether using uniformity correction of the spin excitation and signal reception

摘要

Objectives A common limitation of all ~1H contrast agents is that they only allow indirect visualization through modification of the intrinsic properties of the tissue, making quantification of this effect challenging. ~(19)F compounds, on the contrary, are measured directly, without any background signal. There is a linear relationship between the amount of ~(19)F spins and the intensity of the signal. However, non-uniformity of the radiofrequency field may lead to errors in the quantified ~(19)F signal and should be carefully addressed for any quantitative imaging. Materials and methods Adaptation of the previously introduced B_+~1 mapping technique to the problem of quantifying the ~(19)F signal from perfluoro-15-crown-5-ether (PFCE) is proposed in this work. Initial evaluation of the proposed technique simultaneously accounting for transmit B_+~1 and receive B-1 field inhomogeneities is performed in a PFCE phantom. As a proof of concept, in vivo quantification of the ~(19)F signal is performed in a murine model after application of custom-designed hollow mesoporous silica spheres (HMSS) loaded with PFCE. Results A phantom experiment clearly shows that only compensation for both transmit and receive characteristics outperforms inaccurate quantification based on the non- or partly-corrected signal intensities. Furthermore, an optimized protocol is proposed for in vivo application. Conclusion The proposed B_+~1 /B_-~1 mapping technique represents a simple to implement and easy-to-use solution for quantification of the ~(19)F signal from PFCE in the presence of B1-field inhomogeneities.