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

Abstract

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. ¹⁹F compounds, on the contrary, are measured directly, without any background signal. There is a linear relationship between the amount of ¹⁹F spins and the intensity of the signal. However, non-uniformity of the radiofrequency field may lead to errors in the quantified ¹⁹F signal and should be carefully addressed for any quantitative imaging.

Materials and methods: Adaptation of the previously introduced [Formula: see text] mapping technique to the problem of quantifying the ¹⁹F signal from perfluoro-15-crown-5-ether (PFCE) is proposed in this work. Initial evaluation of the proposed technique simultaneously accounting for transmit [Formula: see text] and receive [Formula: see text] field inhomogeneities is performed in a PFCE phantom. As a proof of concept, in vivo quantification of the ¹⁹F 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 [Formula: see text]/[Formula: see text] mapping technique represents a simple to implement and easy-to-use solution for quantification of the ¹⁹F signal from PFCE in the presence of B₁-field inhomogeneities.

Keywords: 19F MRI; B 1 inhomogeneity; Hollow mesoporous silica spheres; Perfluoro-15-crown-5-ether; Quantification.