Radial Hadamard-encoded 19F-MRI.

Abstract

Objectives: Developing a ¹⁹F imaging method to acquire images of the molecular inflammation tracer perfluorooctyl bromide (PFOB) without chemical shift artifacts.

Materials and methods: PFOB is a molecular tracer that can be used to track the response of myeloid cells. However, imaging of PFOB with ¹⁹F-MRI is challenging due to its complex spectrum which leads to unwanted chemical shift artifacts. Spectral HE allows for separate reconstructions of each peak of the PFOB spectrum, which was combined into a single image after resonance shift correction. In this work, a Hadamard-encoded (HE) radial 3D UTE sequence was tested in phantoms and in vivo in a pig, measuring the ¹⁹F signal in the spleen at different times after injection.

Results: Chemical shift artifacts were effectively suppressed with HE, and an SNR > 100 was observed for the ¹⁹F signal in the spleen 2 days after injection. The signal decreased over time, and 7 days after injection it was reduced by 30%.

Discussion: Chemical shift artifact correction using HE allowed for in vivo ¹⁹F PFOB imaging of labeled monocytes with a high SNR. Compared to spectrally selective excitation, HE increased the PFOB ¹⁹F-MRI signal by 10%, and the simple HE-algorithm could be directly integrated into the image reconstruction of the MRI system.