High-Sensitivity, Low-Field ¹⁹F-MRI Approach Using High Manganese Ferrite Concentrations

Fluorine-19 (¹⁹F) MRI (¹⁹F-MRI) is a promising method for quantifying biomedical research and clinical applications without background interference. Nevertheless, dependency on high-field MRI systems limits the applicability of ¹⁹F-MRI. Low-field MRI systems are more common than high-field MRI systems. Hence, developing ¹⁹F-MRI at low-field MRI devices can promote the ¹⁹F-MRI translation in medical diagnosis. The detection sensitivity of fluorine agents is critical in ¹⁹F-MRI. Reduction of the ¹⁹F spin-lattice relaxation time (T₁) enables an improved detection sensitivity while requiring ultrashort echo time (UTE) imaging methods to reduce the negative spin-spin relaxation (T₂) decay effect. However, conventional UTE sequences require hardware with high performance. Herein, we introduce the k-space scaling imaging (KSSI) MRI sequence that accomplishes sampling k-space with variable scales to implement hardware-friendly UTE ¹⁹F-MRI compatible with low-field MRI systems. We implemented experiments with swine bone, a perfluorooctyl bromide (PFOB) phantom, and one tumor-bearing mouse on two self-customized low-field MRI systems. The swine bone imaging validated the ultrashort TE of KSSI. Under high concentrations of manganese ferrite, a high signal-to-noise ratio was shown in the imaging of a fluorine atom concentration of 658 mM, which indicated high-sensitivity detection of KSSI. Moreover, the KSSI sequence exhibited a 7.1 times signal-to-noise ratio of spin echo sequence on the PFOB phantom imaging with a fluorine atom concentration of 3.29 M. Additionally, the various concentrations of the PFOB phantom imaging revealed quantifiable capacity. Finally, the ¹H/¹⁹F imaging was implemented with KSSI on one tumor-bearing mouse. This method provides the potential for clinical translation of fluorine probes at low-field MRI systems.