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.