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

Fluorine-19 ( 19 F) MRI ( 19 F-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 19 F-MRI. Low-field MRI systems are more common than high-field MRI systems. Hence, developing 19 F-MRI at low-field MRI devices can promote the 19 F-MRI translation in medical diagnosis. The detection sensitivity of fluorine agents is critical in 19 F-MRI. Reduction of the 19 F spin-lattice relaxation time ( T 1 ) enables an improved detection sensitivity while requiring ultrashort echo time (UTE) imaging methods to reduce the negative spin-spin relaxation ( T 2 ) 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 19 F-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 1 H/ 19 F 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.