Preclinical 19 F MRI cell tracking at 3 Tesla.

PURPOSE: To develop methods for fluorine-19 (19 F) MRI cell tracking in mice on a 3 Tesla clinical scanner. Compared to iron-based cell tracking, 19 F MRI has lower sensitivity and, consequently, preclinical 19 F cell tracking has only been performed at relatively high magnetic field strengths (> 3 T). Here, we focus on using 19 F MRI to detect macrophages in tumors; macrophage density is an indication of tumor aggressiveness and, therefore, 19 F MRI could be used as an imaging biomarker.

METHODS: Perfluorocarbon (PFC)-labeled macrophages were imaged at 3 T and NMR spectroscopy was performed to validate 19 F spin quantification. In vivo 19 F MRI was performed on tumor-bearing mice, post-PFC at both 9.4 T and 3 T. 3 T MRI utilized varying NEX and 19 F images were analyzed two different ways for 19 F quantification.

RESULTS: As few as 25,000 cells could be detected as cell pellets at 3 T. 19 F quantification in cell pellets by 3 T MRI agreed with NMR spectroscopy. 19 F signal was observed in the liver, spleen and tumor in all mice at 9.4 T and 3 T and there was no significant difference in 19 F spin quantification.

CONCLUSION: This study demonstrates the ability to detect and quantify 19 F signal in murine tumors using 19 F MRI at 3 T.