Fluorine-19 (19F) MRI has become an established tool for in vivo cell tracking following ex vivo or in vivo labelling of various cell types with 19F perfluorocarbons (PFCs). Here, we developed and evaluated novel mouse-specific radiofrequency (RF) hardware for improved dual 1H anatomical imaging and deep tissue 19F MR detection of PFCs. Three linearly polarized birdcage RF coils were constructed-a dual-frequency 1H/19F coil, and a pair of single-frequency 1H and 19F coils, designed to be used sequentially. RF coil quality factors (Q values), signal homogeneity and sensitivity were benchmarked against a commercially constructed dual-frequency 1H/19F surface coil. RF homogeneity was assessed using a phantom designed to mimic PFC localization at depth in a mouse. The single-frequency birdcage coils (1H and 19F) displayed more uniform coverage and enhanced signal-to-noise ratios (SNRs) compared to both the birdcage and surface dual-frequency coils for 19F detection. Bilateral injection of a perfluoropolyether nanoemulsion into the footpads of female athymic nude mice, resulting in drainage to various lymph nodes and subsequent accumulation in lymph node macrophages, provided a platform to assess differences in SNRs and contrast-to-noise ratios (CNR) between both coil configurations as a function of depth and location. The single-frequency 1H coil provided significantly increased CNR in anatomical images (p < 0.001) with increased anatomical coverage compared to the dual-frequency surface coil. The single-frequency 19F birdcage coil offered increased PFC detectability with significantly higher SNR in renal, lumbar, sciatic and popliteal lymph nodes (p < 0.01) compared to the dual-frequency surface coil. Interestingly, the percentage difference between SNR measurements in lymph nodes between the single-frequency 19F coil and the 1H/19F surface coil had a linear relationship with increasing distance from the surface coil (R2 = 0.6352; p < 0.0001), indicating a potential disagreement for imaging experiments that rely on 19F spin quantification at increasing depth within the mouse using surface RF coils.
Keywords: 19F and 1H radiofrequency hardware development; cell tracking; perfluorocarbon imaging; small animal imaging.
© 2024 The Author(s). NMR in Biomedicine published by John Wiley & Sons Ltd.