Abstract
ObjectiveFluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of 19F MR that can be practically achieved when moving from 9.4 to 21.1 T.Materials and methodsWe studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B0), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B0 with 2D-RARE and 2D-FLASH using 19F volume radiofrequency resonators together. T1 and T2 of PFCE were measured at both B0 strengths.ResultsCompared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of 19F T1 and T2 relaxation on B0 was demonstrated. High spatially resolved 19F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T.DiscussionEnhanced SNR and T1 shortening indicate the potential benefit of in vivo 19F MR at higher B0 to study inflammatory processes with greater detail.
Highlights
Fluorine-19 (19F) magnetic resonance (MR) methods have found their application in a wide range of biomedical research areas
Iron oxide particles such as ultrasmall iron oxide agents are potentially advantageous with regard to their MR sensitivity, but suffer from drawbacks such as signal quantification and a difficulty to distinguish the contrast which they create in the cells they label from other intrinsic tissue contrasts [8]
The ratio between the two field magnitudes (0.76) can be used as a scaling factor in Eq (1) to calculate signal-to-noise ratio (SNR) gain from the quadratically increasing MR signal strength. This yields an estimated SNR gain of ~ 3.8, when reference power is factored into the Eq (1)
Summary
Fluorine-19 (19F) magnetic resonance (MR) methods have found their application in a wide range of biomedical research areas. The usefulness of 19F MR in a wide range of biomedical imaging applications is hampered by the low availability of 19F spins in the living organism. This is compounded by the fact that the signal sensitivity of current state-of-the-art MR equipment remains limited, making 19F MR measurements of fluorine compounds present at low concentrations an extremely challenging task. We investigated how much of the expected sensitivity gain could be achieved in practical experiments The rationale behind these experiments was to make use of higher B0 strengths to study inflammatory cell migration with better resolution and detail. The main driving force for using higher B 0 is to boost sensitivity and resolution of the in vivo 19F MR images
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