Enhanced Fluorine-19 MRI Sensitivity using a Cryogenic Radiofrequency Probe: Technical Developments and Ex Vivo Demonstration in a Mouse Model of Neuroinflammation

Neuroinflammation can be monitored using fluorine-19 (F-19)-containing nanoparticles and F-19 MRI. Previously we studied neuroinflammation in experimental autoimmune encephalomyelitis (EAE) using room temperature (RT) F-19 radiofrequency (RF) coils and low spatial resolution F-19 MRI to overcome constraints in signal-to-noise ratio (SNR). This yielded an approximate localization of inflammatory lesions. Here we used a new F-19 transceive cryogenic quadrature RF probe (19F-CRP) that provides the SNR necessary to acquire superior spatially-resolved F-19 MRI. First we characterized the signaltransmission profile of the F-19-CRP. The F-19-CRP was then benchmarked against a RT F-19/H-1 RF coil. For SNR comparison we used reference compounds including F-19-nanoparticles and ex vivo brains from EAE mice administered with F-19-nanoparticles. The transmit/receive profile of the F-19-CRP diminished with increasing distance from the surface. This was counterbalanced by a substantial SNR gain compared to the RT coil. Intraparenchymal inflammation in the ex vivo EAE brains was more sharply defined when using 150 mu m isotropic resolution with the F-19-CRP, and reflected the known distribution of EAE histopathology. At this spatial resolution, most F-19 signals were undetectable using the RT coil. The 19FCRP is a valuable tool that will allow us to study neuroinflammation with greater detail in future in vivo studies.