In Vivo F-19 Magnetic Resonance Spectroscopy

Fluorine (F-19) is widely present in biomedical compounds. F-19 magnetic resonance (MR) imaging and spectroscopy offer unique possibilities for the in vivo monitoring of the fate of these compounds and of F-19-loaded particles and cells after their administration in animal models or humans. The signal intensity and relaxation times of F-19 spins are applied in MR imaging of tissue perfusion, lung ventilation, tissue oxygenation, and for cell tracking and targeting. With MR spectroscopy the F-19 chemical shift is employed to examine ion binding, enzyme activity, and metabolism of fluorinated drugs and metabolites. This article introduces in vivo F-19 MR of animals and humans with a focus on spectroscopy. It describes the specific properties of the F-19 nucleus that make it suitable for in vivo MR applications. F-19 MR is very sensitive and lacks background signal, which results in a high contrast-to-noise ratio and specificity. Despite its high intrinsic sensitivity, F-19 MR is challenging, especially in clinical applications, due to the low number of F-19 nuclei that typically accumulate in tissues. Therefore, whenever possible the number of F-19 nuclei per molecule and/or particle must be maximized, and the hardware and software for F-19 MR acquisition optimized to obtain the best achievable signal-to-noise ratio.