Dixon and Chimera: Two methods for fast separation of PFC compounds with small chemical shift difference

Introduction Perfluorocarbon (PFC) emulsions have been widely used for cell tracking studies [1,2] and many other biological applications [3]. In contrast to conventional H contrast agents, F markers provide unambiguous signal in vivo due to the low natural abundance of fluorine in living organisms. Furthermore, fluorine markers can possess a unique spectral signal, a further advantage of F MR. Therefore, chemical shift imaging (CSI) methods can be used to distinguish between targets labeled with different fluorine markers. Certain PFC compounds, however, have only a small difference in the chemical shift and thus spectrally selective imaging or standard CSI methods are difficult to apply. This study focuses on two alternative methods to separate PFC compounds with a small chemical shift difference: a TSE sequence based on Dixon's method [4], often used to separate fat from water signal, and a recently presented ssfp Chimera method [5] providing a specific off-resonant behavior.