19F MRI is emerging as a new imaging technique for cell tracking. It is particularly attractive because of its potential for direct and precise cell quantification. The most important challenge towards in vivo applications is the sensitivity of the technique, i.e. the detection limit in a reasonable imaging time. Optimal sensitivity can be achieved with dedicated 19F compounds together with specifically adapted hardware and acquisition methods. In this paper we introduce the 19F MRI technique focusing on these key sensitivity issues and review the state-of-the-art of 19F MRI and developments towards its clinical use. We calculate 19F detection limits reported in preclinical cell and clinical 19F drug studies in terms of tissue concentration in a 1 cm3 voxel, as an alternate way to compare detection limits. We estimate that a tissue concentration of a few millimoles per litre (mM) of 19F is required for a human study at a resolution of 1 cm3. Key Points • Direct and precise cell quantification can be done by19F MRI. •19F MRI sensitivity is the most important parameter towards clinical application. • A number of (technical) considerations can improve sensitivity significantly. • A few millimoles per litre (mM) of19F per voxel is required for adequate detection. © 2014, European Society of Radiology.