Ziele: Despite the great success of applying hyperpolarized 3He and 129Xe in the field of morphological and functional MR-imaging of lungs both contrast gases still remain mostly research tools. Therefore, the interest in using thermally polarized fluorinated gases, such as SF6, C2F6 and C4F8 in the MRI-investigations of lungs has grown. The short T1 relaxation time of these gases (1–50ms at 1bar) allows for a short measurement time (<10 s) if imaging is performed in a large animal. As the fraction of fluorinated gases is not linearly correlated to the spin density due to T1 weighting other functional MR parameters are necessary for gas concentration quantification. One of such parameters is the T1 relaxation time itself. The aim of this study was to prove the feasibility of the 19F T1 mapping for the estimation of local partial pressure of fluorinated gases in vivo. Methode: For all experiments, the variable flip angle (VFA) technique was used. First, a variety of investigations on phantoms containing mixtures of C4F8 and O2 in different proportions aiming to proof the VFA method for fluorinated gases were done. Next, ex-vivo measurements in rat lungs were performed to test the method efficiency. The rat was ventilated in-vivo with a mixture of 80% C4F8 with 20% of O2 and then, immediately after death, 5ml of C4F8 were injected additionally. Finally, in-vivo experiments in domestic pig (20–25kg) lungs were done using the same mixture. The scan time in all measurements during inspiratory hold was 60–70 s. All experiments were run on a Siemens Magnetom Vision Experimental 1.5T whole body MRI system using a 25cm birdcage coil. Ergebnis: In the ex-vivo T1-maps regions with various T1 can be identified corresponding to variations of C4F8 concentration. The in-vivo measurements results show essentially broad T1- time distribution (and therefore related C4F8 concentration) that obviously reflects a metabolic processes of gas exchange. In this case metabolic changes of the proportions of gas mixtures (C4F8:O2:CO2) in different lung regions could lead to corresponding variations of T1. Schlussfolgerung: In conclusion, the applicability of the VFA method of T1 measurement for the in-vivo MRI-measurement of lungs with heavy fluorinated gases was demonstrated. The sensitivity of the method is sufficient enough to detect 5–10% variations of gas mixture content in-vivo. Combined with diffusion weighted 19F imaging techniques this may open up a number of new options for the study of lung functions and pathology.