Imaging plays a major role in assessment of pulmonary diseases and a broad spectrum of imaging techniques are available. The main workhorse modality is still computed tomography (CT), which allows fast and high-resolution assessment of the lung parenchyma and surrounding structures. However, the soft tissue contrast and gain of direct functional information is limited. MRI of the lung is difficult owing to the low proton density of the tissue and, consequently, low signal intensity on conventional ¹H scans. At the same time, large differences in the magnetic susceptibility of the lung tissue and air within the lungs, respectively, reduces the signal strength even further. The hyperpolarization of ³He or ¹²⁹Xe is a viable, but expensive method of lung MRI. To avoid these problems, we investigated the possibility of mouse lung imaging by use of perfluorohexane, a biocompatible liquid at room temperature, and ¹⁹F MRI. Perfluorohexane has a very high oxygen solubility (41mL O₂/100g) which makes "fluid-breathing", and therefore invivo experiments, a possibility. ¹⁹F has 83% of the signal of ¹H in MRI, which combined with the high ¹⁹F concentration in the liquid gives a very high signal. Additionally, the absence of fluorine in the body results in the lungs appearing bright with no background signal [1].As an application of ¹⁹F MRI imaging technique we have chosen a mouse model of lung radiation damage. For the initial time-course study, 16 female CBA mice (4 weeks old) were anaesthetized with isoflurane and the left lung irradiated with a 20Gy dose over 2 minutes (SARRP, Xtrahl Ltd., UK). Starting at week 6, one animal was sacrificed each week for ex-vivo MRI. Each mouse was terminally anaesthetised and tracheotomized, then air in the lungs was replaced with the perfluorohexane (C₆F₁₄). A dual tuned ¹H/¹⁹F 28mm birdcage coil (PulseTeq Ltd., UK) was used in a 7T spectrometer (Agilent Inc., USA). MR images were acquired with standard 3D spin echo sequences: matrix=128×128×128, FOV=25.6×25.6×25.6mm; TR=400ms, TE=4ms; Texp=1h50min. All ¹⁹F lung MR images were superimposed onto ¹H MR anatomical images. Lung images were bisected (left and right sides) for statistical analysis. Throughout the time-course, mice were observed for clinical signs, lung performance measured by plethysmography and behavior monitored.High quality images of the lungs were acquired using ¹⁹F MRI (Fig 1). The typical SNR is broadly similar to those obtained from ¹²⁹Xe hyperpolarization experiments [2]. However, the voxel size in the ¹⁹F images (200µm) was considerably smaller than voxels typically used in pre-clinical ¹²⁹Xe imaging (e.g. 625µm [3]), allowing improved visualization of lung structure. The high image resolution allows qualitative analysis of disease progress: a left lung post irradiation (Fig 1b) appears smaller and less intense than that of a naïve mouse lung (Fig 1a), illustrating subtle anatomical changes invisible on standard ¹H MR images. Quantitative volumetric analysis highlights early changes in relative lung volume (Fig 2a), whilst the mean signal intensity of the irradiated lung (Fig 2b) reveals a highly significant reduction, indicating lung damage starting long before signs begin to appear. The ability to monitor lung damage from early stages could be very important clinically and, also, as a preclinical tool. ¹⁹F based perfluorohexane imaging gives bright and detailed lung images, which allow visualization of structures not apparent on proton MRI. This approach is more easily and cheaply implemented than hyperpolarized gas setups and is immediately applicable in a range of pre-clinical work.