PURPOSE To investigate whether lung tissue characterization by ultra-short echo-time (UTE) magnetic-resonance imaging (MRI) allows ischemia/reperfusion injury to be distinguished from acute rejection in a mouse lung transplantation model. Material and MethodsAfter orthotopic lung transplantation with 6 mice receiving syngeneic (C57BL/6) lung transplants and 6 mice receiving allogeneic (BALB/c) transplants, they underwent postoperative imaging using three-dimensional UTE-MRI (echo-times TE=50μs-5000μs) and conventional T2-weighted fast spin-echo imaging. Quantitative T2* values of lung transplant parenchyma and spin density (SD) were compared by region-of-interest analysis. All samples underwent histological and immunohistochemical workup. RESULTS In the allogeneic group alveolar infiltration resulting from acute organ rejection was visualized in the UTE sequences. This was reflected by the quantitative measurements of SD and T2*values with higher values in the allogeneic group compared to the syngeneic group and non-transplanted lung at the first time point (24h post-operative: Tx allogeneic group SD: 2133.9±516; Tx syngeneic group SD: 1648.61±271; p=0.004; Tx allogeneic group T2*: 1710.16±644 μs, Tx syngeneic group T2*: 577.16±263 ms; p =<0.001). CONCLUSION Changes caused by acute rejection after lung transplantation can be visualized and characterized using a UTE sequence due to different relaxation properties compared to both syngeneic lung transplants and normal lung tissue. This article is protected by copyright. All rights reserved.