AbstractNonuniform disruption of lung architecture is usually assessed by CT, which carries potential radiation risk. Here we report our use of a three‐dimensional ultrashort echo time MR method to image the lungs of normal mice at different positive end‐expiratory pressures in a 3‐T clinical MR system. The ultrashort echo time sequence in conjunction with a projection acquisition of the free induction decay could reduce the echo time to 100 μsec and provide a more inherent MR signal intensity from the lung parenchyma, which is usually invisible due to its short T*2 in conventional MRI methods. The signal intensity and T*2 was reduced as the positive end‐expiratory pressure became higher. Further, these parameters were highly correlated to the changes in lung volume (% lung expansion). The results indicated that the MR signal acquired at ultrashort echo time in the lung parenchyma represents interstitial tissue density including blood. The capability of acquiring sufficient MR signal would have implications for the direct assessment of parenchymal architecture in the lung. Therefore, ultrashort echo time imaging may have the potential to assist detection of early and localized pathological destruction of lung tissue architecture observed in various pulmonary disorders such as emphysema without incurring the risks of radiation exposure. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.