Early detection of lung inflammation: exploiting T1-effects of iron oxide particles using UTE MRI.

At high magnetic fields diagnostic proton MRI of the lung is problematic, because of fast T2* relaxation. The application of superparamagnetic contrast agents and the exploitation of the corresponding T2* effect is inefficient with conventional MRI methods, which limits the early detection of lung diseases. However, a simple theoretical treatment shows that in the lung, by the use of ultra-short echo time sequences, T2* effects can be neglected while T(1) shortening effects can be used for signal detection. In our study, we have applied a theoretically and experimentally optimized 3D ultra-short echo time sequence to lung phantoms and to a mouse model of lung inflammation, which was induced by systemic bacterial infection. Following the systemic application of very small superparamagnetic iron oxide nanoparticles, a significant signal increase in the lung of infected animals was detected already at 24 h postinfection, compared to control mice (17%, P < 0.001). Iron accumulation in the lung parenchyma as consequence of the host immune response was histologically confirmed. By conventional T2*- and T(2)-weighted imaging, neither structural changes nor formation of substantial edema were observed.