Evaluation of lung inflammation induced by intratracheal administration of LPS in mice: comparison between MRI and histology.

PURPOSE

To study the in vivo effect of intratracheal administration of lipopolysaccharide (LPS) in mice by magnetic resonance imaging (MRI) and to investigate the correlation with ex vivo histological evaluation of lung inflammation and oedema.

MATERIALS AND METHODS

LPS (or phosphate buffered saline) was administered intratracheally to thirty male Balb/C mice at a concentration of 0.3 mg/ml in a total volume of 100 microl. Animals were divided into fifteen LPS-treated and fifteen control mice. MR images were acquired 24 h after challenge in freely breathing animals with standard ECG-gated Gradient-Echo (GRE) sequences and, in a limited number of animals, with ECG-gated Ultrashort-echo time (UTE) sequences. After MRI, animals were sacrificed, and lungs were fixed and processed for histological analysis of the total volume of healthy lung tissue.

RESULTS

GRE images revealed the presence of high intensity signal in lungs of LPS-treated mice that was attributable to oedema caused by alveolar inflammation. In histological slices, regions of alterations in the normal alveolar microstructure were observed that could account for MRI findings. A good correlation was observed between the volumes of lesioned tissue measured by MRI and by histology. The volume of the lesion detected by GRE sequences was lower than the volume detected by UTE sequences.

CONCLUSIONS

The effect of intratracheal administration of LPS in mice was investigated by MRI and histology. A good correlation was observed between GRE-MRI and histological findings. MR images obtained with UTE sequences appear to be more sensitive to the presence of lesions than those obtained by standard GRE acquisitions.