chloride and either 2 5 u kg bw ld or 3 5 u kg bw hd of bleomycin sulfate calbiochem la jolla calif was instilled through the trachea tube control animals received saline only with this model it is widely reported that acute lung inflammation peaks about 1 week following intratracheal bleomycin administration then chronic fibrosis begins to appear within 2 4 weeks after dosing animals were temporarily reattached to the ventilator to assist in breathing if necessary the ld group showed a very mild response after the first two weeks of the study the reason why is not clear although the bleomycin activity can range from 1 5 2 0 u mg according to the vendor calbiochem therefore new bleomycin and additional age matched animals were ordered this second group received 3 5 u kg bw and became the hd cohort mri analysis images were reconstructed using a standard 2d fourier transform then they were read into mathematica 6 0 wolfgram research champaign ill for further analysis images of each rat at each time point were sorted into 5 data stacks u2014 one stack for each slice u2014 each composed of the 8 t 2 weighted images the mean background noise was measured from the first image of each stack image stacks were then thresholded to eliminate pixels whose signal intensity was lt 10 u00d7 the noise level typical signal to noise ratio of healthy lung was u2248 20 using the nonlinearregress function of mathematica remaining pixels were.