The Application Of Micro-CT In Model Of Pulmonary Fibrosis Of Rats

Part one:The scan parameters of micro-CT in rats' specimensObjective To study a chest scan protocol of micro-CT in rats.Methods Eight rats' lung tissues were fixed,inflated,dried and examined with micro-CT by changing four parameters including angle of increment,scan technique,detector bin mode and frame to average.Images of specimens were scored by four indexes including detection of anatomy structure,measurement of CT value,artifact from CT apparatus and eyes' feeling on images and different scan protocols were also evaluated.Results Decreasing angle of increment, choosing scan technique of 360°and increasing frame to average could improve image quality,and choosing 2×2 or 4×4 detector bin mode could also improve image quality of the same exposure dose.Conclusion The scan parameters that met the requirements of imaging of rats' specimens were described as follows:Tube voltage 50kVp and tube current 500μA were used;360°views were obtained at 0.7°-degree increments around the subject with two frames per view,450ms per frame;Detector bin mode of 4×4 were used.Part two:The evaluation of model of pulmonary fibrosis in rats with micro-CTObjective To evaluate radiologic findings of pulmonary fibrosis in different stages with micro-CT.Methods Sixty four Sprague-Dawley rats of 8 to 12 weeks were divided randomly into experimental group and control group.The former were given 5mg/kg bleomycin intratracheally.Twenty nine of them were survived.Control group were given physiological saline solution equally.All rats were scanned with micro-CT in vivo and again after sacrifice at follow-up of 3 days to 4 weeks.Tube voltage 80kVp was used;other scan parameters were referred to the first part.Sequentially,the left lungs were removed and scanned with micro-CT for radiologic studies.Management of specimens and scan protocol were referred to the first part.The right lungs were examined histologically with HE stain,masson trichrome stain and immunohistochemical stain.Alveolitis and pulmonary fibrosis was quantified.Observations of thoracic imaging included ground-glass attenuation, consolidation,linear opacities,nodules,traction bronchiectasis,subpleural interstitial thickening,bullas,pneumothorax and honeycomb lung.Imaging findings in vivo and after sacrifice at micro-CT were compared.Pulmonary changes of four sub-groups after sacrifice were evaluated and compared with control group.Images of specimens were investigated and compared with imaging in vivo and after sacrifice.Appearance of radiologic signs in different stages of PF was also compared.Resultsl.Appearance of consolidation,bullae, pneumothorax and honeycomb lung of imaging in vivo and after sacrifice was close to each other.Appearance of ground-glass attenuation,nodules,subpleural interstitial thickening and traction bronchiectasis of imaging in vivo was under it of imaging after sacrifice,but the difference had no statistical significance.Imaging after sacrifice was good at displaying linear opacities(P＜0.05).2.Linear opacities appeared in 14d group and 28d group,bullae and pneumothorax were mainly in 28d group,the difference of appearance of two signs above had statistical significance(P＜0.05).The difference of appearance of ground-glass attenuation and consolidation had no statistical significance in sub-groups.Nodules and subpleural interstitial thickening did not appear in 3d group.Honeycomb lung and traction bronchiectasis appeared in 28d group.3.Specimen imaging was clearer than imaging in vivo and after sacrifice.4.HE stain and masson trichrome stain suggested that it was moderate or severe alveolitis mainly in experimental group of 3d and 7d and it was moderate or severe pulmonary fibrosis mainly in 14d and 28d.5.Immunohistochemical stain showed that positive cells in lungs of experimental group were increased and intensity of staining was boosted,particularly in 7d group.Positive cells in 28d group were less than those in 7d group,but were still significantly higher than those in control group.6.Linear opacities appeared in pulmonary fibrosis of gradeⅡor gradeⅢand had statistical significance(P＜0.05);Bullae and pneumothorax were mainly in pulmonary fibrosis of gradeⅢ,difference of appearance of the sign had statistical significance(P＜0.05).The difference of appearance of ground-glass attenuation,consolidation,nodules and subpleural interstitial thickening had no statistical significance in different stages of pulmonary fibrosis. Honeycomb lung and traction bronchiectasis appeared in pulmonary fibrosis of gradeⅢ.Conclusion 1.This disease model of rats could reflect pulmonary fibrosis in different stages.2.Micro-CT could apply to radiologic researches of model of pulmonary fibrosis in rats.3. Imaging from micro-CT of rats could reflect radiologic changes of pulmonary fibrosis in different stages.Sign of linear opacities is a mark which suggests the formation of moderate or severe pulmonary fibrosis and sign of bullae or pneumothorax is a cue of the formation of severe pulmonary fibrosis.