| X-ray phase-contrast imaging（XPCI）derives contrast from the changes of phase shift information caused by X-ray passing through the sample for imaging.The phase-contrast is about 1000 times of the absorption-attenuation-contrast produced by traditional X-ray imaging.In addition,XPCI can obtain spatial resolution of micron or even submicron magnitude.It has been widely used in the field of biomedical imaging due to its advantages of both clear imaging of soft tissue and hard tissue.Combined with the computed tomography（CT）,XPCI has been developed into X-ray phase contrast CT（PCCT）.PCCT can not only observe the abundant internal microstructures of tissues with high resolution,but also realize three-dimensional（3D）visualization of tissues combined with 3D reconstruction technology,which will obtain the slices of internal structures at any angle.In this work,the imaging experiments of femur of osteoporosis（OP）mice and maxilla of periodontitis rats were performed at line BL13W1 of Shanghai synchrotron radiation facility（SSRF）.By setting the sample-to-detector distance,synchrotron radiation absorption-contrast CT（SR-ACCT）and synchrotron radiation phase-contrast CT（SR-PCCT）of the samples were performed.The common characteristics of the two disease models are the reduced bone mass and morphologic changes in bone microstructure,and the collected specimens are mixed samples of soft tissue and hard tissue.Objective:This work aims to compare and analyze the imaging characteristics of SR-ACCT and SR-PCCT on two mixed samples of soft and hard tissues in mouse femur and rat maxilla,and further explore the feasibility and value of SR-PCCT in the imaging of the OP and periodontitis models.Methods:（1）Fifteen 8-week-old balb/c female mice were randomly divided into 3groups on average.Two groups of mice underwent castration surgery to simulate OP caused by the drop in estrogen after menopause.They were given TSA and saline four weeks latter,hereinafter referred to as the drug group and the saline group.In another group,only a portion of the adipose tissue near the ovaries was removed as a normal control group,hereinafter referred to as the sham operation group.Finally,all the left femurs of the mice were scanned at SSRF’s BL13W1 line station for SR-ACCT and SR-PCCT,respectively,and the signal to noise radio（SNR）and contrast to noise ratio（CNR）were measured to compare the image quality of the two imaging methods.Based on SR-PCCT,the imaging characteristics of OP samples and the improvement effect of TSA drugs on OP were analyzed.（2）Six male Sprague Dawley rats were randomly divided into the periodontitis group（n=3）and the normal group（n=3）.The periodontitis group was constructed by the method of"silk thread ligation and high glucose feeding",and the normal group was fed conventionally.After 8 weeks,the right maxilla of rats were taken for SR-ACCT and SR-PCCT scans,respectively,and their imaging characteristics were analyzed.3D structures of the maxillary were reconstructed by SR-PCCT,and the distance of cemento-enamel junction-alveolar bone crest（CEJ-ABC）and root length in two groups were measured and compared.The alveolar bone height and trabecular arrangement of the two groups of rats were presented to explore the imaging characteristics of periodontitis.Results:（1）The SNR and CNR of SR-PCCT femoral tomographic images were about 3 times that of SR-ACCT（the SNR of bone marrow:22.03±4.28 vs 7.97±1.55;the SNR of bone tissue:43.83±6.87 vs 16.41±3.43;the CNR of bone marrow and bone tissue:17.84±4.79 vs 6.29±1.63）.Compared with SR-ACCT,SR-PCCT presented richer texture details on the surface of femur and clearer 3D structure of trabecular bone inside femur.In addition,the statistical results of bone morphometric parameters measured based on the 3D structure of the femur showed that:compared with BS/TV,BV/TV,BS/BV,Tb.Th,Tb.N and thickness of cortical bone in the sham group(10.75±0.64μm-1,21.47±3.90%,0.072±0.015μm-1,45.89±11.49μm,84.33±22.03μm-1 and 201.55±21.65μm),the corresponding parameters of the saline group significantly changed(7.99±1.02μm-1,13.14±1.61%,0.078±0.009μm-1,29.47±10.58μm,47.22±3.80μm-1,146.53±26.71μm;all P<0.05),and the BS/TV,BV/TV,BS/BV,Tb.Th,Tb.N and cortical thickness of the drug group were 10.84±0.83μm-1,21.06±2.39%,0.072±0.008μm-1,44.13±11.48μm,87.33±11.12μm-1 and 197.13±17.93μm,which significantly changed compared with those of the saline group（P<0.05）.The parameters of the drug group were close to the sham group,and there was no significant difference between the two groups（P>0.05）.（2）Compared with SR-ACCT,SR-PCCT significantly improved the SNR and CNR of alveolar bone and soft tissue such as gingiva（the SNR of gum tissue:7.88±0.85 vs 16.54±1.83,t=19.62,P<0.01;the SNR of alveolar bone:11.04±0.81 vs 30.89±3.84,t=23.16,P<0.01;the CNR of gum and alveolar bone:2.82±0.39 vs 11.65±1.66,t=23.73,P<0.01）,as well as the overall 3D reconstruction quality of maxilla.In addition,the SR-PCCT reconstructed maxillary tomography and 3D images showed that,compared with the normal group,the alveolar bone height reduced,periodontal pocket formed,and CEJ-ABC significantly increased in the periodontitis group（the normal group:1167.22[437.35,830.14]μm,the periodontitis group:620.91[1026.17,1304.08]μm,Z=-9.43,P<0.01）at the first molar of the maxillary bone.The alveolar bone trabecular bone were more less and the arrangement was more disordered in the periodontitis group compared with the normal group.Conclusion:Compared with SR-ACCT,SR-PCCT is more advantageous in imaging the trabecular bone and bone marrow of mice femur and the soft and hard tissue of rat maxilla.Combined with 3D visualization technology,SR-PCCT can realize high-resolution and high-contrast tomographic image and 3D structural reconstruction of femoral and maxillary structures in any direction.Imaging studies based on SR-PCCT of mouse OP femur and rat periodontitis maxillary samples show that the main imaging feature of OP is the morphological changes of trabecular bone,and the main imaging features of periodontitis were increased CEJ-ABC,decreased alveolar bone height,and disordered alignment of alveolar bone trabeculae.Thus,SR-PCCT has great potential value in evaluating the OP femur of mice and the periodontitis maxilla of rats,and is expected to provide a new effective imaging method for the diagnosis evaluation of drug efficacy of OP and periodontitis. |
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