Study On The Relationship Between Portal Vein Branches Hemodynamics Of Different Types Of PVS And Liver Regeneration Of Responsible Liver Segment In Rats Based On Multimodal Ultrasound And CFD

Background: Portal vein stenosis（PVS）is one of the main vascular complications after living donor liver transplantation（LDLT）,which can cause poor liver regeneration in severe cases.Adult right hepatic LDLT is a commonly used procedure for LDLT.In clinical work,we have found that sometimes PVS is not serious but it causes the uneven distribution of blood flow in the right anterior and right posterior branches of the portal vein.The regeneration of local liver lobe is poor and even atrophy due to the significantly reduction of portal vein perfusion.What kind of PVS（degree,location,morphology）can cause the uneven distribution of portal vein branch blood flow and the poor regeneration of responsible liver segment is still unclear,and the relevant literature has not been consulted.Hemodynamic factors play an important role in vascular stenosis,dilation and blood flow distribution.Doppler ultrasound is the main imaging technology of PVS hemodynamics monitoring after LDLT,but it is easily affected by Doppler imaging principle,sound beam direction,operator experience,equipment conditions and other factors;contrast-enhanced ultrasound and ultrasound elastography have been widely concerned and applied in clinic,but the research on different segments after LDLT has not been reported,and its diagnostic value is still unclear;Vector flow imaging（VFM）technology can directly display the blood flow in blood vessels,real-time detect the velocity and direction of each point in blood vessels,calculate blood flow and WSS,but its measurement accuracy in different flow fields remains to be further clarified,and the current commercial VFM technology can only be applied to high-frequency probes and superficial vessels,it is difficult to detect deep vessels.Studies have shown that computational fluid dynamics（CFD）can quantitatively evaluate hemodynamic changes and has been successfully used in arterial diseases,but its application in PVS has not been seen yet.Therefore,this study intends to establish different types of PVS models after 70% partial hepatectomy（PH）in rats.Based on multimodal ultrasound and CFD technology,the hemodynamic changes of portal vein branches of different types of PVS were evaluated.Combined with the liver regeneration of responsible liver segment,the relationship between hemodynamics of portal vein branches of different types of PVS and liver regeneration of responsible liver segment was explored,which provides new ideas and methods for non-invasive evaluation of PVs and liver regeneration.Objective: To establish rat models of moderate and severe PVS in different parts after 70% hepatectomy,and to evaluate the responsible liver segment’s liver regeneration of different types of PVS.Methods: 1.Establishment of different types of PVS models after 70% PH: 78 healthy adult male SD rats were randomly divided into sham operation group（SOR,n = 3）,pH group（n=15）,moderate or severe PVS（PVSM,PVSS）groups,with 30 rats in each group.PVS groups were divided into hilar and non-hilar group with 15 rats repectively.In pH group,70% hepatectomy was performed,and in PVS groups,the portal vein was partial ligated at different parts or degree of the portal vein based on 70% hepatectomy.The stenosis rates of moderate and severe PVS were defined as > 50% 65% and > 65% 99%,and different stenosis parts were divided into hilar and non hilar（located 5mm below the bifurcation of hilar）.2.Evaluation of liver regeneration in the responsible segment of PVB:（1）Evaluation of liver regeneration rate: The responsible segments of portal vein branch（PVB）after PH were right lobe and papillary lobe.In PH group,PVSM and PVSS groups,3 rats were killed at 1,2,3,7 and 14 day post-operation respectively,and the right lobe and papillary lobe were weighed to calculate the overall liver regeneration rate（LRR）,the proportion of responsible liver segment liver regeneration rate（LRRP_r,LRRP_p）and its ratio（LRRP ratio）.LRR = Dtotal liver / E × 100%,LRRP r = D_{right lobe} / E × 100%,LRRP_p = D_{papillary lobe} / E × 100%,where D is the weight of total liver / responsible segment per 100 g body weight at the time of execution,E is the weight of total liver per 100 g body weight before operation,and the weight of total liver before operation = the weight of resected liver / 0.70;（2）Expression of proliferating cell nuclear antigen（PCNA）: After the rats in each group were executed at the corresponding time point,the liver tissue was taken for immunohistochemical training immunization to evaluate the expression of PCNA.The right lobe and papillary lobe tissue sections of each rat was randomly selected from ten 200 times visual fields.The number of PCNA positive cells in 100 liver cells in each visual field was counted,and the average percentage of PCNA positive cells was calculated.In the SOR group,PCNA was detected at 14 d post-operation.One way ANOVA / independent sample t test was used to compare the liver regeneration rate and the percentage of PCNA positive cells in the responsible segment of PVB.Result: 1.Establishment of different types of PVS models after 70% PH: 60 PVS models were successfully established based on 70% PH.30 rats in PVSM group and 30 rats in PVSS group.The stenosis rate was 56.57% ± 3.50% and 68.21% ± 1.89% respectively.2.Evaluation of liver regeneration in the responsible segment of PVB after different degrees of PVS:（1）liver regeneration rate:（1）LRR: the LRR of PH group was 80.36% at 7d and 88.83% at 14 d post-operation;the severer PVS,the lower LRR;the LRR of PVSS group was less than 60% at 7d and 14 d post-operation,which was significantly lower than that of PVSM and PH group（all P<0.05）;（2）LRRP_r: the LRRP_r of PH group was 55.33% at 7d post-operation and 64.07% at 14 d.The LRRP_r of PVSM and PVSS group was significantly lower than that of PH group at 3,7 and 14 d.LRRP_r of PVSS was less than 40%,which was significantly lower than that of PVSM group（all P<0.05）.（3）LRRP_p: In PH group,the LRRP_p was about 25% at 7 and 14 d.In PVSM and PVSS groups at 2,3 and 7 d,the LRRP_p were less than 20%,which were significantly lower than that in PH group（all P<0.05）.There was no significant difference in LRRP_p between PVSM and PVSS groups（all P >0.05）.（4）LRRP_ratio: There was no significant difference in LRRP ratio among groups at different time points after operation（all P >0.05）.（2）PCNA expression in the responsible liver segment of PVB:（1）PCNA expression in the right lobe: At 3 d,the percentage of PCNA positive cells in the right lobe of PH,PVSM and PVSS groups were 79.13%,75.10% and 71.48%,respectively,which were significantly higher than that of SOR group（all P<0.05）.PCNA expression in PVSS group was significantly lower than that of PH group（P<0.05）.（2）Expression of PCNA in papillary lobe: At 3d,the percentage of PCNA positive cells in papillary lobe of PH,PVSM and PVSS groups was significantly higher than that of SOR group（P<0.05）. There was no significant difference in the expression of PCNA between PH and PVS groups（P >0.05）.3.The assessment of liver regeneration in the responsible segment of PVB in the same degree and different stenosis parts of PVS: In moderate PVS,LRRP_r and LRRP_ratio of hilar group was significantly higher than that of non-hilar group at 7 d after operation（P<0.05）,and the percentage of PCNA positive cells in the right lobe of hilar group was significantly higher than that that of non hilar group at 3 d（P<0.05）.In severe PVS group,there was no significant difference in liver regeneration rate and PCNA expression between hilar group and non-hilar group（P >0.05）.Conclusion: 1.This study confirmed that PVS models of different degrees and different stenosis parts can be successfully established by partial ligation of portal vein in different parts based on 70% hepatectomy in rats.2.Different degree and parts of PVS have different effects on the regeneration of the responsible liver segment of portal vein branch.Severe PVS（stenosis rate > 65%）will have obvious poor liver regeneration.Moderate PVS located in the porta hepatis has significantly higher liver regeneration level in the right lobe than that in the non porta hepatis,and the liver regeneration of the remaining two lobes may be significantly unbalanced.Objective: To evaluate the changes of hemodynamics of portal vein trunk / branch,liver parenchymal perfusion and hardness of responsible liver segment in different types of PVS by conventional ultrasound,vector flow imaging（VFM）,contrast-enhanced ultrasound（CEUS）and sound Touch Elastography（STE）.Methods: 1.Conventional ultrasound examination: The diameter of main and branch of portal vein（PVD）was measured by gray scale ultrasound on 1,2,3,7,14 d postoperation by Philips iu22 ultrasonic diagnostic instrument.The blood flow velocity（PVV）of the main and branch of portal vein was measured by Doppler ultrasound.In the PVS group,the diameter of the portal vein at pre-stenotic site(PVD_pre)and at the stenotic site（PVD_s）,the flow velocity at pre-stenotic site(PVV_pre)and at the stenotic site（PVV_s）were measured,and the portal vein diameter stenosis rate（DSR）and the rate of change in blood flow velocity（VR）were calculated.DSR =(PVD_pre –PVD_s)/PVD_pre × 100%,VR =(PVV_s-PVV_pre)/PVV_pre。2.VFM examination: The wall shear stress（WSS）of portal vein trunk and branches were measured with Mindray reasona 7 ultrasonic diagnostic instrument at 1,2,3,7,14 d post-operation.In PVS group,WSS(WSS_pre,WSS_post)was measured at pre-stenotic and post-stenotic site,and the ratio(WSSR_u: WSS_post / WSS_pre,)was calculated.3.CEUS examination:After 70% PH,the responsible liver segments of PVB were right lobe and papillary lobe.CEUS was performed at 1,2,3,7 and 14 d postoperation with Mindray reasona 7 ultrasonic diagnostic instrument.The arrive time（AT）,time to peak（TP）,peak intensity（PI）and area under the curve（AUC）of the time intensity curve of the right lobe and papillary lobe were obtained.4.STE examination: The liver stiffness of right lobe and papillary lobe were measured at 1,2,3,7,14 d post-operation with Mindray reasona 7 ultrasonic diagnostic instrument.Result:1.Conventional ultrasonic testing results:（1）The diameter and flow velocity of portal vein trunk and branches in different degrees of PVS:（1）Portal vein trunk: with the aggravation of stenosis,PVV_s,DSR and VR gradually increased,PVV_s and VR in PVSS group were significantly higher than those in PVSM group at 1,2d.DSR in PVSS group was significantly higher than that in PVSM group at 1,2,3,d（all P<0.05）.（2）Portal vein branches: PVD was difficult to detect due to the slender diameter of portal vein branches.There was no significant difference in PVVr,PVV pand PVVratio（PVVr/ PVVp）（all P>0.05）.（2）The diameter and flow velocity of the portal vein trunk and branch of PVS in the same degree and different parts at 1d were different,VR in severe PVS located porta hepatis was significantly higher than that in non hilar group（P<0.05）,while PVV_s,DSR,PVVr,PVV p,and PVVratio had no significant difference with different stenosis parts（all P>0.05）.2.VFM examination:（1）the difference of WSS in different degree of PVS: after PVS,WSS_pre decreased significantly,WSS_post increased significantly,and there was no significant difference in WSS_pre,WSS_post and WSSR_u at different time points between different degree of PVS groups（all P>0.05）.（2）WSS difference of portal vein trunk in the same degree and different parts PVS at 1d: WSS_pre of moderate PVS located porta hepatis was significantly lower than that of non portal group,and WSSR_u of portal group was significantly higher than that of non hilar group（all P < 0.05）.WSS of portal vein branch is difficult to detect because of the slender diameter.3.CEUS examination:（1）the difference of hepatic parenchymal perfusion in different degrees of PVS: On the 7th day after operation,the PI and AUC of the right lobe in PVSS group were significantly lower than those in PH group and PVSM group（all P <0.05）;the parameters of papillary lobe had no significant difference（all P>0.05）;（2）the difference of hepatic parenchymal perfusion in different parts of the same degree of PVS on the 7th day after operation: the PI of papillary lobe in severe PVS hilar group was significantly higher than that in non-hilar group on the 7th day after operation（P<0.05）.There was no significant difference in the other parameters with different stenosis sites（all P>0.05）.4.STE examination: the stiffness of right lobe and papillary lobe after PVS was not significantly different with the degree of stenosis（all P>0.05）.On the 7th day after operation,the stiffness ratio of right lobe to papillary lobe in PVSM group located porta hepatis was significantly higher than that in non-hilar group（P <0.05）.There was no significant difference in the other parameters with different stenosis sites（all P>0.05）.Conclusion:1.Ultrasound can reflect the changes of blood flow velocity and diameter of the main portal vein in PVS.PVV_s,DSR and VR can reflect the degree of portal vein stenosis in the early postoperative period.The severer PVS is,the higher PVV_s,DSR and VR are.The higher VR is in severe PVS located in the porta hepatis.It is difficult to detect the diameter of portal vein branch by ultrasound.There is no significant difference in the blood flow velocity of PVB in different types of PVS.2.VFM can observe the blood flow after PVS and detect the WSS of main portal vein.WSS decreased significantly at pre-stenotic site and WSS increased at post-stenotic site.But the difference of WSS in PVS is not significant.The WSS_pre decreased significantly when moderate PVS was located in the portal part of liver.WSS of portal vein branch is difficult to detect.3.Quantitative analysis of CEUS can evaluate the hepatic parenchymal perfusion of the responsible segment of portal vein branch.The peak intensity（PI）and area under the curve（AUC）of perfusion parameters can reflect the hepatic parenchymal perfusion of different degrees of PVS to a certain extent.The perfusion of the right lobe of severe PVS decreased significantly at 7 days after operation.The PI of papillary lobe in severe PVS located in porta hepatis was higher than that in non porta hepatis group.4.The diagnostic value of ultrasound elastography in evaluating the changes of liver stiffness in different types of PVS is limited.Objective: Evaluation of the main and branch hemodynamic changes of the moderate PVS portal vein in different parts based on CFD.Methods: CFD was used to simulate the hemodynamics of moderate PVS in different stenotic parts.The main flow includes: 1.The different parts of moderate PVS rats were placed into portal vein,and CTA was detected by injecting CT contrast agent into the catheter to obtain portal vein image;and 3D geometric model was constructed by reverse engineering Mimics based on CTA image of portal vein.2.the unstructured tetrahedron and hexahedron mesh are used to divide the computational mesh by ANSYS IVEM.3.Navier Stokes（N-S）equation is solved by numerical method,and boundary conditions are set according to the measured blood flow velocity range.4.CFD numerical simulation by ANSYS FLUENT 12.0 was carried out on the hemodynamics of 70% PH and different parts of moderate PVS to obtain the velocity distribution of portal vein trunk and branch,wall shear stress distribution(WSS_pre,WSS_s,WSSR_c),and calculate the blood flow,and compare and analyze the changes of blood flow and WSS after moderate PVS in different stenotic parts.Result: 1.In this study,CFD was used to simulate the hemodynamics of different parts of moderate PVS,and the velocity distribution and WSS distribution of portal vein trunk and branches were obtained successfully,and the portal blood flow（PVF）was calculated.2.The PVF of PH rats was 31.91 ml / min.The PVF of right lobe and papillary lobe PVB accounted for 80% and 20% of the total blood flow respectively（4:1）.When the portal vein stenosis was 60%,the PVF decreased significantly,only about 13.27ml/min;the decrease of PVF mainly affected the right lobe,and the proportion of branch blood flow of portal vein in the total blood flow of the two lobes was close to 1:1.3.In 60%PVS,WSS_s increased significantly,and the WSS_pre was decreased,especially in the non-hilar group.WSS_pre in PVSM locate non-hilar was significantly lower than that in porta hepatis group.WSS_s and WSSR_c(WSS_s / WSS_pre)in PVSM locate non-hilar group were significantly higher than those in porta hepatis group（all P <0.05）.WSS of portal vein branch in papillary lobe was significantly lower than that in PH group;there was no significant difference in WSS papillary lobe and right lobe of WSS among different parts of moderate PVS（all P > 0.05）.Conclusion: 1.In this study,CFD was used to simulate the hemodynamics of the moderate PVS in different stenotic parts,and the blood flow velocity distribution,WSS distribution and blood flow of the main and branch of portal vein were successfully obtained.2.At 60% PVS,the blood flow of PVS trunk and right lobe branch of portal vein decreased significantly,and the blood flow distribution of portal vein branch was obviously unbalanced.3.At 60% PVS,the WSS_s was significantly increased and WSS_pre significantly decreased.With the different stenosis sites,WSS_pre and WSS_s of portal vein were significantly different.Objective: Based on multi-modal ultrasound and CFD parameters,the correlation between portal vein hemodynamics and liver regeneration of responsible liver segment in different types of PVS was analyzed.Methods: 1.The correlation between the parameters of multimodal ultrasound and the regeneration of PVB responsible liver segment was evaluated.（1）Portal vein main parameters: Based on the analysis of different types of PVS multimodal ultrasound parameters in Chapter 2,the correlation analysis was conducted between PVV_s,DSR,VR,WSS_pre,WSS_post and WSSR_c on the first day after operation and LRR on the 7th day after operation;（2）parameters of portal vein branches and their responsible liver segments: the correlation analysis was conducted between PVV,PI and AUC of right and papillary lobe at 1d,and the LRRP at 7d as well as PCNA expression at 3d after operation.2.Evaluation of correlation between CFD parameters of different types of PVS and liver regeneration of responsible segment of PVB.（1）Main portal vein parameters: Based on CFD numerical simulation analysis of hemodynamics in different parts of moderate PVS in Chapter 3,correlation analysis was conducted between WSS_pre,WSS_s and WSSR_c of main portal vein and LRR on the 7th day after operation;（2）branch portal vein parameters: correlation analysis was conducted between right lobe of WSS,papillary lobe of WSS and right lobe of LRRP/PCNA expression and papillary lobe of LRRP/PCNA.（3）Based on the portal vein branch blood flow calculated by CFD numerical simulation in the chapter 3,the correlation between the portal vein branch blood flow and responsible liver segment liver regeneration was analyzed.Result: 1.DSR,PVV_s,VR,WSS_post and WSSR_u were negatively correlated with LRR_total（all P<0.05）,and the correlation coefficients were-0.784,-0.549,-0.538,-0.60,-0.572,respectively.2.There was no correlation between PVV right lobe,PI and AUC of right lobe and LRRP,PCNA expression of right lobe（all P>0.05）.There was no correlation between PVV papillary lobe,PI and AUC of papillary lobe and LRRP,PCNA expression of papillary lobe（all P>0.05）.3.WSS_pre was positively correlated with LRR_total,with a correlation coefficient of 0.668.There was a negative correlation between WSS_s,WSSR_c and LRR_total,with correlation coefficients of-0.763 and-0.674.4.The CFD parameters of WSS_r and LRRP_r,WSSp and LRRP_p were highly positively correlated（all P < 0.05）,and the correlation coefficients were 0.913 and 0.824.There was a positive correlation between WSS_r and the right lobe of PCNA expression（P<0.05）,and the correlation coefficient was 0.704.But there was no correlation between the WSSp and the PCNAp（P>0.05）.Conclusion: 1.The related parameters of multi-modal ultrasound of portal vein branches of different types of PVS have little relationship with liver regeneration of responsible liver segment.2.Compared with multimodal ultrasound parameters,the WSS of portal vein branch is highly positively correlated with the liver regeneration of responsible liver segment,suggesting that the WSS of portal vein branch based on CFD is a better index in reflecting the liver regeneration of responsible liver segment.3.The application of CFD to calculate the blood flow of portal vein branch to evaluate the liver regeneration of responsible liver segment has a potential prospect.