Preliminary Study On The Methods Of Reconstructing Three-dimensional Digital Model Of Human Placental Vascular Network Based On CT Data

BackgroudPlacenta is the defining organ that has enabled prolonged intrauterine gestation and fetal growth, with the function of oxygen and nutrients exchange, metabolism, hormone secretion, as well as defense and synthesis. The fetus obtains nutritional substances and oxygen from mother through placental vascular network. Consequently, normal development of placental vascular network and blood circulation establishment are essential for normal function of placenta and normal fetal growth. Numerous literatures indicate that placenta dysfunction caused by defective placental vasculogenesis and vascular developmental abnormalities are closely related to the morbidity of many obstetric diseases, such as fetal growth restriction(FGR), pregnancy-induced hypertension (PIH), gestational diabetes mellitus(GDM). Placentas of patients suffering from abovementioned obstetric diseases develop morphological and pathological changes.As the abnormal placental vasculogenesis plays an important role of morbidity of obstetrics diseases obstetricians have put more emphasis on the studys of placental vascular network. At present, the common methods which are used in studying placental vascular include immunohistochemistry, electron microscopy and pathological examinations,whereas the appropriate methods to study morphological features of placental vascular network are rare.Currently, placental vascular casting technique is the most common method used to study the overall shape of the placental vascular network. Since2000, domestic scholars have reported that they used placental vascular casting technique to establishe the placental vascular three-dimensional structural model of normal and abnormal placentas,such as preeclampsia or FGR. They observed the morphological changes of placental vascular network through the placental vascular casting model and studied the relationship between the morphological changes and the function of placentas. So far, the placental vascular casting technique has been quite mature, the placental vascular network including tiny blood vessels can be perfectly reconstructed in the placental vascular casting model,therefore, the morphological changes of placental vascular network can be clearly shown. However, the placental vascular casting technique has several drawbacks. Without appropriate measurement tools, it’s impossible to measure the diameter of the fourth-grade and tinier placental blood vessels, restraining the scholars from studying the placental vascular network comprehensively and detailedly. In addition, the casting models are easy to be damaged and broken while being moved and become crisp and faded, which makes them unavailable in the following teaching, academic conferences and researches.Therefore, there have great significances to seek a new studying method for promoting the research of placental vascular network. This new method should have the capability of not only showing the comprehensive placental vascular network but also performing measurement of vessels diameter, moreover the study results can be easily stored and repeatedly used, which are benefitical for the following research and teaching.This research intends to perform a preliminary study on the methods of reconstructing three-dimensional digital model of human placental vascular network after placental vascular perfusion.The study is divided into the following two parts.Part one:The study of vascular perfusion technique for digital three-dimensional reconstruction model of placental vascular network[Objective]The objective of this part is to discuss the appropriate vascular perfusion materials, filling sequence and key points of the technique in placental vascular perfusion for reconstructing the digital three-dimensional models of placental vascular network.[Method]1.Placental sourceWe selected18placentas from pregnant women (primipara) who delivered in term in Nanfang hospital. The placentas are divided into3groups randomly according to different filling materials, namely gelatin-ink perfusion group, chloroethylene perfusion group and self-curing resin denture perfusion group. The6placentas in each group are divided into3groups again at random according to the different vascular perfusion sequence, namely simultaneous perfusion group, arterial perfusion group and venous perfusion group. Each group has2placentas.2.Placental vascular perfusion(1)The fresh placentas were squeezed gently to remove the excess blood and rinsed the surface bloodstain, subsequently placed into heparin saline(100iu heparin in per500ml Saline) in square plate. We separated the two arteries and one vein in the umbilical cord and performed intubation in these three vessels, then washed the vessels by repeated perfusion with heparin saline till the placental tissue became pale. After that,the placentas were put into95%alcohol to get fixed.(2)Preparation of vascular perfusion materials ②Gelatin-ink perfusion materials:Per100ml gelatin-ink perfusion solution contains80ml distilled water,20ml ink,5g gelatin and8g lead oxide.②Chloroethylene perfusion materials:Per100ml chloroethylene perfusion solution contains20g CPVC,100ml ethyl acetate,5ml dibutyl phthalate, appropriate amount of oil paints and8g lead oxide.③Self-curing resin denture perfusion materials:Per100ml self-curing resin denture perfusion solution contains35g self-curing denture acrylic,70ml liquid denture acrylic, appropriate amount of oil paints and8g lead oxide.(3)Simultaneous perfusion groupMethods of vascular perfusion using three different kinds of filling materials in this group are the same. We used the filling materials to perfuse umbilical vessels consecutively and slowly (0.5ml/min). In the chloroethylene perfusion group and self-curing resin denture perfusion group, the blue filling materials were used to perfuse the arteries, while the red ones were to perfuse the vein. In the gelatin-ink perfusion group, we used the same black gelatin-ink perfusion materials to perfuse both arteries and vein. When we saw the filling materials exuded on the placenta chorionic surface widely, we stopped the perfusion and removed vascular intubation, then ligated the umbilical arteries and vein. The chloroethylene perfusion group should be refused6-8times before ligating the vessels. The placentas of gelatin-ink perfusion group underwent CT scan immediately after perfusion, while the other two groups made it when the filling materials became solid fully.(4)Umbilical arteries perfusion groupFirst, we used the blue filling materials to perfuse the arteries in the chloroethylene perfusion group and self-curing resin denture perfusion group, while using the black gelatin-ink perfusion solution in the gelatin-ink perfusion group. Methods, pressure, speed and stopping time of vascular perfusion in this group were the same as those in the simultaneous perfusion group. The placentas underwent CT scan after removing vascular intubation and ligating umbilical artery. The gelatin-ink perfusion group underwent CT scan immediately, while the placentas of the other two groups made it when the filling materials became solid fully. Then we perfused the umbilical vein with red filling materials in chloroethylene perfusion group and self-curing resin denture perfusion group and black gelatin-ink perfusion solution in the gelatin-ink perfusion group. CT scan were performed for the second time in the experimental groups except the gelatin-ink perfusion one.(5)Umbilical vein perfusion groupExperimental procedures and methods of this part are the same as the arterial perfusion group except that we perfused umbilical vein first and the umbilical arteries next in this experimental group.3.Enhanced CT scanThe perfused placentas were scanned using dual-source CT (SOMATOM Definition) produced by Germany Siemens company The placentas were placed with the maternal surface side down in conventional axial when scanning. The average scanning thickness and the layer spacing both are0.75mm.The scanning results were output by DICOM format and then stored in disk.4.Three-dimensional reconstructionThe DICOM images were input into the Mimics10.01software.After the image positioning, image organizing and interpolation processing, the reconstruction threshold was set, and we edited the images by using the Edit masks fuction and regional growth fuction of Mimics software. Finally the digital three-dimensional reconstruction model of placental vascular network was reconstructed by using. calculate3D from mask fuction.5. Corrosion and pruningThe perfused placentas were placed in20%concentrated hydrochloric acid for3-5days, then we got the vascular casting models. Subsequently,we used running water to clean the casting model.[Results]1. The digital three-dimensional models of placental vascular network in different experimental groups show different morphological characteristics.Models in gelatin-ink perfusion group can show the tiny blood vessels of the placentas well, but not the overall morphological features. Models in chloroethylene perfusion group can show both the tiny blood vessels and the overall morphological features of the placental vessels well. In this group, we found that the placental vessels are easy to get ruptured during the vascular perfusion and the shape of casting model has changed significantly. Models in self-curing resin denture perfusion group can commendably demonstrates the overall morphological features of the placental vessels well,while some tiny vessels can’t be shown well.2. The influences caused by the first vascular perfusion of the reperfusion in umbilical arteries perfusion group are less than in the umbilical vein perfusion group. The reconstruction models using the same filling materials in different vascular perfusion sequence groups show the similar characteristics.[Conclusion]1.Vascular perfusion technique directly affect the placental vascular network three-dimensional reconstruction models, so we should pay more attention to the details of the operation,such as sample preparation,vascular perfusion materials preparation.2. In three experimental materials,self-curing resin denture perfusion material is the best one which is suitable for reconstructing placental vascular network three-dimensional digital model.3. The placental vascular network digital three-dimensional models which are reconstructed based on the placentas in simultaneous perfusion group can accurately reflect the actual situation of vascular network, suitable for the whole placental vascular research. When we perfuse the placental vessels orderly, we should perform umbilical arteries perfusion first and umbilical vein perfusion next, which makes less influences on the vascular perfusion.Part Two:The study of the methods of digital three-dimensional reconstruction model of human placental vascular network [Objective]The objective of this part is to discuss the appropriate CT scanning parameters and methods which are used for building three-dimensional digital model of placental vascular network based on CT data. Another objective is to preliminarily discuss the methods for measuring the three-dimensional model of placental vascular network.[Methods]1.Placental sourceWe selected40placentas from pregnant women (primipara) who delivered in term in Nanfang hospital.All placentas were obtained from women labored via vaginal delivery or caesarean section. We used self-curing resin denture perfusion material to perfuse the arteries and vein of placenta simultaneously.2.Software and equipmentDual-source CT(SOMATOM Definition,German Siemens), Home computer(Windows7operating system),three-dimensional reconstruction software (Materialise, Belgium),Geomagic Studio software(Geomagic, America)3. Appropriate scan parameter selectionWe selected one perfused placenta and performed enhanced CT scanning on it by Dual-source CT(SOMATOM Definition,German Siemens) with the average scanning thickness and the layer spacing of0.60mm,0.75mm and1.00mm.The scanning results were output by DICOM format and then stored in disk. Then we performed the three-dimensional reconstruction using Mimics10.01reconstruction software and compared the effects of the three-dimensional models to choose the best average scanning thickness and the layer spacing.4.Data collection40perfused placentas were scanned using dual-source CT (SOMATOM Definition) produced by Germany Siemens company.The placentas were placed with the maternal surface side down in conventional axial when scanning.The average scanning thickness and the layer spacing both were0.75mm.The scanning results were output by DICOM format and then stored in disk.5..Three-dimensional reconstructionThe Dicom images were input into the Mimics10.01software.After the image positioning, image organizing and interpolation processing,the reconstruction threshold was set,and we edited the image by using the Edit masks fuction and the regional growth fuction of Mimics software. Finally the digital three-dimensional reconstruction model of placental vascular network was reconstructed by using. calculate3D from mask fuction.6. Measurement of digital three-dimensional modelsWe used Mimics software and Geomagic Studio software to measure the vessels diameter based on a digital three-dimensional model.[Results]1. CT scan layer spacing was0.60mm and a total of371layers were obtained. CT scan layer spacing was0.75mm and a total of318layers were obtained. CT scan layer spacing was1.00mm and a total of233layers were obtained. We saved the data in DICOM format.The digital three-dimensional models reconstructed by Mimics basing on the above CT database have no obvious differences in morphology, degree of showing vessels and smoothness.2.Using the Mimics10.01software, we can successfully construct digital three-dimensional reconstruction model of placental vascular system based on CT data. The reconstructed three-dimensional placental vascular model is realistic and stereoscopically, which possess good vision effect and shows anatomy structure of placental vascular network and its primary branches clearly. It can not only zoom but also revolved freely to observe the placental vessels.3. We can make the measurement of diameter vessels by using both Mimics software and Geomagic Studio software.[Conclusion] 1. The appropriate average scanning thickness and the layer spacing both are0.75mm.2. Mimics is a software specially developed by Materialise for both medical and mechanical image processing. Currently the software is widely used in medicinal research.There exist some superiorities of Mimics when it is used in research of digital three-dimensional reconstruction as follows.First,Mimics can import DICOM images data directly,which can simplify the process and reduce the loss of data information,as well as improve the accuracy of the three-dimensional model.Second,Mimics can be operated. in general Home PC.Third,Mimics has a strong modeling function based on tomography image, therefore, it can solve construction and measurement problems in complex three-dimensional model of anatomical structure well. In short, Mimics is a rapid, convenient, powerful three-dimensional image processing and editing system.3.We can reconstruct the digital three-dimensional models of placental vascular network using Mimics software based on CT database. Image segmentation acts as the most critical factor affecting the three-dimensional model in the reconstruction process. Reconstruction threshold range affects the three-dimensional reconstruction model directly. With the"draw profile line" fuction to choose Image thresholding, favorable three-dimensional model of placental vascular network can be obtained. Through the combination of image thresholding segmentation method, region growing method and manually operated segmentation method, we can improve the quality of the digital three-dimensional models.4.The three-dimensional reconstruction model of placental vascular network, which is reconstructed based on CT data, can fully show the placental vessels. It is an effective and new way to use the three-dimensional reconstruction model to study placental vascular network, providing an useful tool for the following study and teaching.5.Both using Mimics software and Geomagic Studio software can measure the diameter of placental vessels based on the digital three-dimensional models. The measuring results by using Mimics software alone can be accurate to0.01mm. However,when Mimics software measures the vessel diameter by only selecting vessel points on the surface,so the measuring results may be different from the actual ones. In the latter method, we can get the center line of blood vessels by the fitting the cylinder and the center line function of Geomagic software,leading to less manmade error. However, the operation of Geomagic Studio software is more complicated and costs more time.