| Placenta is an important highly vascularized organ that contact the fetus and the mother, capacity vessels account for approximately 50% by volume of the placenta. Placental blood vessels can provide essential nutrients, gas exchange and metabolites excretion for fetal growth and development. Abnormal placental angiogenesis including the formation and development of placental vascular disorders, abnormalities of placental vascular network and reducing the number of capillaries of the placenta. These factors can affect placental blood perfusion, thus affecting the maternal-fetal placental circulation and making the area of material exchange decreased. Placental blood flow perfusion deficiency, causing placental dysfunction, which may cause fetal abnormalities even fetal death. There’re some reports that in the studies of placental formation and function of fetal growth restriction, pre-eclampsia and gestational hypertension found that the overall shape of placenta, blood volume, blood vessels branch network, vascular tube diameter and perfusion scores were significantly different compared with normal placenta.In summary, placental vascular were important in both normal pregnancy and pregnancy complications, while the study of placental blood vessels has also been an important research direction of obstetrics.At present, mainly research methods of the morphology of placental vascular network were vascular casting technology and digital three-dimensional reconstruction of data based on computer tomography (CT). Placental vascular casting technology in vitro is the most commonly used method for the study and observation of placental vascular network morphology, and also the basic of digital three-dimensional reconstruction technique. In 1966 La Torretta attempted to use liquid rubber solution to perfused placental vascular in vitro, but the cast specimen failed to show placental blood vessels good Subsequently, more researchers have researched the placental vascular casting technology and success. They perfused and observed the characteristics of its placental vascular network morphology of the placentas of normal pregnancy, gestational hypertension, pre-eclampsia, fetal growth restriction and gemellary pregnancy. First, placental vascular cast can show the capillaries of the placenta, and clearly reproduce the characteristics of placental vascular network morphology. But as an entity specimen, the cast prone to fracture and drop of microvascular during the process of moving, displaying and touching. Second, the cast specimens may become material brittle and easily broken, faded paint, etc., and increase the extent of its damage. Furthermore, due to the limited number of cast specimens, it unable to meet the requirements of learning for large quantities of student. Learning of damaged cast specimens will also cause some bias. The digital three-dimensional reconstruction based on CT can solve the shortcomings of the placenta cast specimens exist. In 2012 Chen reported the perfusion materials and perfusion method that is applied to CT scan to reconstructed placental vascular network, and successfully constructed 20 cases of digital three-dimensional model of human placental vascular network in vitro. These 3D models were consistent with the cast specimens, showed the 6-7 grade placental vascular clearly. The 3D model of vascular network reconstructed based on CT data can reproduce the structure, branches and vessels angle truly. It also can be arbitrary rotation, zoom in and out, making the researchers convenient to study morphological characteristics of vascular network and improving the accuracy of vascular network research. In addition, the 3D model of vascular network can transfer and display in any computers to meet lots of people learning at the same time, and the data will not change over time. It can be used for long-term scientific research work, greatly facilitate the data transfer and working convenience in teaching and research work. However, since CT scan is radioactive to affect growth and development of the fetus, its use during pregnancy was significantly limited, so that this method can’t be applied in the study of placental vascular network in vivo. Therefore, it’s necessary to find another method that can be used during pregnancy, and the use of this method to scan, reconstruct the placental vascular perfusion cast.Therefore, we propose a new method for the studying placental vascular network morphology-combine of MRI and digital three-dimensional reconstruction, to construct a digital three-dimensional model of normal human placental vascular network based on MR data in vitro.The study is divided into the following two parts.Part One:The study of the presentation of placental vascular network in vitro based on MR scannetwork in vitro based on MR scanChapter One:The study of the contrast agents of placental vascular[Objective]To investigate a contrast agent that is suitable for the presenting of placental vascular network in vitro based on MR scan.[Method]1. Research object8 full term placentas were collected and randomly divided into 4 groups according to the contrast agents. There’re 2 cases of placenta in each group.2. Preparation of vascular perfusion materialUsing a modified self-curing resin denture materials as perfusion agent, in which contain self-curing resin denture powder 30g, self-curing resin denture water 70ml, dibutyl phthalate 20ml and some red and blue oil paint every 100ml perfusion agent.3. Groups(1) Control group:there’re no contrast agent in perfusion material.(2) BaSO4 group:modified self-curing resin denture materials mix with BaSO4 10mg/L.(3) Vermilion group:modified self-curing resin denture materials mix with vermilion powder 1000g/L.(4) Gd-DTPA group:modified self-curing resin denture materials mix with Gd-DTPA 10mmol/L and 20% glycerol.4. Perfusion and MR scan of placental vascular network in vitro(1) Pretreatment of placental blood vessels:the method of pretreatment of placental blood vessels reference to the paper of Chen. Fresh placenta after delivery is squeezed out excess blood, washed bloody on surface, and then placed in a square plate with heparin saline solution (100IU heparin per 500 ml). Then we separated and cannula 1 umbilical vein and 2 umbilical arteriesand flushed with heparin saline solution to clear intravascular blood, until relatively clear liquid effluent or organization become pale.(2) Perfusion of placental arterial vascular network:we used 20ml plastic syringe fitted blue perfusion material, slowly injected from the umbilical artery at the speed control in 0.15ml/min, until the placenta maternal face a wide range of blue perfusion agent leaking out of placental maternal face. Then we removed the glass tube and ligation of the umbilical artery.(3) MR scanning and data retention:MR scanner is Achieva 3.0T which produced by Philips company. Using 16-channel phased surface coil, conventional axial scanning. The scan sequences of control group is T2W TSE, while other three groups were T1 e-THRIVE. Images were obtained from PACS and saved in DVD.(4) Perfusion of placental vein network, MR scanning and data retention:the same method as above with red perfusion material.[Result]The four groups’MR photos are present the same character:the MR signal of placental tissue and placental blood vessels were medium-low and low respectively. The placental blood vessels were rarely presentation.[Conclusion]The 3 kinds of contrast agents are not suitable for the present of placental vascular network in MR scan.Chapter Two:The study of the present method of placental vascular network in vitro based on MR scan[Objective]To investigate a method that is suitable for the presentation of placental vascular network in vitro based on MR scan.[Method]1. Research object6 full term placentas were collected and randomly divided into 3 groups,2 cases of placenta in each group. "positive group" and "negative group" is According whether perfusion agent and soaking solution containing contrast agent, in addition to another group is without a contrast agent for the "control group".2. Preparation of vascular perfusion materialThe same as chapter one.3. Soaking solution0.9% sodium chloride solution.4. Contrast agentGd-DTPA.5. Groups(1) Control group:there’re no Gd-DTPA in both perfusion material and soaking solution.(2) Group 1:modified self-curing resin denture materials mix with Gd-DTPA 10mmol/L while soaking solution without Gd-DTPA.(3) Group2:soaking solution mix with Gd-DTPA 10mmol/L while modified self-curing resin denture materials without Gd-DTPA.6. Construction of 3D model and cast of placental vascular network in vitro(1) Pretreatment of placental blood vessels:the same as chapter one.(2) Perfusion of placental arterial vascular network:the same as chapter one.(3) Soak of placenta:the placenta after perfused is totally immersed in the soaking solution to have enhanced MR scan.(4) MR scanning and data retention:MR scanner is Achieva 3.0T which produced by Philips company. Using 16-channel phased surface coil, conventional axial scanning. The scan sequences of control group is T2W TSE, while other two groups were T1 e-THRIVE. Images were obtained from PACS and saved in DVD.(5) Perfusion of placental vein network, MR scanning and data retention:the same method as above with red perfusion material.(6) Reconstruction of digital three-dimensional model of placental arteriovenous network in vitro:all the DICOM data of placental vascular network MR scan is imported Mimics 14.0. The method of reconstruction is reference to the report of Chen. Then we calculated the digital three-dimensional model of placental arteriovenous network used by region growing, edit masks, calculate 3D from mask and smoothing.(7) Production of placental arteriovenous network cast specimen:the cast specimen is soaked in 37% concentrated hydrochloric acid to corroded soft tissue after MR scan. Then we used digital camera to take pictures after removed the soft tissue.[Result]1. MR images,3D models and cast specimens of control groupThe MR signal of soaking solution, placental tissue and placental blood vessels were high, medium-low and low respectively. The signal of most small diameter vessels is close to the placental tissue so that can’t be distinguished. It can be observed 1-3 levels vessels in the 3D models while 3 of the following vessels appeared to be flaky fusion and can’t be observed.2. MR images,3D models and cast specimens of group1The MR signal of soaking solution, placental tissue and placental blood vessels were medium-low, medium or medium-high and low respectively. Some of the small diameter vessels can’t be distinguished. It can be observed some of 3-5 levels vessels, but there’re still some tiny blood vessels can’t be displayed compared with the same placental vascular cast specimen.3. MR images,3D models and cast specimens of group2The MR signal of soaking solution, placental tissue and placental blood vessels were medium-high, medium-high and low respectively. There’re big differences in the signal between placental vessels and tissue, so that it can be observed clearly whether the size of vascular diameter. The 3D model with more 3D sense, excellent vascular exposure, free rotation and radiation-free. When compared with the casting of placental arterial-venous vascular network, the morphology, structure, angle and trend of vessels of 3D model is consistent with its casting network, with striking similarities.[Conclusion]The best method to show placental vascular network in MR scan is Gd-DTPA contrast agent negative control method.Part Two:The study of reconstruction of digital three-dimensional model of human placental vascular network in vitro[Objective]1. To investigate the suitable MR scan sequence used in reconstruct digital 3D model of human placental vascular network in vitro.2. To investigate the method to registrate the 3D model of placental arteries and veins network in vitro, making the arteries and veins displayed respectively and integration completely.[Method]1. Data sources20 full term placentas were collected and deal with pretreatment of placental blood vessels, perfusion of placental arterial vascular network, soak of placenta, MR scanning, perfusion of placental veins and MR scanning. The perfusion material is modified self-curing denture material without contrast agent, and soaking solution is Gd-DTPA saline solution. The method of retreatment of placental blood vessels, preparation of vascular perfusion material, soaking solution, perfused and cast method are the same as part one.2. Selection of MR scan sequencesPerfused placenta is scanned by Achieva 3.0T MR scanner, using 16-channel phased surface coil, conventional axial enhanced scanning. We used two different sequences:T1-FFE and T1 e-THRIVE.3. Reconstruction of digital three-dimensional model of placental arteriovenous network in vitro(1) Obtain of digital 3D reconstruction model of placental arteries network in vitro:all the DICOM data of placental vascular network MR scan is imported Mimics 14.0. Then we calculated the digital three-dimensional model of placental arteries network used by region growing, edit masks, calculate 3D from mask and smoothing.(2) Obtain of digital 3D reconstruction model of placental veins network in vitro: the method as same as above.(3) Registration of placental arteries and veins vascular network in vitro:the STL format of 3D model of placental arteries network was imported into data of 3D model of placental arteriovenous network, then use different registration methods to calculate 3D model of placental arterial and venous vascular network in vitro. The methods of registration are STL registration and point registration.[Result]1. The MR photos of two MR scan sequences(1) There’re 100 and 160 MR images obtained from T1-FFE and e-THRIVE respectively. The MR images of two sequences are as follows:the MR signal of soaking solution, placental tissue and placental blood vessels were medium-high, medium-high and low respectively. It can clearly distinguish the placental vascular and soft tissue.(2) The digital 3D reconstruction models of placental vascular network in vitro based on two different sequences are with more 3D sense, excellent vascular exposure, free rotation and radiation-free. Compare with the placental vascular network cast specimen, the vascular network of 3D model based on T1-FFE data is sparse, while the vascular network of 3D model based on e-THRIVE data is exhibit sufficient and consistent.2. The digital three-dimensional reconstruction model of human placental arteries and veins network in vitro of two different registrations(1) The 3D model of placental arterial and venous vascular network in vitro calculated by STL registration showed that there’s angle difference between the arterial network and arteriovenous network that can’t be registrated and integration.(2) The 3D model of placental arterial and venous vascular network in vitro calculated by point registration showed that the arterial network and arteriovenous network are registrated and integration accurately, and we can distinguish placental arteries and veins clearly from this model.[Conclusion]1. e-THRIVE sequence is thin slices and well continuous, and the 3D models based on its data of the effect of realistic, blood vessels show fully. So that it can be used for further research.2. Point registration is the best way of registration method that making the placental arteries and veins distinguished clearly with better visual effects. |
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