|Year : 2016 | Volume
| Issue : 1 | Page : 6-12
The three-dimensional reconstruction and visualization of direct intrahepatic portacaval shunt
Hao Du1, Kai Li2
1 Camp Three of Students Brigade, Third Military Medical University, Chongqing 400038, China
2 Institute of Digital Medicine, Third Military Medical University, Chongqing 400038, China
|Date of Web Publication||11-May-2016|
Institute of Digital Medicine, Third Military Medical University, Chongqing 400038
Source of Support: None, Conflict of Interest: None
Objective: Transjugular intrahepatic portacaval shunt (TIPS) is a traditional and effective treatment for variceal bleeding in cirrhotic patients with portal hypertension. However, in patients with a Budd-Chiari syndrome or other unaccessible hepatic veins, a direct puncture through the inferior caval vein may be inevitable. Direct intrahepatic portacaval shunt (DIPS) also has several advantages compared with TIPS. So we are expected to explore a digitalized model of DIPS and find the suitable shunt pathway of DIPS. Materials and Methods: We chose four hundred serial sectional images from the internal jugular vein superior margin to the edge interior hepatic from Chinese Visible Human Dataset. Surface and volume reconstruction were performed by 3D Doctor 3.5 software programs(ABLE SOFTWARE). Results: We reconstructed a digitalized model including liver and relevant vessels. It can display distribution characteristics and spatial structure relationship of intrahepatic vessels from any positions and angles. Conclusion: DIPS represents a useful addition to the endovascular techniques for managing complications of portal hypertension. The model of DIPS provides a good 3D morphological reference of image diagnostics and interventional therapy for DIPS.
Keywords: Direct intrahepatic portacaval shunt, sectional anatomy, three.dimensional reconstruction, visualization
|How to cite this article:|
Du H, Li K. The three-dimensional reconstruction and visualization of direct intrahepatic portacaval shunt. Digit Med 2016;2:6-12
| Introduction|| |
Liver cirrhosis is a common chronic liver disease in clinic. It will cause portal hypertension at an advanced stage with variceal bleeding complication. The biggest challenge for intrahepatic vessel interventional therapy and hepatectomy is the overlapped and interacted anatomic structures of hepatic vein system and portal vein system. An effective shunt pathway between portal vein and inferior caval vein by a stent can make the blood in portal vein flow into inferior caval vein directly, which will be a considerable way to cure portal hypertension., Compared with transjugular intrahepatic portacaval shunt (TIPS), direct intrahepatic portacaval shunt (DIPS) is safer and operational., The advantages include lack of hepatic vein as shunt outflow (and therefore avoid hepatic vein stenosis), real-time imaging guidance during advancement of the needle into the portal vein, decreased radiation by use of intravascular ultrasound during portal vein access, and decreased procedural time. A series of forty patients with DIPS using intravascular ultrasound has also been reported showing a high success and patency rate. In the manipulation of DIPS, the key point is to know clearly about the spatial relationship of anatomic structure of intrahepatic vessels and select correct puncture spots to establish a stable and persistent intrahepatic vein shunt pathway. Hence, it is necessary to build a digitalized model to find the suitable shunt way of DIPS.
| Materials and Methods|| |
The Chinese visible human (CVH) model was set up to produce a dataset of complete normal adults from Asia in October, 2002. This CVH dataset was derived from a middle-sized cadaver (35 years old at the time of death, height of 170 cm, and a weight of 65 kg) without organic lesions. The subject was representative of a completely normal adult male anatomy of an Asian population. The cadaver had been enrolled into the cadaver donation program, which follows the scientific ethic rules of the Chinese Ethics Department.,, The thin serial interval was sampled at 1.0 mm. The cadaver was sterilized using 5% formalin and was artery perfused with 20% red gelatin. Then, embedded with 5% green gelatin, the cadaver was immersed in a saline pool and frozen to −30°C. After 10 days, an improved numerical control milling machine (TK-6350, made in China) was used to shave off serial slices of the body and layer by layer at −25°C from head to foot. The cross sections were photographed by digital camera (Canon EOS-D60, made in Japan) at a high resolution of 3072 × 2048 pixels, each tagged image file format (TIFF) file occupying 36 MB (approximate pixel size was 167 μm).,
Four hundred serial sectional images data (from number 0408–0807) from the plane of the right jugular vein to the edge interior hepatic was chosen from the CVH data set. The amount of the total dataset was 14.4 GB. Photoshop CS2 software (Adobe Systems) was employed to achieve accurate relative positioning through the four reserved fiducial rods on each cross section [Figure 1].
|Figure 1: Four plastic tubes (a-d) were positioned longitudinally to serve as reserved fiducial rods for three-dimensional reconstruction and as markers for cross sections|
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Observation of sectional view
The left-right and anterior-posterior directions of the cross section were defined as X-axis and Y-axis, and the cranial-caudal direction was defined as Z-axis to establish the three-dimensional (3D) coordinates. Then the continuous cross section images data were registered. With uniform 3D coordinates, we can obtain the spatial coordinate position of arbitrary anatomical structure points by coordinate mapping. The image measurement software was employed to measure the pixel coordinates (x, y) of two random points, the interval between sectional views (Δd) and proportion between pixels interval and the actual length of the scale (dr). After the reconstruction of the 3D model, Δd is zero, and the distance between two random points is . The number of voxels of certain structure can be measured from the established volumetric data and then converted to the corresponding measurement unit values.
The registered serial sectional images were imported to 3D-DOCTOR V3.5 software (ABLE SOFTWARE). A new stack file with the extension of “.stl” was created. With the piecewise boundary machine provided by software, the contour line of the internal jugular vein, caval vein, heart, liver, and intrahepatic venous vessels system were segmented section by section. Each organ contour was assigned with different RGB color. Then, we established the boundary data set. With 3D-DOCTOR software rebuilding functional package, virtual vascular guide wire (d = 0.88 mm) was rebuilt that passed through the right hepatic vein via right internal jugular vein, right brachiocephalic vein, superior vena cava, right atrium and inferior vena cava. The anterior wall of inferior vena cava, which is located at the transverse plane of the left branch of the portal vein is the point “A” for DIPS puncture. Puncture point “B” was determined at the left branch of the portal vein from the portal vein bifurcation about 10 mm.
After segmentation, we used surface rendering tool in rendering menu to build the 3D structures of virtual shunt stent, internal jugular vein, caval vein, heart, liver, and intrahepatic venous vessels system. This surface rendering method based on marching-cubes algorithm created a set of 3D primitives such as triangles to form the surface of an object, and we used the primitives to display object surface. After surface rendering, the surfaces of the 3D structures were smoothed with smooth surface toolkit. Then, we could display the digital model of DIPS dynamically. When rebuilding the shunt stent (d = 8 mm), we calculated the surface area data, volume data, central coordinate of the stent, and the angle of axis. The virtual stent can be revolved, photographed, and seen through the appearance. After that, the anatomic structures of vessels and virtual shunt stent of DIPS could be observed clearly at any angle.
| Results|| |
Acquisition of continuous slices image data set
The image data set of DIPS displayed sectional images with complete construction and clear pipes. The interval was 1.0 mm, and effective resolution was 6,300,000 (3072 × 2048) pixels. The anatomic pictures were derived from the CVH data set (from number 0408–0807) and were reconstituted on the visible platform. The pictures were stored in the format of TIFF, and the total dataset was 14.4 GB comprising each sectional image files of 36 Mb.
Reconstruction of three-dimensional digital visualization model
First, the images of the human DIPS route were observed meticulously. After being assigned with different colors accurately with 3D-DOCTOR V3.5 software, the intrahepatic vessels were rebuilt by visualization 3D software. Surface structure and morphological features of every organ and tissue could be manifested exactly by revolving the model. At the same time, orientation of accessory branches of hepatic vein, branches of portal vein in hepatic segments, and adjacent relationship of portosystemic vein in liver parenchyma could be observed clearly at any angle by liver parenchyma hyalinization.
The 3D reconstruction images showed that hepatic portal vein was divided into the left and right branches near the first porta hepatis, leaning to the right of transverse sulcus, and the furcation angle was approximately 150°. The posterior border of bifurcation was toward the anterior border of the retrohepatic inferior vena cava and the caudate lobe of liver is between them. Hepatic vein went out of liver at the secondary porta hepatis above inferior caval vein sulcus of liver's pars dorsalis and drained into anterior wall of retrohepatic inferior vena cava. The main stem of right hepatic vein was located in internal lobes of the right liver and was constituted of right posterior lobe superior vein and inferior vein. The main stem ran toward the top-left and drained into the right anterior lateral wall of inferior vena cave, after leaving liver, it influxed into the lower location compared to the left hepatic vein and the middle hepatic vein [Figure 2].
|Figure 2: Three-dimensional model for intrahepatic vein shunt (norma posterior)|
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Acquiring data of 3D shunt endoprosthesis, which was reconstituted on the visible platform by the 3D-DOCTOR V3.5 software. The distance of the DIPS virtual stent between retrohepatic segment of inferior vena cava and intrahepatic portal vein left branch was about 20 mm, and the caliber was about 8 mm, in a horizontal position forward [Figure 3],[Figure 4],[Figure 5],[Figure 6]. The center coordinates (X, Y, and Z), surface area (s), and volume (v) of DIPS virtual stent are shown in [Table 1].
|Table 1: The center coordinates (X, Y, and Z), surface area, and volume of direct intrahepatic portacaval shunt virtual stent|
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|Figure 3: Three-dimensional reconstruction of direct intrahepatic portacaval shunt pathway (norma anterior). Jugular vein, caval vein, and hepatic vein were blue; portal vein was purple; aorta and heart were red; liver was brown; direct intrahepatic portacaval shunt pathway was yellow; and stent was green|
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|Figure 4: Three-dimensional reconstruction of direct intrahepatic portacaval shunt pathway (norma left side). Jugular vein, caval vein, and hepatic vein were blue; portal vein was purple; aorta and heart were red; liver was brown; direct intrahepatic portacaval shunt pathway was yellow; and stent was green|
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|Figure 5: Three-dimensional construction of direct intrahepatic portacaval shunt stent (norma superior). Caval vein was blue; portal vein was purple; and direct intrahepatic portacaval shunt stent was green|
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|Figure 6: Three-dimensional construction of direct intrahepatic portacaval shunt stent (norma inferior). Caval vein was blue; portal vein was purple; and direct intrahepatic portacaval shunt stent was green|
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The relationship between intrahepatic portal vein and retrohepatic inferior vena cava
By using the measuring function of 3D-DOCTOR V3.5 software, the distance between intrahepatic portal vein and retrohepatic inferior vena cava and the angle between retrohepatic inferior vena cava and the furcation of portal vein branches are shown in [Table 2].
|Table 2: The relationship between intrahepatic portal vein and retrohepatic inferior vena cava|
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| Discussion|| |
The data set of three-dimensional reconstruction
Continuous and accurate image data set is the key to reconstructing an accurate 3D model. After the first trial of the visible human project (VHP) in America, it has also been developed in Korea and China during the past decade. However, acquisition of the sectioned images from cadavers was discontinued in the VHP and the cadavers used in the visible Korean human project had more lesions compared with CVH. What is more, CVH chose more cadavers to acquire sectioned images, and the cadavers were younger. Hence, the VCH data show more appropriate body contours for their ethnic groups.
Three-dimensional reconstruction methods
Intrahepatic venous line system is a hierarchical and complicated structure with high intercommunication. Accuracy and microtrauma of modern intrahepatic vessel interventional therapy are involved in the 3D location of the anatomic structure. Now, available anatomic data were acquired by observing and measuring human body after section. After segmentation, classification and registration of the data set, rendering the 3D reconstruction model, and the meticulous expression of the system can be realized. By 3D data measurement and multidirection exhibition of stereo morphology, the most necessary morphological data for interventional therapy of intrahepatic vessels can be provided. On the basis of the 3D model, further fundamental researches on anatomic morphology of intrahepatic vessel system can be realized, including preoperative localization, puncture pathway design, and a series of exquisite and detailed operation plans. There is no doubt that it will enhance the effect of interventional therapy on liver vascular disease overwhelmingly.,
The DIPS is a treatment via the vein puncture approach with interventional equipment. We intubated jugular vein to retrohepatic inferior vena cava. The shunt way is created from the inferior vena cava through an oblique tract through the caudate lobe. It represents the high level of radical interventional therapy including paracentesis, intraluminal angioplasty per cutem, and endoprosthesis insertion technique. The key point for this technique is successful puncture and appropriate placement of endoprosthesis. Complications such as paracentesis injury, stent desquamation, and even abdominal cavity hemorrhage existed due to the sophisticated construction features of hepatic vein affiliated branches and branches of portal vein. Therefore, it is important for DIPS to investigate the distribution of hepatic vein and portal system.
Because of the 3D and constructional change caused by collapse of hepatic vessels, the data acquired by traditional liver anatomy did not conform to that of the living body.,, Therefore, in this study, CVH data set from jugular vein to the intrahepatic vein was employed. Through precisely paratoping the anchor points of the continuous sectional images, we ensured the accuracy of the 3D reconstructed images. The reconstructed continuous sectional (interval 1.0 mm) images applied 24 bits uncompressed and true color images. 3D-DOCTOR software was applied to recognize, divide, and extract the boundary outline of vein anatomic structure to reconstruct 3D model, and 3D display was performed to view the complicated spatial relationship, which actually revivified its 3D construction to the original state. Data for 3D length, surface area and cross section area and regional histogram of intrahepatic vein piping, intervening catheter, and virtual endoprosthesis could be acquired rapidly by the application of tools, which enhanced further quantificational research of veinule piping construction.
Design of intrahepatic portosystemic shunt pathway
Human visual characteristic facilitated the visualization technique.,,, Meanwhile, computer graphics technique was employed to process 3D data formed by 2D tomoscan image array in the calculation, and 3D image was reconstituted with visualized stereo effective space and displayed on computer. Visualization of intrahepatic vein piping system established a stable foundation for the expansion of vascular interventional therapy and liver surgery. Meanwhile, it provided a more spacious applicative space for further study of visualization liver piping system. This experiment was based on the model of intrahepatic portosystemic system and visible 3D coordinate system. The software was employed to establish puncture pathway and determine the angle for puncture, shunt tunnel distance and puncture depth, which would provide 3D morphological foundation for further research references.
As for TIPS, when debouch of hepatic vein could not be found or the distance between hepatic vein and the main branch of portal vein was too short or it was not appropriate to puncture portal vein via hepatic vein, it is not easy to be operated. Hence, we punctured from retrohepatic inferior vena cava at the level of the second porta hepatis to branch of portal vein via liver parenchyma to build portosystemic shunt tunnel. It avoided relative narrow hepatic veins to be used as draining veins and lengthened patent time for shunt pathway theoretically.
Although the quality of the 3D ultrasound spine image is not so good as the CT and magnetic resonance imaging (MRI), the required information is able to be measured. Furthermore, the surface of the rebuilt image was visually similar to the original object. Although computed tomography (CT) and MRI technologies are becoming popular and mature, the doctors mostly make their diagnosis on 2D planar, which would inevitably lead to a certain rate of misdiagnosis. In contrast, 3D visualization technologies can not only clearly display the relationships between organization structures but also quantitatively characterize the vascular structures. Based on the visualization diagnosis system, doctors can clearly observe the distribution of venous system and adjacent structures. Meanwhile, it simulates ultrasonic directions to conduct virtual dissection on any section. On the sections, the interlobar and intersegmental fissures of the liver were displayed distinctly, thus realizing accurate hepatic segmentation. Hence, this virtual hepatic segment model (VHSM) can facilitate accurate segmental localization of intrahepatic lesions by ultrasonography, particularly those residing in areas without major blood vessels. Therefore, 3D visualization technology is an effective tool in building the interventional treatment model, which can provide precise rebuilding and display method.
The dataset used in the present study was prepared by using a middle-sized young male body, without organic lesions. The 2D and 3D anatomic analysis demonstrated that the hepatic vein and portal vein of the young man were anatomically typical for the Chinese people. Therefore, this VHSM represented the liver and hepatic segments of most Chinese people. The boundary between hepatic segments can be delineated in any section by using the crop editor of Amira Software. However, due to individual differences and anatomical variations in intrahepatic vessels, particularly those of the right liver, the VHSM is not universal., It is the task waiting to be solved in the future.
With the growth of virtual reality technology, we will see an increase in surgical training simulators. These simulators can be based on 3D rebuilding models, and several surgical simulators have been shown to increase patient safety. The simulator in conjunct with DIPS is applied in preoperative surgical simulations, which will not only improve patient safety but also help surgeons choose the best approach.
| Conclusion|| |
In some interventional radiology practices experienced with the DIPS procedure, DIPS has largely replaced the TIPS procedure. The shunt point in DIPS is lower than TIPS; more indications will be operated and the localization in portacaval shunt for orthotopic liver transplantation. Compared with TIPS, DIPS puncture via retrohepatic inferior vena cava, so the shunt pathway of DIPS does not contain hepatic veins, which would decrease the incidence rate. Then, DIPS is also able to avoid the difficulty in puncturing venous tributary in TIPS. DIPS represents a useful addition to the endovascular techniques for managing complications of portal hypertension.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
[Table 1], [Table 2