Research On Digital Virtual Liver And The Surgery

Hepatoma, a widespread disease covering major population, was rated the No. 4 fatal disease across the world in 1990, and escalated to be the No. 3 in 2000. Each year the patients increase 1 million, whilst it causes 260 thousand patients to death, with 42.5% from China. Since the 90^th of twenty century, it has become the No.2 fatal disease in China. Due to the dangerousness of the Hepatoma, surgery is the most preferred and most effective treatment solution. Among the medium and late phase liver cancer patients, 20-30% of them get a surgical liver resection while the 5-year recovery rate reaches 51.6%. The success of liver cancer surgery requires the surgeon to have a comprehensive understanding of the tumor's size, shape, location and the relationship to intrahepatic vessel. Currently the equipment employed for diagnosing the liver tumor mainly includes such image devices as CT and MRI. However, such devices could only provide two-dimensional images on the inside of human body. Surgeon could only estimate the size and shape of lesions based on personal experience through several two-dimensional images, "figuring out" the 3-dimensional relationship between lesions and the surrounding vessel structure. It makes difficulties for the morphologic diagnosis of liver disease and the surgery treatment., causing a low rate of the liver resections and leaving more and more Hepatoma un-removed as expected. Meanwhile, since the liver cancer patients normally get Hepatitis B and hepatic cirrhosis which cause injury to their liver function, make it close to compensation. Hence, when conducting surgery, the surgeon needs to ensure not only resect the liver lesion completely, but he/she needs minimize the unnecessary injury caused by the operation to the normal tissues. The surgery also needs to protect the function of the liver, prevent the complication caused by the operation, and enhance the life quality after the surgery. The question is how to prolong the survival time so as to improve the life quality of the patients with unresectable liver cancer, by choosing the appropriate comprehensive therapy. In order to answer the question as well as to assess the outcome of the selected therapeutic strategies, the comprehensive system construction is required for the therapeutic protocol design, treatment process mimics and efficacy evaluation and prediction.3-dimensional reconstruction of liver and the virtual surgery research through visualization and the virtual reality have made it possible to solve such problems. The digital virtual liver and the surgery makes use of such imagery sequence as CT and MRI, so as to display a 3-dimensional model of the various structures of the liver, making the hiding human organ a visible "live" 3-dimensional object. The strengths include: 1) being specifically located in certain space; 2) Being observable in structure and being measurable and available in various data; 3) Enhancing the advancement of anatomical liver. In various surgeries of virtue liver, the CT or MRT examination data of specific liver cancer patients could be employed for image fusion and updating. Hence the surgeons can use their computers to conduct surgical planning, to repetitively test the operational process. Such computerization exercise will help surgeons to optimize the planning, to ensure the surgery quality and safety, and to reduce the operation complications.ObjectiveTo investigate the methodology of three-dimensional reconstruction, hepatic vascular embolism system of the digitalized virtual liver and its neoplasmic surgical resection mimic system.Methods1. The research on visualization of liver CT scanning and simulation of vasculature embolism.1) The CT image dataset of liver(1) The liver with well preserved the portal region was perfused with filling materials in different colors through hepatic artery, portal vein, inferior vena cava/hepatic vein and bile vessel and scanned by hispeed CT to obtain the image dataset.(2) The format of CT images was converted from DICOM to BMP by ITK (Insight Toolkit).(3) Analyzing the intrahepatic duct structural feature on CT images.2) Visualizing investigation on hepatic vessel structure based upon skeleton line extraction(1) CT images were preprocessed in binary way.(2) The Marching Cube (MC) algorithm, a kind of surface rendering, were employed to reconstruct 3D surface models of liver and intrahepatic ducts, and then these 3D surface models were smoothed and simplified. (3) The abstract vessel trees were constructed, after the skeleton line of the vessel system were extracted from the hepatic CT dataset.(4) The extracted vessel tree was combined with the vessel surface model for analyzing the vessel structure interactively.3) The research of simulation on vasculature embolism.Applying the liver visualization technique to the clinic of vasculature embolism, a virtual medical system was established for the therapeutic protocol planning and testing the efficacy evaluation of hepatic vasculature embolism, which construct surface models of liver and intrahepatic duct using CT images. When hepatic vasculature embolism was simulated, the vasculature knob points was selected and regulated to locate embolism and confine its affected area.4) Virtual stereovision environment was builtBoth the active and passive sets of virtual stereovision environment were built, which enables the audience watch altered transformation matrix of liver model by OpenGL with his or her separate naked right/left eye in stereogram with vertical extent consequently.2. The research on simulation of partial hepatectomy.1) The image dataset and its characteristics: The entire liver with complete porta hepatis was prepared, followed by infusing, fixing and casting the hepatic artery, portal veins, inferior vena cava, bile duct system using filling materials in different colors. Then it was embedded, frozen and slice-cut by a milling machine so as to obtain the image dataset of liver serial sections.2) Visualization of liver (1) Image registration: In our experiment, image registration was conducted by external point force combined with moment-to-force. The markers pre-embedded around the liver were set as registration points and the image registration was performed based on the relatively-fixed positions between the liver and those markers.(2) Image segmentation: It mainly aimed at the segmentation of hepatic and portal veins. The procedures included: (Ⅰ) Gaussian-Rapras algorithm was used to extract all the contour line of both liver and ducts. (Ⅱ) The contour line were expanded and refined to connect their broken lines. (Ⅲ) The type of tissues incorporating in the contours was judged and identified by fully marking the portal veins with red color if they were reddish, fully marking the hepatic veins with blue color if they were bluish and finally marking the liver parenchyma with brown color if they were neither reddish nor bluish. Following the segmentation of all images, the image data of liver parenchyma, hepatic veins and inferior vena cava, portal veins, hepatic artery, bile duct and cholecyst were all extracted, respectively.(3) 3D reconstruction: The 3D reconstruction software MINICS (Materialise' s interactive medical image control system) was used to reconstruct 3D liver model with hepatic surface in surface rendering.3) The virtual surgery systemBased on the FreeForm Modeling System, the software of virtual resection was developed. And then the virtual hepatectomy system was established with the force-feedback equipment (PHANTOM), which can manipulate the virtual scalpel to perform optional resection on virtual liver model. Results1. The research on visualization of liver and simulation of vasculature embolism.1) The CT scanned image dataset of liver242 scanned images of liver were taken. Each image showed relevant hepatic duct conformations. Inferior vena cava, the right, middle and left hepatic veins could be seen clearly in the image through porta hepatis, and portal veins and its branches could be seen clearly in the image through porta hepatis.2) Visualization of hepatic vessel structure based on skeleton line extractionIn the reconstituted liver model, the images of liver parenchyma, hepatic veins and portal veins were vividly displayed respectively or in combination. This visible system of liver provided a graphics user interface to rotate and scale the 3D liver to observe 3D morphological features of the liver and intrahepatic duct by setting the pellucidit value and colors.3) The research on simulation of vasculature embolismIn the demo system of vasculature embolism simulation, the vasculature embolic position, scope and its consequences were simulated by manipulating the nodal points of intrahepatic trees.4) Virtual stereovision environmentIn the two systems, when audience in special glasses watch liver model, it looks like flying in the sky from computer screen or viewing screen with strength stereo.2. The research of simulation on partial hepatectomy.1) The dataset of hepatic sectional images: After slice cutting cast liver and by a milling machine, 910 serial cross-section images were obtained and they were sharp and clear, with hepatic artery, portal veins, inferior vena cava/hepatic veins, bile duct system displayed in red, brownish red, black and blue.2) Visualization of liver(1) Image registration: The registered images were within the rectangular area of 1100×900, which ideally demonstrated the full view of the liver(2) Image segmentation: The image information of cholecyst, intrahepatic ducts and hepatic parenchyma were respectively segmented and their contour line was extracted.(3) 3D reconstruction: The 3D reconstructed liver model looks like the liver sample, and can be magnified, contracted and rotated.3) The virtual partial hepatectomy systemIn the virtual surgery system with interaction and immersion, we can manipulate the virtual scalpel to perform optional resection on 3D liver model with the haptic device (PHANTOM).Conclusions1. 3D liver model with intrahepatic vessel, which was 3-dimensionally reconstructed in the method of skeleton line using CT scanning images, may be helpful in the promotion of hepatic clinical anatomy. Based on 3D reconstruction, a simulative system of vasculature embolism developed, which addresses fully interaction facilities, may be helpful in the research of simulation on vasculature embolism.2. The 3D visualized liver has been satisfactorily developed with the method of surface rendering using the hepatic serial sectional images. Then based on the haptic devices (PHANTOM) the virtual hepatectomy system has been developed, which has good interaction, powerful immersion and great imagination, may be of great significance for the promotion of hepatic clinical surgery.