| BackgroundThe development of modern science and technology more and more reflects interdisciplinary intersection and penetration. The new interdisciplinary studies field-Medical Virtual Reality Technology (Medical Virtual Reality Technology, MVRT) which integrates medicine, biomechanics, mechanics, hylology, computer graphics, mathematical analysis, automatic control and the like is developing rapidly at present, bringing about rapid change on modern medical diagnosis and therapeutic methods and concepts. Computer Aided Surgery (Computer Aided Surgery, CAS) is a new technology which makes the surgery safer and more accurate through providing technical support for surgeons by virtual surgical environment. CAS is based on the high-speed processing and controlling capacity on a vast amount of data information of the computer. In recent years, with the development of image diagnostic apparatus, such as CT, MRI and the like, the application of computer virtual reality technology in medicine has developed rapidly. The computer provides objective, accurate, intuitive and scientific methods for surgery simulation, surgery navigator, surgery orientation and surgery planning through using the image information to reconstruct the three-dimensional images. Since Vining and so on have firstly reported the helical CT virtual endoscope in 1994, the helical CT virtual endoscope has entered in the stage of clinical trial. However, its value in clinical practical work needs to be estimated.Colorectal cancer is the common malignant tumour in gastric bowel path. In recent years, the disease incidence has increased obviously. The disease incidence is only second to gastric cancer and esophageal cancer. The number of new cases of colorectal cancer every year around the world reaches 940,000. Nearly 500, 000 people die of colorectal cancer every year. Mortality is the third of cancer-related death. Surgical treatment is always the main treatment of rectum cancer. So far, the satisfactory fine three-dimensional anatomical structural model for clinical reference has not been established. The computer technology has been applied in imageology field, so slice image technology, such as CT, MRI and the like has realized digital image processing. Collection, storage, transmission, processing, display and so on of the medical image information have changed greatly. Thus, a new medical image processing and diagnostic mode is formed and the virtual imageology is born. The virtual imageology consists of various digital image three-dimensional reconstruction techniques and after-treatment techniques with virtual endoscopy (VE) as the core. The virtual imageology uses the two-dimensional slice images, such as CT, MRI and the like as the data source and utilizes the computer software reconstruction to directly display human organs, especially anatomical images of inner surfaces of lumen organs and three-dimensional virtual images of pathological changes. The virtual imageology can accurately and directly reflect the three-dimensional structures of human body and carry out disease diagnosis, stereoscopic localization, surgical simulation and so on. Large intestine and the surrounding structures are important anatomical structures of the general surgery. To slice image processing, CT and MRI workspace is mainly used for disease diagnosis, the purpose is single. Effective information mining of the slice image, such as CT, MRI and the like is not thorough. Colorectal cancer is the common malignant tumour in gastric bowel path, the regular barium enema and fibercoloscope are the main detection methods. Increasing researches on colonic pathological changes by three-dimensional imaging technology and CT virtual endoscopy (CT virtual endoscopy, CTVE) technology, especially 64-slice helical CT and the volume scanning with high-speed, thinner slice, wider range have largely promoted the development of this technology.Thus, based on CTA slice data sets of different types, we (1) have established the three-dimensional visualization models of the anatomical structures of rectum and the surrounding structures; (2) have established the three-dimensional visualization models of rectal tumor and the surrounding anatomical structures; (3) have reconstructed the volume rendering model and the surface rendering model of large intestine, the spatial adjacent relation model of large intestine and the surrounding anatomical structures and large intestine virtual endoscope in personal computers and have tried to mine the effective information of the slice image and (4) have carried out the large intestine virtual endoscopy and reconstructed the structural models of large intestine and the surrounding structures on 10 cases of colon cancer patients and intestinal polyp patients in personal computers, viewed morphology through CT three-dimensional imaging and CT virtual colonoscope and discussed the clinical application value.Study objectives and methods Purpose1. Seek for the method for reconstructing the digital models of rectum and the surrounding structures and for three-dimensional visualizing based on CTA slice images.2. Research the method for reconstructing the digital model of rectum cancer tumour and for three-dimensional visualizing based on CTA slice images.3. Seek for the method for reconstructing the three-dimensional digital models and for virtual endoscope detecting in personal computers based on 64-slice helical CT slice images.4. Discuss the method for reconstructing the three-dimensional digital models and for virtual endoscope detecting in personal computers based on 64-slice helical CT slice images.Method1. Study object: The first part The study object of reconstruction of the digital models of rectumand the surrounding structures and three-dimensional visualization based on CTAslice images is a healthy male volunteer who is 27-year-old.The second part The study object of the construction of the digital model ofrectum cancer tumour and three-dimensional visualization is a male rectum tumourpatient who is 68-year-old.The third part Image after-treatment based on 64-slice helical CT slice images: thestudy object of the three-dimensional reconstruction of large intestine and virtualendoscopy is a healthy male volunteer who is 31-year-old.The fourth part The study object of the virtual technology based on 64-slice helicalCT slice images and the CT virtual colonoscope clinical application research: collect10 cases of colon cancer patients and intestinal polyp patients during July toSeptember in 2007. The colon cancer patients are 8 cases, wherein, 5 cases are maleand 3 cases are female, who are 36 to 65 years old. The intestinal polyp patients are 2cases, wherein, 1 case is male and 1 case is female, who are 40 to 57 years old.2. Bowel preparation before testingEat liquid food 3 days before testing. Eat 30ml caster oil the night before testing. Fast on the day of testing. Carry out cleansing enema 2 hours before testing till the discharge liquor is clear. Intramuscularly inject 0.5mg atropine 15 minutes before operation.3. Carrying out air enema to inflate intestinal canal before CT scanningUse 1S-818E computer to remote-control an air enemator to carry out enema. Smear liquid paraffin on anus and anal canal. Insert Foley 18F sac duct (anal tube) per anus. The depth of insertion is 10cm. Inject 20-30ml gas to inflate the sac in order to prevent the sac duct from falling out. Begin to carry out enema under X-ray perspective observation. Continuously inject air into rectum with the stable 4-5kPa low pressure to inflate intestinal canal. Keep the pressure at 4kPa.4. Data acquisition equipment:64-slice helical CT-PHILIPS Brilliance64 (Holland) is used. The high-pressure injector uses MEDRAD dual-tube high-pressure injector (America). The image after-treatment processing workspace is attached Mxview workspace of PHILIPS Brilliance64-slice helical CT.5. CT scanning:Carry out CTA arteriography and high-resolution volume scanning under submillimeter state after the air enema is successful. When carry out routine scanning, the patient is in supine position. The scanning area is from twelfth thoracic vertebra to the middle upper part of thighbone along head-foot direction. The scanning condition is 120KV, 300mAs. 0.625×64-slice detector combination is used. Slice thickness is 0.5mm, interval is 0.5mm and pitch is 0.809mm. Time of a pipet rotating one circle is 0.5s. Soft tissue window is selected. Width of the collimator is 41.40mm×0.625 mm. Begin to routine scan. Dynamic CT enhanced scan: carry out arterial phase and venous phase continuous tracking scanning after the routine scanning is finished. Inject a contrast agent (using trocar) per cubital vein. Use a dual-tube CT high-pressure injector. The injection rate is 5ml/s. The used contrast agent is high-concentration non-ionic Iopamiro 370 (370mgI/ml) or Ultravist 370 (370mgI/ml). The dosage is 1.5 ml/kg weight. Use 50ml normal saline solution to rinse the tube after injecting the contrast agent. The scanning condition is the same with the routine scanning. Use the enhanced original data to reconstruct 1mm lamel after finishing scanning and transmit the image data to Mxview workspace.6. Collection of CT lamel scanning data: at Mxview diagnosis workspace, use a compact disk to burn all data, comprising routine scanning phase, arterial phase and venous phase data. The format is DICOM (Digital Imaging and Communications in Medicine)3.0.7. Construct digital models of rectum and the surrounding structuresMimics software respectively reads in arterial phase and venous phase CT slice images of Dicom format. The software automatically sets CT original scanning parameters. The interlamellar spacing is 0.5 mm, the arterial phase pitch is 0.809mm and the venous phase is 0.824mm. The parameters are stored by .MCS file format. Respectively reconstruct the three-dimensional models of bone, intestinal canal, artery, skin, bladder and prostate at the arterial phase data set. Respectively reconstruct arterial system, tumour artery, rectum tumour and so on according to different research needs. Reconstruct the three-dimensional model of ureter at the venous phase data set. Lead out the three-dimensional models in STL format and carry out the three-dimensional model stereoscopic pairing at the arterial phase data set.8. Intestinal canal surface rendering and external microscope Mimics software reads in CT slice images of Dicom format. The software automatically sets CT original scanning parameters. Gray value of each original image is processed by interpolated value in order to reach the precision of subvoxel. Adjust the window position and the window width to make the contrast reach the optimum visibility. Carry out air enema to inflate the intestinal canal. Construct the intestinal canal surface rendering model according to the air threshold value. The threshold value is defined between -1024 and -1024 Hounsfield unit. Inflate 1-2 pixels to make intestinal cavity be full with the selected pixels. Regional growth tools divide rectum and sigmoid colon, ascending colon, transverse colon and part of small intestine. Remove the redundant data. Construct the three-dimensional digital model of rectum through 3D computation. Surface rendering model is displayed by tri-patch. Reconstruct the three-dimensional models of bone system, arterial system, skin and prostate at the arterial phase data set. Manually divide bladder and prostate at 110-layer and 82-layer two-dimensional images. Construct the three-dimensional digital models of bladder and prostate through 3D computation. Reconstruct the three-dimensional model of ureter at the venous phase data set according to the concentration of the residual contrast agent. The threshold value is between 220 and 1641 Hounsfield unit. Reconstruct the three-dimensional model of ureter through regional growth 3D computation. Lead out the three-dimensional models in STL format and carry out the three-dimensional model stereoscopic pairing according to the anatomical structural relation of ureter, double kidneys and bladder at the arterial phase data set.9. Virtual endoscopeTo the intestinal canal surface rendering model constructed based on CT slice image, virtual endoscopy can be used to anatomize intestinal cavity and observe pathological changes. Effective intestinal canal anatomical image and diagnosis information can be obtained through observing the internal information of the tri-patch. Generally observe the two-dimensional images to guide the important observing target of the endoscope. Comprehensively analyze the target through multi-plane cutting function. Roam in intestinal cavity to observe the whole colon. Change the visual angle and the viewing distance, even reversely observe when the observed pathological changes have occurred. Return to the two-dimensional plane image to measure the largest diameter as the diameter.10. CT three-dimensional imaging and virtual endoscopy checkingUse Philips Brilliance 64 CT and 5mm thickness to finish the whole abdomen volume scanning. Reconstruct 0.5mm thickness and 0.5mm interval at the after-treatment workspace (Extended Brilliance workspace) to make volume rendering (volume rendering, VR) and endoscope software. Obtain the three-dimensional image and the endoscope image through rationally adjusting the threshold value. Generally observe shaded surface display (shaded surface display, SSD) and Raysum (RaySum) images to guide the important observing target of the endoscope. Comprehensively analyze the target through combining the axial plane image and multi-plane reconstruction (MRP).Result1. Reconstruction of the digital models of rectum and the surrounding structures and three-dimensional visualization research based on CTA slice imagesSuccessfully construct the digital models of rectum and the surrounding structures. Respectively construct the digital models of bone structures, such as lumber, pelvis, thighbone and so on, abdominal aorta, internal iliac artery, external iliac artery, branch, skin, rectum, sigmoid colon, ascending colon, transverse colon, part of small intestine, bladder, prostate and ureter.The constructed models have vivid geometrical appearance, better visualization effect, clear view and strong reality. The models can be displayed through several colours, tranparancy or arbitrary combinations. The internal structural relation between each component can be observed through the sections of different planes. The models can be rotated or observed at any angles. Dynamic display can be made into AVI format film to store and output. The pictures are clear and smooth.2. Construction of the digital anatomical model of rectum tumour and three-dimensional visualizationConstruct the three-dimensional digital models of rectum and rectum tumour, truly rendering the accurate position of the tumour in rectum. Respectively construct the digital models of bone structures, such as lumber, pelvis, thighbone and so on, abdominal aorta, internal iliac artery, external iliac artery, branch, skin, rectum, anal canal, rectum tumour, sigmoid colon, ascending colon, transverse colon, part of small intestine, bladder, prostate and ureter. The position relation between tumour and the surrounding tissues and the infiltration situation are clear.3. Image after-treatment based on 64-slice helical CT slice image: large intestine three-dimensional reconstruction and virtual endoscopyObserve anatomization and pathological changes of intestinal cavity through using the virtual endoscopy based on 64-slice helical CT slice image. Any part and corner in gastrointestinal tract can be successfully rendered. Anatomization and pathological changes of intestinal cavity can be observed from narrow and block part. Position and size of pathological change can be reliably displayed.4. Virtual technology and CT virtual colonoscope clinical application research based on 64-slice helical CT slice image.Successfully construct the colon surface rendering three-dimensional digital model.Observe anatomization and pathological changes of large intestine through using thevirtual endoscopy. The tumour form is exactly the same with the form seen in theoperation.Conclusion1. The three-dimensional reconstruction method of rectum and the surrounding structures reconstructs the spatial three-dimensional images with stereoscopic effect through using visualization technology, human visual characteristic and computer graphics to process the two-dimensional slice image series. The original and actual structures of intestinal canal, artery and ureter in vivo can be more accurately reconstructed and the three-dimensional models of rectum and the surrounding structures can be simply and effectively constructed based on air enema and CTA angiography.2. The virtual endoscopy based on CT slice image derives from the volume data obtained through helical CT continuous scanning. Compared with the traditional endoscopy, the virtual endoscope and CT workspace virtual endoscope have the same special advantages. (1) It is a perfect non-invasively check method. Patients are free of discomfort. There are no side effects of perforating, bleeding or infecting during the checking process. (2) The regular fiber scope has limited view and can not evaluate outer cavity anatomization and pathological changes. The virtual endoscope can fully display anatomization and pathological change position of colon and can observe anatomization and pathological changes of intestinal cavity from narrow and block part. Besides conditions in the cavity, the conditions of intestinal wall and out of the cavity can be known through combining with the three-dimensional images. It is better for determining tumour and stage diagnosis. The virtual endoscope provides evidence for clinic operation plan. (3) Different roaming plans can be planned out according to different needs and checking process can be arbitrarily repeated. (4) Medical check difficulty, danger and medical cost are reduced. (5) Most colon tumour pathological changes can be determined. At the same time, original data can be completely stored. The virtual endoscopy has better repeatability and flexibility and it is not limited by approaches and can reach the part which is needed to be observed arbitrarily. Repeated observation is good for checking small lesions and multiple lesions, avoiding missed diagnosis caused by human factors.3. Compared with CT virtual colonoscope technology, the advantages of the virtual technology based on 64-slice CTA slice image are: it can more accurately reconstruct bone, intestinal canal, artery and ureter in vivo and simply and effectively construct the three-dimensional models of large intestine and the surrounding structures. The virtual technology based on 64-slice CTA slice image can display from different angles through the three-dimensional visualization method. It is good for learning the actual three-dimensional human body through combining with the images in the traditional teaching material and substantial anatomization. The virtual technology based on 64-slice CTA slice image is supplement to the traditional teaching material. The three-dimensional reconstructed images are good for directly displaying the pathological changes, determining diagnosis and guiding operation. Computer simulation and operation planning can be further realized on the basis of visualization technology. The intestinal canal is soft and easy to deform, and is hard to shape in vitro. The actual shape of the intestinal canal in the human body is hard to understand. The study displays large intestine and the surrounding structure in an all-round manner through the three-dimensional visualization and rotation at any angle, which is good for observing and understanding the surrounding structures and helpful for understanding the anatomic relation of the surrounding structures of rectum. Compared with colon three-dimensional imaging and CT virtual endoscopy, the virtual technology based on 64-slice CTA slice image can realize the same sensitivity and speciality of the CT virtual endoscopy and three-dimensional imaging. Additionally, various tissue three-dimensional reconstruction technologies can provide richer information than the virtual endoscopy, its application future is wide.The constructed models provide a medical teaching platform for anatomic teaching, physical simulation and operation training. Clinic doctors can work out individual diagnosis, plan before operation and carry out operation simulation according to the digital simulated models of patients. Thus, operation safety is enhanced and complications of surgery are reduced. Development of general surgery is promoted.
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