The Establishment Of Three-dimensional Visible Liver And Virtual Hepatic Segment Model And Their Application In Ultrasonography

Background:The human liver is an important organ with perplexing construction and great function in human body. The greatest feature of hepatic ultrasonography is able to display the sectional anatomic structure at arbitrary orientations, but a large number of irregular ultrasonic images would be generated because of multi-directional scanning. It is difficult to recognize the subtle anatomic structure of intra-hepatic vessels on those images. With the improvement of the resolution of ultrasonic transducers, intra-hepatic anatomic structures were displayed more subtly, which demands corresponding thin sectional anatomy. Recent advances in hepatic surgery have made segmental resections, as well as atypical or combined sections and part liver transplantation possible, It is vital for imaging to determine the precise preoperative segmental location of focal hepatic lesions. But detection of any random directions and irregular images limits the research on hepatic segmention by ultrasonography in which only part of the liver and intra-hepatic vessels were displayed on the two-dimensional sonographic planes, and was lack of three-dimensional display. So it is not helpful to determine the segmental location of hepatic lesions accurately. The research of medical visualization has started and developed rapidly in our country. Virtual Reality Medical System based on Chinese Visible Human data set would have very significant value for our medical teaching, clinical diagnosis (including ultrasounic medicine) and surgery.Objectives:The three-dimensional Chinese visible liver model and virtual hepatic segments model is to be established in order to provide thin sectional anatomy at random direction for hepatic ultrasonography and accurate two-dimensional and three-dimensional morpho- logical data for ultrasonography in hepatic segments classification, as well as to explore the clinical value of virtual hepatic segment model on localization diagnosis of focal hepatic lesions assisting the ultrasonography. The software of the virtual hepatic ultrasonic imaging system was designed to provide two-dimensional and three-dimensional visualization platform for liver anatomy teaching and imaging diagnosis in ultrasonography.Methods:1. The thin sectional anatomical images of liver selected from the Chinese Visible Human data set were used to establish three-dimensional visible liver model by volume rendering and surface rendering with AMIRA software. The virtual hepatic segments model was established based on three-dimensional visible liver model, The ultrasound images of health adult were collected to build the database.2. Ultrasonic direction could be simulated at any angle in the three-dimensional visible liver and virtual hepatic segment model. The virtual ultrasound sections were compared with the corresponding ultrasonic images of liver in order to direct the identification of anatomic structure and classification of hepatic segments on ultrasonic images.3. During the recent two years between November 2007 and January 2009, 100 patients underwent hepatic resection surgery for focal hepatic lesions located within two hepatic segment and less than 9cm in diameter in our hospital, 17 patients had benign hepatic lesions and 83 patients had malignant hepatic lesions. After all patients underwent ultrasonography which is an initial imaging examination for the detection of hepatic lesions, contrast enhancement CT was performed before hepatectomy. Corresponding ultrasonic direction was simulated to perform continuous virtual cutting in the virtual hepatic segment model, then the segmental location of the lesion was determined and recorded as Couinaud segment. The localization diagnosis result of intra-operative hepatic lesions was considered as the standard to compare the accurate rate of ultrasonography, contrast-enhanced CT, and virtual hepatic segment model.4. Six groups of ultrasonic images were selected from the health adult database and patients with focal hepatic lesions database respectively. Corresponding ultrasonic section was simulated in the three-dimensional visible liver and the virtual hepatic segment model to acquire the visible sections and hepatic scissure sections. By using Photoshop CS2 9.0 software, the hepatic anatomic structures and hepatic segments were segmented on the visible sectional images and corresponding ultrasonic images. the name of hepatic scissure was marked on the 2D sections and ultrasonic images, Then each structure was established in a layer and finally the segmented image was saved as PSD format.Results:1. The model of 3D visible liver could clearly display the structure of hepatic vessels and their special relationship, and can be cut in arbitrary orientations. The intra-hepatic vessels could be displayed distinctly on each section and each hepatic scissure could be displayed in any section by using"crop editor"function on the virtual hepatic segment model, then related hepatic segment would be determined.2. Ultrasonic direction could be simulated through cutting at any angle in the model of 3D visible liver and each section had good corresponding relationship display compared with those of ultrasonic images, which solve the problem that it is hard to comparing study between ultrasonic images and anatomic sectional images. By comparing with the sectional anatomic images, each hepatic scissure would be determined and the accurate classification of hepatic segment would come true on the ultrasonic images.3. A total of 112 lesions were determined in 148 resected hepatic segments from 100 patients. 74 lesions located in single hepatic segment, 38 lesions located in two hepatic segments and the size of lesions ranged from 0.80 cm to 9.10 cm. Among them, 43 lesions were 3cm or smaller in diameter, 69 lesions were larger than 3cm in diameter. The difference between ultrasonography and virtual hepatic segment model in determining the segmental location of lesions was statistically significant (p<0.05). but there was no statistically significant between the virtual hepatic segment model and contrast-enhanced CT (p>0.05). The difference between ultrasonography and virtual hepatic segment model was statistically significant for preoperative segmental location diagnosis of lesions located in single hepatic segments and 3cm or smaller in diameter (p<0.01). But there was no statistical difference in lesions located in two hepatic segment and larger than 3cm in diameter (P>0.05).4. The software of the virtual liver ultrasonic imaging system was accomplished. We could learn about liver anatomy, hepatic scissure and hepatic segment classification of the standard ultrasonographic sections by this software and further understand the process that the virtual hepatic segment model assisted the ultrasonography on localization diagnosis of focal hepatic lesions. Conclusion:1. The model of the visible liver can provide the distinct sectional anatomic data at random direction for hepatic ultrasonography. The virtual hepatic segment model can provide accurate two-dimensional and three-dimensional morphological data for ultrasonography in hepatic segments classification.2. The virtual hepatic segment model could improve the accuracy of ultrasonography for preoperative segmental location diagnosis of lesions located in single hepatic segment and 3cm or smaller in diameter, especially lesions located in the regions devoid of vessels.3. The software of the virtual liver ultrasonic imaging system can provide two-dimensional and three-dimensional visualization platform for liver anatomy teaching and imaging diagnosis in Ultrasonography, which helps to popularize ultrasonic medicine and improve the accuracy of diagnosis on hepatic disease.