肝脏及其内部血管64排螺旋CT扫描数据三维重建及虚拟手术研究
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摘要
背景
近20年来，原发性肝癌(HCC)患者的整体预后得到明显改善，但相对全球每年50万新发病例和近100万死亡病例而言，目前疗效远不能满足人们的期望。外科手术切除(partial hepatectomy)及肝脏移植(liver transplantation)属于根治性治疗，仍是肝癌治疗的首要选择。肝肿瘤外科手术切除的可行性必须从解剖学上评估，看肿瘤的大小与数目及部位于肝脏何处、与肝脏内血管位置的关系、有无转移、手术后残肝的功能等。随着术前对患者更适当的评估、对肝解剖学和肝脏功能认识的增加、肝脏切除技术及术后护理的改善，肝脏切除的并发症及死亡率已大大下降，现在，国内、外肝脏切除死亡率的标准为＜3％。目前，随着计算机技术、图像处理技术、医学物理学科与医学的交叉融合和迅速发展，外科诊断与治疗的手段正在发生着很大的变化。近年来出现的计算机辅助手术系统，虚拟外科手术系统等就是在信息科学迅速发展并应用于医学领域产生的成果。外科医生通过这些先进的技术手段在术前、术中、术后对手术进行辅助支持。使外科手术越来越安全、可靠、精确，创伤越来越小。利用计算机辅助肝脏及肝内管道结构的三维重建并进行虚拟手术的研究十分活跃。Raptopouls V等行螺旋CT血管造影三维重建，能同时完成显示门静脉、肝静脉全貌及其复杂的空间解剖结构关系，可直观评价门静脉、肝静脉的位置、管径、阻塞程度及其侧支循环情况。Wigmore SJ等则利用螺旋CT肝脏扫描图片进行三维重建、虚拟肝脏切除、评估肝切除手术后肝衰的危险性，从而决定肝脏的切除范围。肝脏3D及其虚拟手术是利用CT，MRI等图像序列进行处理，构造出能显示肝脏各结构的三维几何模型，将看不见的人体器官能以三维形式“真实”地显示出来，即可视化。它的优点是在空间中具有准确的定位，可以立体地从各个角度观察和测量各解剖结构、测量各种数据，促进肝脏临床解剖学的发展，同时虚拟肝脏的各种手术，并可以利用肝脏肿瘤患者的肝脏及其肿瘤的影像(CT、MRI等)扫描数据进行图像融合和更新，从而使外科医师在计算机上反复进行手术规划，反复演练手术过程并优化手术方案，提高手术技能，提高手术的安全性，降低手术并发症。
近年来，随着科学技术的不断发展，尤其是计算机技术，以及CT(计算机断层)，MRI(磁共振)等医学影像技术的不断发展，计算机技术就越来越多地应用到现代医疗领域，尤其是多排螺旋CT的发展，具有强大的后处理功能，使用各种影像重组方法、多角度旋转进行诊断，为临床提供了更为详细、清晰的影像信息。但是多排螺旋CT重建的图像其实仍是平面重建，仍是二维的，是不可操作的，是无法进行切割等外科手术操作，也就无法满足临床的全部要求。所以要重建真正的可满足临床需要的、可任意旋转和进行手术的切割和分离的三维立体空间图像，并且具有力反馈的感觉，这样的立体重建图像对外科手术有深远的实际意义，这正是本课题所要研究的主要内容。
目的
研究肝脏及其内部血管进行64排螺旋CT扫描图像的特点；研究基于64排螺旋CT扫描数据的肝脏及其内部血管的手工分割和程序分割的方法；利用MIMICS软件和自行开发设计三维重建程序进行肝脏及其内部血管结构三维重建；并在此基础上研究虚拟肝脏切割手术仿真系统的方法。
方法
1．基于64排螺旋CT扫描数据的肝脏及腹腔血管三维重建的研究
(1)研究对象：正常体检者，男性，36岁，身高1.76M，体重：74KG
(2)肝脏64排CT原始扫描数据采集设备
64排螺旋CT—PHILIPS Brilliance64(荷兰)。高压注射器采用MEDRAD双筒高压注射器(美国)。图像后处理工作站为PHILIPS Brilliance64层螺旋CT自带的Mxview工作站。
(3)肝脏及肝血管的扫描条件：扫描前准备和扫描参数：管电压120KV、管电流300mAs、每旋转1周时间为0.5s、螺距(pitch)0.984、层厚5mm。
(4)平扫和动态CT增强扫描：
平扫：采用0.625×64排探测器组合，以层厚5mm、间隔5mm，螺距(Pitch)0.984，球管旋转一周时间0.5s，扫描视野40-50cm，矩阵512×512。开始常规上腹部平扫。
CT增强扫描：使用双筒CT高压注射器，注射速率5ml／s，所用对比剂为高浓度非离子型碘必乐370(370mgI／m1)或优维显370(370mgI／m1)，剂量1.5ml／kg体重，对比剂注射完毕后以生理盐水50ml冲管，扫描技术条件同平扫，动脉期注射后扫描延迟时间20-25s，静脉期注射后扫描延迟时间50-55s。
(5)肝脏CT薄层扫描数据集采集
(6)肝脏及其肝内血管的三维重建方法：采用MIMICS(V10.0)三维重建软件，利用阈值法和人工结合的方法来分割图像，对分割好的图像进行三维重建，重建出的目标物体以格式STL和IGS导出并保存，将此模型导入逆向工程软件中，对模型进行精加工，最后得到既忠实于原始数据又适合虚拟操作的模型。
2基于螺旋64排CT扫描数据的肝脏图像的手工分割和三维重建
(1)研究对象：女性，50岁。为左肝占位病变。体重58公斤。身高164CM
(2)肝脏64排CT原始扫描数据采集设备
64排螺旋CT—PHILIPS Brilliance64(荷兰)。高压注射器采用MEDRAD双筒高压注射器(美国)。图像后处理工作站为PHILIPS Brilliance64层螺旋CT自带的Mxview工作站。
(3)肝脏及肝血管的扫描条件：扫描前准备和扫描参数，同第一部分。
(4)平扫：常规平扫时患者取仰卧位，头足方向，由膈顶至肝脏下缘，扫描条件120KV、250mAs；采用0.625×64排探测器组合，以层厚5mm、间隔5mm，螺距(Pitch)0.984，球管旋转一周时间0.5s，开始常规上腹部平扫。扫描结束后应用增强原始数据进行0.67mm的薄层重建，并将图像数据传至Mxview工作站。
(5)平扫及动态CT增强扫描：
5．1 CTA扫描：小剂量预注射试验
5．2 MSCTP扫描：门静脉预试验法
(6)肝脏64排螺旋CT扫描数据的收集
图像分为平扫期、动脉期、静脉期、门静脉期，分别有图像658层。在Mxview工作站，进行数据的刻盘存贮。将各期DICOM格式的图像转换为BMP格式。
(7)肝脏可视化(Visualization)
各期的图像数据将按照不同时期分别进行处理：
7．1肝脏图像配准(Image Registration)
原始数据收集时，要求该数据四个不同时期即平扫、动脉期、门静脉期、肝静脉期的扫描起始点、结束点相同，扫描顺序、层数相同，进行三个不同时期的图像之间的配准。
7．2肝脏图像分割(Image Segmentation)
采用Photoshop7.0图像处理软件。具体方法是：图像导入----肝脏轮廓标注----反选----删除----保存。
7．3肝脏图像的三维重建(Three-dimensional Reconstruction)
使用MIMICS三维重建软件(由南方医科大学解剖研究所免费提供，已获得授权)，将采用上述方法分割好的肝脏图像先导入MIMICS三维重建软件中，利用肝脏实质及肝内管道灰度的不同，设定不同的域值域值范围，将肝脏实质及肝内管道分别提取出来，进行三维重建肝脏及其内部管道的三维模型(图3～6)，并将重建的肝脏及其管道模型输出为STL(Standard Template Library标准模板库)格式。然后将模型导入到FreeForm Modeling System--自由设计模型系统进行平滑和去除一些过多的细节和噪声。
3基于64排螺旋CT扫描数据的肝脏图像的程序分割和三维重建研究
(1) 64排螺旋CT肝脏扫描数据集与第二部分采集的数据集相同。
(2)肝脏可视化(Visualization)各期的图像数据将按照不同时期分别进行处理。
2．1肝脏图像配准(Image Registration)调整各期图像扫描顺序、起始处和结束处一致。
2．2肝脏图像分割(Image Segmentation)
首先在序列中每一幅二维图像上将肝脏及其血管分离出来，然后利用分割的结果序列实现单独器官的三维重建。其重点就是在保证单个图像分割结果正确的同时，提高序列意义上分割的自动化程序。采用区域生长算法，实现序列化分割。
(3)肝脏及其内部血管的三维重建
分别采用MIMICS软件和自行开发的Tony2 image软件三维重建肝脏及其内部血管的表面模型。
4基于64排螺旋CT扫描数据肝脏3D虚拟手术仿真的研究
虚拟肝脏切割手术(Virtual Hepatectomy)
将本课题第二部分三维重建好的肝脏及其血管模型(STL文件格式)导入FreeForm Modeling System--自由设计模型系统二次开发的虚拟切割的软件，利用系统的力反馈设备PHANTOM，操纵模拟手术刀对肝脏模型可以进行随意的切割，建立虚拟肝脏切割手术环境系统，并对肝脏左外叶肿瘤切除手术的不同方式和右半肝脏切除术进行了肝脏切割手术仿真的研究。
结果
1．基于64排螺旋CT扫描数据的肝脏及腹腔血管三维重建的研究
肝脏的64螺旋CT薄层扫描数据集：共获得676层CT扫描图像。图像分为平扫期、动脉期、静脉期、门静脉期。
重建的肝脏模型能真实反映肝脏的实际体积和肝脏的解剖标志，并且通过调节肝脏的透明度可同时显示肝脏和肝内的动脉、静脉、门静脉各分支。
下腔静脉及肝静脉的三维结构能清楚显示，左、中、右肝静脉的主干及一级分支。三支肝静脉的走行、管径以及汇入下腔静脉的方式都能清楚显示。
腹主动脉、腹腔动脉及其分支胃十二指肠动脉、双肾动脉、胃右动脉、胃左动脉、肝固有动脉、脾动脉、肠系膜部分动脉等结构，形态逼真，立体感强。尤其是动脉的迂曲走行，和解剖图谱相比更加立体和真实。动脉的各级分支同时能清楚展示。
门静脉系统显示肝外的主干和脾静脉、肠系膜上静脉。肝内门静脉系统能清楚显示门静脉的左主干和右主干，以及各叶、段的分支：左干横部、左干矢状部、左干外上叶支、左内叶支、右后叶支和右前叶支以及3、4级分支。
重建后门静脉分支类型、行程与扫描完成后将所得数据传至64排螺旋CT后台Mxview工作站薄层重建并行容积再现法(VR)对肝脏门静脉管道重建完全相符。
2基于64排螺旋CT扫描数据的肝脏图像的手工分割和三维重建
(1) 64排螺旋CT肝脏扫描数据图像
共采集四个时期：平扫期、动脉期、门静脉期、静脉期，得到四套完整的数据。每套数据图像658张，格式DICOM。肝脏轮廓清晰，断面管道造影剂充填良好，各种血管管道清晰，动脉期：腹主动脉及其各个分支均清楚显示，肝动脉及左肝动脉、右肝动脉以及下属分支均能清楚显示。静脉期：肝静脉主干显示良好，下腔静脉内造影剂充填不均匀，肝静脉的属支仅能肉眼辨认至三级。门静脉期：门静脉系统管道显示很好，几乎能达到门脉的五级分支以上，门脉内造影剂充填良好，与肝实质分界清晰。
(2)肝脏可视化
2．1肝脏图像的配准
打开不同时期的图像进行比对，在肝脏的外观、大小以及图像的层数和数据集的第一张到最后一张全部配准。扫描顺序一致，无偏差。配准良好，包括了所有序列图像的肝脏全貌，图像连续浏览无晃动。
2．2肝脏图像的分割
根据需要对感兴趣的区域(Region of Interest ROI)肝脏实质进行手工勾勒，不同时间所保存的图像内容不同，肝静脉期：肝脏里包含有肝脏和肝静脉信息，门静脉期含有门静脉管道结构和肝脏实质。肝动脉期仅含有肝动脉和肝脏边缘信息。分割提取后保存，获得相应的图像信息。
MIMICS重建的三维肝脏及其内部管道结构模型表面较粗糙，带有较多的毛边，肝脏表面有阶梯感，管道结构连续，但表面不光滑，甚至肝动脉带有许多三角形的碎片。经FreeForm Modeling System进行平滑和去除一些过多的细节和噪声后，形态逼真。在FreeForm Modeling System中显示时，可以对模型放大、缩小、旋转，全方位观察。将三种不同的管道：肝动脉、肝静脉、门静脉和肝脏全部导入后，得到一个完整的包含有三种血管结构的肝脏。
3基于64排螺旋CT扫描数据的肝脏图像的程序分割和三维重建研究
(1)肝脏图像的分割
采取区域生长法进行图像的快速分割，可以迅速将数据集中的846张图片中的肝脏846张、肝静脉634张、肝动脉312张和门静脉658张分割，分割效果好。
(2)肝脏及管道的三维重建和肝脏管道结构特征
采用MIMICS软件对程序分割的数据图像重建，可见重建的肝动脉、肝静脉、门静脉、肝脏结构清晰，立体感强，形态逼真。其中门静脉系统，清楚显示脾静脉和肠系膜上静脉汇合成门静脉主干以及入肝后的各级分支，并可显示各血管的立体走向。
采用自行设计的软件Tony2image三维重建效果，动脉期肝脏：肝脏外观逼真，立体感强，肝脏的解剖标志基本清楚，与肝脏标本的外观相似。肝门处可见肝动脉走行，迂曲，逼真，可通过透明的肝脏观察肝动脉的位置、分支、口径。将动脉期肝脏与门静脉期肝脏全部导入后，两者几乎重叠，可见两个不同时期肝脏重建后吻合度高。重建后的肝静脉不同方位，左、中、右肝静脉均能很好显示3级分支。门静脉期肝脏重建后，半透明状态，清楚显示其内的门静脉系统管道走向、口径、长度以及在肝脏内的分布。
重建后的肝脏模型具有肝脏、肝动脉、肝静脉和门静脉，形态逼真，立体感强。通过对模型放大、缩小和旋转可全方位观察各结构；通过目标物体的选择控制目标的透明度和颜色设定来单独或组合显示肝脏及其管道结构各部分，基本实现了交互式分析。肝脏可视化后，肝脏、肝动脉、肝静脉和门静脉，立体形态逼真，外形和实物相似。肝脏内部管道空间立体感强，肝动脉、肝静脉和肝门静脉的分布、行程以及相互关系明晰。
4基于64排螺旋CT扫描数据肝脏3D虚拟手术仿真的研究
(1)肝脏可视化
三维重建的肝脏图像
MIMICS重建的三维肝脏及其内部管道结构表面模型经FreeForm ModelingSystem进行平滑和去除一些过多的细节和噪声后，形态逼真。在FreeForm Modeling System中显示时，可以对模型放大、缩小、旋转，全方位观察。
(2)肝脏切割手术仿真
在建立的虚拟肝脏切割手术虚拟环境系统中，沉浸感强，交互性好。可以使用力反馈设备PHANTOM对立体肝脏模型进行随意的控制，包括放大、缩小、全方位旋转等等；可以通过PHANTOM操纵“模拟手术刀”模拟肝脏切割手术过程，对肝脏模型进行单一平面切割或随意地切割，并在切割时实现了“力”的感觉。通过调节切割对象的强度，感受切割时力反馈的大小。
(3)肝左外叶、肝右叶部分切除手术仿真
在建立的虚拟肝脏切割手术虚拟环境系统中，使用力反馈设备PHANToM操纵“模拟手术刀”模拟肝脏切割手术过程，对肝脏模型进行左外叶切除手术、右半肝切除术，其结果符合临床手术的效果。利用GHOST SDK提供的工具，人工绘制的肝脏肿瘤模拟物——不规则形状物，加入到肝脏模型左外叶处。将肝脏表面模型部分透明，通过旋转、放大等观察“肿瘤”与肝内管道的位置空间关系明确，“肿瘤”位于左外叶上段，包绕肝门静脉左外叶上段支和肝左静脉左外叶上段属支，可真实模拟手术切割过程。手术模拟过程逼真，形象，且能有“力”的感受。
结论
1．采用先进的64排螺旋CT肝脏扫描图像，采用MIMICS(V10.0)三维重建软件，利用阈值法和人工结合的方法来分割图像，三维重建肝脏及其内部血管、腹腔血管，重建的肝脏、肝内血管形态逼真，立体感强，尤其是腹腔动脉系统管道形象生动，动脉的各级分支的走向、管径的大小以及血管之间关系清晰，有助于临床手术时的操作，有助于肝脏及腹腔血管的临床教学和肝脏血管的研究。
2．采用特殊的造影方法，使得64排螺旋CT肝脏内部管道图像更加清晰，与肝实质的对比明显。在此基础上，采用图像处理软件，利用手工分割的方法，采用MIMICS(V10．0)三维重建软件，三维重建肝脏及肝内管道结构，得到肝脏模型表面光滑，肝内管道清晰，色彩鲜艳，立体感极强，为肝脏的虚拟手术打下基础，该模型交互性好，具有极强的可操作性和表现性。
3．在第二部分研究基础上，进一步开发设计分割程序和三维重建软件，利用自行设计的程序进行图像的分隔和三维重建，效果理想，与MIMICS软件相比，其重建的肝脏及其内部管道结构表面虽然粗糙，但立体效果好，无论是构象性还是肝脏的结构比例还是管道的立体走向均能完美再现。该项工作的进一步研发，有望开发出具有自主知识产权的针对肝脏图像的分割和三维重建软件。
4．采用先进的64排螺旋CT肝脏扫描图像，采用面绘制的方法三维重建，在力反馈设备的基础上进行手术器械的二次开发和虚拟肝脏切割手术的研究，交互性、沉浸性和构象性好，模拟肝切除手术的过程和结果均比较理想，达到满意的程度，取得了初步的结果，对推进肝脏临床外科手术学研究的发展有重要意义。
Background
The whole prognosis of Primary Hepatocellular Carcinoma have been greatlyimproved since recently twenty years, but at present, therapeutic effect can not reachthe patient hope because of five hundred thousand newly case and ten hundredthousand death case. The partial hepatectomy and liver transplantation, which arebelonged to radical cure, are still the most important choice among the therapy of theliver tumor. The feasibility of the HCC partial hepatectomy should be evaluated inview of the anatomy including of the tumorous size, number, location, the relationwith the vessels inside the tumour, the tumour metastasis, the residue liver functionpost-operation and so on. With the Preoperative adequate evaluation to the patient andthe increasingly knowledge of the anatomy and the liver function and the improvingof the partial hepatectomy skill and postoperative care, the excisional complicationand the death rate had been greatly declined. Now the hepatectomy death ratestandard of the domestic and the abroad is below 3%. At present, with the chiastopicfusion and the rapidly development of the computer skill、the image processing skill、the medicophysics and the medicine, the surgery diagnosis and therapy have great change. In these years, the computer-assisted operation system and the virtual operation system are the achievement of the rapid development of the information science applied in the medical region. The surgeon can make the operation more safe, more reliable and more fidelity by the advanced skill. The flying development in modem science and technology has built a concrete ground for the vital studies on the three-dimensional (3D) reconstruction of hepatic duct systems in recent years. The 3D reconstruction through hispeed CT angiography conducted by Raptopouls V, et al displayed the full views of portal and hepatic veins as well as the spatial conformational relations anatomically so that the portal and hepatic veins can be located and their diameters, obstructions and collateral circulation can be evaluated. Wigmore SJ et al reconstructed liver from the scanned images by helical CT and performed the virtual surgical incision of liver for the purse of assessing the risk of hepatic failure after hepatic incision and deciding the incision range. The three-dimension hepatic and the virtual surgery make use of such imagery sequence as CT and MRI, so as to display a three-dimensional model of the various structures of the hepatic, making the hiding human organ a visible "live" three-dimensional object, Namely visualization. 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 MRI 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.
Recently, with the rapidly development of the science and technology, especially the development of the computer skiU and the modem imageology such as CT、MRI, the computer skill was utilized with the modem medical. The multi-slice helical CT possessed the powerful post-processing function and supplied the detailed image for the clinic with all kinds of the image recombination methods. But the reconstructed image in the 64-slice helical CT workstation actually is plane and two-dimension reconstruction yet, It can not be manipulated as the surgerical organ and be satisfied with the clinic requirement. Therefore, to reconstruct the three-dimension spatial image which can satisfied the clinic requirement including of randomly revolving and dissection and to bring the power feedback feeling when to incision the three-dimension hepatic, these work will bring the far-reaching practical significance for the surgery.
Objective
To investigate the behavior of the liver and its interior vessel scanogra based on 64-slice helical CT; to investigate the image segmentation methodology of hand-made and sequence on the scanogra of the liver and its interior vessel based on 64-slice helical CT; to investigation the methodology of the three-dimensional reconstruction by the software MIMICS and the self-designed reconstruction software for the liver and its interior vessel and the virtual liver neoplasm surgical resection mimic system.
Methods
1. Studies on the three-dimensional reconstruction about the liver image and abdominal cavity artery based on the 64-slice helical CT scanogra
(1)Examiner: common health examination person, male, 36 year olds, Body height: 1.76M, Body weight: 74KG
(2)Scan condition of the hepatic and hepatic vessel: scan parameter: pip voltage 120KV、tube current 300mAs、every cycle 0.5s、pitch 0.984、slice thickness 5mm
(3) Plain scan and Enhanced scan
The Detector 0.625×64, slice thickness 5ram, interval 5ram, Pitch: 0.984, scan sight 40-50cm, matrix 512×512.
(4)Enhanced CT scan
Non-ionic contrast media with an iodine concentration of 300--- 370 mg/ml are most commonly used and are applied at a flow rate of 5 ml/s depending on the kind of examination. The artery phase delay time after injection: 20-25s.The portal vein phase delay time after injection: 50-55s
(5) the liver image collection from the 64-slice helical CT scanogra
(6)the three-dimensional reconstruction methods of the liver with intrahepatic vessel: the image was divided by the method of combining liminal value with man-made, then 3D reconstructed the liver model by MIMICS software. The reconstructed target was induced and reserved as the format STL and IGS. When the object were induced into contra- engineering software and were polished, the achieved model can be either to faithful for the initial data or to suit for virtual manipulative finally.
2. Studies on the man-made segmentation and three-dimensional reconstruction about the liver image based on the 64-slice helical CT scanogra
(1)examiner: the patient suffered left liver tumor, female, 50 year olds, Body height: 1.64M, Body weight: 58KG
(2) the liver image collection from the 64-slice helical CT scanogra
(3)An unenhanced helical CT of the liver was performed before contrast administration. For biphasic helical CT the liver was scanned in the arterial and the portal-venous phase of liver perfusion. With a power injector, 120ml of Iopromid was injected in an antecubital vein at a flow rate of 4.0ml/s.
3.1 CTA scanning: a low-dose preliminary inject test
3.2 MSCTP scanning: The portal-vein preliminary test
(4)The liver image switching from the 64-slice helical CT scanogra
The data were divided into the unenhanced phase, the artery phase, the hepatic vein phase and the portal-vein phase. On the Mxview workstation, all the data were deposited and converted the format DICOM into the format BMP.
(5)Liver Visualization
The different phase image should be treated respectively according to every period image.
5.1 Image Registration
To adjust every phase image scanning sequence so as to keep the initiation point and the end point equal.
5.2 Image Segmentation
The CT image were divided by the software Photoshop 7.0.
The methods: the image introduction - liver outline marking - reverse selecting - delete - preserve.
5.3 Liver three-dimensional Reconstruction
The series of the liver image which had been divided firstly were imported the MIMICS software. Then the liver image and the duct image were extracted according to their different gray scal. The 3D model of the liver and the intrahepatic vessels were reconstructed by the MIMICS software respectively. The 3D model were outputted into the FreeForm Modeling System in the STL format to make the model smooth and removal the fragment.
3. Studies on the sequence segmentation and three-dimensional reconstruction about the fiver image based on the 64-slice helical CT scanogra
(1) 64-slice helical CT liver scanogra
The same as the collection data set of the second chapter.
(2) Liver Visualization
The different phase image should be treated respectively according to every phase image.
2.1 Image Registration
To adjust every phase image scanning sequence so as to keep the initiation point and the end point equal.
2.2 Image Segmentation
Firstly, the liver margin and the vessel were divided from the two-dimensional image in sequence; Secondly, the single organ was 3D reconstructed with the segmentation result. The focal point was to be sure of the image segmentation correct result and to improve the segmentation automatization sequence in the meaning of sequence. In a word, applying for Regions Growth Algorithms realize the sequence segmentation.
(3)The three-dimensional reconstruction of the liver with intrahepatic vessel
The MIMICS software and the self-designed software would be applied to reconstruct the three-dimensional liver with intrahepatic vessel model.
4. Studies on the virtual surgery about the liver three-dimensional reconstruction based on the 64-slice helical CT scanogra
Virtual Hepatectomy
The 3D liver model with intrahepatic vessel, which had been reconstructed in the second chapter, were Introduced into the FreeForm Modeling System. Based on the FreeForm Modeling System, the software of virtual resection and the virtual scalpel were 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. The Virtual Hepatectomy system were established, the different liver resection type were simulated.
Results
1. Studies on the three-dimensional reconstruction about the liver image and abdominal cavity artery based on the 64-slice helical CT scanogra
The 64-slice helical CT scanogra of the liver totally had 676 slice image. The image data were composed of four phase image: the uncontrasted phase; the hetatic artery phase, the portal vein phase, the hepatic vein phase.
The reconstructed liver model could reflect the liver real volume and the liver anatomic landmark and demonstrated the liver and the hepatic artery, the portal vein, the hepatic vein and their branch by adjusting the liver clarity simultaneously and respectively.
The 3D structure of the inferior vena cava and the hepatic venous clearly demonstrated that the stem and the branch of the Left hepatic veins, the Middle hepatic veins and the Right hepatic veins. The Courser、the caliber of the hepatic veins and the way of the three hepatic veins abouchement into the inferior vena cava could be clearly demonstrated.
The abdominal aorta、the arteria coeliaca and its branch suah as: the gastroduoden artery、the renal arteries、the right gastric artery、the left gastric artery、the proper hepatic artery、the splenic artery、the mesentery artery and so on, these artery had the high fidelity and the strong three-dimensional effect. Especially the artery course and caliber was realer and more solid than the anatomy atlas graph.
The portal system demonstrated the portal extrahepatic stem and the splenic vein and the sup. mes. vein. The intrahepatic portal system could clearly demonstrate the portal vein stem and the leaf branch, the segment branch of the liver, for example, the transverse part, the anteroposterior axes, the superior lobar branch, the internal lobe branch, the posterior lobe branch, the anterior lobe branch and its next grade branch. The structure of the reconstructed portal vein system was the same as the image of the portal system which was reconstructed in the method of VR on the Mxview workstation of the 64-slice helical CT.
2. Studies on the man-made segmentation and three-dimensional reconstruction about the liver image based on the 64-slice hdieal CT scanogra
(1) The 64-slice helical CT scanogra
The 64-slice helical CT scanogra of the liver totally had 658 slice image. The image data were composed of four phase image: the uncontrasted phase; the hetatic artery phase, the portal vein phase, the hepatic vein phase.
The liver outline was clear, the contrast agent in the pipeline of the cross-section was filling well. Every kind of vessel was clarification. The artery phase: the abdominal aorta and the hepatic artery and its branch were clearly demonstrated. The hepatic vein phase: the stem of the hepatic vein was clearly showed, but its branch just can be showed to the third grade vessel. The contrast agent in the inferior vena cava was filling uneven, the portal vein phase: the portal vein system was obviously showed, its branch almost can reach the fifth grade branch. The contrast agent in the portal vein can be showed very well. The demarcation with the liver parenchyma was very apparent.
(2)Visualization of liver
The 3D reconstructed liver image
The 3D liver model by the software MIMICS had the rough surface and the feeling of "stair". The vessels structure was continuity, but the artery surface had many triangular fragment. The 3D reconstructed liver model by the MIMICS software looks like the liver sample when the fragment was removed by the FreeForm Modeling System. The 3D model demonstrated in the FreeForm Modeling System can be magnified, contracted and rotated. The model can be observated in omnibearing. The three kinds of the vessels: the artery, the portal vein and the hepatic vein total introduced into FreeForm Modeling System, the integrity liver with intrahepatic vessels can be finished.
3. Studies on the sequence segmentation and three-dimensional reconstruction about the liver image based on the 64-slice helical CT scanogra
(1)Liver Image segmentation
The image rapid segmentation in the method of Regions growth could finish dividing the liver scanned image data as soon as quickly. The scanned dataset included 846 slice liver image.
(2)The three-dimensional reconstruction of the liver and the intrahepatic vessel and the vessel structural feature
The image dataset which had been Divided in sequence were reconstructed by the software MIMICS. The reconstructed model can showed clearly the hepatic artery, the hepatic vein, the portal vein. The model had stero-image and the appearance fidelity. The portal system can clearly demonstrated the stem of the portal vein formulated from the splenic vein and superior mesenteric vein and the intrahepatic branch of the portal vein.
Adopting self-designed software Tony2image, the reconstructed result showed: artery phase hepatic: the appearance fidelity good, the liver anatomic landmark can be clearly observed and the hepatic look like the real hepatic organ. At the hepatic portal, the hepatic artery courser was distorting and fidelity. The hepatic artery location、branch、caliber can observed from the transparent hepatic. After the hepatic in the artery phase and the hepatic in the portal vein phase simultaneously were imported into the software, the two phase hepatic outline almost were overlapping, they had highly goodness of fit. The reconstructed hepatic vein was observed from different direction, the third grade branch of the left hepatic vein, the middle hepatic vein、the right hepatic vein were showed clearly. The reconstructed hepatic in the portal vein phase was translucence, the vessel courser caliber length distribution in the portal vein system were clearly demonstrated.
The reconstructed liver model possessed the liver and the hepatic artery, the portal vein, the hepatic vein. The appearance fidelity was better than the real liver. The model can be observed omnibearing just by magnifying, contracting and rotating the model. The model could be demonstrated solo or combination just by adjusting the objective colour and the clarity, the reciprocation analysis could be realized. After the liver visualization, the intrahepatic vessels could be showed in the stero and distinct. The intrahepatic vessels courser, caliber and their relationship could be clearly demonstrated.
4. Studies on the virtual surgery about the liver three-dimensional reconstruction based on the 64-slice helical CT scanogra
(1) Visualization of liver
The 3D reconstructed liver image.
The 3D reconstructed liver model by the MIMICS software looks like the real liver after the fragment were removed by the FreeForm Modeling System. The 3D model demonstrated in the FreeForm Modeling System can be magnified, contracted and rotated. The model can be observed in omnibearing.
(2) The virtual partial hepatectomy system
In the virtual surgery system with interaction and immersion, the virtual scalpel can be manipulated to perform optional resection on 3D liver model with the haptic device (PHANToM). The power feedback can be felt through adjusting the liver intensity.
(3)The simulation of the left segment Hepatectomy and Right lobe of liver resection operation
In the virtual surgery system, the virtual scalpel can be manipulated to perform optional resection on 3D liver model with the haptic device (PHANTOM). The left segment Hepatectomy and Right hemihepatectomy were simulated, the effect were the same as the clinic operation. The spatial relationship between the simulated tumour and the intrahepatic vessel can be clearly observed by the action such as turning the liver surface into transparent and rotating and so on. The simulated Hepatectomy was the same as the real surgery. Meanwhile, the power feeling can be touched by the haptic device (PHANToM). A simulation tumor can be manmade with the by GHOST SDK tool and was put into the liver 3D model.
Conclusions
1. The 3D liver model with intrahepatic vessel, which was 3-dimensionally reconstructed in the combining method of liminal value and man-made using advanced 64-slice helical CT scanogra and MIMICS software, especially the coeliac artery system image is lively, its branch caliber and the relation among the vessels is clearly, may be helpful to operate in the clinic surgery and teaching, hepatic vascular investigation.
2. The intrahepatic vessel image can be clearly made by the special angiography on 64-slice helical CT. The 3D liver model with intrahepatic vessel, which was three-dimensionally reconstructed in the method of MIMICS software and of man-made segmentation image from the advanced 64-slice helical CT scanogra, always have smooth and glossy surface, clearly vessel structure, bright-colored, strongly stereo feeling and can become the basis of the virtual operation. The 3D model has good interaction and manifestation and is fit to manipulate.
3. In the basis of the second chapter, the segmentation procedural and three-dimensional reconstruction software were self-developed. When the image were divided and reconstructed in the application for the self-device sequence, the result were the same as that using the MIMICS software. Compared with the image using the MIMICS software, the 3D liver model with intrahepatic vessel structure, although the surface was slightly rough, had good stero-effect. Either the liver model imagination or the liver structure and the vessel stereo-position were fully manifested. If the work was continued to be designed, the independence knowledge property right software about the liver image segmentation and the three-dimensional reconstruction will be developed.
4. The 3D visualized liver has been satisfactorily developed with the method of surface rendering using the advanced 64-slice helical CT scanogra. Then the developed virtual hepatectomy system and the virtual operation tool based on the haptic devices (PHANToM), which has good interaction, powerful immersion and great imagination, will be of great significance for the promotion of hepatic clinical surgery.
近20年来，原发性肝癌(HCC)患者的整体预后得到明显改善，但相对全球每年50万新发病例和近100万死亡病例而言，目前疗效远不能满足人们的期望。外科手术切除(partial hepatectomy)及肝脏移植(liver transplantation)属于根治性治疗，仍是肝癌治疗的首要选择。肝肿瘤外科手术切除的可行性必须从解剖学上评估，看肿瘤的大小与数目及部位于肝脏何处、与肝脏内血管位置的关系、有无转移、手术后残肝的功能等。随着术前对患者更适当的评估、对肝解剖学和肝脏功能认识的增加、肝脏切除技术及术后护理的改善，肝脏切除的并发症及死亡率已大大下降，现在，国内、外肝脏切除死亡率的标准为＜3％。目前，随着计算机技术、图像处理技术、医学物理学科与医学的交叉融合和迅速发展，外科诊断与治疗的手段正在发生着很大的变化。近年来出现的计算机辅助手术系统，虚拟外科手术系统等就是在信息科学迅速发展并应用于医学领域产生的成果。外科医生通过这些先进的技术手段在术前、术中、术后对手术进行辅助支持。使外科手术越来越安全、可靠、精确，创伤越来越小。利用计算机辅助肝脏及肝内管道结构的三维重建并进行虚拟手术的研究十分活跃。Raptopouls V等行螺旋CT血管造影三维重建，能同时完成显示门静脉、肝静脉全貌及其复杂的空间解剖结构关系，可直观评价门静脉、肝静脉的位置、管径、阻塞程度及其侧支循环情况。Wigmore SJ等则利用螺旋CT肝脏扫描图片进行三维重建、虚拟肝脏切除、评估肝切除手术后肝衰的危险性，从而决定肝脏的切除范围。肝脏3D及其虚拟手术是利用CT，MRI等图像序列进行处理，构造出能显示肝脏各结构的三维几何模型，将看不见的人体器官能以三维形式“真实”地显示出来，即可视化。它的优点是在空间中具有准确的定位，可以立体地从各个角度观察和测量各解剖结构、测量各种数据，促进肝脏临床解剖学的发展，同时虚拟肝脏的各种手术，并可以利用肝脏肿瘤患者的肝脏及其肿瘤的影像(CT、MRI等)扫描数据进行图像融合和更新，从而使外科医师在计算机上反复进行手术规划，反复演练手术过程并优化手术方案，提高手术技能，提高手术的安全性，降低手术并发症。
近年来，随着科学技术的不断发展，尤其是计算机技术，以及CT(计算机断层)，MRI(磁共振)等医学影像技术的不断发展，计算机技术就越来越多地应用到现代医疗领域，尤其是多排螺旋CT的发展，具有强大的后处理功能，使用各种影像重组方法、多角度旋转进行诊断，为临床提供了更为详细、清晰的影像信息。但是多排螺旋CT重建的图像其实仍是平面重建，仍是二维的，是不可操作的，是无法进行切割等外科手术操作，也就无法满足临床的全部要求。所以要重建真正的可满足临床需要的、可任意旋转和进行手术的切割和分离的三维立体空间图像，并且具有力反馈的感觉，这样的立体重建图像对外科手术有深远的实际意义，这正是本课题所要研究的主要内容。
目的
研究肝脏及其内部血管进行64排螺旋CT扫描图像的特点；研究基于64排螺旋CT扫描数据的肝脏及其内部血管的手工分割和程序分割的方法；利用MIMICS软件和自行开发设计三维重建程序进行肝脏及其内部血管结构三维重建；并在此基础上研究虚拟肝脏切割手术仿真系统的方法。
方法
1．基于64排螺旋CT扫描数据的肝脏及腹腔血管三维重建的研究
(1)研究对象：正常体检者，男性，36岁，身高1.76M，体重：74KG
(2)肝脏64排CT原始扫描数据采集设备
64排螺旋CT—PHILIPS Brilliance64(荷兰)。高压注射器采用MEDRAD双筒高压注射器(美国)。图像后处理工作站为PHILIPS Brilliance64层螺旋CT自带的Mxview工作站。
(3)肝脏及肝血管的扫描条件：扫描前准备和扫描参数：管电压120KV、管电流300mAs、每旋转1周时间为0.5s、螺距(pitch)0.984、层厚5mm。
(4)平扫和动态CT增强扫描：
平扫：采用0.625×64排探测器组合，以层厚5mm、间隔5mm，螺距(Pitch)0.984，球管旋转一周时间0.5s，扫描视野40-50cm，矩阵512×512。开始常规上腹部平扫。
CT增强扫描：使用双筒CT高压注射器，注射速率5ml／s，所用对比剂为高浓度非离子型碘必乐370(370mgI／m1)或优维显370(370mgI／m1)，剂量1.5ml／kg体重，对比剂注射完毕后以生理盐水50ml冲管，扫描技术条件同平扫，动脉期注射后扫描延迟时间20-25s，静脉期注射后扫描延迟时间50-55s。
(5)肝脏CT薄层扫描数据集采集
(6)肝脏及其肝内血管的三维重建方法：采用MIMICS(V10.0)三维重建软件，利用阈值法和人工结合的方法来分割图像，对分割好的图像进行三维重建，重建出的目标物体以格式STL和IGS导出并保存，将此模型导入逆向工程软件中，对模型进行精加工，最后得到既忠实于原始数据又适合虚拟操作的模型。
2基于螺旋64排CT扫描数据的肝脏图像的手工分割和三维重建
(1)研究对象：女性，50岁。为左肝占位病变。体重58公斤。身高164CM
(2)肝脏64排CT原始扫描数据采集设备
64排螺旋CT—PHILIPS Brilliance64(荷兰)。高压注射器采用MEDRAD双筒高压注射器(美国)。图像后处理工作站为PHILIPS Brilliance64层螺旋CT自带的Mxview工作站。
(3)肝脏及肝血管的扫描条件：扫描前准备和扫描参数，同第一部分。
(4)平扫：常规平扫时患者取仰卧位，头足方向，由膈顶至肝脏下缘，扫描条件120KV、250mAs；采用0.625×64排探测器组合，以层厚5mm、间隔5mm，螺距(Pitch)0.984，球管旋转一周时间0.5s，开始常规上腹部平扫。扫描结束后应用增强原始数据进行0.67mm的薄层重建，并将图像数据传至Mxview工作站。
(5)平扫及动态CT增强扫描：
5．1 CTA扫描：小剂量预注射试验
5．2 MSCTP扫描：门静脉预试验法
(6)肝脏64排螺旋CT扫描数据的收集
图像分为平扫期、动脉期、静脉期、门静脉期，分别有图像658层。在Mxview工作站，进行数据的刻盘存贮。将各期DICOM格式的图像转换为BMP格式。
(7)肝脏可视化(Visualization)
各期的图像数据将按照不同时期分别进行处理：
7．1肝脏图像配准(Image Registration)
原始数据收集时，要求该数据四个不同时期即平扫、动脉期、门静脉期、肝静脉期的扫描起始点、结束点相同，扫描顺序、层数相同，进行三个不同时期的图像之间的配准。
7．2肝脏图像分割(Image Segmentation)
采用Photoshop7.0图像处理软件。具体方法是：图像导入----肝脏轮廓标注----反选----删除----保存。
7．3肝脏图像的三维重建(Three-dimensional Reconstruction)
使用MIMICS三维重建软件(由南方医科大学解剖研究所免费提供，已获得授权)，将采用上述方法分割好的肝脏图像先导入MIMICS三维重建软件中，利用肝脏实质及肝内管道灰度的不同，设定不同的域值域值范围，将肝脏实质及肝内管道分别提取出来，进行三维重建肝脏及其内部管道的三维模型(图3～6)，并将重建的肝脏及其管道模型输出为STL(Standard Template Library标准模板库)格式。然后将模型导入到FreeForm Modeling System--自由设计模型系统进行平滑和去除一些过多的细节和噪声。
3基于64排螺旋CT扫描数据的肝脏图像的程序分割和三维重建研究
(1) 64排螺旋CT肝脏扫描数据集与第二部分采集的数据集相同。
(2)肝脏可视化(Visualization)各期的图像数据将按照不同时期分别进行处理。
2．1肝脏图像配准(Image Registration)调整各期图像扫描顺序、起始处和结束处一致。
2．2肝脏图像分割(Image Segmentation)
首先在序列中每一幅二维图像上将肝脏及其血管分离出来，然后利用分割的结果序列实现单独器官的三维重建。其重点就是在保证单个图像分割结果正确的同时，提高序列意义上分割的自动化程序。采用区域生长算法，实现序列化分割。
(3)肝脏及其内部血管的三维重建
分别采用MIMICS软件和自行开发的Tony2 image软件三维重建肝脏及其内部血管的表面模型。
4基于64排螺旋CT扫描数据肝脏3D虚拟手术仿真的研究
虚拟肝脏切割手术(Virtual Hepatectomy)
将本课题第二部分三维重建好的肝脏及其血管模型(STL文件格式)导入FreeForm Modeling System--自由设计模型系统二次开发的虚拟切割的软件，利用系统的力反馈设备PHANTOM，操纵模拟手术刀对肝脏模型可以进行随意的切割，建立虚拟肝脏切割手术环境系统，并对肝脏左外叶肿瘤切除手术的不同方式和右半肝脏切除术进行了肝脏切割手术仿真的研究。
结果
1．基于64排螺旋CT扫描数据的肝脏及腹腔血管三维重建的研究
肝脏的64螺旋CT薄层扫描数据集：共获得676层CT扫描图像。图像分为平扫期、动脉期、静脉期、门静脉期。
重建的肝脏模型能真实反映肝脏的实际体积和肝脏的解剖标志，并且通过调节肝脏的透明度可同时显示肝脏和肝内的动脉、静脉、门静脉各分支。
下腔静脉及肝静脉的三维结构能清楚显示，左、中、右肝静脉的主干及一级分支。三支肝静脉的走行、管径以及汇入下腔静脉的方式都能清楚显示。
腹主动脉、腹腔动脉及其分支胃十二指肠动脉、双肾动脉、胃右动脉、胃左动脉、肝固有动脉、脾动脉、肠系膜部分动脉等结构，形态逼真，立体感强。尤其是动脉的迂曲走行，和解剖图谱相比更加立体和真实。动脉的各级分支同时能清楚展示。
门静脉系统显示肝外的主干和脾静脉、肠系膜上静脉。肝内门静脉系统能清楚显示门静脉的左主干和右主干，以及各叶、段的分支：左干横部、左干矢状部、左干外上叶支、左内叶支、右后叶支和右前叶支以及3、4级分支。
重建后门静脉分支类型、行程与扫描完成后将所得数据传至64排螺旋CT后台Mxview工作站薄层重建并行容积再现法(VR)对肝脏门静脉管道重建完全相符。
2基于64排螺旋CT扫描数据的肝脏图像的手工分割和三维重建
(1) 64排螺旋CT肝脏扫描数据图像
共采集四个时期：平扫期、动脉期、门静脉期、静脉期，得到四套完整的数据。每套数据图像658张，格式DICOM。肝脏轮廓清晰，断面管道造影剂充填良好，各种血管管道清晰，动脉期：腹主动脉及其各个分支均清楚显示，肝动脉及左肝动脉、右肝动脉以及下属分支均能清楚显示。静脉期：肝静脉主干显示良好，下腔静脉内造影剂充填不均匀，肝静脉的属支仅能肉眼辨认至三级。门静脉期：门静脉系统管道显示很好，几乎能达到门脉的五级分支以上，门脉内造影剂充填良好，与肝实质分界清晰。
(2)肝脏可视化
2．1肝脏图像的配准
打开不同时期的图像进行比对，在肝脏的外观、大小以及图像的层数和数据集的第一张到最后一张全部配准。扫描顺序一致，无偏差。配准良好，包括了所有序列图像的肝脏全貌，图像连续浏览无晃动。
2．2肝脏图像的分割
根据需要对感兴趣的区域(Region of Interest ROI)肝脏实质进行手工勾勒，不同时间所保存的图像内容不同，肝静脉期：肝脏里包含有肝脏和肝静脉信息，门静脉期含有门静脉管道结构和肝脏实质。肝动脉期仅含有肝动脉和肝脏边缘信息。分割提取后保存，获得相应的图像信息。
MIMICS重建的三维肝脏及其内部管道结构模型表面较粗糙，带有较多的毛边，肝脏表面有阶梯感，管道结构连续，但表面不光滑，甚至肝动脉带有许多三角形的碎片。经FreeForm Modeling System进行平滑和去除一些过多的细节和噪声后，形态逼真。在FreeForm Modeling System中显示时，可以对模型放大、缩小、旋转，全方位观察。将三种不同的管道：肝动脉、肝静脉、门静脉和肝脏全部导入后，得到一个完整的包含有三种血管结构的肝脏。
3基于64排螺旋CT扫描数据的肝脏图像的程序分割和三维重建研究
(1)肝脏图像的分割
采取区域生长法进行图像的快速分割，可以迅速将数据集中的846张图片中的肝脏846张、肝静脉634张、肝动脉312张和门静脉658张分割，分割效果好。
(2)肝脏及管道的三维重建和肝脏管道结构特征
采用MIMICS软件对程序分割的数据图像重建，可见重建的肝动脉、肝静脉、门静脉、肝脏结构清晰，立体感强，形态逼真。其中门静脉系统，清楚显示脾静脉和肠系膜上静脉汇合成门静脉主干以及入肝后的各级分支，并可显示各血管的立体走向。
采用自行设计的软件Tony2image三维重建效果，动脉期肝脏：肝脏外观逼真，立体感强，肝脏的解剖标志基本清楚，与肝脏标本的外观相似。肝门处可见肝动脉走行，迂曲，逼真，可通过透明的肝脏观察肝动脉的位置、分支、口径。将动脉期肝脏与门静脉期肝脏全部导入后，两者几乎重叠，可见两个不同时期肝脏重建后吻合度高。重建后的肝静脉不同方位，左、中、右肝静脉均能很好显示3级分支。门静脉期肝脏重建后，半透明状态，清楚显示其内的门静脉系统管道走向、口径、长度以及在肝脏内的分布。
重建后的肝脏模型具有肝脏、肝动脉、肝静脉和门静脉，形态逼真，立体感强。通过对模型放大、缩小和旋转可全方位观察各结构；通过目标物体的选择控制目标的透明度和颜色设定来单独或组合显示肝脏及其管道结构各部分，基本实现了交互式分析。肝脏可视化后，肝脏、肝动脉、肝静脉和门静脉，立体形态逼真，外形和实物相似。肝脏内部管道空间立体感强，肝动脉、肝静脉和肝门静脉的分布、行程以及相互关系明晰。
4基于64排螺旋CT扫描数据肝脏3D虚拟手术仿真的研究
(1)肝脏可视化
三维重建的肝脏图像
MIMICS重建的三维肝脏及其内部管道结构表面模型经FreeForm ModelingSystem进行平滑和去除一些过多的细节和噪声后，形态逼真。在FreeForm Modeling System中显示时，可以对模型放大、缩小、旋转，全方位观察。
(2)肝脏切割手术仿真
在建立的虚拟肝脏切割手术虚拟环境系统中，沉浸感强，交互性好。可以使用力反馈设备PHANTOM对立体肝脏模型进行随意的控制，包括放大、缩小、全方位旋转等等；可以通过PHANTOM操纵“模拟手术刀”模拟肝脏切割手术过程，对肝脏模型进行单一平面切割或随意地切割，并在切割时实现了“力”的感觉。通过调节切割对象的强度，感受切割时力反馈的大小。
(3)肝左外叶、肝右叶部分切除手术仿真
在建立的虚拟肝脏切割手术虚拟环境系统中，使用力反馈设备PHANToM操纵“模拟手术刀”模拟肝脏切割手术过程，对肝脏模型进行左外叶切除手术、右半肝切除术，其结果符合临床手术的效果。利用GHOST SDK提供的工具，人工绘制的肝脏肿瘤模拟物——不规则形状物，加入到肝脏模型左外叶处。将肝脏表面模型部分透明，通过旋转、放大等观察“肿瘤”与肝内管道的位置空间关系明确，“肿瘤”位于左外叶上段，包绕肝门静脉左外叶上段支和肝左静脉左外叶上段属支，可真实模拟手术切割过程。手术模拟过程逼真，形象，且能有“力”的感受。
结论
1．采用先进的64排螺旋CT肝脏扫描图像，采用MIMICS(V10.0)三维重建软件，利用阈值法和人工结合的方法来分割图像，三维重建肝脏及其内部血管、腹腔血管，重建的肝脏、肝内血管形态逼真，立体感强，尤其是腹腔动脉系统管道形象生动，动脉的各级分支的走向、管径的大小以及血管之间关系清晰，有助于临床手术时的操作，有助于肝脏及腹腔血管的临床教学和肝脏血管的研究。
2．采用特殊的造影方法，使得64排螺旋CT肝脏内部管道图像更加清晰，与肝实质的对比明显。在此基础上，采用图像处理软件，利用手工分割的方法，采用MIMICS(V10．0)三维重建软件，三维重建肝脏及肝内管道结构，得到肝脏模型表面光滑，肝内管道清晰，色彩鲜艳，立体感极强，为肝脏的虚拟手术打下基础，该模型交互性好，具有极强的可操作性和表现性。
3．在第二部分研究基础上，进一步开发设计分割程序和三维重建软件，利用自行设计的程序进行图像的分隔和三维重建，效果理想，与MIMICS软件相比，其重建的肝脏及其内部管道结构表面虽然粗糙，但立体效果好，无论是构象性还是肝脏的结构比例还是管道的立体走向均能完美再现。该项工作的进一步研发，有望开发出具有自主知识产权的针对肝脏图像的分割和三维重建软件。
4．采用先进的64排螺旋CT肝脏扫描图像，采用面绘制的方法三维重建，在力反馈设备的基础上进行手术器械的二次开发和虚拟肝脏切割手术的研究，交互性、沉浸性和构象性好，模拟肝切除手术的过程和结果均比较理想，达到满意的程度，取得了初步的结果，对推进肝脏临床外科手术学研究的发展有重要意义。
Background
The whole prognosis of Primary Hepatocellular Carcinoma have been greatlyimproved since recently twenty years, but at present, therapeutic effect can not reachthe patient hope because of five hundred thousand newly case and ten hundredthousand death case. The partial hepatectomy and liver transplantation, which arebelonged to radical cure, are still the most important choice among the therapy of theliver tumor. The feasibility of the HCC partial hepatectomy should be evaluated inview of the anatomy including of the tumorous size, number, location, the relationwith the vessels inside the tumour, the tumour metastasis, the residue liver functionpost-operation and so on. With the Preoperative adequate evaluation to the patient andthe increasingly knowledge of the anatomy and the liver function and the improvingof the partial hepatectomy skill and postoperative care, the excisional complicationand the death rate had been greatly declined. Now the hepatectomy death ratestandard of the domestic and the abroad is below 3%. At present, with the chiastopicfusion and the rapidly development of the computer skill、the image processing skill、the medicophysics and the medicine, the surgery diagnosis and therapy have great change. In these years, the computer-assisted operation system and the virtual operation system are the achievement of the rapid development of the information science applied in the medical region. The surgeon can make the operation more safe, more reliable and more fidelity by the advanced skill. The flying development in modem science and technology has built a concrete ground for the vital studies on the three-dimensional (3D) reconstruction of hepatic duct systems in recent years. The 3D reconstruction through hispeed CT angiography conducted by Raptopouls V, et al displayed the full views of portal and hepatic veins as well as the spatial conformational relations anatomically so that the portal and hepatic veins can be located and their diameters, obstructions and collateral circulation can be evaluated. Wigmore SJ et al reconstructed liver from the scanned images by helical CT and performed the virtual surgical incision of liver for the purse of assessing the risk of hepatic failure after hepatic incision and deciding the incision range. The three-dimension hepatic and the virtual surgery make use of such imagery sequence as CT and MRI, so as to display a three-dimensional model of the various structures of the hepatic, making the hiding human organ a visible "live" three-dimensional object, Namely visualization. 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 MRI 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.
Recently, with the rapidly development of the science and technology, especially the development of the computer skiU and the modem imageology such as CT、MRI, the computer skill was utilized with the modem medical. The multi-slice helical CT possessed the powerful post-processing function and supplied the detailed image for the clinic with all kinds of the image recombination methods. But the reconstructed image in the 64-slice helical CT workstation actually is plane and two-dimension reconstruction yet, It can not be manipulated as the surgerical organ and be satisfied with the clinic requirement. Therefore, to reconstruct the three-dimension spatial image which can satisfied the clinic requirement including of randomly revolving and dissection and to bring the power feedback feeling when to incision the three-dimension hepatic, these work will bring the far-reaching practical significance for the surgery.
Objective
To investigate the behavior of the liver and its interior vessel scanogra based on 64-slice helical CT; to investigate the image segmentation methodology of hand-made and sequence on the scanogra of the liver and its interior vessel based on 64-slice helical CT; to investigation the methodology of the three-dimensional reconstruction by the software MIMICS and the self-designed reconstruction software for the liver and its interior vessel and the virtual liver neoplasm surgical resection mimic system.
Methods
1. Studies on the three-dimensional reconstruction about the liver image and abdominal cavity artery based on the 64-slice helical CT scanogra
(1)Examiner: common health examination person, male, 36 year olds, Body height: 1.76M, Body weight: 74KG
(2)Scan condition of the hepatic and hepatic vessel: scan parameter: pip voltage 120KV、tube current 300mAs、every cycle 0.5s、pitch 0.984、slice thickness 5mm
(3) Plain scan and Enhanced scan
The Detector 0.625×64, slice thickness 5ram, interval 5ram, Pitch: 0.984, scan sight 40-50cm, matrix 512×512.
(4)Enhanced CT scan
Non-ionic contrast media with an iodine concentration of 300--- 370 mg/ml are most commonly used and are applied at a flow rate of 5 ml/s depending on the kind of examination. The artery phase delay time after injection: 20-25s.The portal vein phase delay time after injection: 50-55s
(5) the liver image collection from the 64-slice helical CT scanogra
(6)the three-dimensional reconstruction methods of the liver with intrahepatic vessel: the image was divided by the method of combining liminal value with man-made, then 3D reconstructed the liver model by MIMICS software. The reconstructed target was induced and reserved as the format STL and IGS. When the object were induced into contra- engineering software and were polished, the achieved model can be either to faithful for the initial data or to suit for virtual manipulative finally.
2. Studies on the man-made segmentation and three-dimensional reconstruction about the liver image based on the 64-slice helical CT scanogra
(1)examiner: the patient suffered left liver tumor, female, 50 year olds, Body height: 1.64M, Body weight: 58KG
(2) the liver image collection from the 64-slice helical CT scanogra
(3)An unenhanced helical CT of the liver was performed before contrast administration. For biphasic helical CT the liver was scanned in the arterial and the portal-venous phase of liver perfusion. With a power injector, 120ml of Iopromid was injected in an antecubital vein at a flow rate of 4.0ml/s.
3.1 CTA scanning: a low-dose preliminary inject test
3.2 MSCTP scanning: The portal-vein preliminary test
(4)The liver image switching from the 64-slice helical CT scanogra
The data were divided into the unenhanced phase, the artery phase, the hepatic vein phase and the portal-vein phase. On the Mxview workstation, all the data were deposited and converted the format DICOM into the format BMP.
(5)Liver Visualization
The different phase image should be treated respectively according to every period image.
5.1 Image Registration
To adjust every phase image scanning sequence so as to keep the initiation point and the end point equal.
5.2 Image Segmentation
The CT image were divided by the software Photoshop 7.0.
The methods: the image introduction - liver outline marking - reverse selecting - delete - preserve.
5.3 Liver three-dimensional Reconstruction
The series of the liver image which had been divided firstly were imported the MIMICS software. Then the liver image and the duct image were extracted according to their different gray scal. The 3D model of the liver and the intrahepatic vessels were reconstructed by the MIMICS software respectively. The 3D model were outputted into the FreeForm Modeling System in the STL format to make the model smooth and removal the fragment.
3. Studies on the sequence segmentation and three-dimensional reconstruction about the fiver image based on the 64-slice helical CT scanogra
(1) 64-slice helical CT liver scanogra
The same as the collection data set of the second chapter.
(2) Liver Visualization
The different phase image should be treated respectively according to every phase image.
2.1 Image Registration
To adjust every phase image scanning sequence so as to keep the initiation point and the end point equal.
2.2 Image Segmentation
Firstly, the liver margin and the vessel were divided from the two-dimensional image in sequence; Secondly, the single organ was 3D reconstructed with the segmentation result. The focal point was to be sure of the image segmentation correct result and to improve the segmentation automatization sequence in the meaning of sequence. In a word, applying for Regions Growth Algorithms realize the sequence segmentation.
(3)The three-dimensional reconstruction of the liver with intrahepatic vessel
The MIMICS software and the self-designed software would be applied to reconstruct the three-dimensional liver with intrahepatic vessel model.
4. Studies on the virtual surgery about the liver three-dimensional reconstruction based on the 64-slice helical CT scanogra
Virtual Hepatectomy
The 3D liver model with intrahepatic vessel, which had been reconstructed in the second chapter, were Introduced into the FreeForm Modeling System. Based on the FreeForm Modeling System, the software of virtual resection and the virtual scalpel were 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. The Virtual Hepatectomy system were established, the different liver resection type were simulated.
Results
1. Studies on the three-dimensional reconstruction about the liver image and abdominal cavity artery based on the 64-slice helical CT scanogra
The 64-slice helical CT scanogra of the liver totally had 676 slice image. The image data were composed of four phase image: the uncontrasted phase; the hetatic artery phase, the portal vein phase, the hepatic vein phase.
The reconstructed liver model could reflect the liver real volume and the liver anatomic landmark and demonstrated the liver and the hepatic artery, the portal vein, the hepatic vein and their branch by adjusting the liver clarity simultaneously and respectively.
The 3D structure of the inferior vena cava and the hepatic venous clearly demonstrated that the stem and the branch of the Left hepatic veins, the Middle hepatic veins and the Right hepatic veins. The Courser、the caliber of the hepatic veins and the way of the three hepatic veins abouchement into the inferior vena cava could be clearly demonstrated.
The abdominal aorta、the arteria coeliaca and its branch suah as: the gastroduoden artery、the renal arteries、the right gastric artery、the left gastric artery、the proper hepatic artery、the splenic artery、the mesentery artery and so on, these artery had the high fidelity and the strong three-dimensional effect. Especially the artery course and caliber was realer and more solid than the anatomy atlas graph.
The portal system demonstrated the portal extrahepatic stem and the splenic vein and the sup. mes. vein. The intrahepatic portal system could clearly demonstrate the portal vein stem and the leaf branch, the segment branch of the liver, for example, the transverse part, the anteroposterior axes, the superior lobar branch, the internal lobe branch, the posterior lobe branch, the anterior lobe branch and its next grade branch. The structure of the reconstructed portal vein system was the same as the image of the portal system which was reconstructed in the method of VR on the Mxview workstation of the 64-slice helical CT.
2. Studies on the man-made segmentation and three-dimensional reconstruction about the liver image based on the 64-slice hdieal CT scanogra
(1) The 64-slice helical CT scanogra
The 64-slice helical CT scanogra of the liver totally had 658 slice image. The image data were composed of four phase image: the uncontrasted phase; the hetatic artery phase, the portal vein phase, the hepatic vein phase.
The liver outline was clear, the contrast agent in the pipeline of the cross-section was filling well. Every kind of vessel was clarification. The artery phase: the abdominal aorta and the hepatic artery and its branch were clearly demonstrated. The hepatic vein phase: the stem of the hepatic vein was clearly showed, but its branch just can be showed to the third grade vessel. The contrast agent in the inferior vena cava was filling uneven, the portal vein phase: the portal vein system was obviously showed, its branch almost can reach the fifth grade branch. The contrast agent in the portal vein can be showed very well. The demarcation with the liver parenchyma was very apparent.
(2)Visualization of liver
The 3D reconstructed liver image
The 3D liver model by the software MIMICS had the rough surface and the feeling of "stair". The vessels structure was continuity, but the artery surface had many triangular fragment. The 3D reconstructed liver model by the MIMICS software looks like the liver sample when the fragment was removed by the FreeForm Modeling System. The 3D model demonstrated in the FreeForm Modeling System can be magnified, contracted and rotated. The model can be observated in omnibearing. The three kinds of the vessels: the artery, the portal vein and the hepatic vein total introduced into FreeForm Modeling System, the integrity liver with intrahepatic vessels can be finished.
3. Studies on the sequence segmentation and three-dimensional reconstruction about the liver image based on the 64-slice helical CT scanogra
(1)Liver Image segmentation
The image rapid segmentation in the method of Regions growth could finish dividing the liver scanned image data as soon as quickly. The scanned dataset included 846 slice liver image.
(2)The three-dimensional reconstruction of the liver and the intrahepatic vessel and the vessel structural feature
The image dataset which had been Divided in sequence were reconstructed by the software MIMICS. The reconstructed model can showed clearly the hepatic artery, the hepatic vein, the portal vein. The model had stero-image and the appearance fidelity. The portal system can clearly demonstrated the stem of the portal vein formulated from the splenic vein and superior mesenteric vein and the intrahepatic branch of the portal vein.
Adopting self-designed software Tony2image, the reconstructed result showed: artery phase hepatic: the appearance fidelity good, the liver anatomic landmark can be clearly observed and the hepatic look like the real hepatic organ. At the hepatic portal, the hepatic artery courser was distorting and fidelity. The hepatic artery location、branch、caliber can observed from the transparent hepatic. After the hepatic in the artery phase and the hepatic in the portal vein phase simultaneously were imported into the software, the two phase hepatic outline almost were overlapping, they had highly goodness of fit. The reconstructed hepatic vein was observed from different direction, the third grade branch of the left hepatic vein, the middle hepatic vein、the right hepatic vein were showed clearly. The reconstructed hepatic in the portal vein phase was translucence, the vessel courser caliber length distribution in the portal vein system were clearly demonstrated.
The reconstructed liver model possessed the liver and the hepatic artery, the portal vein, the hepatic vein. The appearance fidelity was better than the real liver. The model can be observed omnibearing just by magnifying, contracting and rotating the model. The model could be demonstrated solo or combination just by adjusting the objective colour and the clarity, the reciprocation analysis could be realized. After the liver visualization, the intrahepatic vessels could be showed in the stero and distinct. The intrahepatic vessels courser, caliber and their relationship could be clearly demonstrated.
4. Studies on the virtual surgery about the liver three-dimensional reconstruction based on the 64-slice helical CT scanogra
(1) Visualization of liver
The 3D reconstructed liver image.
The 3D reconstructed liver model by the MIMICS software looks like the real liver after the fragment were removed by the FreeForm Modeling System. The 3D model demonstrated in the FreeForm Modeling System can be magnified, contracted and rotated. The model can be observed in omnibearing.
(2) The virtual partial hepatectomy system
In the virtual surgery system with interaction and immersion, the virtual scalpel can be manipulated to perform optional resection on 3D liver model with the haptic device (PHANToM). The power feedback can be felt through adjusting the liver intensity.
(3)The simulation of the left segment Hepatectomy and Right lobe of liver resection operation
In the virtual surgery system, the virtual scalpel can be manipulated to perform optional resection on 3D liver model with the haptic device (PHANTOM). The left segment Hepatectomy and Right hemihepatectomy were simulated, the effect were the same as the clinic operation. The spatial relationship between the simulated tumour and the intrahepatic vessel can be clearly observed by the action such as turning the liver surface into transparent and rotating and so on. The simulated Hepatectomy was the same as the real surgery. Meanwhile, the power feeling can be touched by the haptic device (PHANToM). A simulation tumor can be manmade with the by GHOST SDK tool and was put into the liver 3D model.
Conclusions
1. The 3D liver model with intrahepatic vessel, which was 3-dimensionally reconstructed in the combining method of liminal value and man-made using advanced 64-slice helical CT scanogra and MIMICS software, especially the coeliac artery system image is lively, its branch caliber and the relation among the vessels is clearly, may be helpful to operate in the clinic surgery and teaching, hepatic vascular investigation.
2. The intrahepatic vessel image can be clearly made by the special angiography on 64-slice helical CT. The 3D liver model with intrahepatic vessel, which was three-dimensionally reconstructed in the method of MIMICS software and of man-made segmentation image from the advanced 64-slice helical CT scanogra, always have smooth and glossy surface, clearly vessel structure, bright-colored, strongly stereo feeling and can become the basis of the virtual operation. The 3D model has good interaction and manifestation and is fit to manipulate.
3. In the basis of the second chapter, the segmentation procedural and three-dimensional reconstruction software were self-developed. When the image were divided and reconstructed in the application for the self-device sequence, the result were the same as that using the MIMICS software. Compared with the image using the MIMICS software, the 3D liver model with intrahepatic vessel structure, although the surface was slightly rough, had good stero-effect. Either the liver model imagination or the liver structure and the vessel stereo-position were fully manifested. If the work was continued to be designed, the independence knowledge property right software about the liver image segmentation and the three-dimensional reconstruction will be developed.
4. The 3D visualized liver has been satisfactorily developed with the method of surface rendering using the advanced 64-slice helical CT scanogra. Then the developed virtual hepatectomy system and the virtual operation tool based on the haptic devices (PHANToM), which has good interaction, powerful immersion and great imagination, will be of great significance for the promotion of hepatic clinical surgery.
引文
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