个体化AC-PC线体表投影在脑立体定向手术中的应用

目的:探讨基于高分辨磁共振(MRI)的个体化大脑前连合后缘中点至后连合前缘中点的连线(AC-PC)体表投影在提高立体定向头架安装精度方面的价值。方法:选取在我科进行立体定向手术的患者18例,列入个体化投影组,利用3D Slicer计算个体化AC-PC体表投影,作为安装头架的基线。对照组选取既往按照常规方法安装头架的病例18例。利用Leksell SurgiPlan系统量出AC-PC线与头架基线的角度,比较两组差异。收集40例无神经系统疾病成年人的3D磁共振数据。计算AC-PC线体表投影,寻找更好的体表参考标志并测量AC-PC长度。结果:(1)个体化投影组AC-PC线与头架基线夹角(1.7±1.0°)显著低于对照组(4.6±2.4°,P<0.05)。(2)测量AC-PC线与外眦-对耳轮下脚下缘连线夹角。平均夹角为-1.12±4.61°,取绝对值后平均夹角为3.32±3.35°,男女无明显差异。(3)男性AC-PC长度为23.28±0.98 mm,女性AC-PC长度为22.45±1.16 mm,二者无显著性差异。结论:基于高分辨磁共振的个体化AC-PC体表投影,可显著提高立体定向头架...     

立体定向脑图谱基准点的测定及其意义

目的　对立体定向脑图谱的基准点进行测定研究,为构建临床立体定向脑手术提供基础。 方法　在立体定向空间坐标系内,应用MR扫描图像处理技术对120例健康自愿者和应用解剖学技术对30例尸脑分别进行脑内基准点前连合（AC）、后连合（PC）的径值和前后连合间距（ICD）进行测量。 结果　在立体定向空间内,无论在大体标本,还是在MR图像上,AC、PC均清晰可见;在尸脑上测得AC的前后径为（2.75±0.76）mm,上下径为（3.85±0.68）mm,PC的前后径为（1.87±0.58）mm,上下径为（2.48±0.64）mm,ICD长度为（22.68±1.46）mm;在健康自愿者测得AC的前后径为（2.80±0.32）mm,上下径为（3.82±　0.37）mm,PC的前后径为（1.76±0.30）mm,上下径为（2.30±0.45）mm,ICD长度为（23.84±1.32）mm。 结论　通过尸脑与健康正常人脑的对比测量研究,在立体定向坐标系内脑内AC、PC是脑内准确定位的基准点,　AC-PC是恒定的参考线。     

Elekta立体定位体架对靶区吸收剂量的影响

目的:研究立体定向放射治疗中Elekta立体定位体架(ESBF)对靶区吸收剂量的影响。方法:将小水箱放入ESBF内做CT扫描,图像传至PrecisePlan计划系统三维重建数字化体模。计算6MV、15MVX线存在和不存在立体定位体架时靶区吸收剂量的差别,并与水箱中的测量值进行比较。结果:TPS计算结果显示对于两侧野,当等中心坐标Y150mm时吸收剂量的差别为5.4%～5.7%;当Y150mm时为9.0%～9.3%。利用后野照射时靶点吸收剂量差别为2.2%～2.4%,后斜野为2.6%～2.9%。两档能量X线计算值无明显差异。水箱测量结果显示,当两侧野Y150mm时剂量差别没有明显变大;两后斜野215°野的差别大于145°野;且15MV的差别均小于6MV。结论:射线经过Elekta立体定位体架时由于衰减会对靶区的吸收剂量造成影响。PrecisePlan剂量计算算法能够根据坐标值对体架影响做出修正,但与测量值存在偏差,实际照射时需要根据测量结果进行修正。     

三维模型中踝关节中心定位的研究

目的　应用不同方法在三维重建模型上定位踝关节中心,并判断各方法的可行性,准确定位踝关节中心,进而为三维模拟下肢膝关节置换术提供形态学基础。 方法　对33例正常成人踝关节行CT扫描,数据导入三维重建软件Mimics,重建出踝关节三维立体模型,在逆向工程软件Geomagic Studio中分别采用距骨顶部中点（A点）、距骨顶部点云质心（B点）和内外踝间距中点（C点）3种方法对踝关节中心进行定位,并在冠状面上对三中心点之间的距离进行测量,应用统计软件SPSS对数据进行分析。 结果　成功建立了踝关节的三维立体模型,并用不同方法定位出踝关节中心。测量结果显示A点与B点之间的距离为(1.058±0.741)mm, B点与C点之间的距离为(1.684±1.283)mm, A点与C点之间的距离为(1.484±1.040)mm。且每个中心点之间的距离差异不具有显著性(P>0.05)。 结论　基于三维重建模型上的踝关节中心定位方法具有可行性,且与二维平面上的定位相比稳定性更高,其中距骨顶部点云质心作为踝关节中心较其他两种方法更简便易行。     

在X线平片上利用头颅骨性标志定位前,后连合

在50个成人颅脑标本上,标出前、后连合后摄X线正、侧位片,在侧位片上利用不同的颅骨骨性标志共作出8组直角坐标系,分别测出各组中前、后连合中点的坐标值,相互进行比较从而选出定位前、后连合最合适的坐标系.在正位片上则分别测量原点至颅前窝底和两眶上缘连线的距离,以及颅顶内面至颅前窝底和两眶上缘连线的距离,经直线回归分析,定出原点和左右向的冠状轴,以完成三向的立体坐标系.     

X线放射外科治疗靶点定位精确度估计方法研究

目的:探讨X线放射外科治疗病人靶点定位精确度估计方法.方法:应用人体头颅模型内特定标记物测定CT定位的精度;用胶片法测定二次等中心系统精度和模拟治疗精度;用CT定位框估计133例病人治疗误差,并用此误差指导制定治疗计划,随访相关并发症发生情况.结果:CT平均定位误差0.65 mm,最大误差1.09mm.SRS200二次等中心系统误差0.19 mm.胶片法检测模拟治疗误差1.43 mm.应用CT定位框估计的治疗误差为(1.71±0.62)mm,用此标准指导治疗计划,随访病人无相关保护器官的并发症.结论:X线放射外科治疗系统精确度已达到立体定向放射外科质量控制要求.用CT定位框估计治疗误差对临床治疗有一定的参考价值.     

丘脑枕三维空间的形态和位置

为了调查并获得丘脑枕的解剖学资料,并为脑的立体定向手术提供定位数据,本文调查了成人４１只整脑８２个丘脑枕的空间形态和位置。碱维切面上作２毫米厚的连续切生,获得丘脑枕的前后经、左右径、上下径,体积及“靶心”坐标值;通过还原、重建,给出三维切面的空间投影轮廓图。本文确定了核团在脑内空间的整体构型;还将获得的结果与脑立体定向手术的关系进行了探讨。     

磁共振图像(MRI)空间几何失真对立体放射治疗中靶点位置精确度影响的分析

目的：分析模拟靶点MRI空间几何失真的因素,以及其对立体放射治疗中靶点位置精确度的影响程度。材料和方法：将5×5矩阵小孔有机玻璃靶点模拟装置和Leksell-G型立体定位头架进行磁共振扫描,分别测量MRI二维横断面和不同扫描层厚情况下选取层面在纵向的几何失真程度。结果：MRI二维横断面上模拟把点X、Y方向精确度分别为（0．03±0．12）mm、（0.44±0．31）mm,平面距离精确度为（0．46±0．31）mm,选取层面在纵向（Z方向）的精确度为（0．46±0．41）mm。结论：梯度场非线性和主磁场的非均匀性以及不同扫描展尽是MRI几何失真的因素。磁共振作为立体放射治疗靶点定位是可行的。     

豆状核与丘脑三维空间形态和位置的研究

目的：为了增加和填补豆状核与丘脑三维空间形态和位置的解剖学资料，并为提高脑立体定向手术中靶点定位的准确性提供定位数据。方法：将成人６１只整脑制成２mm厚的三维连续切片，并在各脑片上直接进行观测。结果：调查了１２２个豆状核与天脑的前后径、左右径、上下径，体积及“靶心”坐标植；通过还原、重建，绘出三维切面的空间投影轮廓图。结论：明确了两核团在脑内空间的整体构型，其结果可指导脑立体定向手术。     

伽玛刀治疗帕金森氏病定位方法探讨

本中心自１９９３年１２月至１９９７年８月期间，利用伽玛刀治疗帕金森氏病９０例。总结了一套伽玛刀治疗功能性疾病的ＭＲ定位方法，包括头架的固定，靶点的选择及其坐标的计算修正公式和由公式推导的修正表。分析了头架固定对靶点坐标确定的影响因素，比较了修正前后的坐标差值，为伽玛刀治疗功能性疾病的定位提出一种新的思想。     

A method for repositioning of stereotactic brain patients with the aid of real-time CT image guidance

This note presents a method that recalculates the coordinates of the isocentre for patients undergoing stereotactic radiotherapy to the brain with a relocatable head frame based on a pre-treatment CT scan. The method was evaluated by comparing initial stereotactic coordinates of the isocentre with the recalculated coordinates for eight single-fraction patients. These patients had the Brown-Roberts-Wells (BRW) frame fixed to the outer table of the skull, and therefore the coordinates of any anatomical point should be identical between the initial scan and the pre-treatment scan. The differences between the two sets of coordinates were attributed to errors in the method. The results showed that the systematic errors in the recalculated coordinates were less than 0.05 mm, and they were not statistically significant. The random errors (one standard deviation) were from 0.35 mm (lateral) to 0.58 mm (vertical). The average value of the combined 3D difference was 0.75 mm.     

Coordinate transformations and calculation of the angular and depth parameters for a stereotactic system

Stereotactic systems have been used to assist in the precise implantation of radioactive sources in selected brain tumors. Use of such systems requires an algorithm that transforms spatial points in computed tomography coordinates into stereotactic frame coordinates. A simple algorithm performing the coordinate transformations, intended for inclusion in treatment-planning software packages for interstitial brain implants, has been developed. This algorithm was formulated using the geometrical configurations of the Brown-Roberts-Wells (BRW) stereotactic system. After the transformations, the BRW angular coordinates and depth specifying the probe direction, defined from the entry point to the target point, are determined from their respective cartesian coordinates. These angular coordinates and depth on the BRW stereotactic system allow accurate neurosurgical implantations of catheters into the brain, and thereafter the insertion of radioactive sources.     

人体大脑数字化解剖模型的构建及可视化

目的构建人体大脑数字化解剖模型,为实现大脑的计算机精确模拟提供可操作的基础平台,为人体大脑功能研究提供解剖学框架。方法采用低温冷冻铣切技术采集人体大脑的横断面图像,用课题组自行开发的软件,将分割提取后的脑断面图像进行重建,建立大脑三维模型。用与香港中文大学合作开发的可视化软件,在三维空间上对人体大脑结构进行可视化研究。结果建立了以前后连合间线中点为原点的大脑三维模型,且模型上每一像素都有相应的解剖标识,其任意一点的坐标均能显示;大脑的三维模型可以任意切割显示大脑内部结构：重构后的大脑结构还可进行三维测量。结论大脑数字化模型建立在临床常用的三维空间坐标系中且模型上每一像素都有相应的解剖标识,为模型驱动分割算法的研究提供了模板,同时也为神经解剖教学提供了一种新的、直观的手段。具有明确解剖标识和量化空间信息的数字化人大脑模型,与坐标系统联系起来,还为人大脑各类图像配准提供了公共参考系统。     

Accuracy and feasibility of cone-beam computed tomography for stereotactic radiosurgery setup

Image fusion, target localization, and setup accuracy of cone-beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) were investigated in this study. A Rando head phantom rigidly attached to a stereotactic Brown-Roberts-Wells (BRW) frame was utilized to study the geometric accuracy of CBCT. Measurements of distances and angular separations between selected pairs of multiple radio-opaque targets embedded in the head phantom from a conventional simulation CT provided comparative data for geometric accuracy analysis. Localization accuracy of the CBCT scan was investigated from an analysis of BRW localization of four cylindrical objects (9 mm in diameter and 25 mm in length) independently computed from CBCT and conventional CT scans. Image fusion accuracy was quantitatively evaluated from BRW localization of multiple simulated targets from the CBCT and conventional CT scan. Finally, a CBCT setup procedure for stereotactic radiosurgery treatments was proposed and its accuracy was assessed using orthogonal target verification imaging. Our study showed that CBCT did not present any significant geometric distortions. Stereotactic coordinates of the four cylindrical objects as determined from the CBCT differed from those determined from the conventional CT on average by 0.30 mm with a standard deviation (SD) of 0.09 mm. The mean image registration accuracy of CBCT with conventional CT was 0.28 mm (SD = 0.10 mm). Setup uncertainty of our proposed CBCT setup procedure was on the same order as the conventional framed-based stereotactic systems reported in the literature (mean = 1.34 mm, SD = 0.33 mm). In conclusion, CBCT can be used to guide SRS treatment setup with accuracy comparable to the currently used frame-based stereotactic radiosurgery systems provided that intra-treatment patient motion is prevented.     

Clearance assurance for stereotactic radiosurgery and radiotherapy

The nature of stereotactic radiotherapy (SRT)/radiosurgery (SRS) requires the use of oblique non-coplanar beams to avoid critical structures and maximize target coverage. These beams are delivered via a combination of gantry, collimator, and couch rotations. Such beam orientations could result in the gantry colliding with the patient or couch. The outcome can be patient injury, damaged equipment, and unrealized treatment. Our objective in this work was to create a treatment planning tool that utilizes each unique patient geometry to quantify clearance for stereotactic beams. Emphasis was placed on developing a general platform that can completely, yet easily, define any user system. Gantry components were described by providing component dimensions to software that generates thousands of surface points. Table components were described as a combination of boxes and measured surface points. During the treatment planning process isocenter coordinates, patient dimensions and beam orientation were specified. Gantry components were then transformed into the table reference frame. The shortest distance between the gantry and patient or couch was computed and compared to a safety margin. This clearance assurance algorithm was developed in response to the need to reduce patient setup time, and to increase the range of potentially useful beams. The software was verified by measuring minimum gantry-table distances at multiple beam orientations and comparing to calculations. Differences between calculated and measured clearances were on the order of 1 cm. The software enabled the safe delivery of noncoplanar oblique beams that are difficult to visualize. The software was used successfully to assure clearance for 50 patients (366 beams). This useful clinical tool became an integral part of the stereotactic quality assurance protocol at St Luke's-Roosevelt Hospital Center.     

Dosimetric accuracy of a staged radiosurgery treatment

For large cerebral arteriovenous malformations (AVMs), the efficacy of radiosurgery is limited since the large doses necessary to produce obliteration may increase the risk of radiation necrosis to unacceptable levels. An alternative is to stage the radiosurgery procedure over multiple stages (usually two), effectively irradiating a smaller volume of the AVM nidus with a therapeutic dose during each session. The difference between coordinate systems defined by sequential stereotactic frame placements can be represented by a translation and a rotation. A unique transformation can be determined based on the coordinates of several fiducial markers fixed to the skull and imaged in each stereotactic coordinate system. Using this transformation matrix, isocentre coordinates from the first stage can be displayed in the coordinate system of subsequent stages allowing computation of a combined dose distribution covering the entire AVM. The accuracy of this approach was tested on an anthropomorphic head phantom and was verified dosimetrically. Subtle defects in the phantom were used as control points, and 2 mm diameter steel balls attached to the surface were used as fiducial markers and reference points. CT images (2 mm thick) were acquired. Using a transformation matrix developed with two frame placements, the predicted locations of control and reference points had an average error of 0.6 mm near the fiducial markers and 1.0 mm near the control points. Dose distributions in a staged treatment approach were accurately calculated using the transformation matrix. This approach is simple, fast and accurate. Errors were small and clinically acceptable for Gamma Knife radiosurgery. Accuracy can be improved by reducing the CT slice thickness.     

数字人脑空间坐标转换方法

Objective To describe a spatial coordinates conversion method for serial anatomical cross-sectional images of the human brain using the software, Excel 2003.Methods Initialization reference frame was established in serial anatomical cross-sectional images of the human brain. Then, a standard spatial coordinates was set up by one time horizontal moving and 3 times rotations of the reference frame. Results A datasheet about coordinates conversion from initialization reference frame to standard spatial coordinates was established. Conclusion Standard spatial coordinates was established in the digital human brain after coordinates conversion. It will be helpful to build Chinese digital brain model.     

Errors in pointing are due to approximations in sensorimotor transformations

1. We define an extrinsic frame of reference to represent the location of a point in extrapersonal space relative to a human subject's shoulder, and we define an intrinsic frame of reference to represent the orientation of the arm and forearm. 2. We examined the relations between coordinates in the extrinsic and intrinsic frames of reference under two experimental conditions: when subjects made inaccurate movements by pointing to virtual targets in the dark and when they made accurate movements by pointing to actual targets in the light. 3. When subjects made inaccurate movements, there was a close-to-linear relationship between the orientation angles of the arm (intrinsic coordinates) at its final position and the extrinsic coordinates of the target. When they made accurate movements, these relationships were more nonlinear. 4. Specifically, arm and forearm elevations depended principally on target distance and elevation, whereas the two yaw angles depended mainly on the target's azimuth. 5. We propose that errors in pointing occur because subjects implement a linear approximation to the transformation from extrinsic to intrinsic coordinates and that this transformation is one step in the process of transforming a visually derived representation of target location into an appropriate pattern of muscle activity.     

Studies on target localization of Parkinson's disease treated with gamma knife]

Ninety cases of Parkinson's disease were treated in our center from Dec. 1993 to Aug. 1997. Based on our work, we have developed a method for the MR localization in the treatment of Parkinson's disease with Gamma knife, including the fixing of stereotactic frame, the selection of target, and the correction of the target's coordinates. In this paper, the effects of fixing of coordinate frame on the localization of target have been analyzed. Also presented are the errors of the coordinates of the selected targets, compared with those corrected. The method reflects a new idea for target localization.