基于电阻抗断层成像的非均匀电导率颅骨物理模型研究

目的 用非均匀电导率分布的颅骨模型进行电阻抗断层成像(EIT)实验,分析颅骨电导率非均匀分布对成像结果的影响.方法 选用石膏材料制作非均匀电导率的颅骨模型,用此模型模拟头颅进行EIT目标成像,并将结果与均匀电导率颅骨模型的成像结果进行比较.结果 相对于均匀电导率模型,在非均匀电导率模型内成像目标更加远离电导率较低一侧,且所在位置边界电压扰动量降低.结论 颅骨模型的电导率非均匀分布对成像定位有明显影响,需要在成像算法上做进一步改进.     

基于磁共振技术的生物电阻抗成像研究进展

磁共振电阻抗成像（magnetic resonance electrical impedance tomography, MREIT）是将MRI与电阻抗成像（electrical impedance tomography, EIT）技术相结合,通过MRI系统测量成像体内部的磁通密度值对成像体的电导率图像进行重建,是无创性地进行阻抗成像的一种新方法。MREIT由Zhang[1]于1992年首次提出,其基本方法是利用物体内的电流密度分布和磁感应强度测量值来重构物体内电导率的分布。传统的EIT需测量多个边界电压值来提高重建图像的精确度与空间分辨率,但求解过程值不稳定,利用磁感应强度进行重构图像能够解决此缺陷。本文拟对MREIT的最新研究作一综述。     

基于电阻抗成像的均质头模型研究

目的 评估低电导率的颅骨对人脑阻抗成像的影响.方法 基于适用于头部的优化的硬件系统和反投影算法,在建立的一个圆筒形和一个半球形的包含"颅骨"的均质头模型上,对多种扰动目标进行成像研究.结果 现有系统对含均质"颇骨"的头部物理模型内电导率、位置和尺寸不同的简单扰动目标成功地进行了图像重建.结论 "颅骨"的存在对重构图像产生了显著的影响,揭示了脑电阻抗图像监护的可行性,为动物实验提供了依据.     

基于径向基函数神经网络的两步核磁共振头部组织电阻抗成像算法

目的 基于径向基函数(radial basic function,RBF)神经网络的两步核磁共振电阻抗成像(magnetic resonance electrical impedance tomography,MREIT) 算法,对人体头部进行MREIT.方法 首先利用高分辨率的核磁共振成像(magnetic resonance imaging,MRI)系统对成像物体进行三维构建和不同组织的边界区分;然后利用RBF MREIT方法对物体内不同组织的均匀电阻抗分布进行估计,并采用基于径向基函数-遗传算法的MREIT技术对每种组织有限元模型中每个单元的电阻抗值进行估计.结果 在三层球头模型(scalp skull brain,SSB)上进行的仿真实验证明了利用两步 MREIT算法进行头部组织三维电阻抗图像重构的合理性与可行性.结论 该两步MREIT算法可以用于头部组织三维电阻抗图像重构,具有潜在的应用价值.     

国产uMI 780型PET/CT仪18F-FDG最适图像采集及处理条件探讨

目的：探讨国产uMI 780型正电子发射体层成像(positron emission tomography,PET)/计算机体层成像(computed tomography,CT)仪在临床应用¹⁸F-FDG进行全身(脑部+体部)显像时的最佳图像采集及处理条件。方法：收集2017年8月—2018年5月符合要求的受试者400例,将400例患者随机纳入预先制订的由¹⁸F-FDG注射量2.96 MBq/kg和3.70 MBq/kg、脑部PET显像时间3 min和2 min、体部2 min/床位和1.5 min/床位三者组合形成的4组(A1、A2、B1、B2,每组100例)研究序列。按照优(3分)、良(2分)、差(1分)对脑部和体部PET图像的代谢分布清晰度、设备性伪影、图像均匀性进行视觉评价,比较¹⁸F-FDG注射量、显像时间和重建算法或重建参数组合对脑部和体部PET图像质量的影响。结果：脑部PET图像质量有序子集最大期望值法(ordered subset expectation maximization,OSEM)均明显优于滤...     

基于扩散张量成像利用一阶有限元方法计算脑白质各向异性电导率对脑电位分布的影响

目的 研究脑白质各向异性电导率对头皮电位分布的影响.方法 把由扩散张量成像得到的水分子扩散张量采用体积约束规则计算出白质组织的电导率张量,并根据成像的空间信息建立了包括头皮、颅骨、灰质、脑脊液及白质5种组织的真实头的有限元模型.基于此模型,推导了各向异性电导率脑电正问题的一阶有限元数值算法.最后,采用电流偶极子模型计算头皮电位分布.结果 脑白质各向异性电导率对头皮电位分布有一定的影响,径切比越大,影响越大;左右分布偶极子比上下分布的影响要大.结论 脑电研究中,白质电导率的各向异性为一不可忽略的因素.     

基于阈值分割的K-最近邻规则的磁共振脑图像分割算法的研究

目的:提取脑组织中的白质(WhiteMatter)、灰质(GreyMatter)和脑脊髓液(CSF)。方法:针对去除颅骨和肌肉等非脑部组织的磁共振脑图像,根据解剖学知识采用最大类别方差法(Otsu法)自动寻找阈值,以此为依据进行分类标记,再通过K-最近邻(K-NearestNeighbor,简称KNN)规则对大脑组织结构进行划分。结果:在脑部T1加权像中分割算法分别提取脑组织中的白质、灰质和脑脊髓液。结论:结果表明该算法具有较好的自动性和稳定性。     

中耳CT仿真内镜成像质量的影响因素分析

目的探讨影响中耳CT仿真内镜(CTVE)成像质量的因素。方法随机选择疑耳部疾病患者12例24耳,采用CT常规耳部高分辨容积扫描后作仿真内镜成像,选择30、75两种卷积核算法图像以及采用不同观察视角对不同含气程度的中耳进行仿真内镜成像。结果采用不同卷积核图像、设置阈值不同、患者鼓室含气程度不同以及进行后处理时观察视角不同,仿真内镜成像质量出现明显差异。结论卷积核算法、鼓室含气程度、阈值、观察视角是仿真内镜成像质量的影响因素,采用恰当的方法可提高中耳CT仿真内镜的成像质量。     

一种微光夜视成像系统设计

目的 设计一种微光夜视成像系统,用于飞行人员夜间视觉体验训练.方法 采用LED光源调光技术、视频信号处理技术、DLP投影显示技术及光学系统设计技术,设计了一种由7个子系统组成的微光夜视成像系统,采用ZEMAX光学设计软件对成像质量进行了仿真分析.结果 DMD处光源辐射照明的均匀性为86.6％,投射主镜光学系统场曲<0....     

CTA诊断颅内血管性病变临床价值

目的：探讨ＣＴＡ对颅内血管性病变的诊断价值。材料与方法：应用螺旋增强ＣＴ扫描获得原始轴面图像,采用ＳＳＤ和ＭＩＰ技术进行扫描范围内脑血管三维成像。本组２０例典型病例,包括颅内动脉瘤１４例,ＡＶＭ５例,静脉性血管畸形１例。结果：ＣＴＡ可以清晰显示颅内动脉瘤及血管畸形的部位、形态、大小、起源及与周围脑血和和颅骨的解剖关系。结论：ＣＴＡ对颅内血管性病变,尤其是动脉瘤或ＡＶＭ引起的急性脑出血、蛛网膜一腔出     

Image reconstruction incorporated with the skull inhomogeneity for electrical impedance tomography

The structural similarity of the head model affects the accuracy of forward solution to electrical impedance tomography (EIT). Generally, the four-concentric circle model (FCCM) is used as the head model, which ignores the inhomogeneous distribution of the conductivity of real skull. In order to decrease the errors caused by using FCCM, a more accurate head model named inhomogeneous skull model (ISM) has been proposed and a reconstruction algorithm incorporated with ISM has been developed for brain EIT. Simulation results have shown improvement in image quality and localization accuracy when using ISM. It is also suggested that the reconstructed image could be more sensitive to the location of bony sutures than to the variation of skull thickness. In conclusion, incorporating skull inhomogeneity into image reconstruction is an effective way to improve image quality and localization accuracy for brain EIT.     

Image Quality Required for the Diagnosis of Skull Fractures Using Head CT: A Comparison of Conventional and Improved Reconstruction Kernels

BACKGROUND AND PURPOSE:Although skull fractures are generally assessed on bone images obtained by using head CT, the combined multikernel technique that enables evaluation of both brain and bone through a change in the window settings of an image set has been reported. The purpose of this retrospective study was to determine the image quality required for the accurate assessment of skull fractures by using head CT.MATERIALS AND METHODS:A random sample of 50 patients (25 nonfracture and 25 simple nondisplaced skull fractures) was selected, and sets of conventional brain and bone images and improved combined multikernel images were reconstructed (4614 images). Three radiologists indicated their confidence levels regarding the presence of skull fractures by marking on a continuous scale for each image set. The mean area under the receiver operating characteristic curve was calculated for each kernel, and the statistical significance of differences was tested by using the Dorfman-Berbaum-Metz method.RESULTS:Although a difference in the diagnostic performance of the 3 radiologists was suggested, the mean area under the curve value showed no significant differences among the 3 reconstruction kernels (P = .95 [bone versus combined]), P = .91 [bone versus brain]), and P = .88 [brain versus combined]). However, the quality of brain images was distinctly poorer than the quality of the other 2 images.CONCLUSIONS:There was no significant difference in the diagnostic performance of brain, bone, and combined multikernel images for skull fractures. Skull fracture diagnosis is made possible by brain image assessments. Combined multikernel images offer the advantage of high-quality brain and bone images.

The quality of CT images reconstructed with conventional filtered back-projection depends on the type of reconstruction kernel used. In head CT, low-pass filter kernels that decrease higher spatial frequencies and noise are generally used to reconstruct brain images, whereas high-pass filter kernels that preserve higher spatial frequencies and increase noise are generally used to reconstruct bone images.^1,2 In all cases, the reconstruction of brain images is required. In contrast, according to the policy of each institution, bone images are reconstructed either in all cases or only for patients with clinically suspected bone disease. Because assessment of bone tissue is not required for all cases, worthless images increase if there is reconstruction for all cases. However, when bone images are reconstructed only in case of clinical suspicion, additional reconstruction is required if the need for bone images is determined after examination (in the situation of assessing brain images) or if the radiology technician forgets to reconstruct before sending the images (despite reconstruction of bone image being ordered in advance). Furthermore, bone image reconstruction is not possible once the raw data are deleted from the CT device. Although observers have to assess the bone tissue on brain images reconstructed by low-pass filter kernels in such cases, to our knowledge, the diagnostic performance for bone lesions has not been reported.To resolve this issue, the usefulness of a combined multikernel technique that enables the evaluation of both brain and bone through a change in the window settings of an image set for the assessment of skull fractures has been reported.^3,4 The use of this technique not only decreases the number of stored images and simplifies head CT examinations, but also enables the assessment of bone tissue in all cases. However, the diagnostic performance of this technique has not been sufficiently investigated.The purpose of this study was to determine the CT image quality required for the assessment of skull fractures by using receiver operating characteristic (ROC) analysis of different reconstruction kernels and to evaluate the diagnostic performance of the combined multikernel technique for skull fractures.     

构建国人头颈三维有限元模型

目的研究构建国人头颈三维有限元模型。方法依据正常国人头颅CT、MRI断层扫描图像，识别确定重建对象，对皮肤、颅骨采用灰度阈值法、轮廓跟踪算法及B样条曲线拟合法进行自动重建；对其他结构采用人机对话方式提取边界关键点，进行重建实体。定义结构材料参数后划分网格。筛选相邻体积交接面节点，粘连节点完成建模。结果完成包含皮肤、颅骨、硬膜、静脉窦、脑灰白质、脑干、小脑、脑室系统、颈椎及颈髓的国人头颈三维有限元模型。模型单元及节点数分别为168733，80535，总质量约5．14kg。结论利用医学影像资料，采用轮廓跟踪算法等数字图像技术可半自动实现人颅脑复杂结构的三维重建。     

Magnetic resonance electrical impedance tomography at 3 Tesla field strength.

Magnetic resonance electrical impedance tomography (MREIT) is a recently developed imaging technique that combines MRI and electrical impedance tomography (EIT). In MREIT, cross-sectional electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an electrically conducting object when an electrical current is injected into the object. In this work we present the results of electrical conductivity imaging experiments, and performance evaluations of MREIT in terms of noise characteristics and spatial resolution. The MREIT experiment was performed with a 3.0 Tesla MRI system on a phantom with an inhomogeneous conductivity distribution. We reconstructed the conductivity images in a 128 x 128 matrix format by applying the harmonic B(z) algorithm to the z-component of the internal magnetic field density data. Since the harmonic B(z) algorithm uses only a single component of the internal magnetic field data, it was not necessary to rotate the object in the MRI scan. The root mean squared (RMS) errors of the reconstructed images were between 11% and 35% when the injection current was 24 mA.     

MRI和CT图像融合构建头面部分层网格模型的研究

目的:分层构建头面部软、硬组织三维网格模型,探讨其在计算机辅助手术中的应用价值.方法:依据正常人头面部MRI和三维CT断层扫描图像,进行MRI与CT图像的融合,识别确定重建对象,对皮肤、皮下组织及骨组织采用灰度阈值法进行自动重建;采用MIMICS软件对获取的医学信息进行分层网格划分,完成建模.结果:完成了包含皮肤、皮下组织和骨组织的正常人头面部三维网格模型.模型单元及节点数分别为皮肤层36524个单元,18263个节点;皮下层38954个单元,19247个节点;头颅68722个单元,33689个节点.结论:利用医学影像资料的图像融合,采用MIMICS软件等数字图像技术可实现人头面部复杂结构的精确三维重建和分层网格划分.     

Effect of the skull on brain perfusion SPECT imaging

Because attenuation gradually decreases reconstructed counts from the periphery to the center portion of the object, the deep region far from the detector is not clearly observed if attenuation is not compensated. In brain perfusion SPECT, diagnosis is sometimes made using filtered back projection images without attenuation compensation (FBP). Brain perfusion SPECT has the unique characteristic that the radiopharmaceutical accumulates only within the brain and is never taken up by the surrounding skull. This study investigated the effect of skull on brain perfusion SPECT reconstructed with FBP. We theoretically derived the relation between the counts of brain and the linear attenuation coefficient of skull. It was found that the difference in reconstructed counts between the deep gray matter and peripheral gray matter decreased due to the existence of the skull. This result indicated that the deep gray matter was inclined to be visible if the FBP images were displayed according to relative counts normalized to the maximum count of each image. In order to confirm this, we made a numerical phantom with realistic human brain and skull contours on the basis of MR images from a normal volunteer. The linear attenuation coefficient of brain was assumed to be 0.15 cm-1, while that of skull was assumed to be 0.26 cm-1 (denoted as BONE+) or 0 cm-1 (BONE-). In accordance with the theoretical results, the deep gray matter of BONE+ images was more clearly observed than that of BONE- images, if these were displayed using the relative counts of each images. The physical phantom experiments also supported the theoretical and numerical phantom studies.     

头颈部肿瘤多层螺旋CT冠状面多平面重建与常规扫描图像的对比研究

目的 分析头颈部肿瘤多层螺旋CT冠状面多平面重建(MPR)与常规扫描图像，探讨冠状面MPR能否替代常规冠状面扫描。方法 使用GE Lightspeed Ultra 8层螺旋CT扫描仪对90例头颈部肿瘤患者进行扫描，在横断面基础上行MPR。由3位资深放射科医生对冠状面MPR像与常规扫描图像进行对比分析。结果 90例冠状面MPR像对正常鼻咽、鼻腔、鼻窦、上颈部等部位软组织的显示与常规扫描冠状面像相似，图像质量好，均为1级。59例(65．6％)冠状面MPR像对骨质的显示优于常规扫描像，68例(75．6％)对颅底孔道的显示优于常规扫描像。增强CT扫描中，51例明显肿瘤病灶，46例(90．2％)对肿瘤的显示优于常规扫描冠状面像。结论 多层螺旋CT扫描MPR图像除对口腔、口咽的显示欠佳外，均近似或优于常规冠状面扫描像，多层螺旋CT扫描的冠状面MPR可以替代常规扫描。     

Investigating tomographic reconstruction with a priori geometrical information

A novel strategy to perform tomographic image reconstruction is presented, based on the integration of a priori information about the target image. Such information may come from a different imaging tool or a synthetic model. For a given image quality, providing a priori image information reduces the amount of image information to be reconstructed. According to the data processing inequality this requires less input data or physical measurements, therefore reducing exposure to ionising radiation. A prototype algorithm is described, consisting of a penalized ART where some a priori edge information is encoded in an inhomogeneous, anisotropic smoothing kernel. The algorithm is tested on a 2-dimensional set-up based on the Shepp-Logan phantom.     

准静态下颞部撞击致颅脑伤的有限元模拟分析及其临床意义

目的建立准静态下颞部撞击致颅脑伤的虚拟模型，研究准静态下颞部撞击所致的应力分布以及应力波的传播，探讨颞部撞击致颅脑伤的生物力学机制。方法在Hypermesh软件中建立准静态颞部撞击伤的有限元模型，用Ls-Dyna软件对该有限元模型进行数值模拟计算，最后用Ls-Prepost软件进行后处理。结果撞击点处颞骨VonMises应力以及颅内压力随撞击速度的提高而增大；应力波在颅骨表面的传播以撞击点为圆心的径向上传播，在颅骨一脑组织耦合处急剧衰减；颅底有应力集中区域。该数值模拟的结果与生物试验结果较吻合。结论本研究对颞部撞击致颅脑损伤的诊断和防护有重要意义。