冠状动脉的三维运动特征提取

提出一种根据X射线造影图像序列提取冠状动脉血管三维运动特征的方法.首先对由两个角度的造影图像重建得到的三维血管骨架进行运动估计,计算出两个时刻间骨架上各点的三维运动向量.然后结合心脏解剖和运动的先验知识,对血管运动进行定性分析,如位移方向、振幅及运动模式.提取、解释运动信息,并采用符号表达,方便医生进行观察和分析.最后给出了对临床得到的造影图像序列进行实验的结果.     

冠状动脉血管的二维提取和运动跟踪

提出了一种基于图像脊提取和snake模型的复合式方法来实现X射线造影图像序列中冠状动脉血管的二维提取和运动跟踪,并分别对临床采集图像序列和模拟图像进行了实验.结果说明,与经典模型相比本算法自动化程度和精度都提高许多.     

基于冠脉造影图像血管树分割的血管狭窄自动识别方法

针对冠状动脉造影图像中的血管狭窄位置进行自动识别,并且定量评估其狭窄程度,为临床医生提供一种计算机辅助诊断方法,从而提高对冠状动脉狭窄的诊断准确率,同时减轻医生的劳动强度。所提出的基于冠脉造影图像的血管狭窄自动识别方法包括血管树分割以及血管狭窄识别两部分。在血管树分割部分,首先通过基于Frangi Hessian的改进模型进行图像增强,随后利用基于统计学区域融合方法对血管区域进行分割。在血管狭窄识别部分,首先利用水平集算法对分割结果进行细化获得血管骨架,随后提取血管边缘进行血管直径测量,最后采用局部最小点法计算整幅图像血管段狭窄的百分比,对狭窄段进行定位并分级。实验在153例患者的血管造影图像中检测出狭窄共计208段,其中轻度84段,中度42段,重度82段。统计分析结果显示,血管狭窄识别平均准确率为93.59%,敏感性为88.76%,特异性为95.58%,阳性预测值为90.51%,表明该方法能够有效地检测和定量评价动脉血管的狭窄程度,有助于心血管疾病的临床诊断。     

基于Hessian矩阵的DSA图像冠状动脉直径的测量

【摘要】目的:通过对冠状动脉血管的数字减影血管造影技术（DSA）图像进行分析处理,得到血管的骨架与中心线,从而实现血管直径测量。方法:采用MATLAB语言进行图像处理,在对DSA图像平滑及均衡化处理后,得到血管的骨架与中心线。以Hessian矩阵的特征向量为参考方向,做与血管垂直的直线,利用该直线与血管骨架的两个交点求得血管直径。结果:实现冠状动脉血管中心线、骨架的自动提取和冠状动脉血管直径的自动测量。结论:对于随机抽取的DSA图像,该方法均取得理想的冠状动脉血管中心线与骨架,以及精确的冠状动脉血管直径数值,可为操作人员提供丰富的信息,具有一定的实用价值。     

血管造影图像序列中冠状动脉的三维运动估计

提出了由两个角度的单面血管造影图像序列估计冠状动脉骨架树三维运动的算法。首先对冠状动脉造影图像序列进行二维预处理和二维运动估计。然后根据冠脉造影系统的透视投影模型得到两幅不同角度的造影图像之间的几何变换关系，以及空间点三维坐标的计算方法。最后，在对整个图像序列进行分析的过程中，将三维运动估计与重建结合起来，得到各骨架点的三维运动向量。采用临床得到的冠状动脉造影图像序列对算法进行了验证，并分析了误差源。     

ICUS图像序列中冠状动脉的三维重建和形态测量

针对冠状动脉内超声(ICUS)图像序列中血管的三维重建问题,提出一种从连续回撒超声导管获取的、覆盖多个心动周期的ICUS序列中准确重建冠脉血管、并定量测量其形态结构参数的方法.首先利用在导管回撤路径起点采集的两幅近似垂直的X射线冠脉造影(CAG)图像之间的交叉信息,重建出导管的回撤路径,然后从各帧ICUS图像中提取出血管壁的内外轮廓;在对ICUS序列中由心脏运动所致的运动伪影进行补偿之后,选择出在各心动周期的同一时相处采集的ICUS帧,并将其沿三维导管路径顺序排列;最后采用NURBS曲面拟合技术,完成血管的三维重建.根据该三维血管模型,对临床重要的血管形态参数进行测量,采用临床图像数据进行验证.实验结果证明,较之仅采用CAG图像或ICUS序列重建出的血管模型的测量结果,该方法更为精确.     

基于X射线相位衬度成像技术的兔眼球血管重建

目的 利用X射线相位衬度成像技术构建兔眼血管网的三维可视化模型,观测兔眼虹膜血管的形态学特征。结果 用硫酸钡对新西兰白兔眼球血管进行造影,利用X射线相位衬度成像技术采集离体兔眼样本的高精度投影图像。图像经由滤波反投影法重建出断层图像,利用Amira 5.2.2软件进行三维重建。方法 高精度投影图像中眼球主干血管清晰连贯,能够观测到部分细小血管的分布及走向,可分辨的最小血管直径约为10 μm;CT扫描图像三维重建后得到兔眼血管网的三维模型,精确到虹膜动脉大环4级分支结构,最小血管直径可达40 μm。结论 利用X射线相位衬度成像技术可以比较清楚地观察到兔眼血管,并且能够在一定程度上构建出血管网的三维可视化模型,为眼球内血管血流动力学分析提供依据,对青光眼的临床研究具有参考价值。     

基于电磁定位的超声图像与CT图像的融合方法

在超声引导经皮介入治疗中,为集成多模态图像信息来弥补单一超声图像的不足,提出一种实时超声图像与CT图像的融合方法,使临床医生在实施介入治疗时得到患者病灶的多模态图像信息成为可能。首先,利用电磁定位系统,得到12个铅球球心的磁场坐标和CT图像坐标,利用两个点集的ICP配准算法,将磁场坐标系和CT图像坐标系进行配准;其次,利用电磁定位系统,将和超声探头固连在一起的电磁传感器自身坐标系与磁场坐标系进行配准;然后,利用超声探头的机械设计尺寸,将超声坐标系与电磁传感器自身坐标系进行配准;最后,通过多个坐标系的转换关系将超声坐标系配准到CT图像坐标系,最终将实时超声图像统一到CT图像中,并在软件中测量融合误差。在该方法下,实时超声图像与CT图像的融合误差为(0.71±0.03)mm,在软件中可以清晰地看到两种图像的实时融合效果。因此,该方法可以有效地将实时超声图像与CT图像进行融合,为介入治疗的精准性提供相应的技术支持。     

基于图像融合的冠状动脉三维重建方法的研究进展

冠状动脉三维重建是心血管力学中不可或缺的一部分,同时可为医生直观确定病变位置、病变程度提供便利。基于图像融合的冠状动脉三维重建能将两种图像的优点结合起来,为医生和研究人员提供血管三维走向、血管形态及斑块形态等信息。本文概括了近年来基于图像融合的冠状动脉三维重建方法,包括血管内超声(intravenous ultrasound,IVUS)与冠状动脉造影(coronary arteriography,CAG)图像融合、光学相干断层扫描技术(optical coherence tomography,OCT)与CAG图像融合、计算机断层扫描血管造影(computed tomography arteriography,CTA)与IVUS或OCT图像融合的三维重建方法,并阐述了各方法在临床以及力学计算研究中的应用现状。     

一种分割冠状动脉X射线造影图像的有效方法

目的 提出一种简单有效的方法进行冠状动脉X射线造影图像的分割。方法 基于Hessian矩阵的多尺度滤波和区域增长等算法,其中多尺度滤波用来增强造影图像中的血管,然后利用多种子点区域增长算法从增强后的图像中提取冠状动脉树。结果 该方法对于造影图像中血管状结构非常敏感,能够清晰提取出冠状动脉树中较细小的末梢,并能有效抑制噪声。结论 该方法适合于分割冠状动脉造影,适用于冠状动脉造影的精确量化分析。     

IVUSAngio Tool: A publicly available software for fast and accurate 3D reconstruction of coronary arteries

There is an ongoing research and clinical interest in the development of reliable and easily accessible software for the 3D reconstruction of coronary arteries. In this work, we present the architecture and validation of IVUSAngio Tool, an application which performs fast and accurate 3D reconstruction of the coronary arteries by using intravascular ultrasound (IVUS) and biplane angiography data. The 3D reconstruction is based on the fusion of the detected arterial boundaries in IVUS images with the 3D IVUS catheter path derived from the biplane angiography. The IVUSAngio Tool suite integrates all the intermediate processing and computational steps and provides a user-friendly interface. It also offers additional functionality, such as automatic selection of the end-diastolic IVUS images, semi-automatic and automatic IVUS segmentation, vascular morphometric measurements, graphical visualization of the 3D model and export in a format compatible with other computer-aided design applications. Our software was applied and validated in 31 human coronary arteries yielding quite promising results. Collectively, the use of IVUSAngio Tool significantly reduces the total processing time for 3D coronary reconstruction. IVUSAngio Tool is distributed as free software, publicly available to download and use.     

Virtual 3D IVUS vessel model for intravascular brachytherapy planning. I. 3D segmentation, reconstruction, and visualization of coronary artery architecture and orientation

Intravascular brachytherapy (IVB) can significantly reduce the risk of restenosis after interventional treatment of stenotic arteries, if planned and applied correctly. To facilitate computer-based IVB planning, a three-dimensional vessel model has been derived from information on coronary artery segments acquired by intravascular ultrasound (IVUS) and biplane angiography. Part I describes the approach of model construction and presents possibilities of visualization. The vessel model is represented by a voxel volume. Polygonal information about the vessel wall structure is derived by segmentation from a sequence of IVUS images automatically acquired ECG gated during pull back of the IVUS transducer. To detect horizontal, vertical, and radial contours, modified Canny-Edge and Shen-Castan filters are applied on Cartesian and polar coordinate representations of the IVUS tomograms as edge detectors. The spatial course of the vessel wall layers is traced in reconstructed longitudinal IVUS scans. By resampling the sequence of IVUS frames the voxel volume is obtained. For this purpose the frames are properly located in space and augmented with additional intermediate frames generated by interpolation. Their spatial location and orientation is derived from biplane X-ray angiography which is performed simultaneously. For resampling, two approaches are proposed: insertion of the vertices of the rectangular goal grid into the cells of a deformed hexahedral mesh derived from the IVUS sequence, and insertion of the vertices of the hexahedral mesh into the cells of the rectangular grid. Finally, the vessel model is visualized by methods of combined volume and polygon rendering. The segmentation process is verified as being in good agreement with results obtained by manual contour tracing with a commercial system. Our approach of construction of the vessel model has been implemented into an interactive software system, 3D IVUS-View, serving as the basis of a future system for intracoronary brachytherapy treatment planning being currently under development (Part II).     

Accurate 3D reconstruction of complex blood vessel geometries from intravascular ultrasound images: in vitro study

We present a technique that accurately reconstructs complex three dimensional blood vessel geometry from 2D intravascular ultrasound (IVUS) images. Biplane x-ray fluoroscopy is used to image the ultrasound catheter tip at a few key points along its path as the catheter is pulled through the blood vessel. An interpolating spline describes the continuous catheter path. The IVUS images are located orthogonal to the path, resulting in a non-uniform structured scalar volume of echo densities. Isocontour surfaces are used to view the vessel geometry, while transparency and clipping enable interactive exploration of interior structures. The two geometries studied are a bovine artery vascular graft having U-shape and a constriction, and a canine carotid artery having multiple branches and a constriction. Accuracy of the reconstructions is established by comparing the reconstructions to (1) silicone moulds of the vessel interior, (2) biplane x-ray images, and (3) the original echo images. Excellent shape and geometry correspondence was observed in both geometries. Quantitative measurements made at key locations of the 3D reconstructions also were in good agreement with those made in silicone moulds. The proposed technique is easily adoptable in clinical practice, since it uses x-rays with minimal exposure and existing IVUS technology.     

Accurate 3D reconstruction of complex blood vessel geometries from intravascular ultrasound images: in vitro study

We present a technique that accurately reconstructs complex three dimensional blood vessel geometry from 2D intravascular ultrasound (IVUS) images. Biplane x-ray fluoroscopy is used to imagethe ultrasound catheter tip at a few key points along its path as the catheter is pulled through the blood vessel. An interpolating spline describes the continuous catheterpath. The IVUS images are located orthogonal to the path, resulting in a non-uniform structured scalar volume of echo densities. Isocontour surfaces are used to view the vessel geometry, while transparency and clipping enable interactive exploration of interior structures. The two geometries studied are a bovine artery vascular graft having U-shapeand a constriction, and a canine carotid artery having multiple branches and a constriction. Accuracy of the reconstructions is established by comparing the reconstructions to (1) silicone moulds of the vessel interior, (2) biplane x-ray images, and (3) the original echo images. Excellent shape and geometry correspondence was observed in both geometries. Quantitative measurements made at key locations of the 3D reconstructions also were in good agreement with those made in silicone moulds. The proposed technique is easily adoptable in clinical practice, since it uses x-rays with minimal exposure and existing IVUS technology.     

Derivation of spatial information from biplane multidirectional coronary angiograms

Modern biplane multidirectional isocentric X-ray equipment delivers the image information necessary for spatial computations from two simultaneous 2-dimensional coronary angiographic pictures. Using the tools of analytical geometry, the spatial position of well definable points in the fields of view of the two image-intensifiers can be calculated from their corresponding projections knowing the geometrical properties of the system stands. The method developed is independent of the angle between the projections and is applicable even if hemiaxial views are used. The mathematical formulas necessary for these spatial computations are derived. By means of calculating the radiological magnification factor, the method was validated using a wire with known diameter as reference object. 360-diameter measurements of the wire filmed in 18 different simultaneous biplane projections resulted in a mean error of 3.14%. In addition, catheter measurements of routine coronary angiograms yielded a mean diameter of 2.64 +/- 0.19 mm (mean +/- SD, real diameter 2.66 mm). Conclusion: Using this algorithm, a reliable determination of spatial coordinates of distinct points of interest is possible as prerequisite for absolute quantitative measurements from biplane angiograms.     

Intravascular ultrasound studies of arterial elastic mechanics.

A number of new methods are available for the measurement of large artery elastic properties in human subjects in vivo. One powerful tool which has recently been applied to the study of large artery mechanics is intravascular ultrasound (IVUS). IVUS studies are performed using a high frequency ultrasound transducer mounted on the tip of a catheter. This catheter is inserted into a blood vessel and detailed cross-sectional images of the vessel, are obtained from within the lumen. IVUS techniques have been used to study wall mechanics of the human aorta, as well as peripheral and coronary arteries in normal human subjects and in patients with vascular disease. This paper reviews IVUS studies of human arterial elasticity and discusses the strengths and weaknesses of this emerging technique as it is applied to the understanding of arterial mechanical properties.     

Geometrical accuracy and fusion of multimodal vascular images: a phantom study

The aim of this work was to compare the geometrical accuracy of x-ray angiography, magnetic resonance imaging (MRI), x-ray computed tomography (XCT), and ultrasound imaging (B-mode and IVUS, or intravascular ultrasound) for measuring the lumen diameters of blood vessels. An image fusion method was also developed to improve these measurements. The images were acquired from a phantom that mimic vessels of known diameters. After acquisition, the multimodal images were coregistered by manual alignment of fiducial markers, and then by maximization of mutual information. The fusion method was performed by means of a fuzzy logic modeling approach followed by a combination process based on a possibilistic theory. The results showed (i) the better geometrical accuracy of XCT and IVUS compared to the other modalities, and (ii) the better accuracy and smaller variability of fused images compared to single modalities, with respect to most diameters investigated. For XCT, the error varied from 0.4% to 5.4%, depending on the vessel diameter that ranged from 0.93 to 6.24 mm. For IVUS, the error ranged from -0.3% to 1.7% but the smallest vessel (0.93 mm) could not be investigated because of the probe size. Compared to others fusion schemes, the XCT-MRI fused images provided the best results for both accuracy (from -1.6% to 0.2% for the three largest vessels) and robustness (mean relative error of 1.9%). To conclude, this work underlined both the usefulness of the multimodality vascular phantom as a validation tool and the utility of image fusion in the vascular context.     

Fluid Dynamic Analysis in a Human Left Anterior Descending Coronary Artery with Arterial Motion

A computational fluid dynamic (CFD) analysis is presented to describe local flow dynamics in both 3-D spatial and 4-D spatial and temporal domains from reconstructions of intravascular ultrasound (IVUS) and bi-plane angiographic fusion images. A left anterior descending (LAD) coronary artery segment geometry was accurately reconstructed and subsequently its motion was incorporated into the CFD model. The results indicate that the incorporation of motion had appreciable effects on blood flow patterns. The velocity profiles in the region of a stenosis and the circumferential distribution of the axial wall shear stress (WSS) patterns in the vessel are altered with the wall motion introduced in the simulation. The time-averaged axial WSS between simulations of steady flow and unsteady flow without arterial motion were comparable (–0.3 to 13.7 Pa in unsteady flow versus –0.2 to 10.1 Pa in steady flow) while the magnitudes decreased when motion was introduced (0.3–4.5 Pa). The arterial wall motion affects the time-mean WSS and the oscillatory shear index in the coronary vessel fluid dynamics and may provide more realistic predictions on the progression of atherosclerotic disease.     

The effect of vascular curvature on three-dimensional reconstruction of intravascular ultrasound images

Objective: To characterize the effect of vessel curvature on the geometric accuracy of conventional three-dimensional reconstruction (3DR) algorithms for intravascular ultrasound image data.Background: A common method of 3DR for intravascular ultrasound image data involves geometric reassembly and volumetric interpolation of a spatially related sequence of tomographic cross sections generated by an ultrasound catheter withdrawn at a constant rate through a vascular segment of interest. The resulting 3DR is displayed as a straight segment, with inherent vascular curvature neglected. Most vascular structures, however, are not straight but curved to some degree. For this reason, vascular curvature may influence the accuracy of computer-generated 3DR.Methods: We collected image data using three different intravascular ultrasound catheters (2.9 Fr, 4.3 Fr, 8.0 Fr) during a constant-rate pullback of 1 mm/sec through tubing of known diameter with imposed radii of curvature ranging from 2 to 10 cm. Image data were also collected from straight tubing. Image data were digitized at 1.0-mm intervals through a length of 25 mm. Two passes through each radius of curvature were performed with each intravascular ultrasound catheter. 3DR lumen volume for each radius of curvature was compared to that theoretically expected from a straight cylindrical segment. Differences between 3DR lumen volume of theoreticalversus curved (actual) tubes were quantified as absolute percentage error and categorized as a function of curvature. Tubing deformation error was quantified by quantitative coronary angiography (QCA).Results: Volumetric errors ranged from 1% to 35%, with an inverse relationship demonstrated between 3DR lumen volume and segmental radius of curvature. Higher curvatures (r<6.0 cm) induced greater lumen volume error when compared to lower curvatures (r>6.0 cm). This trend was exhibited for all three catheters and was shown to be independent of tubing deformation artifacts. QCA-determined percentage diameter stenosis indicated no deformation error as a function of curvature. Total volumetric error contributed by tubing deformation was estimated to be 0.05%.Conclusions: Catheter-dependent geometrical error arises in three-dimensionally reconstructed timed linear pullbacks of intravascular ultrasound images due in part to uniplanar vascular curvature. Three-dimensional reconstruction of timed linear pullbacks is robust for vessels with low radii of curvature; however, careful interpretation of three-dimensional reconstructions from timed linear pullbacks for higher radii of curvature is warranted. These data suggest that methods of spatially correct three-dimensional reconstruction of intravascularultrasound images should be considered when more pronounced vascular curvature is present.     

Conversion of left ventricular endocardial positions from patient-independent co-ordinates into biplane fluoroscopic projections

Electrocardiographic body surface mapping is used clinically to guide catheter ablation of cardiac arrhythmias by providing an estimate of the site of origin of an arrhythmia. The localisation methods used in our group produce results in left-ventricular cylinder co-ordinates (LVCCs), which are patient-independent but hard to interpret during catheterisation in the electrophysiology laboratory. It is preferable to provide these results as three-dimensional (3D) co-ordinates which can be presented as projections in the biplane fluoroscopic views that are used routinely to monitor the catheter position. Investigations were carried out into how well LVCCs can be converted into fluoroscopic projections with the limited anatomical data available in contemporary clinical practice. Endocardial surfaces from magnetic resonance imaging (MRI) scans of 24 healthy volunteers were used to create an appropriate model of the left-ventricular endocardial wall. Methods for estimation of model parameters from biplane fluoroscopic images were evaluated using simulated biplane data created from these surfaces. In addition, the conversion method was evaluated, using 107 catheter positions obtained from eight patients, by computing LVCCs from biplane fluoroscopic images and reconstructing the 3D positions using the model. The median 3D distance between reconstructed positions and measured positions was 4.3 mm.