Multiscale active contour model for vessel segmentation

This paper presents a novel multiscale active contour model for vessel segmentation. The model is based on accurate analysis of the vessel structure in the image. According to different scale response of the eigenvalues of local second order derivative (Hessian matrix), a new vessel region information function, which shows a valid estimation of the vesselness measure, is defined. We introduce the posteriori probability estimation into the active contours framework and design a new objective function. The defined objective function is minimized using the variational method, and a new region-based external force is obtained, which is more accurate to the vessel structure and not sensitive to the initial condition. This active contour model combines the obtained region-based and conventional boundary-based force, which aims at finding more accurate vessel edges even when the vessel branches are low contrast or blurry. Furthermore, the proposed model is implemented by an implicit method of level set framework, the solution of which is steady and suitable for various topology changes. Moreover, two new speed functions for vessel segmentation in the level set method are presented, one for fast marching and the other for a narrow-band algorithm. The vessel segmentation experiments compared with previous geometric active contour models are shown on several medical images. The experimental results demonstrate the performance of our approach.     

具有初应力的血管的静态力学仿真分析

血管组织具有非线性和初应力等复杂的力学特性.本文在已有的理论基础上,提出一个含有初始应力的三维理论模型分析血管壁的非线性力学性质.在假设血管壁为均质、正交各向异性、横截面各向同性、不可压缩的条件下,建立具有初应力的血管静态力学本构关系,并根据已有的实验数据通过多曲线拟合方法建立比较完善、相对计算简单的血管壁本构方程.通过与不含初应力条件实验曲线进行比较,结果证明含有初应力的本构方程可以更好地反映血管壁的力学特点,并且数值拟合结果也证实血管壁的初始应力不可忽略.     

Automated generation of a four-dimensional model of the liver using warping and mutual information

The use of mutual information (MI) based alignment to map changes in liver shape and position from exhale to inhale was investigated. Inhale and exhale CT scans were obtained with intravenous contrast for six patients. MI based alignment using thin-plate spine (TPS) warping was performed between each inhale and exhale image set. An expert radiation oncologist identified corresponding vessel bifurcations on the exhale and inhale CT image and the transformation for identified points was determined. This transformation was then used to determine the accuracy of the MI based alignment. The reproducibility of the vessel bifurcation identification was measured through repeat blinded vessel bifurcation identification. Reproducibility [standard deviation (SD)] in the L/R, A/P, and I/S directions was 0.11, 0.09, and 0.14 cm, respectively. The average absolute difference between the transformation obtained using MI based alignment and the vessel bifurcation in the L/R, A/P, and I/S directions was 0.13 cm (SD=0.10 cm), 0.15 cm (SD=0.12 cm), and 0.15 cm (SD-0.14 cm), respectively. These values are comparable to the reproducibility of bifurcation identification, indicating that MI based alignment using TPS warping is accurate to within measurement error and is a reliable tool to aid in describing deformation that the liver undergoes from the exhale to inhale state.     

基于数学形态学的视网膜血管提取算法

目的 影像中血管的分割与特征提取,对疾病的早期诊断具有重要意义。针对很多视网膜血管提取算法分割精度不高的问题,提出了运用数学形态学中的高帽变换的方法对其进行检测。方法 首先,选取结构元素为“圆盘形”的形态学对图像进行高帽变换,经过高帽变换后的图像平滑了图像的背景,同时增强了血管在图像中的对比度。其次,对变换后的图像利用Otsu＇s自动分割法对图像进行阈值分割得到血管的二值图像。再次,根据血管在图像中的结构信息和几何信息,利用基于连通域度量的方法,设置连通域的“面积”和“长宽比”两个阈值,去除虚假目标。最后,为保持血管的连续性,对图像进行一次膨胀运算,可将断裂的血管连接起来,减小了实验的误差。结果 通过上述步骤实现了对血管的提取。结论 结果表明,本文算法能有效提取视网膜眼底图像的血管网络,有较强的分割精度。     

Noise in stenosis measurement using digital subtraction angiography

This paper examines statistical errors in the measurement of arterial stenoses by digital videodensitometry. Images of vessel phantoms were acquired using digital subtraction angiographic techniques with low concentrations of an iodine contrast medium and low levels of x-ray exposure. Effects of the spatial and temporal averaging of image information on signal-to-noise ratios in the stenosis measurement were of primary interest. The influences of iodine concentration, x-ray scatter, veiling glare, x-ray energy spectrum, x-ray exposure, and detective quantum efficiency of the system were also included in the theoretical analysis. The agreement between theoretical calculation and experimental measurement of a simulated vessel was verified using measured values of the imaging system parameters. With a 14.2 mg/ml iodine concentration, using 20 mR per image at the entrance to a 13-cm water phantom, and averaging over a 6-mm length of a vessel 6.2 mm in diameter, the standard deviation in a measurement of a vessel's relative cross-sectional area was about 0.05. The extension of these results to practical applications in vivo is discussed.     

The effect of diameter ratio between vascular substitute and blood vessel on anastomosis

It is necessary to maintain mechanical compatibility between a blood vessel and a vascular substitute to promote encapsulation around the anastomosed part. From this point of view, using linear elastic theory, we had previously performed stress analyses at the part anastomosed by tissue adhesion, in order to propose some methods of preventing stress concentration at this junction. In this study, based on the previous analyses, we have attempted to develop a concept that can be applied under the conditions of operation. That is, the initial diameter of a vascular substitute with high rigidity is chosen larger than that of a blood vessel. This will reduce the stress concentration around the anastomosed part, on average, during expansion of the blood vessel. We analysed the optimum diameter ratio between the vascular substitute and the blood vessel which causes the least stress concentration, on average, during this process, using linear elastic theory. Furthermore, numerical analyses of blood vessel deformation were performed using various nonlinear stress-strain laws. These results were compared to the analytical solution based on linear elastic theory.     

A new concept for ultrasensitive fluorescence measurements of molecules in solution and membrane: 2. The individual immune molecule

In the accompanying original article, the universal theoretical and experimental framework was developed for quantifying one and the same single (selfsame), individual fluorescent-tagged biological molecule without immobilization, hydrodynamic flow or photon burst analysis of fluorescence intensity traces. In the present original article, we describe an application to the detection and identification of circulating anti-glomerular basement membrane antibodies (BMAs) in Goodpasture syndrome. The same single, individual two-color molecule complex was observed among many other molecules. The molecule consisted of the green-tagged antigen, sandwiched autoantibody and red-tagged secondary (detecting) antibody. A 200-fold increase in sensitivity was obtained as compared to the conventional ELISAs on solid phase. This novel concept has several advantages, namely (i) the sensitivity to detect an individual molecule in solution; (ii) the association of the signal with the reaction event, independent of any immobilization procedure and the artifacts thereof; (iii) the assessment of the broad field of natural antibodies. The theoretical and experimental results obtained bring advanced ultrasensitive analytics to the direct investigation of one and the same single, individual immune molecules as exemplified by the experiments performed with Goodpasture antibody. The novel universal theoretical and experimental framework for continuous measuring the same single, individual immune molecule can be readily transferred to other applications.     

锥形血管内血液脉动流的数值模拟

将锥形血管与人体血液的脉动流动联系起来研究发展中的血液流动问题 ,给出了锥形血管的几何模型、血液流动的理论模型、生理边界条件以及计算条件 ;根据人体生理脉动流条件 ,建立了血流平均速度函数 ,并就此对三维锥形血管内的血液脉动流动进行了数值模拟 ,获得心动周期不同时刻的轴向速度、径向速度、断面压力和轴向压力分布曲线。将数值模拟计算结果与实验和分析计算结果进行对照 ,讨论了锥形血管内血液脉动流的特点。     

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。     

Prediction of olfactory response based on age, gender and smoking habits.

The measurement of olfaction has been neglected compared with the other senses. Recently, some progress has been made in the search for an instrument to objectively measure olfaction. This article outlines the early test results of a low cost, computer-based olfactometer which uses the frequency content of evoked potentials to quantify a subject's response to an olfactory stimulus. Clinical trials have been undertaken to establish the validity of the olfactometer and several thousand tests have been carried out using patients with olfactory dysfunctions as well as normals for norm referencing. The paper discusses a theoretical model for olfaction based on the age, gender and smoking habits of a subject. The validity of the model is then compared with the experimental data. The correlation between the model and the experimental results is strong.     

A Magnetic Device to Eliminate Endograft Migration: Theory and Experiment

Endograft migration is a recognized problem in endovascular aneurysm repair, which may lead to aneurysm rupture, acute vessel thrombosis, or occlusion. This study presents a novel device to eliminate endograft migration that involves the use of a ferromagnetic stent graft (internal of vessel) and two magnetic rings (external to vessel, at the two necks of the stent). The magnetic rings (proximal and distal on the graft) with sufficient adhesion force were proposed to eliminate migration without overcompression of the aorta. Specifically, the objectives of the study are (1) to design the geometry and magnetic properties of the magnetic ring based on a mathematical model to produce the necessary tangential force to prevent endograft migration and (2) to validate the theoretical model with in vitro experiments. Our experimental results were in agreement with the numerical model, which showed feasibility of the approach to eliminate migration. This magnetic approach to eliminate endograft migration may lay the foundation for improvement of endograft repair of aortic aneurysm.     

Dose distributions in bifurcated coronary vessels treated with catheter-based photon and beta emitters in intravascular brachytherapy

The dose distributions in the bifurcated vessels treated with intravascular brachytherapyline sources are complicated and depend on the bifurcation geometry consisting of a main and a branch vessel at different angles. To investigate the dosimetric effects at the bifurcation, calculations were performed on branching vessels of various bifurcation angles ranging from 20 degrees to 90 degrees. Two catheter based delivery systems were considered in the calculations using a 40 mm long radioactive sources of 192Ir or 90Sr/Y. It was assumed that the bifurcated vessel was treated in twoseparate source insertions, once for the main vessel and later for the branch vessel. Calculations were performed for different values of source gap from 0 to 9 mm, at the junction of main and branch vessels. Our results indicate that main vessel always receives a higher dose (up to 200%) when the branch vessel is also treated. Hot spots at portions of the main vessel near the junction cannot be totally avoided without severely underdosing the branch vessel. For bifurcation angle greater than 45 degrees, a 4 mm source gap can almost ensure that overdosing of the main vessel does not exceed 60% and underdosing of the branch vessel does not exceed 10% for 192Ir. However, for 90Sr/Y, the same is not possible unless the bifurcation angle is larger than 70 degrees. Dose heterogeneity using 90Sr/Y is more sensitive to the value of source gap than 192Ir because 90Sr/Y source provides a sharper dose-fall-off than 192Ir. For both photon and beta emitters, there is no acceptable solution for bifurcation angles less than 30 degrees, where the activity of the line source has a uniform distributions. Appropriate choice of gap at the junction can only help to reduce either overdosing of the main vessel or underdosing of the branch vessel, but not both.     

Tetramethylbenzidine staining procedure after starch gel electrophoresis of human haemoglobin

The purpose of the present work was to increase the stability of tetramethylbenzidine-stained electrophoretic patterns of human haemoglobin through use of a suitable fixing agent. Since haemoglobin examination is quite important in the study of numerous pathologies, in prenatal analyses and in forensic medicine, it was considered worthwhile to attempt to stabilise the specific tetramethylbenzidine-based stain, which is notoriously unstable. The other stain frequently used is amido black 10 B, a generic protein stain, which reveals both haemoglobin and non-haemoglobin bands, hence interpretation of the results can lead to errors and the identification of false pattern heterogeneity. Following several experimental tests we have observed that it is possible to make tetramethylbenzidine-based stains stable by using a suitable fixative. Treatment with the fixing solution prevents the colour from fading, and can keep it intact for over a year. The method also appears promising for studying haemoglobin in a variety of other species of vertebrates.     

Tetramethylbenzidine staining procedure after starch gel electrophoresis of human haemoglobin

The purpose of the present work was to increase the stability of tetramethylbenzidine-stained electrophoretic patterns of human haemoglobin through use of a suitable fixing agent. Since haemoglobin examination is quite important in the study of numerous pathologies, in prenatal analyses and in forensic medicine, it was considered worthwhile to attempt to stabilise the specific tetramethylbenzidine-based stain, which is notoriously unstable. The other stain frequently used is amido black 10 B, a generic protein stain, which reveals both haemoglobin and non-haemoglobin bands, hence interpretation of the results can lead to errors and the identification of false pattern heterogeneity. Following several experimental tests we have observed that it is possible to make tetramethylbenzidine-based stains stable by using a suitable fixative. Treatment with the fixing solution prevents the colour from fading, and can keep it intact for over a year. The method also appears promising for studying haemoglobin in a variety of other species of vertebrates.     

Retinal vessel segmentation using a multi-scale medialness function

Recently, automated segmentation of retinal vessels in optic fundus images has been an important focus of much research. In this paper, we propose a multi-scale method to segment retinal vessels based on a weighted two-dimensional (2D) medialness function. The results of the medialness function are first multiplied by the eigenvalues of the Hessian matrix. Next, centerlines of vessels are extracted using noise reduction and reconnection procedures. Finally, vessel radii are estimated and retinal vessels are segmented. The proposed method is evaluated and compared with several recent methods using images from the DRIVE and STARE databases.     

Preservation of quadrature Doppler signals from bidirectional slow blood flow close to the vessel wall using an adaptive decomposition algorithm

A novel approach based on the phasing-filter (PF) technique and the empirical mode decomposition (EMD) algorithm is proposed to preserve quadrature Doppler signal components from bidirectional slow blood flow close to the vessel wall. Bidirectional mixed Doppler ultrasound signals, which were echoed from the forward and reverse moving blood and vessel wall, were initially separated to avoid the phase distortion of quadrature Doppler signals (which is induced from direct decomposition by the nonlinear EMD processing). Separated unidirectional mixed Doppler signals were decomposed into intrinsic mode functions (IMFs) using the EMD algorithm and the relevant IMFs that contribute to blood flow components were identified and summed to give the blood flow signals, whereby only the components from the bidirectional slow blood flow close to the vessel wall were retained independently. The complex quadrature Doppler blood flow signal was reconstructed from a combination of the extracted unidirectional Doppler blood flow signals. The proposed approach was applied to simulated and clinical Doppler signals. It is concluded from the experimental results that this approach is practical for the preservation of quadrature Doppler signal components from the bidirectional slow blood flow close to the vessel wall, and may provide more diagnostic information for the diagnosis and treatment of vascular diseases.     

Hemodynamic parameters and early intimal thickening in branching blood vessels

Intimal thickening due to atherosclerotic lesions or intimal hyperplasia in medium to large blood vessels is a major contributor to heart disease, the leading cause of death in the Western World. Balloon angioplasty with stenting, bypass surgery, and endarterectomy (with or without patch reconstruction) are some of the techniques currently applied to occluded blood vessels. On the basis of the preponderance of clinical evidence that disturbed flow patterns play a key role in the onset and progression of atherosclerosis and intimal hyperplasia, it is of interest to analyze suitable hemodynamic wall parameters that indicate susceptible sites of intimal thickening and/or favorable conditions for thrombi formation. These parameters, based on the wall shear stress, wall pressure, or particle deposition, are applied to interpret experimental/clinical observations of intimal thickening. Utilizing the parameters as "indicator" functions, internal branching blood vessel geometries are analyzed and possibly altered for different purposes: early detection of possibly highly stenosed vessel segments, prediction of future disease progression, and vessel redesign to potentially improve long-term patency rates. At the present time, the focus is on the identification of susceptible sites in branching blood vessels and their subsequent redesign, employing hemodynamic wall parameters. Specifically, the time-averaged wall shear stress (WSS), its spatial gradient (WSSG), the oscillatory shear index (OSI), and the wall shear stress angle gradient (WSSAG) are compared with experimental data for an aortoceliac junction. Then, the OSI, wall particle density (WPD), and WSSAG are segmentally averaged for different carotid artery bifurcations and compared with clinical data of intimal thickening. The third branching blood vessel under consideration is the graft-to-vein anastomosis of a vascular access graft. Suggested redesigns reduce several hemodynamic parameters (i.e., the WSSG, WSSAG, and normal pressure gradient [NPG]), thereby reducing the likelihood of restenosis, especially near the critical toe region.     

A multimodality vascular imaging phantom with fiducial markers visible in DSA, CTA, MRA, and ultrasound

The objective was to design a vascular phantom compatible with digital subtraction angiography, computerized tomography angiography, ultrasound and magnetic resonance angiography (MRA). Fiducial markers were implanted at precise known locations in the phantom to facilitate identification and orientation of plane views from three-dimensional (3-D) reconstructed images. A vascular conduit connected to tubing at the extremities of the phantom ran through an agar-based gel filling it. A vessel wall in latex was included around the conduit to avoid diffusion of contrast agents. Using a lost-material casting technique based on a low melting point metal, geometries of pathological vessels were modeled. During the experimental testing, fiducial markers were detectable in all modalities without distortion. No leak of gadolinium through the vascular wall was observed on MRA after 5 hours. Moreover, no significant deformation of the vascular conduit was noted during the fabrication process (confirmed by microtome slicing along the vessel). The potential use of the phantom for calibration, rescaling, and fusion of 3-D images obtained from the different modalities as well as its use for the evaluation of intra- and inter-modality comparative studies of imaging systems are discussed. In conclusion, the vascular phantom can allow accurate calibration of radiological imaging devices based on x-ray, magnetic resonance and ultrasound and quantitative comparisons of the geometric accuracy of the vessel lumen obtained with each of these methods on a given well defined 3-D geometry.     

Numerical evaluation of minimal biochemical test combinations for the identification of Enterobacteriaceae species

Species identification of 572 clinical isolates of Enterobacteriaceae was determined using an in-house biochemical test panel and API 20E. The overall agreement was 82.7 per cent. When a numerical identification programme for Enterobacteriaceae was used to analyze the results of 440 E.coli isolates, the agreement with API 20E increased from 81.4 to 91.1 per cent. Numerical identification was then employed to evaluate 14 routine biochemical test panels used in 12 Swedish laboratories, and an additional 18 potential new test panel variants. The theoretical identification power of the panels was measured by a scoring system, based on simulated test results for the 14 most common species of Enterobacteriaceae. The results showed wide variations in the performance of different panels, with a number of panels being of insufficient quality. Among the 32 test panels, 6 panels indicated excellent performance. These should be further evaluated for routine laboratory performance. Numerical identification methods constitute powerful tools in the hands of the clinical microbiologist to aid in species identification as well as to analyze the quality of identification charts in use.