Multichannel magnetocardiographic measurements with a physical thorax phantom

Artificial dipolar sources were applied inside a physical thorax phantom to experimentally investigate the accuracy obtainable for non-invasive magnetocardiographic equivalent current dipole localisation. For the measurements, the phantom was filled with saline solution of electrical conductivity 0.21 Sm⁻¹. A multichannel cardiomagnetometer was employed to record the magnetic fields generated by seven dipolar sources at distances from 25 mm to 145 mm below the surface of the phantom. The inverse problem was solved using an equivalent current dipole in a homogeneous boundary element torso model. The dipole parameters were determined with a non-linear least squares fitting algorithm. The signal-to-noise ratio (SNR) and the goodness of fit of the calculated localisations were used in assessing the quality of the results. The dependence between the SNR and the goodness of fit was derived, and the results were found to correspond to the model. With SNR between 5 and 10, the average localisation error was found to be 9±8 mm, while for SNR between 30 and 40 and goodness of fit between 99.5% and 100%, the average error reduced to 3.2±0.3 mm. The SNR values obtained in this study were also compared with typical clinical values of SNR.     

Bone Age Assessment in Young Children Using Automatic Carpal Bone Feature Extraction and Support Vector Regression

Boundary extraction of carpal bone images is a critical operation of the automatic bone age assessment system, since the contrast between the bony structure and soft tissue are very poor. In this paper, we present an edge following technique for boundary extraction in carpal bone images and apply it to assess bone age in young children. Our proposed technique can detect the boundaries of carpal bones in X-ray images by using the information from the vector image model and the edge map. Feature analysis of the carpal bones can reveal the important information for bone age assessment. Five features for bone age assessment are calculated from the boundary extraction result of each carpal bone. All features are taken as input into the support vector regression (SVR) that assesses the bone age. We compare the SVR with the neural network regression (NNR). We use 180 images of carpal bone from a digital hand atlas to assess the bone age of young children from 0 to 6 years old. Leave-one-out cross validation is used for testing the efficiency of the techniques. The opinions of the skilled radiologists provided in the atlas are used as the ground truth in bone age assessment. The SVR is able to provide more accurate bone age assessment results than the NNR. The experimental results from SVR are very close to the bone age assessment by skilled radiologists.     

Optimization of the protrusion shape for a couette-type flow

A study is made of the longitudinal 2D viscous steady flow and heat flux between two plates. Optimal shape design problems are solved in explicit form and shown to have unique global extrema. Conformal mappings are used to bring the problems into a fixed domain and solve them as Dirichlet boundary value problems in the form of Cauchy integrals and series expansions. For the simplest problem statement the optimum is shown to coincide with the well-known concrete dam outline of constant hydraulic gradient.     

Numerical solution of a drug displacement problem with bounded state variables

The interaction of the two drugs warfarin and phenylbutazone has previously been considered as a time-optimal control problem with state inequality constraints. We include bounds for the control and show that necessary optimality conditions and junction conditions for bounded state variables lead to boundary value problems with switching and junction conditions. A special version of the multiple-shooting algorithm is employed for solving the different types of boundary value problems. The switching structure of the optimal control is determined for a range of parameters in the state constraint. Owing to the special structure of the control, a state space solution is obtained in a first step which reduces the numerical complexity of the problem. It is shown how the numerical results can be used to compute the generalized gradient of the optimal value function explicitly.     

分形理论的骨肿瘤边界特性的研究

[目的]探讨一种有效反映骨肿瘤边界特性的分析方法。[方法]采用分形理论对骨肿瘤边缘组织进行分析研究。[结果]分形维数能较好地反映肿瘤边缘组织的浸润性生长。[结论]分形维数从某种意义上表征了骨肿瘤的边界特性。     

基于边界信息的医学图像三维插值

目的Cubic卷积插值是医学图像三维插值的常用方法,针对其插值处的结果边界模糊和精度不高的缺陷,建立一种精确度较高的插值方法。方法首先通过模糊对比度增强精确定位图像边界,再运用形态学运算确定出新插值图像边界,对于新插值图像边界点采用最佳匹配对应点插值;对于非边界点采用一种新的Cubic卷积插值方法确定其灰度值。结果本文方法的均方差、不符合像素点数和最大误差均小于传统插值方法。结论本文提出的方法具有较高的精确性。     

肝局灶性病变边界和周围肝组织的弹性特征及其影响因素分析

目的:定性分析实时剪切波弹性成像(shear wave elastography,SWE)图像上肝局灶性病变(focal liver lesion,FLL)边界和周围肝组织的弹性特征及相关影响因素。方法:选取2012年2月至2013年12月于中山大学附属第一医院就诊的152例FLL患者(152个病灶),所有患者均行FLL及其周围肝组织SWE检查,同时记录其临床及实验室指标,分析FLL的弹性边界(清楚或不清楚)、病变周围肝组织弹性分布类型及两者的影响因素。结果:本研究共纳入良性病变26例,恶性病变126例。良性病变中25例(96.2%)表现为弹性边界清楚,1例(3.8%)表现为弹性边界不清;恶性病变中82例(65.1%)表现为弹性边界清楚,44例(34.9%)表现为弹性边界不清。多因素分析显示,病变良恶性是弹性边界是否清楚的独立影响因素(P<0.05);良、恶性病变周围肝组织弹性分布表现为A型(均匀蓝色)、B型(蓝绿色)、C型(不均匀呈五彩状)分别为20例(76.9%)、6例(23.1%)、0例和17例(13.5%)、60例(47.6%)、49例(38.9%);病变周围肝组织的弹性分布类型(A型、B型、C型)在良恶性病变、有无病毒性肝炎背景、不同性别及不同白蛋白、总胆红素、丙氨酸转氨酶水平之间差异有统计学意义(均P<0.05),而在不同大小病变之间的分布类型差异无统计学意义(P=0.346)。结论:定性分析FLL边界和周围肝组织的弹性特征可为FLL的良恶性鉴别诊断提供参考,FLL边界和周围肝组织弹性特征受病变性质及肝病背景影响,而与病变大小无关。边界弹性特征鉴别诊断不同类型FLL仍需进一步的定量研究。     

A neural architecture for visual motion perception: Group and element apparent motion

A neural network model of motion segmentation by visual cortex is described. The model's properties are illustrated by simulating on the computer data concerning group and element apparent motion, including the tendency for group motion to occur at longer ISIs and under conditions of short visual persistence. These phenomena challenge recent vision models because the switch between group and element motion is determined by changing the timing of image displays whose elements flash on and off but do not otherwise move through time. The model clarifies the dependence of short-range and long-range motion on a spatial scale. Its design specifies how sustained response cells and transient response cells cooperate and compete in successive processing stages to generate motion signals that are sensitive to direction-of-motion, yet insensitive to direction-of-contrast. Properties of beta motion, phi motion, gamma motion, and Ternus motion are explained. A number of prior motion models are clarified, transformed, and unified, including the Reichardt model, Marr-Ullman model, Burt-Sperling model, Nakayama-Loomis model, and NADEL model. Apparent motion and real motion generate testably different model properties. The model clarifies how preprocessing of motion signals by a motion OC Filter is joined to long-range cooperative motion mechanisms in a motion CC Loop to control phenomena such as induced motion, motion capture, and motion after effects. The total model system is a motion Boundary Contour System (BCS) that is computed in parallel with the static BCS of Grossberg and Mingolla before both systems cooperate to generate a boundary representation for 3-D visual form perception.     

Proteoglycan 4 (PRG4) synthesis and immunolocalization in bovine meniscus.

Proteoglycan 4 (PRG4) is synthesized and secreted into the synovial fluid by articular chondrocytes and synovial cells, lining the cavity of joints. A thin layer of PRG4 is also present at the articular surface, where it appears to be involved in boundary lubrication. This study investigated if PRG4 is also synthesized and secreted by the cells within meniscus, and if PRG4 is also present in, and at the surface of, meniscus. PRG4 was visualized in sections of bovine calf menisci by immunohistochemistry. PRG4 was detected in two regions: (1) at the femoral and tibial surfaces of the meniscus, and within cells below these surfaces; and (2) within and near cells along the radial tie fibers and circumferential fibers. From meniscus tissue harvested from these surfaces, PRG4 was extracted with 4M GuHCl and quantified by ELISA. There was 0.20 +/- 0.01 and 0.25 +/- 0.04 microg PRG4/cm(2) area of lateral and medial meniscus surface, respectively. ELISA analysis of spent medium from other samples of meniscus surface tissue incubated in medium supplemented with serum and ascorbate showed that 8.1 +/- 1.1 microg PRG4/cm(2) area of meniscus surface was secreted over six days. These results demonstrate that PRG4 is synthesized and secreted by certain cell populations in the meniscus, and that PRG4 is present in the meniscus at surfaces and also internal fibers where it may contribute to boundary lubrication.     

Overcoming gendered and professional hierarchies in order to facilitate escalation of care in emergency situations: The role of standardised communication protocols

It has been suggested that as many as 23,000 in-hospital cardiac arrests in the UK could be prevented with earlier detection and intervention (Hodgetts et al., 2002). Cases of ‘failure to rescue’ are often linked with difficulties relaying and interpreting information across occupational and professional boundaries. Standardised communication protocols have been recommended as a means of enabling the transmission of concise, salient information, licensing and empowering the individual to overcome established hierarchies in speaking out and asking for help. This paper critically examines the current discourse around such protocols. We find that there is a paucity of evidence regarding the complex relationship between social contexts, individual applications of these protocols and short- and long-term impact on safety and ‘failure to rescue’ rates. The paper highlights the complexities of the underlying power dynamics that are located within gendered and occupational hierarchies and explores the role of standardised communication protocols as a potential boundary object. The paper discusses the potential for these protocols to inter-relate and act as a mediating boundary object between nursing and medical staff, enabling understanding and sharing of cultural context.