一种快速有效的医学图像灰度插值算法

介绍一种用于快速有效的医学图像灰度插值算法。通过在两幅已知图像上寻找对应点，有效地解决了线性插值边界模糊的问题，同时避免了基于形状的插值算法中图像分割的问题，具有较强的适用范围。实验结果表明此算法能得到令人满意的插值结果。     

Activation cross-sections of proton induced reactions on natural Ni up to 65 MeV

Production cross-sections of the ^natNi(p,x)^60,61Cu, ^56,57Ni, ^55,56,57,58Co nuclear reactions were measured in five experiments up to 65 MeV by using a stacked foil activation technique. The results were compared with the available literature values, predictions of the nuclear reaction model codes ALICE-IPPE, TALYS-1.4, and extracted data from the TENDL-2012 library. Spline fits were made on the basis of selected data, from which physical yields were calculated and compared with the literature values. The applicability of the ^natNi(p,x)⁵⁷Ni, ⁵⁷Co reactions for thin layer activation (TLA) was investigated. The production rate for ⁵⁵Co was compared for proton and deuteron induced reactions on Ni.     

Numerical determination of extended semi integrals and semi differentials by using spline cubic functions. Applications to an EE reversible mechanism in cyclic voltammetry

In this work, we propose a new general method based on the use of cubic spline functions, suitable for the numerical determination of extended semi integrals and semi differentials. The procedure combines these interpolation functions with different numerical integration and differentiation standard methods, including commercial software. The method has been applied to the electrochemical reduction of the meso-tetra(4-N-methylpyridyl)porphyrin in acidic aqueous solution, where this compound exhibits a two-electron wave in cyclic voltammetry. In this work, we determine the semi differential of the current and demonstrate that the signals obtained correspond to an EE process, where both electrochemical steps are reversible and their formal potentials are very close.     

Assessment of myocardial regional strain and strain rate by tissue tracking in B-mode echocardiograms

To date, established ultrasonic methods for myocardial regional deformation recovery are based on the Doppler effect, which has inherent limitations restricting its accuracy and use. The reported time domain methods show in vivo insufficient accuracy. A novel approach is elaborated mimicking the human observer who reaches robust diagnosis upon the B-mode data. In a region-of-interest (ROI), acoustic markers stable for tracking are selected. A weighting index presenting the quality of tracking of each marker is used for spatial polynomial fitting. For the feasibility study, a simple straight ROI was selected, which matches the septum. A thorough proof of concept is provided by comparing with a gold standard method and by applying the method to clinical datasets. The peak systolic longitudinal strains of 12 normals were -15% + -2.3% and, of 12 patients with a light-to-mild dysfunction of the apical-septal segment, they were -9% + -0.8% (p < 0.05). Enhancements of the method using spline fitting are introduced.     

A Visual study of surface potentials and Laplacians due to distributed neocortical sources: Computer simulations and evoked potentials

Summary A "picture book" of surface potentials, Laplacians, and magnetic fields due to distributed, neocortical sources is presented. The mathematically simulated data is based on 4200 current sources at the macrocolumn scale. Estimated scalp surface maps are based on the three-concentic spheres model of the head. Emphasis is placed on the effects of sampling with a limited number of electrodes, the choice of reference electrode, and the use of the spline Laplacian to improve spatial resolution. The spline Laplacian is applied to median and ulnar nerve somatosensory evoked potentials and to auditory evoked potentials including P300. Substantial improvement in spatial resolution over conventional methods is obtained. The implementation of practical high resolution EEG systems based on the spline Laplacian is considered.The authors greatfully acknowledge the technical assistance of Chris Fritton, Laurie Orth, and Chiraprakash Nayak. This research was supported by NIH grant RO1 NS24314.Invited paper, Submitted to Brain Topography, July, 1991     

提高回归模型拟合优度的策略(Ⅳ)——优化计分变换与其他变量变换

本文目的是介绍第四种提高回归模型拟合优度的策略,即优化计分变换与其他变量变换。具体方法包括以下几个方面:①第一,对多值名义自变量采取"优化计分变换";②对有序自变量分别采取"单调变换"与"优化计分变换";③对定量自变量分别采取"样条变换"和"单调样条变换";④对定量因变量分别采取"样条变换""单调样条变换"和"BOX-COX变换"。全部变量变换方法组合起来共12种,共创建了12个多重非线性回归模型。依据"拟合优度评价指标"的取值,从12个回归模型中挑选出一个,即本文中的"模型1",其"均方误差平方根=0.30935、R~2=0.9586、调整R~2=0.9527"。结合本期科研方法专题同类文章的结果和结论,得出提高回归模型拟合优度的策略主要在于以下四点:①应对"定量因变量""定量自变量"和"多值有序自变量"采取合适的变量变换方法;②在拟合回归模型的过程中,应尽可能多地引入派生变量;③应假定回归模型中不含截距项;④在构建回归模型的过程中,应尽可能多地使用筛选自变量的策略,如"前进法""后退法"和"逐步法"。     

变量变换回归分析(Ⅰ)——拟合含间断点资料的方法

本文目的是介绍一种能很好地拟合具有间断点资料的方法。当资料中具有明确的间断点或整个资料包含多段不同变化趋势的曲线类型时,为了提高曲线回归模型对资料的拟合优度,需要充分发挥"节点"的作用。可基于两种不同视角来利用"节点":其一,人为设定不同数目的节点,利用样条变换方法拟合分段多项式曲线;其二,在客观存在的节点上,求曲线的一阶乃至四阶导数,并据此构建曲线回归模型。得到的结论是:后者的拟合效果优于前者。     

Bidirectional elastic image registration using B-spline affine transformation

A registration scheme termed as B-spline affine transformation (BSAT) is presented in this study to elastically align two images. We define an affine transformation instead of the traditional translation at each control point. Mathematically, BSAT is a generalized form of the affine transformation and the traditional B-spline transformation (BST). In order to improve the performance of the iterative closest point (ICP) method in registering two homologous shapes but with large deformation, a bidirectional instead of the traditional unidirectional objective/cost function is proposed. In implementation, the objective function is formulated as a sparse linear equation problem, and a sub-division strategy is used to achieve a reasonable efficiency in registration. The performance of the developed scheme was assessed using both two-dimensional (2D) synthesized dataset and three-dimensional (3D) volumetric computed tomography (CT) data. Our experiments showed that the proposed B-spline affine model could obtain reasonable registration accuracy.     

Effects of Various Parameters on Lateral Displacement Estimation in Ultrasound Elastography

Complementary to axial, lateral displacement and strain can provide important information on the biological soft tissues. In this paper, the effects of key parameters (i.e., lateral displacement, pitch, beamwidth, beam overlap and interpolation) on lateral displacement estimation were investigated, in simulations and homogeneous phantom experiments, using lateral rigid motion only to study its fundamentals separately from the effects of axial motion and 2-D deformation on lateral displacement estimation. The performance of the lateral motion estimator was evaluated by measuring its associated bias, jitter and correlation coefficient. Simulation results showed that the bias and jitter of the lateral displacement estimation and correlation coefficient of RF signals undergo periodic variations depending on the lateral displacement, with a period equal to the pitch. The performance of the lateral estimation was improved when a smaller pitch or a larger beamwidth, was used. The effect of the pitch on the lateral estimation on lateral displacement estimation was found to be greater than the beamwidth effect. Therefore, a smaller pitch is preferred when the beam overlap remains the same. The use of cubic spline, instead of linear interpolation, increases the correlation coefficient, and decreases the jitter, with the trade-off of increased bias. The results of the phantom experiments were shown in good agreement with the simulation findings, including the periodic variation of the performance with lateral displacement and effects of pitch, beamwidth and interpolation method on lateral displacement estimation. In conclusion, smaller pitch, wider beamwidth and spline interpolation were shown to be key in reducing the jitter error in the lateral displacement estimation. (E-mail: ek2191@columbia.edu)     

适应性回归分析(Ⅲ)——构建具有混合结构的回归模型

本文目的是通过两个实例介绍适应性回归样条算法对具有混杂结构的数据集进行回归建模的实践。当一个数据集包含多个不同的回归模型时,只要给定分类变量的具体取值,SAS中的"ADAPTIVEREG过程"可以比较准确地发掘出其内在规律,并以图形方式呈现模型对资料的拟合效果,还能呈现由"基函数"及其组合所构造出的"回归模型"。图形呈现的结果确实可以给分析者提供一些有价值的"分析线索"或"积极暗示",缩小"探索性研究的空间"。