薄板样条插值的改进及其在图像配准中的应用

薄板样条插值是应用较多的弹性配准方法。深入研究了这种方法,并就此方法的不足,采用薄板样条归一化弹性近似策略,减少了因标记点定位带来的配准误差。提出了在插值过程中加入邻近插值、加权插值的混合插值方法,同时边界处理等改进策略,使得薄板样条插值具有可靠的平滑性。     

基于平面插值的快速光线投射算法

插值算法是光线投射法中基本的计算方法,计算量很大,直接影响成像速度.传统的三元线性插值比较费时,许多人对其进行改进.本文提出一种平面插值算法,可以明显地提高成像速度并且图像质量仍可以接受.     

单帧图像的超分辨率重建技术

本文通过仿真实验研究了单帧低分辨率图像的超分辨率重建技术。首先,阐述了用于单帧超分辨率重建的插值法、IBP法和POCS法,然后通过matlab7.0仿真程序验证了双三次插值法、双线性插值法、POCS法和IBP法,并根据仿真实验的结果分析这些方法重建效果的好坏。实验结果表明,实验结果证明,双线性插值方法的重建结果要优于双三次插值的重建结果;IBP的重建效果要优于POCS方法;对于IBP和POCS来说,2种方法都能获得较好的重建结果,并且用于图像的帧数越多,重建的效果越好;此外,客观评价方法与主观评价方法有时不能获得相同的评价结果,但在多数情况下,客观评价方法都能取得与主观评价方法一致的结果。     

Dependence of vessel area accuracy and precision as a function of MR imaging parameters and boundary detection algorithm

PURPOSE: To determine the appropriate image acquisition parameters for an accurate measurement of vessel cross-sectional area from MR angiography (MRA) images. MATERIALS AND METHODS: A series of images with different vessel cross-sectional areas, resolutions, and signal-to-noise ratios (SNRs) were simulated and validated experimentally. Dynamic programming (DP) was employed to determine the accuracy and precision of the vessel cross-sectional area as a function of vessel size, sampling matrix, acquisition time, and postprocessing parameters such as zooming and bias correction. RESULTS: We show that there is an optimal value of lambda (the ratio of vessel diameter to resolution) for a given intrinsic SNR that yields the most accurate and precise area measurement. Specifically, when the SNR is > or =10:1, this value of lambda is 8 and yields a cross-sectional area error of <5% with a zoom factor of > or =2. CONCLUSION: The predicted ideal result of lambda = 8 is within reach with current technology to image vessels such as the carotid artery or aorta. It is possible to determine the ideal resolution that minimizes errors in the measurement of the vessel cross-sectional area for a given SNR, processing algorithm, and vessel of interest.     

A segmentation-based method for metal artifact reduction

RATIONALE AND OBJECTIVES: We propose a novel segmentation-based interpolation method to reduce the metal artifacts caused by surgical aneurysm clips. MATERIALS AND METHODS: Our method consists of five steps: coarse image reconstruction, metallic object segmentation, forward-projection, projection interpolation, and final image reconstruction. The major innovations are 2-fold. First, a state-of-the-art mean-shift technique in the computer vision field is used to improve the accuracy of the metallic object segmentation. Second, a feedback strategy is developed in the interpolation step to adjust the interpolated value based on the prior knowledge that the interpolated values should not be larger than the original ones. Physical phantom and real patient datasets are studied to evaluate the efficacy of our method. RESULTS: Compared to the state-of-the-art segmentation-based method designed previously, our method reduces the metal artifacts by 20-40% in terms of the standard deviation and provides more information for the assessment of soft tissues and osseous structures surrounding the surgical clips. CONCLUSION: Mean shift technique and feedback strategy can help to improve the image quality in terms of reducing metal artifacts.     

利用三次样条差值法抑制脉搏波基线漂移

目的脉搏波检测过程中,必须克服由于呼吸运动和身体移位会导致脉搏信号的基线漂移。本文提出一种基于三次样条差值的脉搏波基线漂移抑制方法。方法选择脉搏波的各个起始点为给定点,根据各个给定点的数值利用三次样条插值拟合出基线。然后用脉搏波在各个采样时间点上的采样值减去对应时间点上的基线函数数值,得到去基线的脉搏波波形。结果通过实际测量实验表明,脉搏波去基线后,基线比较平稳,波形比较稳定。结论三次样条差值法能有效抑制脉搏波的基线漂移,并且能够很好地应用在脉搏波实时检测中。     

Facilitation by view combination and coherent motion in dynamic object recognition

We compared the effect of motion cues on people’s ability to: (1) recognize dynamic objects by combining information from more than one view and (2) perform more efficiently on views that followed the global direction of the trained views. Participants learned to discriminate two objects that were either structurally similar or distinct and that were rotating in depth in either a coherent or scrambled motion sequence. The Training views revealed 60° of the object, with a center 30° segment missing. For similar stimuli only, there was a facilitative effect of motion: Performance in the coherent condition was better on views following the training views than on equidistant preceding views. Importantly, the viewpoint between the two training viewpoints was responded to more efficiently than either the Pre- or Post-Training viewpoints for both the coherent and scrambled condition. The results indicate that view combination and processing coherent motion cues may occur through different processes.     

Variable resolution reconstruction for Cartesian data acquired with nonconstant sampling density in phase-encoding direction.

The variable-kernel extent technique is applied for providing local high-resolution images from k-space data sampled on a Cartesian sampling grid with gradually decreasing sampling density in the phase-encoding direction. The approach is based on a variable spatial resolution reconstruction technique providing gradually decreasing resolution in the phase-encoding direction with increasing distance to the image center, while preserving full spatial resolution in a narrow slab centered in spatial domain. Reconstruction is performed by a variable convolution kernel gridding technique. The convolution kernel width is chosen proportional to the k-space sampling spacing to utilize the respective apodization in the image for reduction of the aliasing artifacts. Application of this technique to carotid artery wall imaging shows the potential of the technique for a significant reduction of image acquisition time without sacrificing image quality in the region of the carotid arteries.     

Deriving meteorological variables across Africa for the study and control of vector-borne disease: a comparison of remote sensing and spatial interpolation of climate

This paper presents the results of an investigation into the utility of remote sensing (RS) using meteorological satellites sensors and spatial interpolation (SI) of data from meteorological stations, for the prediction of spatial variation in monthly climate across continental Africa in 1990. Information from the Advanced Very High Resolution Radiometer (AVHRR) of the National Oceanic and Atmospheric Administration's (NOAA) polar-orbiting meteorological satellites was used to estimate land surface temperature (LST) and atmospheric moisture. Cold cloud duration (CCD) data derived from the High Resolution Radiometer (HRR) on-board the European Meteorological Satellite programme's (EUMETSAT) Meteosat satellite series were also used as a RS proxy measurement of rainfall. Temperature, atmospheric moisture and rainfall surfaces were independently derived from SI of measurements from the World Meteorological Organization (WMO) member stations of Africa. These meteorological station data were then used to test the accuracy of each methodology, so that the appropriateness of the two techniques for epidemiological research could be compared. SI was a more accurate predictor of temperature, whereas RS provided a better surrogate for rainfall; both were equally accurate at predicting atmospheric moisture. The implications of these results for mapping short and long-term climate change and hence their potential for the study and control of disease vectors are considered. Taking into account logistic and analytical problems, there were no clear conclusions regarding the optimality of either technique, but there was considerable potential for synergy.     

有理函数插值的一种降介算法

通过对有理插值给定型值特点的分析,得到有理函数插值的一个重要性质：描述了有理插值函数的阶与给定型值的关系。根据这个性质,给出了计算有理插值函数的一种逐步降阶算法,这个算法具有运算量小,实现简单的特点,最后用实例证明其有效性。