指甲电子顺磁共振谱图基线修正方法与精度分析

目的 在指甲电子顺磁共振剂量重建实验测量中风速、温度及湿度发生大范围变化时波谱则会出现较大程度的基线漂移,进而使得读出的数值不能反映真实的自由基浓度,最终会降低实验结果的可信度.本研究将提出一种基线修正的方法以解决这个问题.方法 找寻发生漂移后的基线,然后选定波谱修正范围和相应的修正函数或将原始波谱还原成能量吸收谱,选择点修正的方法对波谱进行修正.结果 在同一样品测量中,对发生基线漂移的波谱未加以修正得到的数值与未发生基线漂移时得到的数值在误差允许范围内相等的概率仅为31％;而利用此方法修正后概率则达到91％,提高了近3倍.结论 在对波谱进行读数之前,应使用此种修正方法对波谱进行基线修正,以此来提高剂量估算的准确度.     

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。     

An automated technique for analysis of current transitions in multilevel single-channel recordings

Detailed kinetic studies of ion channel gating are best carried out using the patch-clamp technique which permits the measurement of the ionic current through individual channels. Typical patch-clamp recordings show the current signal, in the form of a sequence of rectangular pulses (analogous to a random telegraph signal), riding on slow baseline drift, partially obscured by high-frequency noise and distorted by filtering. In order to analyze such recordings, we have developed a set of interactive Pascal programs based on a feature-detection algorithm capable of identifying current transitions in multiple-channel recordings in the presence of substantial levels of noise and drift. Software operation is largely automated but includes provisions for examination and correction of the output. The software was optimized and systematically evaluated using simulated data with variable amounts of noise and drift. Results indicate that satisfactory performance is obtained for signal-to-noise ratio as low as four even with uncommonly large baseline drift. Steady-state processing speeds varied from 1000 to 4000 samples per second depending on data complexity.     

基于小波变换的自适应滤波器消除脉搏波基线漂移

脉诊仪的研制中,由于呼吸运动和身体移位导致脉搏信号的基线漂移是必须克服的.本文提出了一种新的基于Meyer小波变换的自适应滤波器,其参考输入选择原始信号经小波分解后的高频分量.通过仿真和实际测量实验表明,该方法能有效消除脉搏波的基线漂移.     

Application of the spirometer in respiratory gated radiotherapy

The signal from a spirometer is directly correlated with respiratory motion and is ideal for target respiratory motion tracking. However, its susceptibility to signal drift deters its application in radiotherapy. In this work, a few approaches are investigated to control spirometer signal drift for a Bernoulli-type spirometer. A method is presented for rapid daily calibration of the spirometer to obtain a flow sensitivity function. Daily calibration assures accurate airflow measurement and also reduces signal drift. Dynamic baseline adjustment further controls the signal drift. The accuracy of these techniques was studied and it was found that the spirometer is able to provide a long-term drift-free breathing signal. The tracking error is comprised of two components: calibration error and stochastic signal baseline variation error. The calibration error is very small (1% of 3 l) and therefore negligible. The stochastic baseline variation error can be as large as 20% of the normal breathing amplitude. In view of these uncertainties, the applications of spirometers in treatment techniques that rely on breathing monitoring are discussed. Spirometer-based monitoring is noted most suitable for deep inspiration breath-hold but less important for free breathing gating techniques.     

心电信号QRS波的识别算法及程序设计

实现心电图QRS波检测的算法有很多,本文介绍了一种算法,即利用波变换的多尺特性,可以将QRS波从高P波,高T波,噪声,基线漂移和伪迹中分离出灵,并采用Microsoft VisualC 5.0编程实现算法,使用该方法对MIT／BIH心电数据库中带有严重基线漂移和噪声的心电信号进行处理,对QRS的识别率高达99．8％,文中给出给程序设计要点和程序流程图。     

Baseline drift removal and denoising of MCG data using EEMD: Role of noise amplitude and the thresholding effect

We adopt the Ensemble Empirical Mode Decomposition (EEMD) method, with an appropriate thresholding on the Intrinsic Mode Functions (IMFs), to denoise the magnetocardiography (MCG) signal. To this end, we discuss the two associated problems that relate to: (i) the amplitude of noise added to the observed signal in the EEMD method with a view to prevent mode mixing and (ii) the effect of direct thresholding that causes discontinuities in the reconstructed denoised signal. We then denoise the MCG signals, having various signal-to-noise ratios, by using this method and compare the results with those obtained by the standard wavelet based denoising method. We also address the problem of eliminating the high frequency baseline drift such as the sudden and discontinuous changes in the baseline of the experimentally measured MCG signal using the EEMD based method. We show that the EEMD method used for denoising and the elimination of baseline drift is superior in performance to other standard methods such as wavelet based techniques and Independent Component Analysis (ICA).     

Retrospective correction of frequency drift in spectral editing: The GABA editing example

GABA levels can be measured using proton MRS with a two‐step editing sequence. However due to the low concentration of GABA, long acquisition time is usually needed to achieve sufficient SNR to detect small differences in many psychiatric disorders. During this long scan time the frequency offset of the measured voxel can change because of magnetic field drift and patient movement. This drift will change the frequency of the editing pulse relative to that of metabolites, leading to errors in quantification. In this article we describe a retrospective method to correct for frequency drift in spectral editing. A series of reference signals for each metabolite was generated for a range of frequency offsets and then averaged together based on the history of frequency changes over the scan. These customized basis sets were used to fit the in vivo data. Our results demonstrate the effectiveness of the correction method and the remarkable robustness of a GABA editing technique with a top hat editing profile in the presence of frequency drift.     

基于三次B─样条函数心电图数据滤波

本文介绍一种心电图（ＥＣＧ）滤波方法。该方法以‘最小二乘法’为准则,用三次Ｂ－样条函数构成拟合函数,相应地滤除ＥＣＧ信号中的基线漂移、５０Ｈｚ工频干扰和肌电干扰。实验结果表明：该方法不失为一种ＥＣＧ滤波方法。     

一种基于提升小波和中值滤波的心电去噪方法

小波变换在心电去噪中有非常好的效果,但传统的小波变换计算量大,不利于实时处理和嵌入式系统的实现,提升小波是一种快速有效的小波变换的实现方法,本文提出了一种运用提升小波和中值滤波去除心电信号工频干扰、肌电干扰和基线漂移三种噪声的方法。该方法运用提升小波对含噪声的心电信号做三层分解,并根据小波基的特性在不同层次采用不同的小波基,去除心电信号的工频干扰和肌电干扰;对第三层分解后得到的数据做中值滤波,去除心电信号的基线漂移。将以上方法与传统的小波方法相比,去噪结果表明两者去噪效果相当,但提升方法运算速度有很大的提升。结果证实将提升小波与中值滤波方法结合可以有效地去除心电信号的工频干扰、肌电干扰和基线漂移,而且可以较大地提高运算速度,便于进行实时处理和嵌入式系统的实现。     

基于三次样条插值技术的去除胸阻抗基线漂移的方法研究

目的:胸阻抗信号常伴随呼吸等干扰造成基线漂移,这给临床分析计算、测量带来不良影响,为了消除胸阻抗基线漂移,作者在分析现有去除方法优劣的基础上提出一种新的方法。方法:采用labVIEW编程语言,以阻抗波波谷为插值基准点,利用三次样条差值技术去除胸阻抗基线漂移。结果:利用该方法消除基线后的胸阻抗波形底部非常整齐,而且没有使原有信号变异或者失真。结论:三次样条插值技术去除胸阻抗波基线漂移方法在仿真和实测实验中都取得很好的效果,这种方法是行之有效的。     

Correcting Baseline Drift Artifact in Slow Potential Recording

A problem frequently encountered by investigators measuring scalp-recorded DC potentials is baseline drift artifact. The sources of baseline drift are many and it is often very difficult to remove drift from the primary data. The problem is particularly acute when long recording epochs are under investigation. The present paper proposes a software solution. A FORTRAN IV computer program defines drift as a significant linear trend in prestimulus voltage on successive experimental trials. When drift is determined to be present, its slope is computed and statistically removed from the data in the poststimulus (response) period. A sample data set is included which demonstrates the method's marked improvement of signal-to-noise ratios, as represented by reduced error variance and improved statistical discrimination between the independent variables of an experiment.     

Computer-assisted method for the analysis of postprandial gastrointestinal motility in conscious dogs

A fully automated system to quantify different parameters of gastrointestinal motility and gastroduodenal co-ordination in conscious dogs was designed and built around a personal technical computer (HP 9816). Online it performs sampling of contractions on four different sites of the digestive tract for two dogs simultaneously, data reduction, drift correction and storage of data on hard disk. Offine it performs baseline determination, peak detection, calculation of motility parameters such as amplitude and interval, plus co-ordination between gastric and duodenal motility and presentation of the results in both tabular and graphic form. To illustrate the possibilities and advantages of the computer analysis the early postprandial motor patterns for antrum, duodenum and jejunum were quantified during the first hour after administration of a small test meal.     

Circuit for automatically zeroing aortic flow base line from electromagnetic flowmeter.

We describe an inexpensive circuit designed to correct base-line drift of electromagnetic flowmeters automatically when cardiac output is being measured. The circuit measures the flowmeter output voltage during a portion of each diastole when blood flow in the aorta is assumed to be zero. Any deviation of the flowmeter output voltage from zero during this time represents either base-line offset or drift. The output voltage obtained during zero flow conditions is stored throughout the next cardiac cycle and subtracted continuously from the flowmeter output during each beat, thus giving a beat-by-beat correction of any base-line drift.     

颈动脉波特征提取的小波变换分析方法

本文把小波变换应用于颈动脉波的特征提取，为检测ＣＡＰ上升支起点的降支重搏波切迹提出了一种新方法。文中讨论了利用小波变换的极值点和零交叉点检测信号的奇异点的原理，并给出了适当利用平滑信号在拐点处的斜率帮助检测ｕ点的方法。分析了表明，即使在严重基线漂移和强噪声干扰下，这一方面也能得到准确的检测结果。     

心电图波形基线漂移的数学形态滤波在线实时处理

研究数学形态学滤波器消除心电图波形的基线漂移。选择Maragos类型形态滤波器,得到平结构元为消除波形基线漂移最佳形态滤波形式,信号的衰减幅度由信号数字频率与结构元长度的比值唯一决定,由此归纳出平结构元长度大于或等于要滤波除去的分量的横向宽度的结论。借助Matlab软件进行算法模拟,并移植到DSP硬件平台上进行工程调试,实验表明,该方法运算简单,花费时间少于1 ms,能有效并实时地滤除基漂。     

How much baseline correction do we need in ERP research? Extended GLM model can replace baseline correction while lifting its limits

Baseline correction plays an important role in past and current methodological debates in ERP research (e.g., the Tanner vs. Maess debate in the Journal of Neuroscience Methods), serving as a potential alternative to strong high‐pass filtering. However, the very assumptions that underlie traditional baseline also undermine it, implying a reduction in the signal‐to‐noise ratio. In other words, traditional baseline correction is statistically unnecessary and even undesirable. Including the baseline interval as a predictor in a GLM‐based statistical approach allows the data to determine how much baseline correction is needed, including both full traditional and no baseline correction as special cases. This reduces the amount of variance in the residual error term and thus has the potential to increase statistical power.     

脉搏波自动采集系统关键技术的研究

目前的脉搏波波形采集分析系统需要人为干预,其自动化程度低,且受人为因素影响比较大。本文结合心血管血流动力学参数的无创检测理论,利用光调制技术、单波提取以及基线漂移实时滤除等信号处理技术,设计了自动化程度较高的脉搏波自动采集分析系统,实现了脉搏波信号的增益自动调节、波形自动识别、基线漂移的实时滤除及波形的有效性自动判定。此脉搏波自动采集分析系统实现了脉搏波波形的自动采集,且无需人为干预,适宜在社区和家庭中应用。     

利用小波变换去除针电极肌电信号噪声的实验研究

小波变换能将各种交织在一起的由不同频率组成的混合信号分解成不相同频段的信号。本文采用小波变换的方法对针电极肌电信号（ＮＥＭＧ）进行去噪声处理,并进行对比实验。结果表明,在应用小波变换处理ＮＥＭＧ信号过程中,只要适当选取变换尺度就可以在处理信号的同时,有效地消除原信号中高频噪声和基线漂移的影响。     

On the sources of drift in a turbine-based spirometer

A systematic study on the sources of drift in a turbine-based spirometer (VMM-400) is presented. The study utilized an air-tight cylinder to pump air through the spirometer in a precise and programmable manner. Factors contributing to the drift were isolated and quantified. The drift due to imbalance in the electronics and the mechanical blade increased from 1% per breathing cycle to as much as 10% when the flow rate decreased from 0.24 to 0.08 l s(-1). A temperature difference of 16 degrees between the ambient and the air in the cylinder contributed about 3.5%. Most significantly, a difference in the breathing between inhalation and exhalation could produce a drift of 40% per breathing cycle, or even higher, depending on the extent of the breathing asymmetry. The origin of this drift was found to be rooted in the differential response of the spirometer to the different flow rate. Some ideas and suggestions for a correction strategy are provided for future work. The present work provides an important first step for eventual utilization of a spirometer as a stand-alone breathing surrogate for gating or tracking radiation therapy.