The automated analysis of data from single ionic channels

The development of single channel recordings has brought with it the need to analyse enormous amounts of data. The data analysis is time consuming and subject to observer biases since the events are random in time and are contaminated with uncorrelated noise. We have developed a heuristic pattern recognition program which identifies with high precision single channel currents and rejects contaminating noise. The program interactively provides for a variety of amplitude and duration measures. Analysis is flexible and rapid: a file containing over 10,000 events can be analysed in under 2 h.Specific detection features include variable lowpass filtering, automatic baseline restoration, and adaptive amplitude thresholds. A record is analysed through duration histograms, binomial estimates of the number of active channels present, cross-correlation estimates between parameters, spectral analysis of events and background noise, and stationarity of mean channel current. The graphic output facilities can plot raw data (after filtering and baseline restoration) with the idealized signal superimposed or with detected events underlined. A batch processing facility has been included to allow processing of data during periods of low computer demand.     

Noise and filtration in magnetic resonance imaging

Noise in two-dimensional Fourier transform magnetic resonance images has been investigated using noise power spectra and measurements of standard deviation. The measured effects of averaging, spatial filtering, temporal filtering, and sampling have been compared with theoretical calculations. The noise of unfiltered images is found to be white, as expected, and the choice of the temporal filter and sampling interval affects the noise in a manner predicted by sampling theory. The shapes of the imager's spatial frequency filters are extracted using noise power spectra.     

A novel method for analysis of single ion channel signal based on wavelet transform

A single ion channel signal was analysed by the power distribution fraction constructed by a discrete wavelet transform. Average opening time and energy distribution of the signal can be obtained directly by this method. The method can also be used when the signal is corrupted by noise. By contrast, the conventional frequency domain analysis method--power spectral density--is less effective. Power distribution fraction will therefore give more useful information in analysis of experimental ion channel signals, principally by giving values of the mean channel opening time. The method may be applied to distinguish different ion channels more efficiently and to find their reactions to drugs.     

基于小波包变换与自适应阈值的ECG信号滤波算法研究

目的:在心电信号(ECG)的采集过程中,常常会受到噪声的影响,为了正确进行心电参数测量、波形识别和病情诊断,在低信噪微弱信号检测中必须要进行噪声抑制,提高信噪比.噪声的滤波处理是心电图分析的一个重要步骤.方法:本文提出了一种基于小波包变换及与分解层次相关的自适应阈值的去噪方法,利用小波包对心电信号进行分解,可以同时对信...     

Implementation of a Multi-sampling-frequency System for RR-interval Timing and Blood Pressure Detection

INTRODUCTION Researchers study on cardiac electrophysiology and haemodynamics for more effective methods of di-agnosis and treatment. During these studies, howto obtain information as much as possible, depends onnot only the progress of analysis methods, but also the improvement of signal acquisition and the condi-tions for further analysis. Without automatic data processing, the analysis of experimental data might bewith poor accuracy,time-consuming and even impossible in some new cardiov…     

Generalized multi-dimensional adaptive filtering for conventional and spiral single-slice, multi-slice, and cone-beam CT

In modern computed tomography (CT) there is a strong desire to reduce patient dose and/or to improve image quality by increasing spatial resolution and decreasing image noise. These are conflicting demands since increasing resolution at a constant noise level or decreasing noise at a constant resolution level implies a higher demand on x-ray power and an increase of patient dose. X-ray tube power is limited due to technical reasons. We therefore developed a generalized multi-dimensional adaptive filtering approach that applies nonlinear filters in up to three dimensions in the raw data domain. This new method differs from approaches in the literature since our nonlinear filters are applied not only in the detector row direction but also in the view and in the z-direction. This true three-dimensional filtering improves the quantum statistics of a measured projection value proportional to the third power of the filter size. Resolution tradeoffs are shared among these three dimensions and thus are considerably smaller as compared to one-dimensional smoothing approaches. Patient data of spiral and sequential single- and multi-slice CT scans as well as simulated spiral cone-beam data were processed to evaluate these new approaches. Image quality was assessed by evaluation of difference images, by measuring the image noise and the noise reduction, and by calculating the image resolution using point spread functions. The use of generalized adaptive filters helps to reduce image noise or, alternatively, patient dose. Image noise structures, typically along the direction of the highest attenuation, are effectively reduced. Noise reduction values of typically 30%-60% can be achieved in noncylindrical body regions like the shoulder. The loss in image resolution remains below 5% for all cases. In addition, the new method has a great potential to reduce metal artifacts, e.g., in the hip region.     

Reduction of aliasing in modulation transfer function measurements

The images formed by many radiological systems are difficult to sample at spatial intervals small enough to avoid aliasing in the calculation of the system's modulation transfer function. However, if a system's response can be assumed to be symmetrical, this assumption can be used to effectively double the sampling density and to double the frequency limit before aliasing occurs. To accomplish this, a more complex algorithm is required. In this work, the formula for the calculation of the modulation transfer function from a symmetrical, one-dimensional line spread function is derived and a similar result for a symmetrical, two-dimensional point spread function is presented. The effect of noisy data and errors in the estimation of the offset of the center of the line spread function from a sampling point are investigated by simulation studies. For low noise (relative standard deviation of 1%) and an offset error of no more than 2% or 3% of a sampling interval, reasonable precision is obtained. These conditions appear to be achievable, especially when the noise is Poisson distributed.     

CT—3D rotational angiography automatic registration: A sensitivity analysis

Preprocessing, binning and dataset subsampling are investigated with regard to simultaneous maximisation of the speed, accuracy and robustness of CT-3D rotational angiography (3DRA) registration. Clinical diagnosis and treatment can both take advantage of this integration, because 3DRA allows the shape of vessel structures to be evaluated three-dimensionally with respect to standard 2D projective angiography. The method for optimising preprocessing, binning and subsampling consisted of independent variation of the corresponding parameters to maximise robustness and speed while maintaining subvoxel accuracy; the latter was computed as the sum of the mean squared errors initially present in the registrations with the errors relative to both binning and subsampling. The results suggest the choice of 256 bins, steps between 14 mm (coarse optimisation) and 2.5 mm (fine optimisation) and bone segmentation by threshold, for binning, subsampling and preprocessing, respectively. The application of this parameter set-up to 50 CT-3DRA registrations resulted in a saving, on average, of 40% of the time with respect to the method previously used, while registration error was maintained within 2 mm (1.97 mm, 90% confidence interval) and robustness was increased, so that no manual initial realignment was needed in 48 registrations. Validation by the registration of images acquired for a head phantom showed subvoxel residual errors. In conclusion, the proposed procedure can be considered a satisfactory strategy to optimise CT-3DRA registration.     

GPU-accelerated 3D mipmap for real-time visualization of ultrasound volume data

Ultrasound volume rendering is an efficient method for visualizing the shape of fetuses in obstetrics and gynecology. However, in order to obtain high-quality ultrasound volume rendering, noise removal and coordinates conversion are essential prerequisites. Ultrasound data needs to undergo a noise filtering process; otherwise, artifacts and speckle noise cause quality degradation in the final images. Several two-dimensional (2D) noise filtering methods have been used to reduce this noise. However, these 2D filtering methods ignore relevant information in-between adjacent 2D-scanned images. Although three-dimensional (3D) noise filtering methods are used, they require more processing time than 2D-based methods. In addition, the sampling position in the ultrasonic volume rendering process has to be transformed between conical ultrasound coordinates and Cartesian coordinates. We propose a 3D-mipmap-based noise reduction method that uses graphics hardware, as a typical 3D mipmap requires less time to be generated and less storage capacity. In our method, we compare the density values of the corresponding points on consecutive mipmap levels and find the noise area using the difference in the density values. We also provide a noise detector for adaptively selecting the mipmap level using the difference of two mipmap levels. Our method can visualize 3D ultrasound data in real time with 3D noise filtering.     

Impairment of Na+ transport across frog skin by Tl+: Effects on turnover,area density and saturation kinetics of apical Na+ channels

Na+ transport across abdominal skin of the frogs, Rana temporaria and Rana esculenta was followed by measuring Na+-dependent short-circuit, current (INa) kinetics and INa fluctuations induced by triamterene, a diuretic. Exposure of the skin to serosal Tl+ led to a pronounced and irreversible drop in INa and INa-blocker noise. At low serosal Tl+ concentrations, we observed mainly a decrease in the apparent Michaelis constant for INa saturation while, at larger [Tl+], the maximal INa dropped irreversibly. Tl+ acts even when serosal Tl+ "transporters" like the Na+-K+ pump, or the K+ channel are nonfunctional. The rate constants for the triamterene/Na+ channel reaction were unchanged after Tl+ whereas the relaxation noise from channel blockage decreased in amplitude. Noise analysis in terms of a two-state blocking model suggested that Tl+ poisoning results in a small decrease in single-channel current through apical Na+ pathways, as well as in a drastic and irreversible drop in channel density. The impairment of Na+ transport by Tl+ can be attributed to the above cited concerted events at the level of the apical membrane.     

Quantitative image quality evaluation of pixel-binning in a flat-panel detector for x-ray fluoroscopy

X-ray fluoroscopy places stringent design requirements on new flat-panel (FP) detectors, requiring both low-noise electronics and high data transfer rates. Pixel-binning, wherein data from more that one detector pixel are collected simultaneously, not only lowers the data transfer rate but also increases x-ray counts and pixel signal-to-noise ratio (SNR). In this study, we quantitatively assessed image quality of image sequences from four acquisition methods; no-binning and three types of binning; in synthetic images using a clinically relevant task of detecting an extended guidewire in a four-alternative forced-choice paradigm. Binning methods were conventional data-line (D) and gate-line (G) binning, and a novel method in which alternate frames in an image sequence used D and G binning. Two detector orientations placed the data lines either parallel or perpendicular to the guide wire. At a low exposure of 0.6 microR (1.548 x 10(-10) C/kg) per frame, irrespective of detector orientation, D binning with its reduced electronic noise was significantly (p<0.1) better than the other acquisition methods. On average, alternate binning performed better than G binning. At a higher exposure of 4.0 microR (10.32 x 10(-10) C/kg) per frame, with data lines parallel to the guidewire, detection with D binning was significantly (p<0.1) better than G binning. However, with data lines perpendicular to the guidewire, G binning was significantly (p<0.1) better than D binning because the partial area effect was reduced. Alternate binning was the best binning method when results were averaged over both orientations, and it was as good as the best binning method at either orientation. In addition, at low and high exposures, alternate binning gave a temporally fused image with a smooth guidewire, an important image quality feature not assessed in a detection experiment. While at high exposure, detection with no binning was as good, or better, than the best binning method, it might be impractical at fluoroscopy imaging rates. A computational observer model based on signal detection theory successfully fit data and was used to predict effects of similar acquisition methods. Results from this study suggest the use of exposure-dependent detector binning in fluoroscopy that switches between D binning and alternate binning at low and high exposures, respectively.     

Effects of Measurement Error and Sampling Resolution on Estimates of Atrial Tissue Recovery Parameters

We studied the effect of sampling resolution and measurement error on estimates of tissue recovery parameters using experimental and simulated data. Action potential duration (APD) was estimated from monophasic action potentials recorded at 250 sites (x=3.5 mm) on the endocardium of the canine right atrium (n=8) during control and acetylcholine perfusion. APD distributions were also simulated using a random number generator, then scaled and filtered to physiological values. The following parameters were estimated at increasing APD sampling interval and measurement error: mean APD, standard deviation of APD, mean APD gradient, standard deviation of APD gradient, APD wavelength, and APD correlation length. We found that large errors can result from APDs collected at inadequate sampling intervals and adequate sampling intervals may be 3–6 times less than the Nyquist interval. Large parameter errors also resulted from data with relatively low levels of measurement error. The effect of measurement error was dependent upon the standard deviation of APD, sampling resolution, and APD wavelength. Inadequate sampling resolution was the largest source of error in experimental parameter estimates. Estimates of mean and standard deviation of APD gradient decreased with spacing as estimates of correlation length and wavelength increased. Careful selection of spacing interval, taking into account the spatial complexity of recovery, as well as considerably low measurement errors will produce accurate estimates of gradients, correlation length, and wavelength. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8719Hh, 0620Dk     

Error, stress and the role of neuromotor noise in space oriented behaviour

In this article both movement errors and successful movements are considered to be the product of varying ratios of muscle force signals and the composite of neuromotor noise in which the force signal is embedded. Based on earlier work we derived four propositions, which together form a theoretical framework for understanding the incidence of error in conditions of time pressure and mental load. These propositions are: (1) motor behaviour is an inherently stochastic and therefore noisy process; (2) biophysical, biomechanical and psychological factors all contribute to the level of neuromotor noise in a movement signal; (3) endpoint variability of movement is related to the signal-to-noise ratio of the forces which drive the moving limb to the target; and (4) optimal signal-to-noise ratios in motor output can be arrived at by adjusting limb stiffness. In an experiment with a graphical aiming task in which subjects made pen movements to targets varying in width and distance, we tested the prediction that time pressure and dual task load would influence error rates and movement noisiness, together resulting in biomechanical adaptations of pen pressure. The latter is seen as a manifestation of a biomechanical filtering strategy to cope with increased neuromotor noise levels. The results confirmed that especially under time pressure error rates and movement noise were enhanced, while pen pressure was higher in both conditions of stress.     

Memory Retrieval in Noise and Psychophysiological Response in the Young and Old

Both noise and aging induce changes in memory performance that have been attributed to physiological overarousal. The aim of the current experiment was to examine variation in performance due to noise and aging and to determine if this variation was related to variation in general arousal or, alternatively, to changes in processes specifically required by memory retrieval. The cardiovascular responses of young and old men (n=30) were compared during a memory retrieval task performed in acoustic noise. Noise (90dBA) and old age independently increased the number of associatively cued recall errors relative to orthographically cued recall errors. Despite the change in errors, changes in general arousal were not observed in response to noise in either young or old volunteers. The task sequence induced consistent cardiac and vascular responses which were related to attention and rehearsal requirements, and also to performance. This suggests that task processing induces supportive physiological changes rather than that physiological change (arousal) constrains performance. Noise and age may alter physiological change independently by altering task processing and requirements for physiological support.     

Short openings in high resolution single channel recordings of mouse nicotinic receptors

The temporal fine structure of single channel currents was studied to obtain information on how agonists open nicotinic acetylcholine receptor channels. Currents were recorded from mouse myoballs with quartz pipettes in the on-cell mode of the patch-clamp technique. With 62 kHz filter cut-off and root mean square (r.m.s.) noise levels as low as 1.45 pA at 200 mV hyperpolarization, events down to 6 μs duration could be resolved with negligible error rate. Three types of openings with mean durations of 750 μs, 89 μs and 4 μs were identified with 0.1–10 μ m suberyldicholine (SubCh). The relative frequencies of the three types of openings were 84% for long, 5% for medium and 11% for short openings with 1 μ m SubCh. Stability plots and single channel current amplitude comparisons suggest that the three types of openings arise from a homogenous channel population. Above 10 μ m SubCh, the three types of openings could not be discerned because channel openings occurred too closely spaced and open channels were increasingly blocked. Three types of openings can be generated with a mechanistic receptor model with two unequal binding sites, short and medium openings arising from one or the other monoliganded state, and long openings from the fully liganded state of the receptor. Maximum likelihood fitting of the rate constants of this model directly to the sequence of observed open and shut times accurately predicted the main physiological properties of the receptors with 0.1 μ m SubCh. However, fitting recordings with 0.1–10 μ m SubCh simultaneously revealed that this model cannot reproduce the weak influence of SubCh concentration on the proportions of the three types of openings. Therefore we conclude that short and medium openings are unlikely to arise preferentially from one or the other monoliganded state of nicotinic acetylcholine receptor channels.     

Single-channel current/voltage relationships of two kinds of Na+ channel in vertebrate sensory neurons

The electrical signals of nerve and muscle are fundamentally dependent on the voltage-gated Na⁺ channel, which is responsible for the rising phase of the action potential. At least two kinds of Na⁺ channel are expressed in the membrane of frog dorsal root ganglion (DRG) cells: Na⁺ channels with fast kinetics that are blocked by tetrodotoxin (TTX) at high affinity, and Na⁺ channels with slower kinetics that are insensitive to TTX. Recordings of single-channel currents from frog DRG cells, under conditions favoring Na⁺ as the charge carrier, reveal two distinct amplitudes of single-channel events. With 300 mM external Na⁺, single-channel events that can be measured in the presence of 1 M TTX have a slope conductance 7.5 pS. In the absence of TTX, events with a slope conductance of 14.9 pS dominate. Ensemble averages of the smaller single-channel events display the slower kinetics characteristic of the macroscopic TTX-insensitive Na⁺ currents, and ensemble averages of the larger events display the faster kinetics characteristic of the TTX-sensitive currents. The results are consistent with the idea that the toxin-binding site is sufficiently close to the pore to influence ion permeation.     

QRS wave detection

A QRS complex detector based on optimum predetection with a matched filter is described. In order to improve the accuracy of the QRS complex recognition under conditions of Gaussian noise and variable QRS amplitude, the first derivative of the e.c.g. was used with zero threshold detection. In addition, two nonlinear circuits cut off low amplitude noise and all spikes which appear for a fixed time after QRS detection. Calculation of errors shows that differentiation reduces Gaussian error by √6 and errors caused by variable QRS amplitudes are close to zero. This detector is especially useful with biotelemetry systems since it reduces many interferences due to patient movement and communication channel distortion.     

Arduino-based noise robust online heart-rate detection

This paper introduces a noise robust real time heart rate detection system from electrocardiogram (ECG) data. An online data acquisition system is developed to collect ECG signals from human subjects. Heart rate is detected using window-based autocorrelation peak localisation technique. A low-cost Arduino UNO board is used to implement the complete automated process. The performance of the system is compared with PC-based heart rate detection technique. Accuracy of the system is validated through simulated noisy ECG data with various levels of signal to noise ratio (SNR). The mean percentage error of detected heart rate is found to be 0.72% for the noisy database with five different noise levels.     

The impact of noise on the reliability of heart-rate variability and complexity analysis in trauma patients

This study focused on the impact of noise on the reliability of heart-rate variability and complexity (HRV, HRC) to discriminate between different trauma patients and to monitor individual patients. Life-saving interventions (LSIs) were chosen as an endpoint because performance of LSIs is a critical aspect of trauma patient care. Noise was modeled and simulated by modifying original R–R interval (RRI) sequences via decimation, concatenation, and division of RRIs, as well as R-wave detection using the electrocardiogram. Results showed that under increasing simulated noise, entropy and autocorrelation measures can still effectively discriminate between LSI and non-LSI patients and monitor individuals over time.     

Calcium-activated potassium channels in goldfish hair cells.

1. Characteristics of Ca(2+)-activated K+ channels in the basolateral membrane of hair cells isolated from the caudal part of the goldfish saccular macula were studied mainly with the inside-out mode of the patch clamp method. 2. Several types of Ca(2+)-activated K+ channels differing in unitary conductance were identified. The conductances (n = 156) ranged from 130 to 320 pS (when measured in symmetrical 125 mM KCl) and could be roughly separated into four groups, centred on values of 150, 200, 250 and 300 pS. The pharmacological profile, assessed by, for example, tetraethylammonium blockade, and the relatively large conductance indicated that these channels can be classified as large-conductance Ca(2+)-activated K+ channels (BK channels). The relative permeability of these channels to different ion species was in the order K+ (1.0) > Rb+ (0.8) > NH4+ (0.14) > Na+, Cs+ (< 0.05). 3. Curves relating open state probability to [Ca2+]i, for membrane potentials between -50 and +50 mV, were similar to those observed for BK channels of rat muscle. However, the maximum open state probability (100-1000 microM [Ca2+]i and 50 mV membrane potential) was 0.4-0.9, and always less than 1. 4. These channels had a short arithmetic mean open time ranging from 0.08 to 1.2 ms (0.08-0.5 ms in 88% of cases) and an arithmetic mean shut time ranging from 0.24 to 1.2 ms (10 microM [Ca2+]i and 50 mV membrane potential). The shut intervals were more sensitive to changes in [Ca2+]i and membrane potential than were the open intervals. 5. The distribution of individual open and shut intervals was fitted with the sum of exponential functions. Except for the slowest shut component, which only accounted for less than 1% of shut events, all other components had time constants shorter than 1 ms. As a result of these short open and shut intervals, the current trace had a flickery pattern rather than a burst-interburst pattern. 6. There was a rough correlation between unitary conductance and mean open time, i.e. channels with a large unitary conductance had a longer mean open time. 7. The sensitivity to [Ca2+]i of the Ca(2+)-activated K+ channel in goldfish hair cells was one to two orders of magnitude lower than that of BK channels in rat muscle. Channels with a longer mean open time had a higher Ca2+ sensitivity. 8. The stability of the single Ca(2+)-activated K+ channel kinetics was studied by measuring the 'moving' mean duration of open and shut intervals.(ABSTRACT TRUNCATED AT 400 WORDS)