Ultrasound systems are widely used to visualize in real-time internal structures and blood flow velocity distributions. The latter are estimated from the received ultrasound radio frequency (RF) signals using a mean frequency estimator, capable of estimating the temporal and spatial mean frequency within a given depth and time window (estimation ...

One potential way to reduce patient and staff X-ray fluoroscopy dose is to reduce the quantum exposure to the detector and compensate the additional noise with digital filtering. A new filtering method, spatio-temporal filtering with object detection, is described that reduces noise while minimizing motion and spatial blur. As compared ...

Measurement of a relative afferent pupillary defect (RAPD) can be carried out by attenuation of light received by the normal eye during the swinging flashlight test. Such measurements may be useful in the management of central retinal vein occlusion (CRVO). In this study a method employing cross polarised filters (CPFs) ...

Frequency-specific, i.e., narrow-band brain, activity is traditionally analyzed on the basis of either a time- or frequency-domain representation of the signal. Here we demonstrate an alternative method based on Gabor functions which are well known for their optimal concentration in time and frequency. Using Gabor filtering, amplitude and frequency information ...

In this paper, a new spatio-temporal filtering method for removing noise from image sequences is proposed. This method combines the use of motion compensation and signal decomposition to account for the effects of object motion. Because of object motion, image sequences are temporally nonstationary, which requires the use of adaptive ...

Using computer simulations, we investigate the performance of a minimum-mean-square-error filter for input-scene noise that is spatially nonoverlapping (disjoint) with a target for a limited set of images. Different input-scene-noise statistics are used to test the filter performance. We show that in the presence of spatially nonoverlapping target and input-scene ...

The FluorImager fluorescence imaging system uses monochromatic 488-nm laser light to excite fluorochromes. It contains a built-in 515-nm long-pass filter that rejects excitation laser light, but allows emission light with wavelengths longer than 515 nm to pass through. A fluorochrome appropriate for use in the system is excitable by 488-nm ...

The reflection and transmission coefficients of holographic Fabry-Perot filters (HFPF's) are derived. Angular selectivities and wavelength sensitivities of the HFPF's on transmitted light are investigated. The effects of transmission by a HFPF on the spectrum and on the coherence properties of a partially coherent incident light are also analyzed. Numerical ...

Impedance rheopneumography is a simple non-invasive technique that can reflect the vascular condition in the human pulmonary circulatory system. However, the much larger and almost in-banding respiratory artefact present has greatly restricted its usefulness to only respiratory patients of a less severe type, in view of the existing practice of ...

In light-dark entrained rabbits, the intraocular pressure (IOP) increases around the onset of dark due to the increased activities of ocular sympathetic nerves. This circadian elevation of IOP can be eliminated by exposing the rabbits to constant white light in the early subjective dark phase. The spectral effectiveness of light ...

Psychometric functions were measured for spectral-shape discrimination (profile analysis) with the signal frequency either fixed, what we call the signal-known condition, or randomly varied, what we call the signal-unknown condition. The functions were obtained using an adaptive, up-down procedure. In the signal-unknown condition, independent tracks for each signal frequency were ...

We describe the implementation of a scale-invariant binary phase-only matched filter using a 128 × 128 ferroelectric spatial light modulator. A 5-dB discrimination was obtained between a 10-image training set of highly correlated characters (E's and F's) over a scale range of 1.0 to 1.5.

A multicriteria optimization method is introduced in order to find optimal filters for implementation on arbitrary spatial light modulators in the Fourier plane of an optical correlator. This method is applied to the trade-offs between noise robustness, sharpness of the correlation peak, and optical efficiency. A fast and simple algorithm ...

Adaptive cancellation of motion artifacts in the electrogastrogram (EGG) is presented in this paper. The EGG is a surface measurement of gastric electrical activity. Like other noninvasive electrophysiological measurements, the EGG contains motion artifacts. A number of papers have been published on the adaptive cancellation of motion artifacts or interferences ...

The main transforms of Cohen's class allow signal representation simultaneously in time and frequency domains. Wavelet transforms make it possible to link the temporal window width to the analyzing frequency and leads to a "modified wavelet transform" which improves resolution both in time and frequency. A simulation study illustrates the ...

The basic spin filter for interferometric fringe patterns is improved and developed into several new versions for different applications. These spin filters can filter off random noise efficiently and have almost no blurring effect and phase distortion for the fringe patterns. First, they find the local fringe tangent direction, and ...

This paper investigates adaptive digital notch filters for the elimination of powerline noise from biomedical signals. Since the distribution of the frequency variation of the powerline noise may or may not be centered at 60 Hz, three different adaptive digital notch filters are considered. For the first case, an adaptive ...

The multiplicative and low-bandpass filtering characteristics of real-time holograms in photorefractive media are used as a basis for a baseband frequency demodulator by means of holographic homodyne detection. We experimentally demonstrate the demodulation of spatial bandpass signals in the kilohertz regime and homodyne detection in the gigahertz regime.

The time-frequency characteristics are studied of averaged and filtered ECG records from 21 patients with sustained ventricular tachycardia and 29 healthy control subjects. Simulated data as well as real ECG records reveal the detection accuracy of the wavelet transform of signals with late potentials. The wavelet-transforms of preprocessed ECG signals ...

The reflection and transmission coefficients of holographic mirrors (HM's) and holographic Fabry-Perot filters (HFPF's) are studied. The diffraction efficiencies, the angular selectivities, and the wavelength sensitivities of HM's and HFPF's and their effects on the spectrum and on the coherence properties of the incident light are investigated. The results show ...

A technique is presented for the reconstruction of signals that suffered sampling-frequency decimation. Two assumptions are made: the original signal has to be repetitive, and no anti-aliasing filter has been used before frequency decimation. The performance of the technique is assessed by using test signals of which the original signal ...

17 subjects provided magnitude estimations in the form of quality judgments of a filtered speech stimulus which was a nonsense sentence containing all of the consonants of English from Fairbanks. It was presented to subjects at 8 high-pass and 8 low-pass filtering conditions. Consistent magnitude estimations to the filtered stimulus ...

Vibroarthrography (VAG) is an innovative, objective, non-invasive technique for obtaining diagnostic information concerning the articular cartilage of a joint. Knee VAG signals can be detected using a contact sensor over the skin surface of the knee joint during knee movement such as flexion and/or extension. These measured signals, however, contain ...

This paper presents a method to analyze and filter digital signals of finite duration by means of a time-frequency representation. This is done by defining a purely invertible discrete transform, representing a signal either in the time or in the time-frequency domain, as simply as possible with the conventional discrete ...

The prevailing view of motion detection in human vision is that the retinal image is convolved with each of a set of spatiotemporal filters and that perceived speed emerges from a process of pooling the outputs of these filters. Such a system can operate only if multiple filters exist; ideally ...

Consider three main ideas about spatial filtering and feature coding in human spatial vision. (1) Computational theory: the representation of local luminance features--bars and edges--is a crucial step in human vision, forming the basis for many decisions in pattern discrimination. (2) Algorithm: features may be located and characterized in terms ...

The experiment investigated subjects' ability to detect short-duration changes in frequency. In an adaptive, 2AFC task, three normal-hearing subjects were asked to distinguish a sinusoidal signal that increased in frequency in a series of discrete steps from a standard that was identical except that its frequency increased essentially continuously. The ...

In Part I we present an approximate mathematical analysis and exact computer simulations for optical correlation in correlators having pixellated spatial light modulators with transmissive (or reflective) dead zones in both the input and filter planes. We show that the correlation amplitude consists of four terms: a true correlation plus ...

In the human small intestine there is omnipresent electrical activity with a frequency of 0.15-0.2 Hz. The electrical activity of the small intestine can be measured by surface electrodes placed on the abdominal skin. The most annoying problem in the surface electrical recording is the respiratory artifact which is not ...

It is shown that time frequency signal analysis could be a useful technique in detecting late potentials (LP). In particular, the spectrogram, the Wigner distribution and the wavelet transform have been applied to ECG signals from patients with sustained ventricular tachycardia. Comparisons of the three algorithms reveals that much better ...

The practice of clinical neurophysiology requires fast, reliable and accurate assessment of a variety of biologic signals. Appropriate filters and rates of analog-to-digital sampling must be used to avoid distorting the signal. Using principles of sampling theory and examples, we describe the frequency content of signals encountered in clinical neurophysiology ...

Minimizing a Euclidean distance in the complex plane optimizes a wide class of correlation metrics for filters implemented on realistic devices. The algorithm searches over no more than two real scalars (gain and phase). It unifies a variety of previous solutions for special cases (e.g., a maximum signal-to-noise ratio with ...

This study assesses the feasibility of beat-to-beat measurement of the R-T interval in Holter ECG recordings. The low sampling rate of the Holter system was increased by a specific interpolating filter, and the precision and accuracy of two T-wave fiducial point (T-wave maximum: Tm, T-wave end: Te) detection algorithms were ...

The high-pass Fourier filtering technique with an opaque stopper is commonly used for the reconstruction of shearograms. We believe that no analysis of this technique as applied to the shearogram reconstruction has been described. We present here a theoretical analysis of this reconstruction system taking into account the stopper that ...

The process of QRS alignment as required in signal-averaged ECG can impose serious limitations on the spectral range of the signal output. This effect depends basically on the particular alignment technique being used and on the level and type of noise present in the recorded ECG. In clinical studies where ...

Three-dimensional acoustic display systems have recently been developed that synthesize virtual sound sources over headphones based on filtering by head-related transfer functions (HRTFs), the direction-dependent spectral changes caused primarily by the pinnae. In this study 11 inexperienced subjects judged the apparent spatial location of headphone-presented speech stimuli filtered with non-individualized ...

Contrast sensitivity functions were measured with five light filters and without a filter, in the presence of a glare source, in 12 retinal degeneration subjects and 9 normal subjects. The light filters included yellow-tinted, CPF 527, NoIR 111, 0.6 neutral density and sunglasses with a 95% UV filter. Retinal degeneration ...

Most filtering facepieces used today are made of electret material (material with significant electrical charges on the filter fibers). Because of the addition of this electrical removal force, the filtration efficiency can be significantly increased without increasing the air pressure drop inside the respirator; pressure drop is closely related to ...

Japanese cellular radios employ reverse frequency-allocations of the transmitter and receiver frequency bands. A rather narrowband surface acoustic wave (SAW) transmitter prefilter and a new type of SAW low-loss and high-power transmitter final stage filter-dual configurations to previously developed US cellular radio system filter-have been developed. The dual configurations provide ...

A voice activated garage door opener was designed for a handicapped person to open a garage door without assistance. This design uses speech recognition of one word. The activating word that was chosen is "up". The frequency spectrum of "up" was captured on a soundboard and is the basis of ...

Various methods have been used in the analysis of visually evoked potential signals. Due to the high noise content of the ssVEP signal, the signal is usually filtered using averaging or an order statistic filter, and then analyzed for frequency content. A frequency analysis technique often employed is the short-time ...

In using filtered backprojection to compute the inverse Radon transform, the ramp filter amplifies noise. Spatially invariant noise filters reduce resolution. It is desirable to filter noise where projections have no local high-frequency components. Using the short-time Fourier transform, the authors apply a time-frequency mask filter that zeroes out projections ...

We presented in this communication a computer algorithm that offers the advantage of simultaneous analysis of the power spectrum of multiple physiologic signals, including systemic arterial pressure, single-neuronal and electroencephalographic signals, on a continuous, on-line and real-time basis. It provided sensitive definition, discrimination and quantification (graphic and digital) of the ...

Detection of picogram quantities of Botulinus toxin-B (BoTX), using Protein A purified biotin- and fluorescein-labelled antibodies, is described in this report. All assays were performed on the Light Addressable Potentiometric Sensor. Results indicate a near linear dose response curve for increasing the amounts of BoTX (10-1,000 pg). The presence of ...

Phase-only and binary-phase spatial light modulators can be employed in the filter plane of incoherent pattern recognitionsystems. We employ computer simulations to show that advanced filter design techniques can be used to achieve a close approximation to classical matched filtering.

The shape of the auditory filter at a given centre frequency can be estimated by measuring the threshold for detecting a sinusoid presented in a spectral notch in a noise masker, as a function of notch width. Laboratory studies using this method have typically been based on threshold measurements for ...

By gradually translating the peak frequency of guiding filters along its length, we create a fibertransmission line that is substantially opaque to noise while remaining transparent to solitons. This trick allows the use of stronger filters, and hence greater jitter reduction, without incurring the usual penalty of exponentially rising noise ...

Many bioelectric signals result from the electrical response of physiological systems to an impulse that can be internal (ECG signals) or external (evoked potentials). In this paper an adaptive impulse correlated filter (AICF) for event-related signals that are time-locked to a stimulus is presented. This filter estimates the deterministic component ...

Photorefractive BaTIO3 is used as an optical novelty filter to highlight the high spatial frequency components of the photothermal signal. A real-time phase grating recorded in BaTIO3 acts as a matched rejection spatial filter for the probe laser. This reduces the stationary background from the optical signals thereby increasing signal ...

Flash visual evoked potentials (FVEPs) were recorded from the rat in order to determine the effects of low-pass filtering on the wave form. The low-frequency (high pass) filter remained fixed at 3.2 Hz while the setting of the high-frequency (low-pass) filter was progressively raised from 32 Hz to 3.2 kHz. ...