Biomedical subjects

F H Chan

Publications and source records attributed to F H Chan.

11 recordsLinked to original sources

PubMed1995

Detection of brainstem auditory evoked potential by adaptive filtering.

A method of detecting brainstem auditory evoked potential (BAEP) using adaptive signal enhancement (ASE) is proposed and tested in humans and cats. The ASE in this system estimates the signal component of the primary input, which is correlated with the reference input to the adaptive filter. The reference input is carefully designed to make an optimal and rapid estimation of the signal corrupted with noise, such as ongoing EEG. With a good choice of reference input, it is possible to track the variability of BAEP efficiently and rapidly. Moreover, the number of repetitions required could be markedly reduced and the result of the system is superior to that of ensemble averaging (EA). To detect BAEP in cats, only 30 ensemble averages are needed to obtain a reasonable reference input to the adaptive filter, and, for humans, 350-750 ensemble averages are sufficient for a satisfactory result. Using the LMS adaptive algorithm, individual BAEP can be obtained in real-time.

Algorithms↗

PubMed1994

Visual evoked potential measurement by adaptive filtering.

The method of ensemble averaging (EA), commonly used to improve signal-to-noise ratio (SNR) in evoked potential measurements, loses potentially useful information regarding response variability across trials. Due to the usually low SNR, it is difficult to extract the response from individual trials. The present paper describes an adaptive signal enhancer (ASE) that is capable of tracking the variation of visual evoked potential (VEP) from trial to trial as well as improving SNR. This ASE requires two inputs: a primary input, which is the raw noise-corrupted response, and a reference input, which is designed for an optional performance of ASE. We used moving ensemble averaging (MEA) to form the dynamic reference input. Experimental results in humans show a satisfactory performance of the ASE in determining VEP to single stimulus and in tracking the temporal changes of the signal.

Algorithms↗

PubMed1994

An enhanced approach to adaptive processing of the brain stem auditory evoked potential.

The present paper describes an adaptive signal enhancer (ASE) method for improving signal-to-noise ratio (SNR) and also for tracking the variation of brain-stem auditory evoked potential (BAEP). The enhancer has two inputs: a primary input which is the original data to be processed, consisting of signal badly corrupted by noise, and a reference input. A method called dynamic averaging (DA) is introduced to obtain the reference input. The improved reference signal allows closer tracking of evoked potential in each subsequent trial. For BAEP measurement in human, the SNR is typically very low. It requires about 200 ensembles to generate the reference input acceptable for ASE, and tracking of the variation of BAEP can be obtained satisfactorily. Our results show that while ensemble averaging is still needed, the total number of ensembles is greatly reduced. The adaptive method thus reduces the time of measurement for BAEP compared with the conventional method of ensemble averaging.

Electricity↗

PubMed1993

Spectral characteristics of embolic heart sounds detected by precordial Doppler ultrasound during venous air embolism in dogs.

We have studied the frequency spectrum of embolic heart sounds as detected by precordial Doppler ultrasound after injecting air 0.01-0.1 ml into the external jugular vein of anaesthetized dogs (n = 7). At volumes of 0.05 ml and greater, there was a significant increase in both the maximum frequency of the spectrum and the power of those high frequency components to greater than control values. Both changes correlated significantly with the volume of air injected (P < 0.05). With repeated injections of air at 5-min intervals, there was a small increase in the high frequency components in the control signal between injections (P < 0.05). We conclude that such spectral changes could be used to quantify the volume of air in transit through the heart, and to reflect the short-term history of venous air embolism.

Animals↗

PubMed1992

Measurement of human BAERs by the maximum length sequence technique.

The traditional brainstem auditory evoked response (BAER) measurement technique (ensemble averaging) is time-consuming and is not acceptable for some time-critical clinical applications. In the paper the application of a pseudorandom binary sequence, the maximum length sequence, to human BAER measurements is examined. This technique permits a faster click rate to stimulate the test subject, and obtains a higher signal-to-noise ratio (SNR) response through deconvolution. When compared with conventional averaging, the method can result in an improved SNR or in faster measurement of BAER. The theory of the technique and the experimental setup are presented, and theoretical analysis on the SNR improvement by this technique against averaging is also given. Actual measurements of BAER on both humans and cats indicate that this technique is effective, especially when the measurement time is not too long, or the number of trials is not too large.

Algorithms↗

PubMed1991

Visual evoked potential measurement by maximum length sequence technique.

The maximum length sequence (MLS) technique is applied to improve data collection of a clinically important long latency visual potential. Given a limited time for measuring the response and with low number of stimulus presentation, the MLS technique exceeded the conventional method of ensemble averaging in attaining a higher signal-to-noise ratio (SNR). The theoretical consideration of such improvement is developed along with the system implementation. Typical examples of the results obtained in a human subject are presented.

Algorithms↗

PubMed1988

Maximum length sequence applied to the measurement of brainstem auditory evoked responses.

An evoked response may be assumed to consist of synchronous electrical activities of groups of neurons in response to a stimulus. Unfortunately, this response is usually weak and often masked by the background EEG activity generated spontaneously by the brain. In order to extract the embedded evoked response we have employed the theory of maximum length sequence, assuming only a temporal linearity of the system from which measurements are taken. The technique has been applied successfully with the aid of a microcomputer. The system also supports the same measurement by a conventional averaging technique. The results of the two are compared, indicating the advantages of the maximum length technique: improved signal-to-noise ratio, repeatability and speed.

Animals↗

PubMed1984

A microcomputer-based binaural measurement system.

A microcomputer is used to control a dual-channel, sine-wave generator as the excitation to both the left and right ears in experimental subjects, and for on-line measurement of the neuronal spike counts. The effects of varying the walking pattern and phase angle between the two channels can be investigated. After normalisation of spike counts, the result can be displayed as a 3-D plot on a CRT or an x-y plotter. The system is useful for general steady state and transient binaural measurement.

Biomedical Engineering↗

PubMed1979

The changing perinatal and maternal outcome in chorioamnionitis.

Chorioamnionitis is difficult to detect clinically, but its recognition in those at risk is essential. A retrospective study of 140 patients from among 26,129 deliveries was conducted over a 2-year period. The findings suggest that in modern obstetric practice, both perinatal and maternal complications associated with chorioamnionitis (particularly sepsis) are infrequent problems. Four neonatal deaths occurred but no infants died of sepsis. There were no maternal deaths, but 38 patients developed postpartum infections. Cesarean section did not appear to improve either perinatal or maternal outcome. With the use of appropriate modern antibiotics, extraperitoneal cesarean section and cesarean hysterectomy are probably no longer indicated. Not all neonates born out of a microbiologically contaminated intrauterine environment required antibiotic therapy, however, and individualization is recommended.

Amnion↗

PubMed1976

An ultrasonogram display system using a natural color scale.

The gray scale display used in B scan ultrasonography limits the perceptibility of clinically useful information. Presentation in color can increase perceptibility, but current color displays have no natural scale and may have the fault of a discrete color spectrum. The continuous heated-object color spectrum solves these problems. To produce a display using this spectrum, we have built an inexpensive system to adapt the scan converter output of a gray scale ultrasonograph to a commercial color television.

Adult↗

PubMedDate not supplied

Microcomputer-based spike train analysis.

A system has been developed to analyse statistically the information contained within neuronal spike trains in the central nervous system. The system consists of a microprocessor development system, together with the peripheral components and transducers. Suitable software packages have been developed to analyse statistical parameters including the mean, variance, entropy, conditional entropy, serial correlation coefficients, Markov dependency and Markov order. By linking up the required routines, the system is capable of responding in real-time and plotting the desired results from the spike train obtained. Such system has been used to study the neuronal spike trains recorded from central vestibular neurons which could be affected by positional changes, anaesthetics and various drugs for the relief of motion sickness.

Animals↗