Biomedical subjects

N M Gibson

Publications and source records attributed to N M Gibson.

7 recordsLinked to original sources

PubMed2001

A computerised quality control testing system for B-mode ultrasound.

Current methods of ultrasound (US) imaging quality control involve an observer taking a series of measurements on test object images. This process is very labour-intensive, rapidly becoming more so as the complexity of US scanners increases. Also, many of the measurements are based on the subjective judgement of the operator and are, therefore, prone to an undesirable level of intraobserver and interobserver variation. We have developed a suite of programs to analyse captured US images to estimate a number of performance parameters, including resolution, high- and low-contrast penetration depths and high- and low-contrast sensitivity. In this system, images of the ATS Laboratories Multipurpose Phantom Model 539 are acquired on a PC with a video capture card, and analysed using the software developed. Automated tests have been developed for resolution, low- and high-contrast penetration and low- and high-contrast sensitivity. A preliminary validation of the system was carried out using images from two curvilinear probes and a linear-array probe operating at 5 MHz, 7.5 MHz and 10 MHz, respectively. The 95% confidence intervals ranged from +/- 17% to +/- 21% for resolution measurements and from 0% to +/- 1.5% for low-contrast penetration. The system provides an index of visibility for high- and low-contrast targets, as compared to the coarse visual assessment of a human observer, with 95% confidence intervals ranging from +/- 6% to +/- 13% for low-contrast sensitivity and from +/- 3% to +/- 25% for high-contrast sensitivity. Advantages of the system over the human observer include improved reproducibility and increased information regarding visibility of targets. A more detailed multicentre validation is currently being undertaken.

Automation↗

PubMed1997

Detection of fetal electrocardiogram signals using matched filters with adaptive normalisation.

The authors discuss the application of matched litters to the detection of R-waves in fetal electrocardiogram (FECG) data, recorded during labour using a scalp electrode. When using the basic matched filter, one correlates a template representing the clean signal with the noisy signal. This method is optimal when the underlying noise is white in nature. However, it is known that false detection of R-waves can occur in the presence of extraneous peaks which have a similar shape to the fetal R-wave. It is proposed to switch between two different normalisations of the impulse response of the matched filter to alleviate this problem. When the signal-to-noise ratio is lower than a predetermined threshold, then normalisation to the geometric mean of the template and noisy data energies is carried out, otherwise only normalisation to the template energy is made. In the former case, the background noise and spikes that are larger than the underlying FECG are attenuated, hence increasing the probability of detection of the R-waves. In the latter case, noise, which has a lower amplitude than the underlying R-wave, is reduced. The effectiveness of this method is demonstrated by application to scalp electrode data.

Electrocardiography↗

PubMed1996

Antenatal assessment using the FECG obtained via abdominal electrodes.

During the past decade a variety of intrapartum fetal monitors have been constructed that process the entire fetal electrocardiogram (FECG), obtained via a scalp electrode. They therefore differ from conventional monitors in aiming to extract relevant timing and magnitude information from the morphology of the FECG rather than simply the RR interval and hence heart rate. An intrapartum monitor such as this has been successfully developed by ourselves. This paper describes the early results obtained whilst attempting to extend this form of monitoring forward into the antenatal period. In order to achieve this the FECG must be acquired via surface electrodes placed on the maternal abdomen, which yields a signal containing the FECG amidst a number of noise sources. Our investigations into the feasibility of "antenatal abdominal FECG analysis" have been on two fronts. The first has been to produce a bedside monitor similar in function to our intrapartum device, whilst the second has been to address the possibility of performing such monitoring in ambulant subjects. At present the antenatal bedside monitor has successfully extracted and processed the FECG in approximately 75% of the cases studied, with subjects ranging from 20 weeks through to term having been monitored. We also have demonstrated the feasibility of the long term monitoring of maternal and fetal heart rate using a portable instrument.

Abdomen↗

PubMed1995

Iterative method to derive an approximate matched filter template for fetal electrocardiogram signals.

Fetal electrocardiogram (FECG) signals that are extracted from the maternal abdomen have a signal-to-noise ratio that is so low that the determination of the times of location of the R-waves can be difficult. A matched filter could, in principle, be used, but in theory this requires prior knowledge of the shape of the QRS complex of the FECG. In the work that is described in this paper, a digital low-pass filter, with an impulse response that is triangular in shape, is applied to the first M complexes of a simulated FECG signal. An average based on the detected R-wave locations is determined and this is used as an approximation to the matched filter template for the next block of M complexes. It is shown that this method can be iterated to obtain an effectiveness in detecting R-wave locations that is competitive with the corresponding performance that is obtained with the pure matched filter. The resilience of this technique to increasing noise levels is investigated.

Algorithms↗

PubMed1993

The application of finite impulse response filters to the detection of fetal electrocardiogram signals.

An investigation is made into the potential application of linear phase digital filters to the detection of fetal electrocardiogram signals buried in noise. Such an assessment is made by applying both matched and linear phase filters to six computer simulated fetal signals and also to experimental data. The number of times that the R-wave locations are correctly located (N), the RMS error in R-wave location (RMS) and the correlation coefficient between the averaged and clean signals are computed. It is found that the averaged fetal complexes computed using these two types of filter are almost identical. However, for three of the signals, the values for N and RMS obtained using the linear phase filter are inferior to the corresponding results obtained with the matched filter. It is suggested that the averaged complex obtained using the linear phase filter could be used as an approximation to the matched filter template; it is found that this procedure results in an effectiveness of detecting R-waves that is, for the most part, comparable with the performance of a matched filter based on the QRS complex.

Abdomen↗

PubMed1992

Wavelet transform as a potential tool for ECG analysis and compression.

The recently introduced wavelet transform is a member of the class of time-frequency representations which include the Gabor short-time Fourier transform and Wigner-Ville distribution. Such techniques are of significance because of their ability to display the spectral content of a signal as time elapses. The value of the wavelet transform as a signal analysis tool has been demonstrated by its successful application to the study of turbulence and processing of speech and music. Since, in common with these subjects, both the time and frequency content of physiological signals are often of interest (the ECG being an obvious example), the wavelet transform represents a particularly relevant means of analysis. Following a brief introduction to the wavelet transform and its implementation, this paper describes a preliminary investigation into its application to the study of both ECG and heart rate variability data. In addition, the wavelet transform can be used to perform multiresolution signal decomposition. Since this process can be considered as a sub-band coding technique, it offers the opportunity for data compression, which can be implemented using efficient pyramidal algorithms. Results of the compression and reconstruction of ECG data are given which suggest that the wavelet transform is well suited to this task.

Electrocardiography↗

PubMedDate not supplied

Linking maternal efficacy beliefs, developmental goals, parenting practices, and child competence in rural single-parent African American families.

With a sample of 139 rural, single-parent African American families with a 6- to 9-year-old child, we traced the links among family financial resource adequacy, maternal childrearing efficacy beliefs, developmental goals, parenting practices, and children's academic and psychosocial competence. A multimethod, multiinformant design was used to assess the constructs of interest. Consistent with the hypothesized paths, financial resource adequacy was linked with mothers' sense of childrearing efficacy. Efficacy beliefs were linked with parenting practices indirectly through developmental goals. Competence-promoting parenting practices were indirectly linked with children's academic and psychosocial competence through their association with children's self-regulation.

Achievement↗