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Biomedical subjects

R I Kitney

Publications and source records attributed to R I Kitney.

At least 19 recordsLinked to original sources
PubMed1997

Interactive algorithms for the segmentation and quantitation of 3-D MRI brain scans.

Interactive algorithms are an attractive approach to the accurate segmentation of 3D brain scans as they potentially improve the reliability of fully automated segmentation while avoiding the labour intensiveness and inaccuracies of manual segmentation. We present a 3D image analysis package (MIDAS) with a novel architecture enabling highly interactive segmentation algorithms to be implemented as add on modules. Interactive methods based on intensity thresholding, region growing and the constrained application of morphological operators are also presented. The methods involve the application of constraints and freedoms on the algorithms coupled with real time visualisation of the effect. This methodology has been applied to the segmentation, visualisation and measurement of the whole brain and a small irregular neuroanatomical structure, the hippocampus. We demonstrate reproducible and anatomically accurate segmentations of these structures. The efficacy of one method in measuring volume loss (atrophy) of the hippocampus in Alzheimer's disease is shown and is compared to conventional methods.

Algorithms↗
PubMed1997

Real-time heart rate variability extraction using the Kaiser window.

A new method for real-time heart rate variability (HRV) detection from the R-wave signal, based on the integral pulse frequency modulation (IPFM) model and its similarity to pulse position modulation, is presented. The proposed method exerts low-pass filtering with a Kaiser window. It can also be used for off-line HRV analysis in both the time and frequency domains. Real-time bandpass filtering as a new HRV investigation method and as a by-product of the proposed algorithm is also introduced. Furthermore, the discrete time domain version of the French-Holden algorithm is developed, and it is thoroughly proved that low-pass filtering is an ideal method for detection of HRV.

Algorithms↗
PubMed1996

Object-based three-dimensional X-ray imaging.

A form of three-dimensional X-ray imaging, called Object 3-D, is introduced, where the relevant subject material is represented as discrete 'objects'. The surface of each such object is derived accurately from the projections of its outline, and of its other discontinuities, in about ten conventional X-ray views, distributed in solid angle. This technique is suitable for many applications, and permits dramatic savings in radiation exposure and in data acquisition and manipulation. It is well matched to user-friendly interactive displays.

Humans↗
PubMed1993

Use of the frequency-tracking locus in estimating the degree of respiratory entrainment in preterm infants.

In order to define the complex interactions between external stimuli and non-linear physiological systems, a technique (the frequency-tracking locus, FTL) was devised that describes the cycle-by-cycle changes in phase angle and amplitude between two signals. Qualitative assessment of the nature of interactions between the signals can be made by examining the FTL. Quantitation of the extent of entrainment of the spontaneous physiological rhythm is possible after deriving a numerical index (the path-length index, PLI) describing the departure of the system from a fully entrained state. The FTL was applied to the study of interactions between spontaneous respiratory effort and mechanical inflation in preterm newborn babies undergoing mechanical ventilation. Stable and unstable states of 1:1 interaction were noted while integer-ratio relationships were seen at low rates of mechanical ventilation. Stable states of entrainment corresponded to a PLI value near unity, and the value of PLI increased rapidly as interactions became unstable. The FTL may be used to describe complex interactions in physiological systems, and may be used as a guide to baby-ventilator matching during mechanical ventilation of the newborn.

Humans↗
PubMed1992

Study of the relationship between estimates of enzyme kinetic parameters.

Previous indications of an intrinsic relationship between estimates of Km and Vmax calculated from the Michaelis-Menten equation have been explored further. A mathematically linear relationship could be established for the estimates of the two parameters. The relationship--the trend line--holds whether or not the experimental error is linked to the rate of reaction, the substrate concentration or both, provided that the distribution of errors is symmetrical. The practical implication is that enzyme variants with low values of Km and Vmax may not be distinguishable from those with high values of Km and Vmax.

Enzymes↗
PubMed1992

Advanced spectral estimators for detailed blood flow studies.

Recent publications have emphasized the relationship between the spectrum of the backscattered acoustic signal, beam geometry, and flow patterns in the measurement of blood flow by Doppler ultrasound. On this basis, we believe that in the future more importance will be placed on analyzing various characteristics of the spectral shape rather than absolute parameters of measurement, such as the mean frequency. The potential of this approach for extracting more information from the raw Doppler signal is introduced by considering the Spectral Broadening Index (SBI). We explain the use of the SBI parameter for measuring flow angle under restricted flow conditions. This is done by using an analytic/computational model for prediction of the spectral broadening effect. By simulation study, the performance of various spectral estimators for determining the SBI from finite Doppler signal segments is evaluated.

Blood Flow Velocity↗
PubMed1991

Biomedical signal processing (in four parts). Part 2. The frequency transforms and their inter-relationships.

This is the second in a series of four tutorial papers on biomedical signal processing, and it concerns the relationships between commonly used frequency transforms. It begins with the Fourier series and Fourier transform for continuous time signals and extends these concepts for aperiodic discrete time data and then periodic discrete time data. The Laplace transform is discussed as an extension of the Fourier transform. The z-transform is introduced and the ideas behind the chirp-z transform are described. The equivalence between the time and frequency domains is described in terms of Parseval's theorem and the theory of convolution. The use of the FFT for fast convolution and fast correlation is described for both short recordings and long recordings that must be processed in sections.

Biomedical Engineering↗
PubMed1991

Biomedical signal processing (in four parts). Part 3. The power spectrum and coherence function.

This is the third in a series of four tutorial papers on biomedical signal processing and concerns the estimation of the power spectrum (PS) and coherence function (CF) od biomedical data. The PS is introduced and its estimation by means of the discrete Fourier transform is considered in terms of the problem of resolution in the frequency domain. The periodogram is introduced and its variance, bias and the effects of windowing and smoothing are considered. The use of the autocovariance function as a stage in power spectral estimation is described and the effects of windows in the autocorrelation domain are compared with the related effects of windows in the original time domain. The concept of coherence is introduced and the many ways in which coherence functions might be estimated are considered.

Biomedical Engineering↗
PubMed1990

Biomedical signal processing (in four parts). Part 1. Time-domain methods.

This is the first of a series of four tutorial papers on biomedical signal processing. It provides an introduction to terminology and basic ideas for testing for randomness and trend, and for the determination of basic signal properties in the time domain, given the uncertainties associated with the estimation process. Techniques outlined in the paper are: the coherent average, cross-correlation and covariance, autocorrelation and phase-shift averaging.

Biomedical Engineering↗
PubMed1990

Intravascular ultrasound imaging and three-dimensional modeling of arteries.

In this article, we describe the reconstruction of arterial structures using solid modeling. The alternative approaches to three-dimensional modeling are discussed and the voxel space system we use for intra-arterial imaging, based on ultrasonic data, is described. The complete three-dimensional ultrasonic imaging system comprising a purpose-built, catheter-mounted ultrasound probe, ultrasonic transceiver, and computer system is presented. This system has been used to recreate three-dimensional computer models of arterial sections in vitro and in vivo. Examples to illustrate the power and flexibility of voxel space modeling in terms of postprocessing and software manipulation are given. Preliminary work on tissue differentiation, using arterial models and color coding of the image, and three-dimensional presentation of flow data is included.

Arteries↗
PubMed1989

3-D visualization of arterial structures using ultrasound and Voxel modelling.

In this paper, a new type of vascular imaging system is presented which is designed for use in conjunction with percutaneous transluminal treatment techniques (balloon and laser angioplasty, atherectomy etc). Three dimensional computer models of arterial sections are reconstructed in full voxel space from data acquired using a purpose-built, catheter-mounted ultrasound probe. The system is standalone, using commercially available computer hardware and specially written software. The software is equally compatible with source data from other modalities (e.g. CT and MR), and the system can therefore be incorporated into a PACS environment.

Arterial Occlusive Diseases↗
PubMed1989

On the discrimination between band-limited coherent and random apparent stresses in transitional pulsatile flow.

A frequency domain approach that incorporates a matched filter was examined for discriminating between ordered velocity fluctuations with band-limited frequency content and random velocity variations in pulsatile disturbed flows. Fluctuations at pseudo-discrete frequencies may yield a significant contribution to the apparent stress tensor computed from the unsteady Navier Stokes equations, and an estimate of the stresses arising from these ordered structures can be obtained once the velocity variations have been decomposed. This type of decomposition permits the estimation of the apparent stresses in turbulent flows, consisting of coherent and random parts, in blood flow applications such as diseased constricted arteries or downstream of artificial heart valves.

Blood Flow Velocity↗
PubMed1988

Maximum likelihood frequency tracking of the audio pulsed Doppler ultrasound signal using a Kalman filter.

Accurate estimation of velocity from the audio Doppler signal is important in the study of disease. The paper addresses this problem by considering the application of maximum likelihood as the basis for frequency tracking using a Kalman filter. The effectiveness of the algorithm in velocity estimation on both test signals and clinical data is discussed. This is particularly important in tracking of the oscillations which occur in the deceleration phase of the cardiac cycle.

Animals↗
PubMed1988

Dynamic measurement of human capillary blood pressure.

1. Capillary blood pressure was measured in man using a dynamic servo-nulling system and direct micropuncture. This enabled assessments of the normal variations in pressure which influence fluid filtration and reabsorption. 2. Seventy-eight capillaries in 19 subjects were punctured in one of three positions around the capillary loop with the hand at the level of the sternal angle. Mean pressure around the loop fell from 37.7 +/- 3.7 mmHg (arteriolar limb, mean +/- SEM, n = 12) to 19.4 +/- 1.0 mmHg (apex, n = 25) to 14.6 +/- 0.5 mmHg (venular limb, n = 41) at skin temperatures of 18.7-33.1 degrees C. These values agree closely with Landis' original studies in 1930 [E. Landis (1930) Heart, 15, 209-228]. 3. The mean filtration/reabsorption state of any particular capillary limb was not static because of cardiac, vasomotor and respiratory fluctuations in capillary pressure. From a total of 38 capillaries in which recordings were analysed for 30 s, the fluctuations in pressure were such that 27 capillaries probably had periods of both filtration and reabsorption. 4. Computerized superimposition and coherent averaging of trains of capillary pulses enabled an accurate description of the pulse waveform to be made in three capillaries. This was remarkably similar to waveforms from the radial artery, albeit at reduced amplitude (average 3.6 +/- 3.4 mmHg, mean +/- SD overall). The time for the pulse to travel between the radial artery and the finger capillary was approximately 10 ms, which implies a propagation velocity of several metres per second.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

The Zoom Wigner transform and its application to the analysis of blood velocity waveforms.

The analysis of blood velocity using noninvasive Doppler ultrasound is now an important clinical technique. The paper discusses the application of the Wigner transform to the estimation of blood velocity from the Doppler signal. A new type of Wigner transform, the Zoom Wigner Transform or ZWT is developed. The ZWT has certain advantages over the standard Wigner transform, particularly in relation to the frequency resolution of specific components, these are discussed. The final section of the paper considers practical aspects of blood velocity estimation and illustrates the use of the WZT in relation to other methods.

Blood Flow Velocity↗
PubMed1986

The analysis of blood velocity measurements by autoregressive modelling.

Analysis of velocity disturbances arising in poststenotic flow is examined using the technique of autoregressive modeling. The essential elements of this method are described including relevant criteria for selecting the model order. Velocity data employed in the analysis are taken from in vivo measurements in the dog aorta, and the results indicate that the autoregressive method improves the resolution of coherent features in disturbed flow patterns. By applying homomorphic filtering to individual beats, the occurrence of organized structures convected from their origin in the shear layer is readily identified.

Animals↗
PubMed1986

Application of the Pisarenko Harmonic Decomposition method to physiological data.

In this paper the Pisarenko Harmonic Decomposition (PHD) method is presented as a technique for short duration spectral estimation; it has been tested under various conditions to provide guidelines for its implementation. There appears to be a range of frequencies for which the PHD method gives non-biased frequency estimates. A rapid method for obtaining the sampling frequency required for non-biased frequency estimates is also discussed.

Adult↗