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Biomedical subjects

C J Kotre

Publications and source records attributed to C J Kotre.

At least 19 recordsLinked to original sources
PubMed1996

Variations in in vivo electrical impedance tomography images due to inaccuracy in boundary representation.

A comparison of in vivo image results is performed for five image-reconstruction programs, featuring an increase in accuracy of boundary modelling from a simple 2-D disk to a true boundary shape with each current drive field individually calculated. Variations are found both in the positions of imaged features and their appearance, but reasonable consistency in reconstructed impedance changes is obtained for both phantom and in vivo data. In terms of quantitative measurements, the programs based on the simpler boundary assumptions generally perform more reliably than the more complex versions. It is concluded that the quantitative use of EIT with simple boundary assumptions is not compromised by body contour variations between patients, provided that the appropriate regions of interest can be correctly identified.

Algorithms↗
PubMed1996

Subsurface electrical impedance imaging: measurement strategy, image reconstruction and in vivo results.

In conventional cross-sectional electrical impedance tomography, most of the spatial information is concentrated at the periphery of the image, close to the measurement electrodes. Increasing the number of electrodes tends not to increase the poor resolution at the centre of the cross-sectional image due to the physics of three-dimensional current flow. In this work an alternative approach. INSEIT (imaging near the surface by electrical impedance tomography), is explored in which the image plane lies at a selected depth in the object parallel to a surface electrode array. This approach has been investigated using a prototype data measurement system. The preliminary in vivo results include subsurface images of respiration, the gastro-intestinal tract and limb blood flow.

Arm↗
PubMed1996

An experimental investigation of the effect of light-box luminance on the detection of low contrast objects in mammography.

It has been hypothesized that light-box luminance is an important factor in the detection of objects on radiographs. In this work, existing psychophysical data relating to the measurement of visual thresholds at various scene luminance levels are applied to the problem of the observation of radiographs on a light-box. These data suggest that for a given stimulus size, the threshold contrast varies little over several orders of magnitude of scene luminance. In a series of contrast detail experiments performed over a wide range of light-box luminances it has been demonstrated that the detection of low contrast objects on mammographic film is dominated by external noise, that is noise on the film, rather than the internal visual noise of the observer. It is therefore suggested that in mammography it is inappropriate to base recommendations for optimal values of light-box luminance on psychophysical studies of visual noise. It has been shown that commonly used light-box luminances are suitable for viewing mammograms at the higher average optical densities now being recommended, provided that precautions are taken to avoid glare and reflection.

Contrast Sensitivity↗
PubMed1995

Computed tomography evaluation of renal parenchymal volume in patients with chronic pyelonephritis and its relationship to glomerular filtration rate.

The measurement of renal parenchymal volume using a calibrated computed tomography image processing method has been evaluated clinically on a cohort of patients with chronic pyelonephritis. Comparison of renal volume with function as assessed by 99Tcm DTPA renography demonstrated a simple linear relationship in patients who were normotensive and aproteinuric. The implications of this result on the interpretation of prognostic factors determining declining renal function in chronic pyelonephritis are discussed.

Chronic Disease↗
PubMed1995

The use of a contrast-detail test object in the optimization of optical density in mammography.

In mammography, it is important that the maximum amount of diagnostic information is obtained from each radiograph. One of the factors influencing image quality is the optical density of the film. In this study, a contrast-detail test object was used to establish the optimum optical density value on the basis of signal-to-noise ratio (SNR) for two mammographic film-screen combinations under particular processing conditions. The optimum optical density, taken as being the point at which the threshold contrast is a minimum varied little with detail size. The optimum optical density for the Fuji film-screen combination with Photosol chemistry was found to be higher than that for the Kodak film-screen combination and Kodak processing conditions studied. Although the actual values of optical density are specific to the fixed processing conditions encountered, the technique has more general applicability.

Breast Neoplasms↗
PubMed1995

A linear modelling approach to automatic interpretation of quality control measurements in mammography.

An approach to the automated interpretation of quality control data is described in which the relationship between small changes in system performance and the resulting small changes in the measured quality control test results are approximated as a set of linear equations in matrix form. The inverse of this forward matrix is then used to identify causal changes from the set of measured changes. This approach has been investigated for the case of mammographic screening quality assurance and shown to provide a potentially useful tool to assist in the interpretation task.

Autoanalysis↗
PubMed1994

EIT image reconstruction using sensitivity weighted filtered backprojection.

A set of specifications thought useful to advance the utility of electrical impedance tomography as a clinical imaging modality is proposed, together with an approach to image reconstruction designed to fulfil these specifications. Computer simulations are used to investigate the performance of this reconstruction approach on simple, known, impedance distributions and to develop the method to the stage of a complete reconstruction algorithm. The algorithm is then tested on data sets produced by measurements on a physical phantom, and on a set of measurements made on a volunteer human subject.

Algorithms↗
PubMed1994

Measurements of the frequency distribution of optical density in screening mammography.

A method for obtaining histograms of the frequency of occurrence of optical densities in mammograms has been implemented. Averaged optical density distributions were produced for approximately 50 screening mammograms at each of two centres using different film-screen and processing chemistry combinations. Additional measurements were made on films of two commercially available anthropomorphic breast phantoms. The results show that screening mammograms, on average, exhibit a strongly peaked optical density distribution which corresponds closely to the target optical density measured using the current recommended test protocol for automatic exposure control devices.

Breast Neoplasms↗
PubMed1993

A micro-computer based CT and digital fluorography system for radiotherapy simulators.

A low cost system designed to produce low resolution CT images from a radiotherapy treatment simulator is described. The system is based upon a standard micro-computer and operates using the simulator's image intensifier as the CT detector. The resulting images are intended to supply cross-sectional anatomical information appropriate for the application of inhomogeneity corrections to treatment plans for megavoltage radiotherapy of the thorax. Options for digital fluorography and hold-last-frame fluoroscopy are also described. Examples of clinical images are presented.

Computer Simulation↗
PubMed1992

The determination of total filtration on mammographic X-ray sets.

Data produced by a computer model are presented which allow the amount of molybdenum filtration on a molybdenum target mammographic X-ray set to be estimated from the measurement of the half value layer (HVL) in aluminium. Existing data refer either to tungsten target tubes or to molybdenum target tubes for a single anode angle and a constant potential waveform with the compression plate present. In addition to the tube voltage, the present data take account of the waveform of the tube potential and target angle. The results of an experimental verification of the model are presented and the effect of the geometry used in the experimental set-up discussed. Theoretical predictions of the molybdenum filter thickness made using the data from the model are in good agreement with the measured filter thickness, provided that attention is paid to the experimental geometry.

Computer Simulation↗
PubMed1992

An alternative approach to contrast-detail testing of X-ray image intensifier systems.

The difficulties of making the results of threshold contrast-detail diameter tests on X-ray image intensifier systems consistent with published performance standards are discussed. The current approach to contrast-detail testing is described and an alternative method intended to give greater consistency for all image intensifier input field diameters proposed. The current and alternative test conditions are compared on two image intensifier systems. The results obtained show that the contrast-detail curves for image intensifier systems with a wide range of input field diameters can be effectively normalized to be directly comparable to a common reference standard by applying the proposed alternative test conditions. The implications of this result on the interpretation of the contrast-detail test are discussed.

Quality Control↗
PubMed1990

Automated quality assurance and patient dosimetry in diagnostic radiology.

It has been generally considered that improved methods of quality assurance would reduce the population dose from diagnostic radiology. This paper describes the development of a computerized method of automatically monitoring tube and generator parameters to perform on-line quality assurance, whilst undertaking various patient dosimetry measurements and calculations for each exposure. The method involves interfacing a microcomputer to a microprocessor controlled X-ray generator. Details of the various interfacing methods and modifications to the X-ray unit are given. The instrument enables quality assurance to be performed for every exposure by comparing tube and generator parameters against nominal settings. The software automatically warns the operator of any deviations from accepted limiting values. When a patient is examined, details of the examination and projection are entered into a database. The exposure area product and field size are monitored for each exposure. This data, together with information on tube potential and examination/projection is used to deduce patient entrance skin dose and energy imparted. Doses to individual organs are estimated using normalized organ dose data and a knowledge of tube potential and field size.

Equipment Design↗