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W B Tindale

Publications and source records attributed to W B Tindale.

36 records · Page 2Linked to original sources
PubMed1994

Background subtraction in 99Tcm-DTPA renography using multiple background regions: a comparison of methods.

In order to obtain quantitative information from a 99Tcm-diethylenetriaminepentaacetate (DTPA) renogram it is first necessary to correct for the presence of background activity in the kidney time-activity curve. Three different methods of background subtraction which have been previously described are compared. Method 1 is a linear regression technique which uses separate tissue and heart time-activity curves to represent the background. Method 2 also uses multiple background regions and involves multiple regression. Method 3 uses a single heart region to represent the background. The three techniques are assessed using both simulation studies and patient data. The results show that method 3, which does not correct for extravascular activity, overestimates renal function particularly in poorly functioning kidneys. Method 1 gives the most accurate and reproducible results for both the simulation studies and patient data.

Computer Simulation↗
PubMed1994

Background subtraction: a new approach to the assessment of disease activity in Crohn's disease using 99mTc-HMPAO-labelled leucocytes.

A computer-based technique for the quantification of abnormal bowel uptake in Crohn's disease has been developed and compared with pre-existing clinical, laboratory and scintigraphic methods of assessment. The standard technique for labelling leucocytes with 99mTc-HMPAO is applied. Images were obtained at 40, 120 and 240 min after the injection of radiolabelled leucocytes. The count in the bowel area after subtracting background activity corrected to the injected dose and image acquisition times is the 'scan score', an objective measure of disease activity. The scan score is significantly higher in patients with clinically active disease (mean 82.1 +/- SEM 13.6) than in those with quiescent disease (24.7 +/- 7.0) (p < or = 0.005). Optimum separation between active and quiescent disease is achieved with a threshold scan score of 20. The scan score was comparable in small bowel disease (73.3 +/- 16.2), large bowel (94.4 +/- 33) and disease at both locations (94.1 +/- 19.2). The scan score correlated favourably with Crohn's Disease Activity Index (rs = 52, p < or = 0.0001), Harvey & Bradshow Simple Index (rs = 0.4, p < or = 0.001), serum C-reactive protein (rs = 0.72, p < or = 0.001), serum alpha acid glycoprotein (rs 0.67, p < or = 0.001), haemoglobin (rs = 0.66, p < or = 0.001), platelet count (rs = 0.47, p < or = 0.006), albumin (rs = 0.61, p < or = 0.0001) and faecal 111Indium excretion (rs = 0.78, p < or = 0.001), but not with the ESR (rs = 0.22, p < or = 0.4).(ABSTRACT TRUNCATED AT 250 WORDS)

Crohn Disease↗
PubMed1993

Quantification of disease activity in Crohn's disease by computer analysis of Tc-99m hexamethyl propylene amine oxime (HMPAO) labelled leucocyte images.

The reliability and clinical applications of computerised image analysis measurement of bowel uptake of Tc-99m HMPAO labelled leucocytes has been examined as a measure of disease activity in Crohn's disease. In 54 studies carried out on 33 patients with established Crohn's disease, the mean 'scan score', a quantitative assessment of image intensity, was 82.1 SEM (13.6), in patients with clinically active disease compared to 24.7 (7.0) in those with quiescent disease, p < or = 0.0005. A significant correlation was found between the scan score and Crohn's Disease Activity Index (rs = 0.52, p < 0.0001), and Harvey and Bradshaw Simple Index (rs = 0.4, p < 0.004). A low scan score correctly identified seven patients whose raised Crohn's Disease Activity Index incorrectly indicated active disease because symptoms used in calculation of the index were not caused by active inflammation. Of the laboratory measurements, the scan score correlated with the haemoglobin (rs = 0.66, p < 0.0001), albumin level (rs = -0.6, p < 0.0001), C-reactive protein (rs = 0.7, p < 0.0001), alpha-acid glycoprotein (rs = 0.57, p < 0.001), and platelet count (rs = 0.47, p < or = 0.006), but not with the erythrocyte sedimentation rate (rs = 0.2, p < or = 0.25). The scan score was raised in all patients who had clinically active disease but normal laboratory tests. The results of this study indicate that the scan score provides an objective indicator of disease activity in Crohn's disease which may be superior to clinical indices, and also to laboratory tests which although objective are often normal in the presence of active disease.

Acute Disease↗
PubMed1992

99Tcm HMPAO-labelled leucocyte imaging in Crohn's disease: a subtraction technique for the quantification of disease activity.

A new technique for the quantitative analysis of labelled leucocyte images from patients with inflammatory bowel disease is described. The method involves the computer generation of a 'background' image which, after appropriate registration, is subtracted from the patient's image to leave a residue which represents abnormal uptake in the bowel. Quantification of the residual activity yields a scan score which can be related to the level of disease activity in patients with Crohn's disease. In 54 investigations on 33 patients the scan scores correctly agreed with a clinical assessment of disease activity in 16 of 20 cases with inactive disease and 32 out of 34 cases with active disease. Most of the discrepancies reflected inaccuracies in the clinical assessment of activity rather than shortcomings of the imaging technique.

Crohn Disease↗
PubMed1992

Determination of the arterial flow fraction in normal and diseased livers using constrained deconvolution.

There is some evidence that the ratio of the blood flow to the liver through the hepatic artery to the total flow to the liver through the hepatic artery and portal vein (the hepatic arterial flow fraction, AFF) is altered in the presence of cirrhosis. Several methods have been published that seek to provide an index of this ratio. These indices are dependent on factors other than the AFF and cannot provide a true measure of it. The impulse retention function of the liver has two components and these may be derived using a model-driven deconvolution of the arterial tracer concentration curve and the curve of tracer concentration in the liver. The AFF may then be obtained from the relative heights of these two components. Simulation studies show that the AFF calculated using this method is reasonably accurate and a small clinical series shows that it is capable of appropriate clinical classification of patients into cirrhotic and non-cirrhotic groups.

Colloids↗
PubMed1992

Liver blood flow: non-invasive estimation using a gamma camera.

A non-invasive radioisotope technique for the measurement of total liver blood flow (TBF) is described. The method requires the use of two intravenously administered tracers, 99mTc (technetium 99m) human serum albumin (HSA) and 99mTc colloid. Computer analysis of first-pass time activity curves for HSA for liver and lung tissues yields values for the arterial and portal contributions to liver blood flow, from which TBF can be determined. These values are then corrected for attenuation using the images of the colloid distribution. The use of the method is illustrated in 17 subjects. Assumptions, limitations and possible applications of the technique are discussed.

Colloids↗
PubMed1990

The effect of forced expiration on the uniformity of 99Tcm-DTPA aerosol ventilation images in patients with excess sputum production.

This study examines the use of the forced expiratory technique (FET) as a means of improving the uniformity of radionuclide aerosol ventilation images in patients with excess sputum production. Ventilation images are objectively classified by two computer derived indices to characterize the degree of radioaerosol clumping and overall uniformity. In a series of twenty five patients with a long-standing history of daily sputum production, images acquired before and after forced expiration and again after a second ventilation immediately following FET showed no significant change in either index. The results obtained do not provide evidence to support the routine use of FET in conjunction with radioaerosol scintigraphy. The method of image classification correlates well with a visual assessment of image uniformity and has general application.

Aerosols↗
PubMed1987

The effect of methodology and tracer identity on a non-invasive index of liver blood flow.

There are a number of clinical conditions in which quantification of the relative flow in the arterial and portal vessels supplying the liver may be of diagnostic use. The hepatic perfusion index has been proposed as a non-invasive indicator of relative blood flows. The technique involves analysis of first-pass time-activity curves over the liver and kidney with the calculations of an index which is derived from the slopes of the hepatic curve before and after the renal peak. In previously published studies, the methodology adopted has been variable, both in the analysis and in tracer identity. This study examines the effect of both physical and physiological variables on the index. The results indicate that in addition to relative arterial and portal flows, the index is dependent on bolus quality, the length of time over which the slopes are averaged, transit times through the liver and splenic and mesenteric circulations, and the degree of tracer extraction. Furthermore, the data suggest that values in the currently considered abnormal range may be poor indicators of relative arterial and portal venous flows.

Humans↗
PubMed1986

Modification of the Gorlin equation for use with heart valve substitutes.

The Gorlin equation, which was used to assess the obstruction to flow by a stenosed heart valve, is based on steady flow (time independent) criteria derived from hydraulics. Recently, this equation has been used to obtain an effective orifice area for heart valve substitutes both in vitro and in vivo. In this study, a modification of the original Gorlin equation for use with heart valve substitutes considers both the pulsatility of the valvar flow and possible variations in volumetric flow waveforms induced by differences in myocardial performance. The modified equation also allows for the possibility of regurgitant flows. Its use is illustrated in a study of the hydrodynamic performance of a series of heart valve substitutes and recommendations are made concerning its application to cardiac catheterisation procedures.

Blood Flow Velocity↗
PubMed1985

The physics of red cell sedimentation.

Blood was withdrawn from the ante-cubital vein of five normal volunteers and the erythrocytes were washed and resuspended in isotonic saline. The rate of descent of the erythrocyte-saline boundary was measured every hour for a period of at least 4 h for different suspended cell concentrations. The velocity of this boundary remained constant during the period of observation for a specific concentration. There was, however, an experimental variation of sedimentation rate with red cell concentration. Extrapolation to zero concentration allowed the 'Svedberg constant' for normal red cells to be evaluated. A continuum physics theory was used to explain the observations. The sedimentation rate was also measured in anticoagulated whole blood. The rates of descent in whole blood and the red cell-saline suspension were significantly different. Furthermore, the erythrocyte boundary in whole blood displayed both acceleration and deceleration during the period of observation. These experiments support the concept, proposed in an earlier theoretical study, of an internal energy dissipative mechanism which occurs in heterogeneous fluids (such as blood) but not in homogeneous fluids (such as water).

Adult↗
PubMed1982

In vitro evaluation of prosthetic heart valves: anomalies and limitations.

The in vitro evaluation of fifteen commercially available prosthetic heart valves is described. The group comprised both mechanical and bioprosthetic valves. The experimental studies were carried out in a steady flow circuit which included a flexible valve test section, the geometry of which was modelled on the aortic anatomy. The fluidic performance of the valves was examined over a range of flows and in particular, the phenomenon of "pressure recovery" distal to the valve was studied in depth. A number of theoretical parameters which might be used to define valve performance were evaluated but none was found to be ideal. The conclusions of the study emphasise the limitations of such in vitro testing and the danger of extrapolating such experimental data to the possible valve performance in vivo.

Aortic Valve↗
PubMedDate not supplied

Computer aided test selection (CATS) for nuclear medicine--a prototype system for renal investigations.

An expert system for renal test selection in nuclear medicine has been developed as the first stage of a collaborative project on test selection in nuclear medicine. The stages of knowledge elicitation and knowledge representation were addressed by means of a questionnaire which was completed by five experts in the field of renal nuclear medicine. A flow chart was developed from the responses and implemented using a commercially available expert system shell (Crystal 4.5). A menu specifying clinical problems, for which renal nuclear medicine is useful, is displayed to the user who is prompted for a choice. Specific aspects of the chosen problem are then shown and again a choice is requested. Selected tests, in order of expert preference, are displayed and further information on any of these is available, if required, on selection from a menu subdivided into categories such as patient preparation, preliminary investigations, etc. The system provides cross-referencing to other areas of investigation and is currently being evaluated using a structured approach commonly employed in the assessment of user interfaces.

Decision Making, Computer-Assisted↗
PubMedDate not supplied

Modelling dual isotope parathyroid scans: objective decision making for tumour detection.

Parathyroid subtraction imaging using the radioisotopes thallium-201 and technetium-99m was first described in 1983. Since then it has become a routine method for the pre-operative localization of parathyroid tumours. Despite its widespread use, the interpretation of the subtraction images remains very subjective. This paper describes and evaluates an automatic objective method for the analysis of parathyroid scans. The method is based on the calculation of a likelihood ratio (the probability of obtaining a count in a given pixel if a tumour is present divided by the probability of obtaining that same count if a tumour is not present). The likelihood ratio is calculated for each pixel in a subtraction image. The calculated value is compared with a threshold. Pixels with likelihood ratios greater than the threshold are classified as belonging to tumour sites. Pixels with likelihood ratios less than, or equal to, the threshold are classified as belonging to 'no tumour' sites. The probability density functions required were obtained from computer simulated images. The likelihood ratio technique has a similar sensitivity and specificity to that of experienced human observers analysing computer simulated images. Furthermore, it is a completely automatic method which can provide the basis of a decision support system.

Computer Simulation↗