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D C Barber

Publications and source records attributed to D C Barber.

At least 37 records · Page 2Linked to original sources
PubMed1994

Image reconstruction using non-adjacent drive configurations.

The standard 'back projection' image reconstruction algorithm developed at Sheffield uses data obtained by passing current between adjacent pairs of electrodes and measuring voltage differences between the remaining pairs. Previously it has been argued that this configuration gives the best resolution compared to all other bipolar drive configurations. However, it also gives the worst signal to noise ratio data and it is possible that under conditions of poor signal to noise ratio it may be advantageous to use an alternative drive configuration, even at the expense of resolution. A general image reconstruction algorithm for any bipolar drive configuration has been produced. Reconstruction algorithms for the adjacent, cross (drive electrodes 90 degrees apart) and polar drive (drive electrodes 180 degrees apart) have been examined and compared in terms of their resolution and noise performance.

Algorithms↗
PubMed1994

Cardiac and respiratory related electrical impedance changes in the human thorax.

Electrical impedance measurements have been made from the human trunk over the frequency range 9.6 kHz to 614 kHz. Measurements have been made from 12 normal subjects and the amplitude of the impedance changes associated with the cardiac and respiratory cycles have been recorded. It was found that the real part of the impedance fell to 64.0% of its low frequency value over the measured range of frequencies and that the changes associated with respiration fell in a similar manner. However, the cardiac related changes fell more rapidly with increasing frequency to 28.2% of the low frequency value. The origin of the measured changes is discussed with a view to understanding why the cardiac related changes fall more rapidly. It is not possible to relate in any simple way the frequency dispersion of a single component to that of the whole trunk. However, the results are consistent with the lungs being the major origin of both the cardiac and respiratory related components. The origin of the cardiac related impedance changes could be the pulsatile volume changes in the pulmonary tree. These could be shunted by nonpulsatile lung tissue that has decreasing impedance at high frequency and thus decreases the relative magnitude of the cardiac related changes. This hypothesis needs to be tested using localized measurements from the thorax and 3-D modeling of the trunk.

Adult↗
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

Registration of low resolution medical images.

There are several situations in which the registration of two medical images is desirable. One example is the registration of two images of the same organ taken using different radionuclide tracers, for example the ventilation and perfusion components of a V/Q lung scan, where the aim is to compare the regional uptake of the two tracers. Another example is the registration of images of an organ belonging to a single patient but taken at different times, where the aim is to follow changes in tracer uptake. Such techniques require a reliable method of registering images. One image is usually brought into registration with another image using a coordinate transfer function (CTF) and the central problem in image registration is the determination of the appropriate CTF. A new semi-automatic approach to the problem of finding the CTF for similar images is described which is especially applicable to low resolution images.

Diagnostic Imaging↗
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

Back-projection distortions in applied potential tomography images due to non-uniform reference conductivity distributions.

An investigation was conducted to determine and quantify the distortions in applied potential tomography (APT) images reconstructed from data originating from bodies of non-uniform reference conductivity distributions. The results show that the distortions in the images are dependent on the reference conductivity distribution and on whether the images are formed by back projection along the assumed equipotentials of a uniform reference conductivity distribution or along the equipotentials of the true conductivity distribution. We believe that this last finding is significant since our previously held expectation, similar to that of Yorkey and Webster (1987), that back projection along the true equipotentials of the reference conductivity distribution should result in an accurate reconstruction, is shown to be incorrect.

Electric Conductivity↗
PubMed1992

Noise and spatial resolution of a real-time electrical impedance tomograph.

The Sheffield real-time electrical impedance tomograph produces 25 images per second, using 16 electrodes with adjacent-pair current drive and non-iterative image reconstruction. We describe the data acquisition timing of this instrument and present quantitative measurements of its signal-to-noise ratio and spatial resolution.

Electric Conductivity↗
PubMed1992

Blood flow imaging using electrical impedance tomography.

It is shown that a real-time electrical impedance tomography (EIT) system can be used to image the flow of saline through the human vascular system. A 10 ml bolus of 0.9% saline injected intravenously distal to an EIT imaging plane allows venous flow to be observed. Measurements on a cylindrical tank with flow along axial conductive tubes have been used to establish that the area under a concentration against time curve can be obtained from the EIT images and used to determine the flow rate down the tube. In vivo results show that flow images of the venous system in a limb can be obtained and that there is adequate sensitivity to follow the passage of a saline bolus though the cardiac chambers.

Blood Flow Velocity↗
PubMed1992

Monitoring body fluid distribution in microgravity using impedance tomography (APT (applied potential tomography)).

For an astronaut, the excitement of going into orbit is accompanied by a shift of 1 to 1.5 l of fluid from the legs into the upper body. Information on the way the redistributed fluid is handled by the body is very useful to space physiologists studying the process of adaptation to zero-gravity. Applied potential tomography (APT) can be used to image changes in fluid distribution. To ensure that the technique was capable of measuring fluid shifts induced by changing gravitational forces on the body, a standard Sheffield APT system was used to study several subjects during the eight ESA parabolic flight campaign. The results clearly demonstrated the feasibility of using APT for monitoring fluid redistribution during space flight. A battery-powered, body-worn APT system has now been developed for use in space. The equipment was tested on the eleventh parabolic flight campaign. The data collected with the miniaturised system was comparable to that obtained in the earlier experiment. Ergonomic tests indicated that the equipment is no more difficult to operate and maintain under weightless conditions than on earth. The system is undergoing space qualification tests in Munich. If no problems arise it will be used by German astronauts on missions to MIR and Skylab.

Body Fluids↗
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↗
PubMed1991

Photosensitizing activities of picket fence porphyrins in vitro and in vivo.

A set of structurally distinct o-substituted tetraphenylporphyrins, the picket fence porphyrins, were evaluated for their ability to photosensitize tumor mitochondria in vitro, in vivo-in vitro, and tumor implants in situ. Differential photosensitized inactivation efficiencies toward mitochondrial enzymes in vitro are reported for the 12 compounds studied as a function of side chain length and isomer structure. Fluorescence studies in aqueous solution coupled with mitochondrial uptake studies indicate that the observed range of inactivation efficiencies are due to different inherent solubilization properties for the picket fence porphyrins. Studies with the most soluble compound, 3,1-meso-tetrakis(o-propionamidophenyl)porphyrin, using an in vivo-in vitro protocol indicate that a more effective photosensitization can be obtained by using an interval of 4 h between photosensitizer administration and irradiation as compared to 24 h for Photofrin II. Irradiation of tumors in vivo 4 h following administration of 3,1-meso-tetrakis(o-propionamidophenyl)porphyrin, resulted in a mean tumor doubling time more than eight times longer than that observed for untreated tumors. 31P NMR spectroscopy in situ indicated that photodynamic therapy using 3,1-meso-tetrakis(o-propionamidophenyl)porphyrin induced a rapid and significant reduction in high energy phosphate metabolites.

Animals↗
PubMed1991

Trans-thoracic fluid shifts and endocrine responses to 6 degrees head-down tilt.

A tomographic method of measuring electrical impedance known as Applied Potential Tomography (APT) has been used to image the impedance changes within the thoraxes of 8 healthy volunteers (4 male, 4 female) during 4-h periods of 6 degrees head-down tilt (HDT). A large decrease in impedance, reflecting an increase in thoracic fluid, was apparent within 1 min of tilting, peaked after 45 min, and was maintained throughout, although during the 4 h there was an 8% return towards baseline resistivity. Resistivity changes were most obvious in the region of the lungs. Simultaneous measurements of the key fluid regulating hormones revealed a significant increase in atrial natriuretic peptide (ANP) and a significant decrease in angiotensin II (AII) and aldosterone. There was no significant difference in plasma antidiuretic hormone level. These results illustrate the dynamic nature of fluid shifts during HDT, the spatial distribution of the fluid within the thorax and the associated endocrine responses.

Adult↗
PubMed1990

Quantification in impedance imaging.

Applied potential tomography (APT) is a technique for producing tomographic images of the distribution of electrical resistivity within electrically conducting objects. Human tissues exhibit a wide range of resistivities and images of resistivity within the body should show good contrast. The data used to reconstruct such images are measurements of the voltages developed on the surface of the object when various patterns of current are passed through the object. The reconstruction problem is much harder than for other tomographic modalities but we have shown that provided we restrict ourselves to imaging changes in resistivity, it is possible to reconstruct images from data collected in vivo. We describe some possible clinical uses of the technique.

Electric Conductivity↗
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↗