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Biomedical subjects

N T Evans

Publications and source records attributed to N T Evans.

17 recordsLinked to original sources
PubMed1992

Pattern of 2-deoxy-2-[18F]-fluro-D-glucose accumulation in liver tumours: primary, metastatic and after chemotherapy.

Eight patients with liver metastases from adenocarcinoma of the colon or rectum, two with suspected hepatic metastases and one with primary hepatoma were studied with 2-deoxy-2-[18F]-fluro-D-glucose (18F-FDG) using positron emission tomography (PET). In five of the patients with metastatic tumour a second examination was performed four weeks after treatment with recombinant interleukin-2 (rIL2) and fluorouracil (5FU). In all tumours (one primary and eight metastatic) the radioactivity was seen to accumulate in a rim around each tumour with a large central area showing no uptake. In the five cases imaged after treatment with rIL2, the appearance of the tumour uptake was the same as before treatment. In the two cases of suspected but not proven metastases, no abnormal accumulation of 18F-FDG was seen.

Adenocarcinoma↗
PubMed1992

Measurement of blood flow in tibial fracture patients using positron emission tomography.

The quantification of local bone blood flow in man has not previously been possible, despite its importance in the study of normal and pathological bone. We report the use of positron emission tomography, using 15O-labelled water, to measure bone blood flow in patients with closed unilateral fractures of the tibia. We compared fractured and unfractured limbs; alterations in blood flow paralleled those found in animal models. There was increased tibial blood flow at the fracture site as early as 24 hours after fracture, reaching up to 14 times that in the normal limb at two weeks. Blood flow increase was less in displaced than in undisplaced fractures. The muscle to bone ratios of blood flow were similar to those in previous animal work using other techniques. Positron emission tomography will allow study of human bone blood flow in vivo in a wide variety of pathological conditions.

Adult↗
PubMed1990

Combining imaging techniques.

There are many potential advantages in being able to compare corresponding images produced by different modalities. For example, the fine anatomical detail produced by MRI can be combined with the functional data from SPET. Using brain imaging as an example, techniques for selecting the image plane, displaying the images and quantifying the data are discussed.

Diagnostic Imaging↗
PubMed1990

Regional cerebral blood flow imaging: a quantitative comparison of technetium-99m-HMPAO SPECT with C15O2 PET.

The aim of this study was to compare technetium-99m-hexamethylpropyleneamineoxime (99mTc-HMPAO) single-photon emission computed tomography (SPECT) with regional cerebral blood flow (rCBF) imaging using positron emission tomography (PET). As investigation of dementia is likely to be one of the main uses of routine rCBF imaging, 18 demented patients were imaged with both techniques. The PET data were compared quantitatively with three versions of the SPECT data. These were, first, data normalized to the SPECT cerebellar uptake, second, data linearly corrected using the PET cerebellar value and, finally, data Lassen corrected for washout from the high flow areas. Both the linearly-corrected (r = 0.81) and the Lassen-corrected (r = 0.79) HMPAO SPECT data showed good correlation with the PET rCBF data. The relationship between the normalized HMPAO SPECT data and the PET data was nonlinear. It is not yet possible to obtain rCBF values in absolute units from HMPAO SPECT without knowledge of the true rCBF in one reference region for each patient.

Aged↗
PubMed1988

Gated cardiac tomography.

An ECG gated tomographic system is described and its application to routine diagnosis of cardiac wall dyskinesis discussed. The tomographic sections are gathered by a single section scanning system (Aberdeen Section Scanner). Technetium labelled red blood cells are used as the imaging agent. The time of the occurrence of the ECG R-wave is superimposed on the tomographic projection data stream and the gated images produced subsequently. The average patient study requires 15 min. Images at 8 phases of the cardiac cycle are generated at each of 5 levels, 16 mm apart, covering the length of the left ventricle. The images are stored as a three dimensional matrix and may be analysed in sections at any orientation. Fourier analysis of computer generated short axis sections are used to generate a set of coefficients describing the contraction of the left ventricle. The coefficients for each patient study are displayed as a series of two dimensional polar images, schematically displaying the spatial distribution of the coefficient over the left ventricle. These polar images are further analysed by comparison with distributions obtained from normal patient studies. The calculated deviations from the normal are then used to diagnose the magnitude and position of any dyskinesis. Initial results show that the tomographic system is capable of routinely detecting inferior cardiac wall dyskinesis, showing an advantage over non tomographic techniques.

Cardiomyopathies↗
PubMed1986

The Aberdeen Mark II single-photon-emission tomographic scanner: specification and some clinical applications.

The construction, operation and physical characteristics of a single-section multi-detector single-photon-emission scanner are described. The machine has 24 detectors arranged along the sides of a square. Movements and data collection are under the control of a series of distributed microprocessors. Both head and trunk tomograms can be produced. The spatial resolution at the collimator focus is 9 mm in the transverse plane, and the effective slice thickness is 14 mm. The volume sensitivity is 300 counts/s kBq ml with a 20 cm diameter cylindrical phantom filled with 99Tcm solution. The application of this machine to the examination of the brain, liver and heart has been found to be clinically useful.

Brain↗
PubMed1986

Technetium-99m HM-PAO stereoisomers as potential agents for imaging regional cerebral blood flow: human volunteer studies.

A total of nine normal volunteer subjects were studied with three forms of [99mTc] hexamethylpropyleneamineoxime (HM-PAO), a potential cerebral blood flow imaging agent. One, the d,l isomer, showed 4.1% uptake in the brain which remained constant over 8 hr. There was good differentiation between uptake in gray and white matter on tomographic slices. We propose that this agent may allow regional cerebral blood flow imaging to be performed on a routine basis.

Adult↗
PubMed1979

The accuracy and spatial resolution of the measurement of tissue oxygen removal rate.

An analysis is presented of factors determining the accuracy and spatial resolution of a method for the estimation of oxygen removal rate in tissues using a multi-cathode electrode placed on the tissue surface. The effect of oxygen consumption by the cathodes is shown to be small for 25-micrometer diameter cathodes, but covering the tissue surface with a thin oxygen oxygen-permeable plastic film can introduce a systematic error into the estimate of removal rate, the size of which depends upon the oxygen diffusion coefficient and solubility in the plastic compared with those in the tissue. Spatial resolution is shown to be adequate for distinguishing changes in removal rate over distances of a few hundred microns, and the averaging of removal rate in the direction normal to the tissue surface is weighted heavily towards the superficial tissue layer.

Oxygen Consumption↗
PubMed1978

Comparison between the oxygen removal rate and the histological structure of normal and tumour tissues.

A technique has been used to measure distributions of oxygen removal rate, QR, in samples of recently excised tissue where QR is defined as the ratio of the oxygen uptake rate to the oxygen solubility. QR was measured at 91 sampling points across a cross section of tissue of diameter 5 mm. By placing markers in the tissue and using special procedures to obtain sections of the tissue samples it was possible to compare the distributions of QR with the histological structure of the tissues. The overall resolution of the system is about 1/2 mm so that structures of the order of a millimetre or more could be examined. There are considerable inhomogeneities in QR within some normal tissues, for example 4-19 mm Hg/s in rat kidney and 0.4-1.5 mm Hg/s in human cervix. Inhomogeneities in tumour tissues are also associated with the histological structure and examples for the Lewis lung mouse carcinoma show a correlation between QR and regions of viable or necrotic tissue. For a biopsy sample of human carcinoma of the cervix QR correlates with the degree of local infiltration by tumour cells.

Animals↗
PubMed1978

Permeability and diffusion coefficient of oxygen in membranes for oxygen electrodes.

Oxygen diffusion coefficient and permeability in thin membranes of low-density polythene and laminated polytetrafluorethylene (PTFE) are measured over the temperature range of about 20 to 30 degrees C. The diffusion coefficient is estimated from the time response of a large area platinum electrode covered with the membrane material and exposed to a sudden change in PO2. outside the membrane. The electrode is operated at a very low polarising voltage so that consumption of oxygen at the cathode surface is made negligible. This method is considered to be more reliable than that based on operating the electrode at more normal polarising voltages at which the boundary condition for oxygen tension at the cathode surface is often ill-defined. Oxygen permeability is estimated from the flux of oxygen across an area of membrane separating a nitrogen gas stream from one containing oxygen, the oxygen being measured with a platinum/zirconium oxide reversible cell. Diffusion coefficient in the membranes is very temperature dependent, whereas oxygen solubility is only weakly so. The diffusion coefficient at 25 degrees C is 0.28 +/- 0.06 . 10(-6) and 1.0 +/- 0.2 . 10(-6) cm2 . sec-1 for PTFE and polythene respectively. The corresponding values for permeability are 0.80 +/- 0.08 . 10(-7) and 0.43 +/- 0.04 . 10(-7) ml O2 atm-1 . cm-1 . sec-1.

Diffusion↗
PubMed1977

The spatial correlation of fluctuations of the blood flow in forearm skin.

The oxygen tension at the skin surface, with the atmospheric oxygen supply excluded, may be measured polarographically on the human forearm. Under suitable environmental conditions, spontaneous fluctuations in skin surface oxygen tension can be recorded and these are the result of fluctuating blood flow in the superficial skin vessels. An array of separate cathodes in a single polarographic electrode assembly has been used to measure the fluctuations in blood flow which are occurring simultaneously at seven different points in the skin. Spectral analysis of a long recording of such fluctuations shows that most of the power is concentrated at the lower frequencies but does not reveal any clearly defined dominant frequency. It is clear, however, from inspection of the fluctuation patterns, that recurring bursts of activity occur with quite well-defined periodicities in the range of 30s to 5 min. There is a stronger correlation between the fluctuations occurring at points on the skin surface less than 1 mm apart than between points further apart, although there are clearly some components which are common to points separated by up to 5 mm which was the largest separation of cathodes used in these experiments. These observations are supported by the value of cross correlation coefficients between the channels. These results suggest that the observed fluctuations are the result of at least two factors. The first one is common to all the channels but the effect of this may be overridden by a second and more local one controlling the blood flow.

Arm↗
PubMed1975

A method for measuring the spatial distribution of tissue oxygen removal rates.

Distributions of oxygen removal rates are measured over cut surfaces of samples of recently excised tissue. The samples are initially equilibrated with a gas of known oxygen tension and the surface is occluded by bringing it into contact with the end of a glass rod which has a number of polarographic electrodes embedded in it. The oxygen removal rate in mm Hg/sec is calculated from the rate of fall of surface oxygen tension. 91 electrodes are arranged in an array with 0.5 mm separation and each gives an estimate of the oxygen removal rate with a spatial resolution of a few hundred microns. An artificial medium of uniform and controllable respiration rate was used to test the system. Spatial variations in oxygen removal rate were demonstrated in some transplantable rodent tumours.

Animals↗