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Biomedical subjects

S Webb

Publications and source records attributed to S Webb.

318 records · Page 18Linked to original sources
PubMedDate not supplied

Splanchnic and hepatic metabolism of somatostatin: a study in cirrhotic patients with a portacaval shunt.

Experimental data suggest that somatostatin is metabolized by both liver and kidneys. Results in humans are conflicting. By studying a group of cirrhotic patients with surgically induced end-to-side portacaval shunts, basally and during a somatostatin infusion, we have been able to analyze separately the hepatic and splanchnic metabolism of this peptide. After catheterization, samples were obtained from the pulmonary artery, portal and hepatic veins. Basal pulmonary artery immunoreactive somatostatin (IRS) was significantly higher (p less than 0.001) in the cirrhotic patients (96 +/- 11 pg per ml) than in a sex- and age-matched control group (31.4 +/- 5.8 pg per ml). During the infusion of exogenous somatostatin, IRS values were higher in arterial (12,269 +/- 1,198 pg per ml) than in hepatic venous blood (7,648 +/- 1,234 pg per ml), indicating hepatic extraction of the peptide; but there was also a substantial splanchnic extraction demonstrated by higher arterial (12,269 +/- 1,532 pg per ml) than portal values (6,754 +/- 1,040 pg per ml) of IRS. During the somatostatin infusion, at very high circulation IRS levels, the liver was able to extract 38% of the peptide. This suggests that the high basal IRS levels found in liver cirrhosis are not likely to be due to hepatic failure. Possible mechanisms may involve increased somatostatin secretion, predominance of high molecular weight moieties of IRS which may not be as effectively removed by the liver, and/or portal-systemic shunting.

Adult↗
PubMedDate not supplied

Lesion volume measurement in multiple sclerosis: how important is accurate repositioning?

This study was designed to estimate the contribution of repositioning inaccuracies to measured intracranial lesion volumes in multiple sclerosis (MS). Five patients with MS were each scanned 10 times, using spin-echo imaging (2,000/34/90), contiguous 5-mm slices, and different scanning positions. The maximum displacements from baseline were +/-4 degrees (AP rotation) and 3 mm (slice offset). Lesion volume was measured twice for each scan using a semiautomated contour technique. Measured lesion volumes ranged from 4,328 mm3 to 164,831 mm3. The mean intrarater coefficient of variation (CV) calculated for individual patients ranged from 1.1 to 4% (median, 1.7%). Using analysis of variance, the overall variance and CV due to altered scan position were greater than that due to rater error (repositioning CV 4.0%, intrarater CV 3.5%). The worst-case difference between volumes in the same patient ranged from 8.9 to 32% (median, 9.9%). Both rater and repositioning errors were greater for smaller lesion volumes. The maximum potential error due to repositioning inaccuracies is of a similar magnitude to the 5 to 10% expected change in lesion volume over 1 year. This study justifies continued careful attention to accuracy in repositioning for serial MR studies in patients with MS.

Brain↗
PubMedDate not supplied

Quantitative magnetic resonance spectroscopy by optimized numerical curve fitting.

A technique is reported for generating the quantitative area under selected peaks within a 31P NMR spectrum. A numerical iterative method generates the fitted curve so as to minimize the RMS deviation between the fit and the experimental data. The curve is constructed from elemental grains of spectral density ('spexels'), each of which represents an elemental Lorentzian distribution, where the centre frequency and line width of the spexel may be varied within predetermined limits. This provides a fit that in principle is not restricted to a Lorentzian model. The method allows peak areas to be estimated, including the case of overlapping peaks. The method has been tested using simulated spectra containing six overlapping spectral lines each of known amplitude (ranging from 367 to 661 mV) and area; together with additional Gaussian noise with a standard deviation ranging from 30 to 646 mV. The results of fitting both unfiltered and filtered spectra were compared. The variation of quality of fit with spectral noise and filtering has been evaluated. In all cases, the method fitted the peak amplitudes to within 1% of the simulated value. The optimization processes provide an excellent non-linear spectrum filtering algorithm. Provided the noise in the spectra did not exceed ca 400 mV, prefiltered data could be adequately fitted.

Computer Simulation↗
PubMedDate not supplied

Linkage of AD HSP and cognitive impairment to chromosome 2p: haplotype and phenotype analysis indicates variable expression and low or delayed penetrance.

We report linkage of a family affected with autosomal dominant hereditary spastic paraparesis (HSP) and/or cognitive impairment to the HSP locus on chromosome 2p. To date all families linked to this locus have been affected with 'pure' HSP. The specific pattern of cognitive impairment in this family is characterised primarily by deficits in visuo-spatial functions. We also present genetic studies that indicate variable expression and low or delayed penetrance. We have constructed a haplotype flanked by polymorphic markers D2S400 and D2S2331 that was present in 12 individuals affected with spastic paraparesis. The severity of spasticity varied markedly among these individuals. In addition four of these individuals (aged 62-70) also had a specific form of cognitive impairment. The disease haplotype was also present in an individual (age 57) who had an identical pattern of cognitive impairment as the only sign of the disease supporting the hypothesis that spastic paraparesis and cognitive impairment are the result of variable expression of a single gene (rather than a co-incidental occurrence). Haplotype reconstruction for all participating family members revealed the presence of this disease haplotype in six individuals who had normal neurological and neuropsychological examinations. All six are below the maximal age of onset in the family--60 years. This is evidence for low or late penetrance of the AD HSP gene in this family. The identification of normal individuals carrying the disease haplotype demonstrates the importance of genetic studies in combination with clinical examination when counselling at risk family members.

Aged↗
PubMedDate not supplied

A rotate-translate CT scanner providing cross-sectional data suitable for planning the dosimetry of radiotherapy treatment.

An isotope scanner (J & P Engineering Multipoise scanner, Mk. III) has been converted to provide a simple transmission Ct scanning device, using a 137Cs gamma-ray source. The performance of the scanner has been evaluated by imaging a variety of phantoms and an anaesthetised rabbit. The relationship between the measured linear attenuation coefficient and the known electron density was found to be linear, for a range of materials with densities between those of bone and air. For reconstructed pixels of size 5 X 5 mm2 the percentage standard deviation of linear attenuation coefficient is typically 2.4% for bone and 3.6% for muscle. The spatial resolution of the device was measured and the performance of the scanner with the maximum design source strength was predicted. In the reconstruction of a cross section of the rabbit and of a human thorax phantom, air-muscle, lung-muscle, and muscle-bone interfaces are clearly visible. From experience gained with this scanner the role of simple CT scanning devices in radiotherapy treatment planning is considered. The resolution in linear attenuation coefficient and the spatial resolution available from the scanner are considered sufficient for radiotherapy treatment planning.

Animals↗
PubMedDate not supplied

Constrained deconvolution of SPECT liver tomograms by direct digital image restoration.

Several techniques for performing digital image restoration are reviewed and the problems associated with evaluating image processing are discussed. An application of constrained deconvulution to images of the liver produced by single-photon emission computed tomography is presented. Specific evaluation criteria are suggested and based on these, the choice of conditions best suited for processing liver images is proposed. Typically cold tumor contrast can be improved by a factor of greater than 2 whilst image mottle increases negligibly.

Filtration↗
PubMedDate not supplied

Improved quantification of radionuclide uptake using deconvolution and windowed subtraction techniques for scatter compensation in single photon emission computed tomography.

A comparison of two methods of scatter compensation in single photon emission computed tomography (SPECT) imaging is made on the basis of improvements in quantification. The methods, scatter-window subtraction and constrained deconvolution of an average point source response function (PSRF), are described; the theoretical basis of each method is also briefly assessed. Improvements in relative quantification offered by each method are measured by examining ratios of counts in hot cylinders to counts in a slightly radioactive background. The cylinder/background concentration ratio was varied by a factor of five; the sizes of the cylinders remained constant. Keeping the diameter of the cylinders constant allowed for an assessment of the effect of concentration differences, without the conflicting effect of variation in the size of the hot source. Results showed that while both scatter-window subtraction and constrained deconvolution offer quantification improvements in the final image, the method of prereconstruction deconvolution of a planar PSRF from each planar projection is substantially more successful than either scatter-window subtraction or other methods of implementing the deconvolution procedure.

Biophysical Phenomena↗
PubMedDate not supplied

Psychiatric problems of the 1970's.

This paper describes some of the social trends of the 1970's that may be affecting patterns of psychiatric needs and presents data showing their impact. It suggests possible psychiatric and sociopolitical responses to meet these needs. Patients were studied in the outpatient and inpatient services of the Shands Teaching Hospital and Student Mental Health Services at the University of Florida. The main findings were that single youth, both females and especially males, were requiring less help since the winding down of American participation in the Vietnam War, perhaps indicating that youth are feeling less alienated from the national effort. Black women are seeking help more than ever before, probably because the black liberation movement has offered them hope that psychiatry can help them. Despite the women's liberation movement, white women still remain the largest group of psychiatric outpatients, as they were in the 1950's and 1960's.

Adult↗
PubMedDate not supplied

Advances in treatment with intensity-modulated conformal radiotherapy.

The modern practice of radiotherapy centres on the development of conformal radiotherapy, techniques to ensure the high-dose volume is tightly wrapped around the diseased tissue and excluded as far as possible from adjacent normal structures. The development of conformal radiotherapy is a chain of processes involving treatment planning, development of new methods to deliver radiation, verification of the accuracy of radiation delivery and improvement of biological outcome. This is an enormous field of activity. This invited review paper summarises some of the main elements of progress towards implementing intensity-modulated conformal radiotherapy. This is the newest and most exciting development and, when achieved clinically, will lead to a quantum leap in tumour control probability with a fixed level of normal tissue damage.

Humans↗