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Biomedical subjects

N M Spyrou

Publications and source records attributed to N M Spyrou.

At least 37 records · Page 2Linked to original sources
PubMed1996

Photon linear attenuation coefficients and water content of normal and pathological breast tissues.

Normal and pathological breast tissue samples were scanned using a Photon Transmission Tomography (PTT) technique in order to determine their averaged photon linear attenuation coefficients (mu). Subsequent to being freeze-dried the samples were examined, using a high purity germanium detector (HPGe) and the gamma-rays of energy 59.5 keV from an americium source, and the results were corrected for the water reduction by the use of the Mixture Rule. The ratio of our experimental findings to the published data for mu for various breast tissues were 88, 96 and 88% for adipose, glandular and tumour tissues, respectively. The mean accuracy in our study, investigated relative to standard chemical compounds, was about 3%. The water content of each tissue type was determined as the weight loss during the freeze drying process. This work was initiated in order to evaluate the suitability of new tissue substitute materials for mammography applications.

Adipose Tissue↗
PubMed1996

Correction for scatter in 3D brain PET using a dual energy window method.

A method for scatter correction using dual energy window acquisition has been developed and implemented on data collected with a brain-PET tomograph operated in the septa retracted, 3D mode. Coincidence events are assigned to (i) an upper energy window where both photons deposit energy between 380 keV and 850 keV or (ii) a lower energy window where one or both photons deposit within 200 keV and 380 keV. Scaling parameters are derived from measurements of the ratios of counts from line sources due to scattered and unscattered events in the two energy windows in head-sized phantoms. A scaled subtraction of the two energy windows produces a distribution of scatter which is smoothed prior to subtraction from the upper energy window. In phantoms, the correction was found to restore the uniformity, contrast and linearity of activity concentration. Relative activity concentrations were restored to within 7% of their true values in a multicompartment phantom. The method was found to provide accurate correction for scattered events arising from activity outside the direct detector field of view. In a three-compartment phantom containing water, 18F and 11C scanned in dynamic, multiframe mode, the half-lives of the two isotopes were restored to within 2% of their true value.

Brain↗
PubMed1995

Low energy photon attenuation measurements of hydrophilic materials for tissue equivalent phantoms.

The object of the study was to measure the linear attenuation coefficients of hydrophilic materials with the aim of investigating their suitability as tissue equivalent materials. Hydrophilic materials are used in the ophthalmic industry for the manufacture of soft contact lenses. Hydrophilic materials have the trade name "Biogel" and are commonly known as hydrogels. Two types of hydrophilic material were tested, ED4C (72% water uptake by weight) and EDIS (60% water uptake by weight). The measurements were obtained using gamma-ray photons of energy 59.5 keV, and x-ray photons of energies 44.23 and 17.44 keV. Measurements were made for material types ED4C and EDIS in both the dry and fully hydrated state. Measurements were also made on powdered samples of ED4C at different hydration levels using a photon energy of 17.44 keV and powdered samples of EDIS at different hydration levels using a photon energy of 59.5 keV. The precision of the measurements was approx. 1%. It was found that material ED4C has linear attenuation coefficients that closely match those of the calculated values for soft tissue across the range of energies used.

Contact Lenses, Hydrophilic↗
PubMed1995

Reconstruction of megavoltage photon spectra by attenuation analysis.

A simple analytical model for reconstructing photon spectra from the indirect measurement of transmission or depth-dose curves is presented, based on the Schiff expression for forward-directed bremsstrahlung differential in photon energy with added inherent filtration. Calculated transmission curves for 21 simulated and measured bremsstrahlung spectra with maximum photon energies in the range 4 to 30 MeV covering a broad range of filtration conditions were used to assess the model's ability to represent megavoltage spectra. Input data were reproduced to within 0.1 per cent in all cases, which is the same order of magnitude as the uncertainty involved in its calculation. Inclusion of a fourth parameter in the model is shown to allow the effective maximum photon energy present in the spectrum to be derived to an accuracy of approximately 3 per cent.

Humans↗
PubMed1994

Developments in tomographic methods for biological trace element research.

Neutron-induced gamma-ray emission tomography for quantitative determination of concentration and distribution of elements in a selected plane through a biological specimen is briefly explained and applied by way of illustration to the analysis of gallstones. A system capable of carrying out studies of the binding site of 75Se is different matrices using time differential perturbed angular correlation spectroscopy is also briefly described. Developments in the detector technology of positron emission tomography have allowed small-diameter imaging devices to be built for in vivo preclinical evaluation of new tracers in small animals and are discussed in the context of a proposed experiment combining the techniques mentioned above.

Animals↗
PubMed1994

Study of trace elements in blood of cancer patients by proton-induced X-ray emission (PIXE) analysis.

Proton-induced X-ray emission (PIXE) analysis was employed to determine the concentrations of six elements in the plasma and erythrocytes of 18 cancer subjects (15 males and 3 females) with neoplastic disorders and in 70 controls (35 males and 35 females). It was found that the concentrations of Br, K, and Zn were significantly elevated in the erythrocytes of the cancer subjects compared to the controls, whereas the concentration of Fe was significantly depressed, but with no difference observed in the concentration of Ca. In the plasma, the concentrations of Br, Cu, Ca, and K were significantly elevated, whereas the concentrations of Fe and Zn were found to be significantly depressed compared to the controls.

Adolescent↗
PubMed1994

Elemental concentrations in nigerians with affective disorders using proton-induced X-ray emission.

The concentrations of a number of elements are determined in the plasma and erythrocytes of 21 Nigerians (11 females, 10 males) with symptomatic affective disorders (11 depressives, 10 manics) and in 40 normal controls using proton-induced X-ray emission (PIXE) analysis. The study shows that there is significant elevation of plasma K and Zn, as well as the erythrocyte S in the patients relative to the controls. The plasma and erythrocyte Cu, and the erythrocyte P, Ca, Fe, and Zn are significantly lower in the patients compared to the controls. However, the plasma levels of Ca, S, Fe, and Br are similar in both the patients and the controls. Similarly, the concentrations of K, Br, and Rb show no significant difference in the erythrocytes of patients and controls.

Adolescent↗
PubMed1994

Elemental composition of head hair and fingernails of some Nigerian subjects.

In this article, we present the elemental concentrations determined by INAA for 30 elements measured in some or all head hair samples of 100 Nigerian subjects and 20 elements in the fingernails of some of the same subjects. Measurements of the skewness of the distribution of each element in both tissues confirm previous reports that many tend toward a log-normal distribution. Thus, their concentrations in the tissues may not be under any homeostatic control. The ranges of elemental concentrations together with the medians, and the arithmetic and geometric means, with their respective standard deviations are presented and compared with literature values for other populations. Correlations between elements detected in hair are also sought.

Adolescent↗
PubMed1994

Correlations between trace element levels in head hair and blood components of Nigerian subjects.

Elemental concentrations in head hair and blood (whole-blood, erythrocytes and plasma) of 28 Nigerian subjects were determined using instrumental neutron activation analysis (INAA) and proton-induced X-ray emission (PIXE) techniques. Correlations found between different elements in hair and blood are reported. Hair levels of both zinc and chlorine were found to be significantly correlated with their levels in erythrocytes.

Adolescent↗
PubMed1994

Baseline levels of elemental concentrations in whole blood, plasma, and erythrocytes of Nigerian subjects.

In this pioneering effort on Nigerians, the arithmetic means, ranges, and standard deviations for the concentrations of the 13 elements, Br, Ca, Cl, Cu, Fe, K, Na, P, Pb, Rb, S, Se, and Zn, detected in freeze-dried whole blood, erythrocytes, and plasma of 120 subjects drawn from different geographical regions of Nigeria are reported. Elemental analyses have been carried out largely using instrumental neuron activation analysis (INAA) with both proton-induced X-ray emission (PIXE) and graphite furnace atomic absorption spectrometry (AAS) serving as complementary techniques. Our values, compared with similar data from other parts of the world, show a general good agreement. Values in male and female subjects are compared. Correlations between different elements are also noted.

Adolescent↗
PubMed1994

A comparative study of elemental composition of human breast milk and infant milk substitutes.

Instrumental neutron activation analysis (INAA) and proton-induced X-ray emission (PIXE) analysis have been employed to determine the concentration of 13 elements in human breast milk, various infant formulas, and locally produced cereals from Nigeria, as well as from various infant formulas and natural cow and goat milk available in the UK. The study shows that if the locally produced cereal is to be used on a regular basis for babies in Nigeria, then their diet must be supplemented with essential trace elements. Furthermore, parents should be discouraged from giving their infants cow and goat milk because of the high concentration of major elements compared to human breast milk.

Adult↗
PubMed1993

Photon transmission tomography techniques for screening organs in biological specimen banking.

Biological specimen banking methodology dictates that when a number of specimens of a particular type are available then the selected specimen be representative of the population in question. It is apparent though that this sorting process may present a formidable task which can be facilitated by employing tomographic transmission techniques using photons. Thus it is possible to discriminate between and discern abnormalities in specimens by obtaining the distribution of the photon linear attenuation coefficient, a function of atomic number and physical density, in sections through the specimen whilst maintaining its integrity. Fresh and freeze-dried specimens of porcine kidney were initially examined under differing temperature conditions using a single point photon transmission method, which was not successful due to the heterogeneity of the tissues. Whereas photon transmission tomography is shown to be well suited in testing for homogeneity, highlights the importance of scanning before cryogenic treatment and provides the possibility of monitoring tissue status over storage period by observing small changes in linear attenuation coefficient.

Adipose Tissue↗
PubMed1993

The computer as referee in the analysis of human small bowel motility.

The aim of this study was to determine whether visual analysis of graphic records of small bowel motility is a reliable method of discriminating pressure events caused by bowel wall contraction from those of extraenteric origin and to compare this method with computerized analysis. Each of six independent observers was supplied with the same pair of records of 1 h of fasting diurnal duodenojejunal motility, acquired with a 3-channel ambulant data-logging system; one record included many artifacts due to body movement while the other did not. The observers were asked to identify and classify pressure events and to measure the duration and amplitude of "true" contractions. A computer program for on-line analysis is described; the algorithm was designed to overcome the problems of a variable baseline and sudden changes in pressure due to body movements that are unavoidable in prolonged recording from the small bowel of ambulant subjects. For regular contractions (phase III of migrating motor complex) there was good agreement between observers but not for irregular contractions, particularly when movement artifacts were abundant. When the observers were asked to repeat the analysis 6 mo later, there was poor agreement with their original identification of irregular contractions and artifacts. There was, however, good agreement between the computer analysis, which was totally reproducible, and the median decisions of the observer group; this agreement supports the validity of our computer algorithm. We conclude that computer analysis is not merely a valuable ergonomic aid for analysis of large quantity of data acquired in prolonged ambulatory monitoring, but also that, even for brief recordings, it provides a standard of reproducibility unmatched by "expert" inspection. Visual analysis is unreliable and thus susceptible to subjective bias; this may, in part, account for conflicting reports of small bowel motility under similar conditions reported by different workers in our own and other laboratories.

Algorithms↗
PubMed1990

Scattering and attenuation correction in emission tomography in the nuclear industry.

A multi-energetic gamma-ray source has been used in conjunction with titanium and water-bath phantoms to simulate the scattering and attenuation effects encountered in nuclear industrial applications. The effect of scattered photons on the image reconstructions has been investigated by the subtraction of varying fractions of the scattered counts from the photopeak counts. A dual energy attenuation correction has also been applied to the data. In order to evaluate the effects of these corrections a "fidelity" factor has been calculated.

Image Processing, Computer-Assisted↗
PubMed1982

Multielemental analysis of bulk matrices by measurement of prompt and delay gamma-rays as well as cyclic activation using an isotopic neutron source.

An inexpensive prototype irradiation facility is described which employs a 5 Ci Am-Be neutron source. This permits the comparison of prompt with delay gamma-ray analysis as well as cyclic activation for application to partial body neutron activation analysis. The detection limits in a tissue equivalent phantom for elements of clinical interest: N, O, Na, P, Cl, Ca and Cd are given. Calculated detection limits for general multielemental analysis of bulk matrices are also presented. These are normalised with respect to experimentally obtained detection limits, with the energy dependence of the background, the detection efficiency and the self attentuation of gamma-rays in the sample being taken into account.

Activation Analysis↗
PubMed1980

The abundance of some elements in hair and nail from the Machakos District of Kenya.

Hair and nail samples collected from a population group in the Machakos District, Kenya, were studied for their elemental content using instrumental neutron activation analysis. In order to test for the type of probability distribution, frequency histograms of elemental concentration of 9 elements in hair, both for male and female subjects in the population, were plotted and chi 2-tests applied for normal distributions. Plots of cumulative frequency, using logarithmic probability paper, were used to illustrate the lognormal nature of the distributions of elements in hair such as Hg. Arithmetic and geometric means with respective standard deviations are presented for 15 elements in hair, divided into four groups according to age and sex. Results from nail samples available for a small number of subjects are also presented for males and females. Differences in concentrations for the various groups were investigated and discussed. Comparison was made with published data for a number of different populations.

Adolescent↗