Biomedical subjects

N M Spyrou

Publications and source records attributed to N M Spyrou.

At least 19 recordsLinked to original sources

PubMed2003

Physiological interpretation of electrical impedance epigastrography measurements.

Measurement of the electrical impedance of the gastric region is carried out with the epigastrograph. This generates and applies alternating current around the abdominal area and measures the potential difference in order to determine the impedance externally, via electrodes. The change of epigastric impedance for a subject, given a meal after fasting, depends on the conductivity of the meal compared to the stomach and surrounding tissues. Typically a conductive meal has conductivity >7 mS cm(-1), non-conductive <2 mS cm(-1) and neutral about 4.5 mS cm(-1). Half-emptying times (T50s) from gastric emptying studies in volunteers using three test meals of 450 ml volume were obtained and found to be shorter than expected from the literature. The meals were a 10% glucose solution and two milk shakes of energy 1,300 kJ and 2,850 kJ, respectively. These electrical impedance epigastrography (EIE) measurements were carried out with scintigraphy. The T50 values of the latter were significantly longer. The direct comparison of the normalized experimental data obtained by both methods led to the concept that EIE measurements are mainly influenced by gastric secretion. Thus the EIE trace of a 'neutral' meal suggests the hypothesis that the volume of the meal is not the significant factor but is influenced by gastric acid secretions. Physiology of the gastric mucosa during the digestion of a meal and intragastric pH values also suggests this. Gastric function studies using EIE measurements may therefore reflect gastric ionic concentration rather than the volume of the contents of the stomach. In turn this could lead to the development of a non-invasive method for the continuous recording of gastric acid secretions.

Beverages↗

PubMed2003

Whole body [O-15]water pharmacokinetics measured in blood.

A simple pharmacokinetic model to explain the time course of [O-15] water in human whole blood after bolus injection is described. The model has been derived from measurements in twelve healthy volunteers who were measured repeatedly, resulting in 67 datasets, made in the context of PET blood flow studies. In contrast to traditional volume of distribution estimates of total body water (TBW) which rely on measurements after many hours, the model and data provide insights into the fast uptake components in the distribution of water in the body. Data fitting shows that the volume of distribution of fast exchanging tissues is 21 l. TBW was calculated to be 37 l. Monte Carlo simulation showed that the expected inaccuracy of determination of parameters due to unsystematic sources in the measurement data was around 5% for most parameters. Our data show that water extraction to tissue is somewhat higher than would be predicted from the tabulated values, probably because skeletal blood flow is sensitive to physiological status and environmental conditions. The study provides valuable reference data on the distribution and kinetics of water in man. Using the parameters and model from this study, reference input time-activity curves can be calculated, e.g. for the Monte Carlo study of error propagation in PET studies.

Adult↗

PubMed2002

Determination of cadmium and zinc in Alzheimer's brain tissue using inductively coupled plasma mass spectrometry.

In this work, brain tissue was taken from Alzheimer's Disease (AD) subjects (n=11), 'normal' subjects (n=10) and from subjects with senile involutive cortical changes (SICC) (n=6). Concentrations of Cd and Zn were determined in all samples, using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The brain tissue was selected and obtained from the Netherlands Brain Bank. Samples were taken in each case, from both hemispheres of the superior frontal gyrus, the superior parietal gyrus, the medial temporal gyrus, the hippocampus and the thalamus of the same brain.Cd which is known to have no essential role in the brain was found to follow, as expected, a lognormal distribution of concentrations in 'normal' subjects (Shapiro-Wilk's test (0.98) (p<0.18)). For the Alzheimer's Disease subjects and SICC subjects, the data tends to follow a lognormal distribution, rather than a normal distribution, but is still significantly different from it (Shapiro-Wilk's test (0.97) (p<0.03); (0.93) (p<0.0067), respectively)). In the case of Zn concentrations, the data tends to follow a normal distribution for the 'normal' subject group, even though the data is significantly different from it (Shapiro-Wilk's test (0.95) (p<0.001)). Whereas in the Alzheimer's Disease and SICC subject groups, the data follows a normal distribution (Shapiro-Wilk's test (0.98) (p<0.21); (0.97) (p<0.2002), respectively)). When comparing age-matched groups, for all regions and both hemispheres, no significant differences (p>0.1) for Cd were found between 'normals' and Alzheimer's Disease subjects and Alzheimer's Disease subjects and SICC but at a low level of significance, lower concentrations of Cd were found in the SICC group compared to the 'normals'. For all regions and both hemispheres, Zn was found to be significantly decreased in the Alzheimer's Disease group, compared to the 'normal' and SICC groups. Zn concentrations were also found to be significantly decreased in the 'normals' compared to the SICC group. It is also of interest that Cd negatively correlates with the scale of tangles in both 'normals' (p<0.001) and Alzheimer's Disease subjects (p<0.01). In the SICC subjects Cd correlates negatively with the tangles but not significantly so (p>0.1).

Aging↗

PubMed2000

Variance in parametric images: direct estimation from parametric projections.

Recent work has shown that it is possible to apply linear kinetic models to dynamic projection data in PET in order to calculate parameter projections. These can subsequently be back-projected to form parametric images--maps of parameters of physiological interest. Critical to the application of these maps, to test for significant changes between normal and pathophysiology, is an assessment of the statistical uncertainty. In this context, parametric images also include simple integral images from, e.g., [O-15]-water used to calculate statistical parametric maps (SPMs). This paper revisits the concept of parameter projections and presents a more general formulation of the parameter projection derivation as well as a method to estimate parameter variance in projection space, showing which analysis methods (models) can be used. Using simulated pharmacokinetic image data we show that a method based on an analysis in projection space inherently calculates the mathematically rigorous pixel variance. This results in an estimation which is as accurate as either estimating variance in image space during model fitting, or estimation by comparison across sets of parametric images--as might be done between individuals in a group pharmacokinetic PET study. The method based on projections has, however, a higher computational efficiency, and is also shown to be more precise, as reflected in smooth variance distribution images when compared to the other methods.

Animals↗

PubMed1999

Improvements in the determination of radionuclide distribution in the analysis of irradiated samples using double-differentiation method.

The spatial response of an 8 x 4 block detector made up of 5.6-mm-wide, 12.9-mm-high, 30-mm-thick individual detector crystals to a collimated line source of 511 keV annihilation photons was examined. The response of each crystal showed a spread around the average positioning values and distributions from adjacent crystals overlapped as the collimated source scanned the individual detectors. This leads to possible errors in the event assignment. The implementation of double differentiation or the second derivative method was proposed for the removal of scattered photons so as to reduce the overlap and, hence, avoid mis-positioning. This method is a mathematical solution implemented when analysing the results. A curve in a spatial spectrum could be considered to be a function f(x), where x is the position. When double differentiation of f(x) is carried out, then the normalized curve d2f(x) appears with some reduction in the wings. It was shown that a reduction of the scattering contribution in the tails without overestimating the contribution of scattered events could be achieved by implementing a double-differentiation process.

Radiation, Ionizing↗

PubMed1999

Determination of trace elements in porcine brain by inductively coupled plasma-mass spectrometry, electrothermal atomic absorption spectrometry, and instrumental neutron activation analysis.

Methods have been developed for the analyses of trace metals in various areas of porcine brains, (temporal, parietal, frontal cortex, both right and left hemispheres). Determinations were carried out using inductively coupled plasma-mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS). The elements investigated were Li, Mn, Cu, Zn, Cd, Hg, and Pb by ICP-MS and Cu, Cd, and Mn by ETAAS. For determination by ICP-MS, a method of standard additions calibration coupled with internal standards was used, and for ETAAS, standard additions calibrations were prepared. The accuracy of all methods was determined using NIST and IAEA certified reference material. A small number of pig brains were analyzed by instrumental neutron activation analysis for Cr, Co, Cs, Fe, Rb, Se, Sc, Sb, and Zn using the comparator method of analysis. Four separate NIST standard reference materials have been used to examine the validity of the comparator method.

Animals↗

PubMed1999

A comparative study in Alzheimer's and normal brains of trace element distribution using PIXE and INA analyses and glucose metabolism by positron emission tomography.

The onset of Alzheimer's disease has been shown to affect trace element concentrations in the brain when compared to "normal" subjects in ex vivo samples. The techniques used to determine trace element concentrations were proton-induced X-ray emission and instrumental neutron activation analysis. With these methods, significant differences are seen between lobes within a hemisphere and between the same lobes of opposing hemispheres for "normal" brains. The change observed in trace element concentrations may indicate a possible alteration in the function of the blood-brain barrier, the effect of which can be investigated in vivo using the imaging technique of positron emission tomography (PET). A PET study was performed on nine female and nine male subjects to determine whether the regional metabolic rate of glucose (rCMRGlu) varied between hemispheres and sex in the Alzheimer diseased brain as was seen in the trace element study. Glucose metabolism was measured using [F-18]-fluorodeoxyglucose (18F-FDG). Hemispherical differences were observed for the frontal, occipital, parietal lobes, and the temporolateral region in both males and females for rCMRGlu. Variation was also seen between sexes, where the frontal lobe had a lower rCMRGlu in females compared to that of males.

Alzheimer Disease↗

PubMed1999

Elemental composition changes between breast tissue with and without silicone gel sheeting and hypertrophic scar tissue.

Hypertrophic scars occur after dermal trauma and are characterized by being elevated above normal skin level as a result of an abundance of collagen. The application of silicone gel sheeting (SGS) has been found to be an effective method of treatment, causing them to regress much quicker than they would do naturally. Normal skin and hypertrophic scar tissue were characterized using proton-induced X-ray emission (PIXE). Skin tissue that had been covered in SGS was also analyzed. For each element and sample type, the concentrations in the epidermis were plotted against the dermis. By considering the concentrations of breast tissue with and without SGS, it could be seen if the SGS changed the compositional structure of the skin. It was found that for the elements P, S, Cl, and K the SGS has no effect on the structure of the skin, as both breast types (with and without SGS) have regression lines that overlap. However, this work shows that there are significant differences for P in the dermis and Cl in the epidermis between the breast tissue with SGS and its control. Therefore, this work shows that the effect the SGS has on concentration occurs similarly for both the epidermis and dermis.

Breast↗

PubMed1999

Hydrophilic crosslinked copolymers as tissue-equivalent materials for breast cancer detection.

Crosslinked hydrophilic copolymers have the potential to be used as breast phantom materials because they can be made to have similar elemental composition to that of body soft tissues. The copolymer, which consists of a combination of hydrophobic monomers (methyl methacrylate [MMA]) and hydrophilic monomers (vinylpyrolidone [VP]), have all the required major elements, such as hydrogen, carbon, nitrogen, and oxygen, found in tissues. Photon attenuation measurements were performed on the crosslinked hydrophilic copolymers in order to ascertain whether they are good representatives of breast tissues in the photon energy range of interest. The results of the measurements of transmission of photons by the hydrophilic copolymers at different discrete energies between 10 and 60 keV are presented.

Breast Neoplasms↗

PubMed1999

Elemental analysis of blood of Nigerian hypertensive subjects.

Proton-induced X-ray emission (PIXE) has been used to obtain the concentrations of 11 elements (P, S, Cl, K, Ca, Fe, Cu, Zn, Br, Rb, and Cd) in whole-blood samples of 16 hypertensive subjects (mean age: 52.5 +/- 0.5 yr) and 18 age-matched controls (mean age: 51.5 +/- 0.5 yr) in a Nigerian population. The results of the study indicate that the hypertensive subjects have significantly higher mean concentration of Cl, Cd, Cu, and Zn when compared with the controls, and the mean concentration of P, K, and Ca was found to be significantly lower in the hypertensive group in comparison to the controls. Furthermore, the Zn:Cd ratio was found to be significantly higher in the controls than in the hypertensives, and the Cu:Zn ratio was significantly higher in the hypertensives.

Case-Control Studies↗

PubMed1999

No effect of glucagon-like peptide-1 on short-term satiety and energy intake in man.

Centrally administered glucagon-like peptide-1 (GLP-1) inhibits feeding in fasted rats, but its role in human satiety has been largely unexplored. The present study investigated the effect of peripheral GLP-1 infusion on gastric emptying and satiety in man. Ten non-obese male subjects were infused in a randomized single-blind within-subject crossover study using saline infusion as control. They received either a GLP-1 infusion (1.2 pmol/kg per min) or a saline infusion for 1 h, at 18.00 hours. At 20 min after starting the infusion the gastric emptying of a 400 ml water load was measured. Subjects completed behavioural self-rating scales to assess hunger and satiety. After 40 min subjects were given a buffet meal ad libitum and their food intake was recorded. GLP-1 infusion raised circulating GLP-1 concentrations to approximately twice those seen following a meal. It did not affect circulating insulin levels but caused a small fall in glucose levels. Gastric emptying of the water load was significantly delayed by the GLP-1 infusion. Energy intake from the buffet was unaffected by GLP-1 infusion. Self-assessment of hunger and satiety was similarly unaffected by the infusion before the buffet meal, although subjects tended to be less hungry after the buffet meal following GLP-1 infusion (P < 0.09). GLP-1 infusion delayed gastric emptying but had a minimal effect on food intake and satiety. This study casts doubts on whether GLP-1 is a major satiety factor in man, although a raised circulating plasma glucose level, as would normally occur postprandially, might be necessary for GLP-1 to increase satiety.

Adult↗

PubMed1998

Electron density of normal and pathological breast tissues using a Compton scattering technique.

Compton (incoherently) scattered photons which are directly proportional to the electron density of the scatterer, have been employed in characterising human breast tissues. Gamma ray photons scattered incoherently from normal and pathological breast tissue samples of nine breast cancer patients were measured using a high purity germanium detector and an americium (Am-241) source. The breast tissue samples were obtained from female patients undergoing mastectomy. The samples were examined in freeze dried form and the results were corrected for the reduction in the water content of each tissue type by use of the Mixture Rule. This study is aimed at providing electron density information in support of the introduction of new tissue substitute materials for mammography phantoms.

Americium↗

PubMed1997

Trace elements in drinking and groundwater samples in southern Nigeria.

The levels of Al, Sn, Cs, Rb, Sr, Br, Cr, Mo, Co, Ba, Cu, Zn, Cd, Pb, Mn, Se, As, V and Ni were determined in drinking water supplies (public taps, domestic taps and treated water from public water sources) and groundwater supplies (boreholes and shallow wells) in some parts of Southern Nigeria. The water samples were analysed using inductively coupled plasma mass-spectrometry (ICP-MS). The mean levels (microgram/l) of all the elements ranged between 0.35 microgram/l for Cs and 87.3 micrograms/l for Zn in the drinking waters and between 0.54 microgram/l for Co and 420.3 micrograms/l for Ba in the groundwaters. A comparison of the elemental concentrations with WHO guidelines showed that with the exception of violations of Cd, Cr and Se limits in some of the drinking water samples, the levels of all the other elements investigated were below the WHO maximum allowable concentrations.

Environmental Monitoring↗

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↗