Biomedical subjects

G Kitis

Publications and source records attributed to G Kitis.

At least 19 recordsLinked to original sources

PubMed2006

Molecular epidemiology of hepatitis C virus (HCV) in Greece: temporal trends in HCV genotype-specific incidence and molecular characterization of genotype 4 isolates.

This study aimed to estimate the overall HCV genotype distribution and to reconstruct the HCV genotype-specific incidence in Greece during the recent decades. It also focused at the identification of genotype 4 subtype variability in Greek isolates. A total of 1686 chronically infected HCV patients with detectable serum HCV RNA by RT-PCR, belonging to different risk groups were studied. Amplified products from the 5'-noncoding region were typed using a commercially available assay based on the reverse hybridization principle. The HCV genotype-specific incidence was estimated using a previously described back calculation method. HCV genotype 1 was the most prevalent (46.9%) followed by genotype 3 (28.1%), 4 (13.2%), 2 (6.9%) and 5 (0.4%). A high prevalence of genotype 1 (66.3%) in haemophilia patients was recorded whereas HCV genotype 3 was found mainly among patients infected by I.V. drug use (58.2%). Data on the temporal patterns of HCV genotype-specific incidence in Greece revealed a moderate increase (1.3-1.6 times) for genotypes 1 and 4, and a decrease (1.5 times) for genotype 2 from 1970 to 1990, whereas there was a sharp (13-fold) increase for genotype 3. The molecular characterization of 41 genotype 4 HCV isolates belonging to various risk groups revealed that, subtype 4a was the most frequently detected (78%). Phylogenetic comparison of the Greek 4a isolates with all HCV-4a isolates reported worldwide so far revealed a topology which does not discriminate Greek isolates from the others. HCV-4 does not represent a recent introduction in Greece.

Adolescent↗

PubMed2006

European evidence based consensus on the diagnosis and management of Crohn's disease: current management.

This second section of the European Crohn's and Colitis Organisation (ECCO) Consensus on the management of Crohn's disease concerns treatment of active disease, maintenance of medically induced remission, and surgery. The first section on definitions and diagnosis includes the aims and methods of the consensus, as well as sections on diagnosis, pathology, and classification of Crohn's disease. The third section on special situations in Crohn's disease includes postoperative recurrence, fistulating disease, paediatrics, pregnancy, psychosomatics, extraintestinal manifestations, and alternative therapy for Crohn's disease.

Adrenal Cortex Hormones↗

PubMed2005

Thermoluminescence properties of Chile Guajillo paprika Mexicano.

The thermoluminescence properties of the inorganic dust extracted from the Chile Guajillo (paprika) Mexicano, were studied in order to verify the possibility of using the TL technique to discriminate between irradiated and non irradiated peppers. The inorganic dust was found to consist of quartz 60%, albite (NaAlSi(3)O(8)) 30%, and ortose (KAlSi(3)O(8)) 10%. Its thermoluminescence dose response covers the wide dose range of 1 Gy--10 kGy, which was attributed mainly to feldspars. Its high sensitivity and its stability over 10 irradiation-readout cycles allow the application of a single grain--single aliquot regeneration dosimetry in Chile Guajillo (paprika). Evaluations based on trapping parameters show that thermal fading at room temperature for glow-peaks above 180 degrees C, is not a problem in the dosimetry of paprika.

Capsicum↗

PubMed2002

Detailed kinetic study of the thermoluminescence glow curve of synthetic quartz.

A detailed kinetic analysis has been performed of the thermoluminescence (TL) glow curve of high purity synthetic quartz. The kinetic parameters of the glow peak at 110 degrees C were evaluated for doses ranging from 0.1 Gy to 100 Gy using glow curve deconvolution (GCD), initial rise, variable heating ratc and phosphorescence decay methods. All the methods gave results that agree within the experimental errors.

Hot Temperature↗

PubMed2002

Thermoluminescence properties of LiMgF3 doped with Ce, Er and Dy.

The main dosimetric properties are reported of a new perovskite, LiMgF3, doped with Ce, Er and Dy impurities. An annealing temperature of 400 degrees C for one hour is necessary to erase any previous signal and to stabilise its sensitivity. A readout up to 450 degrees C gives the same result. The glow curve structure consists of two intense and isolated glow peaks at 170 degrees C and 315 degrees C. The sensitivity of both glow peaks to beta irradiation increases as the dopant concentration increases. The sensitivity is higher than that of LiF:Mg,Ti using the glow peaks 4+5 integral. Other properties like TL dose response, fading, sensitivity versus successive readout and ammealing cycles, sensitivity versus the heating rate, sensitivity to light and trapping parameter evaluation were also carried out.

Cerium↗

PubMed2002

Search for common characteristics in the glow curves of quartz of various origins.

The thermoluminescence (TL) glow curves of quartz of various origins were measured under two different conditions, (1) unannealed samples and (2) samples annealed at 500 degrees C and 900 degrees C. The different glow curves obtained were analysed using first order kinetics and glow curve deconvolution (GCD) analysis. The comparison of the glow curves obtained was mainly concentrated in studying the sensitivities of the glow peaks as a function of the annealing temperature, and in obtaining the kinetic parameters of the glow peak at '110 degrees C'. Furthermore, in four samples the detailed comparison was extended to the trapping parameters of all existing glow peaks. It was found that despite their different origin and the different shapes of the glow curves, there are several basic characteristics that are common to all samples studied.

Hot Temperature↗

PubMed2002

Mapping of the thermal neutron distribution in the lead block assembly of the PS-211 experiment at CERN, using thermoluminescence and nuclear track detectors.

The main purpose of the TARC (Transmutation by Adiabatic Resonance Crossing) experiment (PS-211), was to demonstrate the possibility to destroy efficiently Long-Lived Fission Fragments (LLFF) in Accelerator Driven Systems (ADS). The experimental set-up which consisted of a lead block with dimensions 3.3 x 3.3 x 3 m3, was installed in a CERN Proton Synchrotron (PS) beam line. The proton beam at 2.5 GeV/c and 3.5 GeV/c, was incident in the centre of the lead block assembly producing neutrons via spallation reactions. In this study, neutron flux measurements are presented in the lead block assembly using thermoluminescence and nuclear track detectors. The results are in good agreement with Monte Carlo calculations as well as with the results of the other methods used in the framework of the TARC experiment.

Fast Neutrons↗

PubMed2002

Computerised glow curve deconvolution using general and mixed order kinetics.

Some accurate glow curve fitting functions for general and mixed order kinetics glow peaks are proposed and discussed. These mathematical expressions are used together with peak search and non-linear minimisation algorithms in order to provide a fast glow curve deconvolution for those materials which cannot be well fitted using first order kinetics. To test the accuracy of the proposed method. the result of the fitting of synthetic glow curves is compared with the original data giving negligible errors for values of parameters currently found in TL materials.

Computer Simulation↗

PubMed2002

On the possibility of using commercial software packages for thermoluminescence glow curve deconvolution analysis.

This paper explores the possibility of using commercial software for thermoluminescence glow curve deconvolution (GCD) analysis. The program PEAKFIT has been used to perform GCD analysis of complex glow curves of quartz and dosimetric materials. First-order TL peaks were represented successfully using the Weibull distribution function. Second-order and general-order TL peaks were represented accurately by using the Logistic asymmetric functions with varying symmetry parameters. Analytical expressions were derived for determining the energy E from the parameters of the Logistic asymmetric functions. The accuracy of these analytical expressions for E was tested for a wide variety of kinetic parameters and was found to be comparable to the commonly used expressions in the TL literature. The effectiveness of fit of the analytical functions used here was tested using the figure of merit (FOM) and was found to be comparable to the accuracy of recently published GCD expressions for first- and general-order kinetics.

Kinetics↗

PubMed2001

Thermoluminescent (TL) properties of the perovskite KMgF3 activated by Ce and Er impurities.

The perovskites are very interesting for their thermoluminescent properties and for their possible application as thermoluminescent dosimeters (TLD). In this paper we present results concerning the main dosimetric properties of KMgF3 activated by Ce and Er at various concentrations, i.e. annealing procedure, reproducibility of the TL signal, linearity and fading behaviour.

Journal Article↗

PubMed2001

Fit of first order thermoluminescence glow peaks using the Weibull distribution function.

A new thermoluminescence glow curve deconvolution (GCD) function is introduced which accurately describes first order thermoluminescence (TL) curves. The new GCD function is found to be accurate for first order TL peaks with a wide variety of the values of the TL kinetic parameters E and s. The 3-parameter Weibull probability function is used with the function variables being the maximum peak intensity (Im), the temperature of the maximum peak intensity (Tm) and the Weibull width parameter b. An analytical expression is derived from which the activation energy E can be calculated as a function of Tm and the Weibull width parameter b. The accuracy of the Weibull fit was tested using the ten reference glow curves of the GLOCANIN intercomparison program and the Weibull distribution was found to be highly effective in describing both single and complex TL glow curves. The goodness of fit of the Weibull function is described by the Figure of Merit (FOM) which is found to be of comparable accuracy to the best FOM values of the GLOCANIN program. The FOM values are also comparable to the FOM values obtained using the recently published GCD functions of Kitis et al. It is found that the TL kinetic analysis of complex first-order TL glow curves can be performed with high accuracy and speed by using commercially available software packages.

Computer Simulation↗

PubMed2001

Fit of second order thermoluminescence glow peaks using the logistic distribution function.

A new thermoluminescence glow curve deconvolution (GCD) function is introduced which accurately describes second order thermoluminescence (TL) curves. The logistic asymmetric (LA) statistical probability function is used with the function variables being the maximum peak intensity (Im), the temperature of the maximum peak intensity (Tm) and the LA width parameter a2. An analytical expression is derived from which the activation energy E can be calculated as a function of Tm and the LA width parameter a2 with an accuracy of 2% or better. The accuracy of the fit was tested for E values ranging from 0.7 to 2.5 eV, for s values between 10(5) and 10(25) s(-1), and for trap occupation numbers no/N between 1 and 10(-6). The goodness of fit of the logistic asymmetric function is described by the Figure of Merit (FOM) which is found to be of the order of 10(-2). Preliminary results show that the GCD described here can easily be extended to the description of general order TL glow curves by varying the asymmetry parameter of the logistic asymmetric function. It is concluded that the TL kinetic analysis of first, second and general order TL glow curves can be performed with high accuracy and speed by using commercially available statistical packages that incorporate the Weibull and logistic asymmetric functions.

Computer Simulation↗

PubMed2000

Dosimetric considerations in mammography.

The aim of this study was to measure the absorbed dose to seven organs other than the breast in mammography in order to calculate their contribution to the effective dose. The absorbed dose to these organs was measured using a lucite upper body anthropomorphic phantom containing thermoluminescent dosimeters (TLD) at appropriate locations, exposed as in a mammographic examination. In addition, the dependence of the absorbed dose on kVp, mAs and breast thickness was examined. The absorbed dose due to scattered radiation was found to be negligible to all organs except to the sternum red bone marrow (SRBM) and the thyroid. The mean doses to the SRBM and the thyroid, for a set of four exposures, one craniocaudal and one 90 degrees mediolateral per breast, simulating a complete breast screening examination, varied between 0.40 and 1.27 and 0.05-0.17 microGy mAs(-1), respectively, depending on the breast thickness and the kVp selection. Effective dose from mammography was also calculated based on the absorbed dose to the breast, the SRBM and the thyroid and tissue-weighting factors. The effective dose was found to vary between 0.66 and 0.85 microSv mAs(-1) depending on the breast thickness and the kVp value selected. The radiation dose to the breast contributes over 98% to the effective dose.

Humans↗

PubMed2000

Dosimetric characterisation of a new production of MgB4O7:Dy,Na thermoluminescent material.

Thermoluminescent dosimetric characteristics of MgB4O7:Dy,Na are presented. MgB4O7:Dy,Na is a newly prepared TL material with attractive features for dosimetric applications, such as near-tissue equivalence, simple glow curve, high sensitivity and low fading. The dosimetric properties of this material examined in this study include glow curve shape, TL sensitivity, annealing procedure, photon dose response, minimum detectable dose, precision of TL measurements, reproducibility, energy response and fading characteristics.

Borates↗

PubMed1999

Interferon alfa for chronic hepatitis B infection: increased efficacy of prolonged treatment. The European Concerted Action on Viral Hepatitis (EUROHEP).

Interferon alfa (IFN-alpha) is the primary treatment for chronic hepatitis B. The standard duration of IFN-alpha therapy is considered 16 weeks; however, the optimal treatment length is still poorly defined. We evaluated the efficacy and acceptability of prolonged IFN-alpha treatment in patients with chronic hepatitis B. To investigate whether treatment prolongation could enhance the rate of hepatitis B e antigen (HBeAg) seroconversion, we conducted a prospective, controlled, multicenter trial in which all patients were treated with a standard regimen of 10 million units IFN-alpha 3 times per week over 16 weeks. Patients who were still HBeAg-positive after 16 weeks of therapy were randomized to prolongation of the identical regimen up to 32 weeks (prolonged therapy) or discontinuation of treatment (standard therapy). Among the 162 patients who entered the study, 27 (17%) were HBeAg-negative after the first 16 weeks of treatment, and 118 were randomized to standard or prolonged therapy. After randomization, a response (HBeAg seroconversion and sustained hepatitis B virus [HBV]-DNA negativity) was observed in 7 of the 57 (12%) patients assigned to standard therapy versus 17 of the 61 (28%) patients assigned to prolonged therapy (P =.04). A low level of viral replication after 16 weeks of treatment, as indicated by serum HBV-DNA values under 10 pg/mL, was found to be the only independent predictor of response (52% vs. 0%; P <.001) during prolonged therapy. The prolonged IFN-alpha schedule was well tolerated in the large majority of patients. In chronic hepatitis B, prolongation of IFN-alpha therapy up to 32 weeks is superior to a standard course of 16 weeks. Those patients who exhibit a low level of viral replication at the end of the standard regimen benefit most from prolonged treatment.

Adolescent↗

PubMed1999

The use of a dura mater patch to cover oesophageal defects of different sizes: an experimental study in chickens.

OBJECTIVE: To find out the optimal size of full thickness oesophageal defects that can be repaired with patches of Tutoplast Dura (solvent dehydrated human dura mater in the form of absorbable collagen). DESIGN: Experimental study. SETTING: Teaching hospital, Greece. MATERIAL: 96 female Hubbard chickens in four groups of 24. INTERVENTIONS: In the three experimental groups longitudinal defects were made in the cervical oesophagus 30 x 5, 10, or 15 mm and covered with Tutoplast. Subgroups of 6 chickens were weighed, had a barium swallow examination, and were then killed at 2, 4, 6, and 8 weeks. The oesophagus was removed and examined histopathologically. MAIN OUTCOME MEASURES: Weight, extent of healing macroscopically and microscopically. RESULTS: All chickens that had had defects 30 x 15 mm in size died between days 5 and 10, and the oesophagus in all cases was obstructed by food. There were no deaths or complications in the other three groups, and no evidence of dysphagia on barium swallow. In chickens with defects of 30 x 5 and 30 x 10 mm the prosthetic material gradually disappeared, and they healed well. CONCLUSIONS: Defects in the chicken's cervical oesophagus larger than 30 x 10 mm cannot be repaired with a Tutoplast patch, but smaller defects can. Further studies are needed to clarify the mechanisms of healing.

Animals↗

PubMed1992

Sucralfate and ranitidine twice daily in the treatment of gastric ulcer. A multicenter randomized double-blind study.

Sucralfate and ranitidine were compared in the treatment of gastric ulcer (GU) in this multicenter randomized double-blind study. Sixty-four patients with endoscopically diagnosed GU initially included in the trial were randomly assigned to treatment with sucralfate, 2 g b.i.d. (morning and evening on an empty stomach), or ranitidine, 150 mg b.i.d. Nine patients were subsequently excluded for various reasons. The remaining 55 were examined endoscopically after 4 and, if unhealed, 8 weeks. At 4 weeks, 54.2% (13 of 24) of the sucralfate group had a healed ulcer, in comparison to 45.2% (14 of 31) of the ranitidine group (NS). At 8 weeks, cumulative healing rates were 87.5% (21 of 24) and 84% (26 of 31), respectively (NS). No differences were found in the healing effects of the drugs on smokers and nonsmokers or in side effects. These results suggest that both drugs are equally effective in the short-term treatment of GU.

Adult↗

PubMed1991

Comparison of sucralfate and ranitidine twice daily in duodenal ulcer treatment: a multicenter randomized double-blind study.

Sucralfate and ranitidine were compared in the treatment of duodenal ulcer in this multicenter, randomized, double-blind study. A total of 165 patients with endoscopically proven duodenal ulceration were included in the trial and randomized to treatment with sucralfate, 2 g b.i.d. (morning and evening with an empty stomach), or ranitidine, 150 mg twice daily. All patients were endoscopically examined after 4 and, if unhealed, 8 weeks. Of the patients considered suitable for analysis at 4 weeks, 73.5% (61 of 83) of the sucralfate group demonstrated healing of the ulcer in comparison with 63.3% (50 of 79) of the ranitidine group. At 8 weeks cumulative healing rates were 89% (74 of 83) and 84.8% (67 of 79), respectively. When smokers were considered separately, healing rates at 4 weeks were 69.2% (36 of 52) for sucralfate and 53.3% (24 of 45) for ranitidine. At 8 weeks cumulative healing rates were 92.3% (48 of 52) and 77.7% (35 of 45), respectively (p less than 0.05). Overall, there was no difference in the two groups regarding symptom relief and side effects. These results suggest that these drugs are equally effective in the short-term treatment of duodenal ulcer, although in smokers sucralfate appears to be more effective than ranitidine.

Adult↗