Biomedical subjects

A Wieser

Publications and source records attributed to A Wieser.

At least 19 recordsLinked to original sources

PubMed2006

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis.

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

Electron Spin Resonance Spectroscopy↗

PubMed2006

Comparison of EPR occupational lifetime external dose assessments for Mayak nuclear workers and film badge dose data.

The Mayak worker cohort is one of the major sources of information on health risks due to protracted exposures to plutonium and external ionizing radiation. Electron paramagnetic resonance (EPR) measurements in tooth enamel in combination with personal dose monitoring can help to improve external dose assessment for this cohort. Here, the occupational lifetime external exposure was evaluated individually for 44 nuclear workers of three plants of the Mayak Production Association by EPR measurements of absorbed doses in collected tooth enamel samples. Analysis included consideration of individual background doses in enamel and dose conversion coefficients specific for photon spectra at selected work areas. As a control, background doses were assessed for various age groups by EPR measurements on teeth from non-occupationally exposed Ozyorsk residents. Differences in occupational lifetime doses estimated from the film badges and from enamel for the Mayak workers were found to depend on the type of film badge and the selected plant. For those who worked at the radiochemical processing plant and who were monitored with IFK film badges, the dose was on average 570 mGy larger than estimated from the EPR measurements. However, the average difference was found to be only -4 and 6 mGy for those who were monitored with IFKU film badges and worked at the reactor and the isotope production plant respectively. The discrepancies observed in the dose estimates are attributed to a bias in film badge evaluation.

Adult↗

PubMed2006

The use of deciduous molars in EPR dose reconstruction.

In the present study naturally loose deciduous molars were investigated. The feasibility of separating enamel from small size molars was analysed. EPR spectrum parameters of whole molars and separated enamel only were evaluated before and after laboratory irradiation. The Electron paramagnetic resonance (EPR) signal amplitudes of CO (2) (-) and native signals were determined by spectrum deconvolution, as a function of radiation dose in the range 0.1-10 Gy. A detection threshold of absorbed dose from deciduous molars of 198 and 21 mGy is estimated for massive (that contained both enamel and dentine) and grainy samples (that contained enamel only), respectively. The elimination of the organic material from the massive deciduous samples reduced the mean bias dose for the native signal from 90+/-18 to 34+/-13 mGy. A decay of the background signal within 2 weeks after irradiation was found, while the dosimetric signal was stable before and after the irradiation process. The presented results suggest deciduous teeth to be suitable for retrospective dose assessment. To get reasonable dose estimates, however, any organic material must be eliminated, and the measurements should be performed 2 weeks after the chemical and mechanical preparation and the irradiation process are done.

Body Burden↗

PubMed2005

[Sonographically guided, minimally invasive biopsy of uncertain mammary lesions. Clinical experience with a new biopsy system].

METHODS: We performed Vacora biopsy on 53 patients for minimally invasive breast diagnostics. Each histologically malignant lesion underwent surgery. The histopathology of the Vacora biopsy was then compared to the surgical report. When there was a discrepancy between Vacora histopathology and the report, the patient underwent open biopsy. In all patients with benign histopathology results, sonography was performed 5-7 days after biopsy and after 3 months. RESULTS: We performed biopsies on two lesions in eight patients, and on three lesions in one patient. Mean age of the patients was 52.1+/-12.8 years. A total of 62 lesions were examined. Mean size of the lesions was 13.3+/-9.6 mm. Fourteen (26.4%) were malignant (n=2 DCIS, n=12 invasive carcinoma). Histological grading was identical for Vacora biopsy and the surgical specimens. One case showed ADH by Vacora biopsy, which was confirmed by open biopsy. Vacora biopsy generated one false negative. There were a total of 36 benign lesions. CONCLUSION: Vacora biopsy under sonographic guidance is a method which is easy to handle, diagnostically accurate and without severe complications. Due to higher costs in comparison to high speed core biopsy, Vacora biopsy should be performed only in cases in which high speed core biopsy is not expected to result in a valid result.

Adult↗

PubMed2005

The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis.

The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.

Benchmarking↗

PubMed2005

Photon dose conversion coefficients for human teeth in standard irradiation geometries.

Photon dose conversion coefficients for human tooth materials are computed in energy range from 0.01 to 10 MeV by the Monte Carlo method. The voxel phantom "Golem" of the human body with newly defined tooth region and a modified version of the EGS4 code have been used to compute the coefficients for 30 tooth cells with different locations and materials. The dose responses are calculated for cells representing buccal and lingual enamel layers. The computed coefficients demonstrate a strong dependence on energy and geometry of the radiation source and a weaker dependence on location of the enamel voxels. For isotropic and rotational radiation fields, the enamel dose does not show a significant dependence on tooth sample locations. The computed coefficients are used to convert from absorbed dose in teeth to organ dose or to integral air kerma. Examples of integral conversion factors from enamel dose to air kerma are given for several photon fluences specific for the Mayak reprocessing plant in Russia. The integral conversion factors are strongly affected by the energy and angular distributions of photon fluence, which are important characteristics of an exposure scenario for reconstruction of individual occupational doses.

Humans↗

PubMed2003

[Visualization of radiographically occult osteochondrosis dissecans of the talus using MRI].

Posttraumatic disorders of the ankle are a common cause of chronic pain. Magnetic resonance imaging (MRI) has proved to be highly useful in clarifying a wide spectrum of underlying lesions which frequently cannot be detected on radiographs. Even if the assessment of the lateral collateral ligaments of the ankle is not regarded as a primary indication for MRI, it allows the diagnosis of subchondral contusions or cysts, anterolateral impingement syndrome, sinus tarsi syndrome, osteochondral fractures and osteochondrosis dissecans of the talus (ODT),which may not be detected with other imaging modalities. A 42 year old female patient suffered from persisting non-specific pain following an inversion trauma 4 months previously. MRI enabled the detection of an ODT which was not diagnosed on plain radiographs and which was verified upon arthroscopy. A superficial cartilage defect, as shown arthroscopically,was not delineated using MRI. Our observations indicate that MRI may be useful in patients with unclear persisting pain following ankle trauma and that it may contribute to the early detection of lesions which require surgical intervention.

Adult↗

PubMed2002

An in vitro L-band electron paramagnetic resonance study of highly irradiated whole teeth.

Regarding in vivo L-band dosimetry with human teeth, a number of preliminary experiments were carried out that were linked to the resonators response and the relative contribution of enamel to the EPR signal intensity of irradiated whole teeth. The sensitivity of the extended loop resonator varies in the antenna plane, but this variation tends to vanish when the sample is moved away from this plane. When the loop antenna is placed just above the highly irradiated molar, around 88% of the dosimetric signal is due to the crown enamel. The sensitivity inside a birdcage cavity is approximately equal over the volume of a molar; only 30% of the molar's total dosimetric signal results from enamel. Some decrease in the intensity of the dosimetric signal from enamel is observed after irradiation. At room temperature, the signal is reduced by about 20% within 90 days and approaches a plateau with a time constant of about 35 days.

Bicuspid↗

PubMed2002

Electron paramagnetic resonance of human tooth enamel at high gamma ray doses.

Powdered human tooth enamel was exposed to 60Co gamma rays up to a dose of 100 kGy. The electron paramagnetic resonance (EPR) signal intensity (1) of the radiation-generated carbon dioxide radicals was measured for dependence on absorbed dose (D). The EPR dose response can be fitted with an exponential saturation function I = I(M)[1 - exp(-D/D37)] with the saturated signal intensity (I(M)) and the dose saturation value (D37). The obtained value D37 = 9.64 (+/- 0.96) kGy (measured at least one month after irradiation) exceeds those given in the literature. The saturated concentration of orthorhombic CO2- radicals was estimated at 6.5 x 10(17) per gram of enamel by comparing the integrated EPR spectra of enamel and a standard MgO:Cr probe. For enamel samples, which were heated before irradiation for one hour at +405 degrees C, the value of D37T = 3.89 (+/- 0.44) kGy and the saturated value of CO2- radicals 3.4 x 10(17) per gram of enamel were lower than for unheated samples. The initial rise of the signal with the dose was slightly higher (8.8 x 10(13) radicals/g x Gy) for heated compared with unheated samples (6.8 x 10(13) radicals/g x Gy).

Cobalt Radioisotopes↗

PubMed2002

Thin layer alpha-Al2O3:C beta dosemeters for the assessment of current dose rate in teeth due to 90Sr intake, and comparison with electron paramagnetic resonance dosimetry.

The use of thin-layer alpha-Al2O3:C thermoluminescent detectors (TLDs) for the assessment of current beta dose rate in human teeth due to 90Sr intake is investigated. The teeth used in this study were collected from members of the Techa river population who were exposed to radiation as a result of releases of the Mayak plutonium production facilities (Southern Urals-Russia) between 1949 and 1956. The beta dose rates from different parts of the tooth (enamel, crown dentine, and root) were determined by storing the detectors over the samples in a shielded environment. The cumulative dose measured by electron paramagnetic resonance (EPR) in different dental tissues is found to be proportional to current dose rate obtained from alpha-Al2O3:C thermoluminescence dosemeters. The retention of 90Sr in various parts of the teeth is discussed.

Aluminum Oxide↗

PubMed2002

Dose reconstruction with electron paramagnetic resonance spectroscopy of deciduous teeth.

In the present study the feasibility of using whole, naturally loose deciduous incisors for dose reconstruction with electron paramagnetic resonance (EPR) spectroscopy was investigated. The properties of EPR signals were analysed before and after laboratory irradiation. The parameters of the native EPR signal of deciduous incisors was found to be different from those from enamel of permanent molars. The native EPR signal of deciduous incisors with peak-to-peak line width of 0.65 mT was located at g = 2.0050. The evaluated parameters of the dosimetric EPR signal (CO2-) of deciduous incisors were in agreement with those for enamel of permanent molars. A detection threshold for absorbed dose of about 100 mGy was estimated.

Child↗

PubMed2002

Monte Carlo calculation and experimental verification of the photon energy response of tooth enamel in a head-sized plexiglas phantom.

The use of electron paramagnetic resonance (EPR) tooth dosimetry for calculation of organ doses requires conversion of the measured absorbed dose in enamel. Before deriving conversion factors from simulation calculations with a realistic anthropomorphic human phantom, in the current study a simplified phantom was chosen to compare EPR measurement and Monte Carlo calculation. The dose response of tooth enamel of molars at various positions inside a cylindrical Plexiglas phantom of head-size was calculated hy Monte Carlo modelling in parallel photon beams of X rays of 63 keV equivalent energy and 60Co gamma rays (1.25 Mev). For X ray exposure, preliminary results of EPR dosimetry with tooth enamel samples prepared from molars irradiated in the phantom were in agreement with calculation. The mean value of the ratio of the measured to the calculated dose was 0.93 +/- 0.08.

Adult↗

PubMed2001

Dependencies of the radiation sensitivity of human tooth enamel in EPR dosimetry.

The EPR dose response of tooth enamel was determined for human molars collected in Egypt. The influence of age, gender and residence of the tooth donors as well as tooth position and sample preparation on EPR sensitivity and its variability over the enamel samples was investigated. The EPR sensitivity and its variability were found to depend only on the sample preparation procedure. The variability in EPR sensitivity of enamel from Egyptian teeth was maximally 10% and the mean sensitivity was in good agreement with that of German teeth.

Age Factors↗

PubMed2001

Correction factors in the EPR dose reconstruction for residents of the Middle and Lower Techa riverside.

During 1949-1956, the first Soviet nuclear weapons plant, Mayak, released about 7.6 x 10(7) m(-3) of liquid radioactive waste with a total activity of 10(17) Bq into the Techa River (Southern Urals, Russia). 90Sr contributed 11.6% to the total waste radioactivity. As a result of these radioactive discharges, about 28,000 local residents were exposed to ionizing radiation, and some of them received relatively high doses. Internal exposure of the population residing at the Middle and Lower Techa riverside was mostly from 90Sr deposited in bone and tooth tissues. In order to reconstruct radiation doses to this population group, a study of 35 teeth extracted from local residents was carried out using electron paramagnetic resonance measurements. A total of 73 samples from these 35 teeth (tooth enamel, 33; crown dentin, 20; and root dentin, 20) were prepared and measured with electron paramagnetic resonance. The study revealed high doses (up to 15 Gy) absorbed in tooth enamel of the individuals born during 1945-1949, which was attributed to very high local 90Sr concentration in tooth enamel of this particular age group in the population. The analysis presented here takes into account (a) the time courses both of the release/intake of 90Sr and of the tooth formation, and (b) expected variations in measured absorbed doses due to differing geometric sizes of tooth structures. This methodology enables a more consistent picture to be developed of the 90Sr intake by the Middle and Lower Techa riverside population, based on electron paramagnetic resonance tooth dosimetry.

Age Factors↗

PubMed2000

Fixation of proximal tibia fractures by a retrograde nail: a biomechanical investigation.

Surgical treatment of proximal tibial fractures requires open reduction and internal fixation. The operative exposure causes additional soft-tissue injury and reduces the blood supply to the bone. A cephalograde tibial nail should offer comparable mechanical stability without these disadvantages. We compared the stability of both osteosyntheses in a fracture model with 12 fresh-frozen cadaver bones. While both implants exhibited comparable stiffness under sagittal loading, the plate had a higher rotational and varus stiffness. Despite this higher stiffness, rotational displacements at the fracture gap were nearly twice as large for this implant during loading. We conclude that the retrograde nail provides similar mechanical stability to plate fixation for proximal tibial fractures, while the closed reduction and soft-tissue preservation of this new technique are definite advantages.

Biomechanical Phenomena↗

PubMed2000

Strontium metabolism in teeth and enamel dose assessment: analysis of the Techa river data.

People living on the banks of the Techa river were exposed to 90Sr in the early 1950s. Data obtained by radiochemical measurements of extracted permanent teeth, 90Sr autopsy measurements in bone and tooth samples, in vivo measurements of surface beta activity of the anterior teeth and whole-body counter (WBC) measurements of 90Sr in the skeleton have been analyzed. Surface beta activity measurements indicate a biological half-life of 90Sr of about 35 years in enamel. The WBC measurements have been performed since 1974 and a model for the age-dependent strontium retention in human bone has been used to extrapolate to previous time periods when the other measurement results were obtained. For the first decade after the intake, the ratio of the 90Sr concentrations in teeth and bones were found to decrease with age at the time of major intake, from about 10 for 1-year-old children to about 0.3 for adults. There was a considerable variability of individual data within each age group. For adults, the correlation between 90Sr in skeleton and teeth was not high at 0.47 according to radiochemical data for posterior teeth (molars and premolars) and 0.43 according to measurements of surface beta activity for anterior teeth. For children and adolescents there was no correlation between individual measurements in the skeleton and teeth. The absorbed dose in enamel due to 90Sr in dentine has been calculated by Monte Carlo simulations of the electron transport. The results are in agreement with EPR measurements of the absorbed dose in the enamel of persons exposed, mainly due to 90Sr ingestion.

Adolescent↗

PubMed2000

Comparison of sample preparation and signal evaluation methods for EPR analysis of tooth enamel.

In dose reconstruction by EPR dosimetry with teeth various methods are applied to prepare tooth enamel samples and to evaluate the dosimetric signal. A comparison of seven frequently used methods in EPR dosimetry with tooth enamel was performed. The participating Institutes have applied their own procedure to prepare tooth enamel samples and to evaluate the dosimetric signal. The precision of the EPR measurement and the dependence of the estimated dosimetric signal with irradiation up to 1000 mGy were compared. The obtained results are consistent among the different methods. The reproducibility of the dosimetric signal and its estimated relation with the absorbed dose was found to be very close for the applied methods with one possible exception.

Dental Enamel↗

PubMed2000

New computer procedure for routine EPR-dosimetry on tooth enamel: description and verification.

A software code was developed for fitting the EPR tooth enamel spectrum using linear combinations of Gaussian functions. The software is fastening EPR dose reconstruction for routine applications. The verification of the software was done comparing with the selective saturation method as an independent procedure of signal evaluation. Both methods were applied for the dose reconstruction of 13 teeth mostly from the Techa riverside. The evaluated doses by the two methods demonstrate an excellent agreement.

Dental Enamel↗