Chasing quantitative biases in neutron imaging with scintillator-camera detectors: a practical method with black body grids.

We propose a method for improving the quantification of neutron imaging measurements with scintillator-camera based detectors by correcting for systematic biases introduced by scattered neutrons and other sources such as light reflections in the detector system. This method is fully experimental, using reference measurements with a grid of small black bodies (BB) to measure the bias contributions directly. Using two test samples, one made of lead alloy and having a moderate (20%) neutron transmission and one made of stainless-steel and having a very low (1%) transmission, we evaluated the improvement brought by this method in reducing both the average quantification bias and the uncertainty around this average bias after tomographic reconstruction. The results show that a reduction of the quantification bias of up to one order of magnitude can be obtained. For moderately transparent samples, little sensitivity is observed to the parameters used for the correction. For the more challenging sample with very low transmission, a correct placement of the BB grid is of utmost importance for a successful correction.

A Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystals.

The development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.

Unlocking high spatial resolution in neutron imaging through an add-on fibre optics taper.

The demand for high resolution neutron imaging has been steadily increasing over the past years. The number of facilities offering cutting edge resolution is however limited, due to (i) the design complexity of an optimized device able to reach a resolution in the order of ≈ 10 µm and (ii) limitations in available neutron flux. Here we propose a simple addition, based on a Fibre Optics Taper (FOT), that can be easily attached to an already existing scintillator-camera imaging detector in order to efficiently increase its spatial resolution and hence boost the capability of an instrument into high resolution applications.

Cold neutron diffraction contrast tomography of polycrystalline material.

Traditional neutron imaging is based on the attenuation of a neutron beam through scattering and absorption upon traversing a sample of interest. It offers insight into the sample's material distribution at high spatial resolution in a non-destructive way. In this work, it is expanded to include the diffracted neutrons that were ignored so far and obtain a crystallographic distribution (grain mapping). Samples are rotated in a cold neutron beam of limited wavelength band. Projections of the crystallites formed by the neutrons they diffract are captured on a two dimensional imaging detector. Their positions on the detector reveal their orientation whereas the projections themselves are used to reconstruct the shape of the grains. Indebted to established synchrotron diffraction contrast tomography, this 'cold neutron diffraction contrast tomography' is performed on recrystallized aluminium for experimental comparison between both. Differences between set-up and method are discussed, followed by the application range in terms of sample properties (crystallite size and number, mosaicity and typical materials). Neutron diffraction contrast tomography allows to study large grains in bulky metallic structures.

Dual spectrum neutron radiography: identification of phase transitions between frozen and liquid water.

In this Letter, a new approach to distinguish liquid water and ice based on dual spectrum neutron radiography is presented. The distinction is based on arising differences between the cross section of water and ice in the cold energy range. As a significant portion of the energy spectrum of the ICON beam line at Paul Scherrer Institut is in the thermal energy range, no differences can be observed with the entire beam. Introducing a polycrystalline neutron filter (beryllium) inside the beam, neutrons above its cutoff energy are filtered out and the cold energy region is emphasized. Finally, a contrast of about 1.6% is obtained with our imaging setup between liquid water and ice. Based on this measurement concept, the temporal evolution of the aggregate state of water can be investigated without any prior knowledge of its thickness. Using this technique, we could unambiguously prove the production of supercooled water inside fuel cells with a direct measurement method.

Energy-selective neutron imaging for morphological and phase analysis of iron-nickel meteorites.

We propose energy-selective neutron imaging as a new and non-destructive method to investigate rare metallic meteorites. It is based on attenuation of a neutron beam of limited spectral distribution in a sample depending on the elemental composition and crystalline structure. Radiography and tomography allow obtaining the presence, morphology and orientation information in the bulk of mineral inclusions, oxide crust and crystalline structure. Its usage in classification and meteor formation studies would be of great value.

Using 2H labeling with neutron radiography for the study of solid polymer electrolyte water transport properties.

A method combining (2)H labeling of different sources of H atoms (hydrogen, water vapor) with neutron imaging for the analysis of transport parameters in the bulk and at the interfaces of Nafion polymer electrolyte membranes is proposed. The use of different isotope compositions in the steady state allows evaluation of the relation between bulk and interface transport parameters, but relies on literature data for evaluating absolute values. By using transients of isotope composition, absolute values of these parameters including the self-diffusion coefficient of H can be extracted, making this method an attractive alternative to self-diffusion measurements using nuclear magnetic resonance (NMR), allowing measurements in precisely controlled conditions in real fuel cell structures. First measurements were realized on samples with and without electrodes and we report values of the self-diffusion coefficient of the same order of magnitude as values measured using NMR, although with slightly higher numbers. In our particular case, lower interfacial exchange rates for water transport were observed for samples with an electrode.

Hydrogen distribution measurements by neutrons.

The paper describes how hydrogenous materials can be investigated with state-of-the-art neutron radiography detection methods. The methodical problems for a precise quantification and steps towards their solution are demonstrated. Based on several practical examples, the diversity of problems to be solved by neutron imaging is illustrated.

Neutron capture autoradiographic study of the biodistribution of 10B in tumor-bearing mice.

For the study on boron neutron capture therapy, the whole-body sections of tumor-bearing mice infused with 10B attached to CR-39 plastic track detectors were exposed to thermal and cold neutron beams. Neutron capture autoradiographic images obtained by the cold neutron irradiation were extremely superior in quality to those of the thermal neutron beams. From the autoradiographic images, the 10B reaction dose of the neutron-induced particles was estimated using the differential LET distribution.

The Sp1 binding site polymorphism in the collagen type I alpha 1 (COLIA1) gene is not associated with bone mineral density in healthy children, adolescents, and young adults.

Up to 85% of the variance in bone mineral density (BMD) is genetically determined. A putative candidate gene involved in the regulation of bone mass is the COLIA1 gene encoding type I collagen, which is the major protein of bone. We examined possible allelic influences of a G to T COLIA1 gene polymorphism in a recognition site for the transcription factor Sp1 on: (i) gain of forearm BMD using single photon absorptiometry (SPA); and (ii), BMD of the forearm, spine, hip, and whole body with dual X-ray absorptiometry (DXA). At baseline, 269 healthy boys and girls aged 8.2-16.5 years were eligible for the study. Forearm BMD measurements obtained at baseline and after 3.8+/-0.1 years (+/-s.d.) were used to calculate the annual percentage change in BMD. Calcium intake and physical activity were determined by a detailed questionnaire at baseline and after 1 year. Essentially no significant differences in forearm BMD gain or in BMD assessed at the forearm, spine, and whole body were observed among the three COLIA1 genotypes. In conclusion, the data indicate that the polymorphism at the Sp1 site in the COLIA1 gene is not associated with BMD or gain of forearm BMD in healthy boys and girls.

Lack of relationship between vitamin D receptor genotype and forearm bone gain in healthy children, adolescents, and young adults.

Recent studies have suggested that genetic effects on bone mineral density (BMD) are related to allelic variation in the vitamin D receptor (VDR) gene. We examined 1) allelic influences of the VDR gene on BMD of the forearm, spine, hip, and whole body; and 2) allelic influences of the VDR gene on forearm BMD gain. Two hundred and seventy-three healthy boys and girls, aged 8.2-16.5 yr, at baseline were eligible. Forearm BMD was assessed with single photon absorptiometry at baseline. BMD gain was calculated as the annual percent change in BMD measured by single photon absorptiometry from the baseline and after 3.8 +/- 0.1 (+/-SD) yr. Calcium intake and physical activity were assessed by a detailed questionnaire at baseline and after 1 yr. VDR alleles were determined by BsaMI endonuclease restriction fragment analysis after PCR amplification. No significant differences in forearm BMD gain or in BMD assessed at the forearm, spine, hip, and whole body were observed among the three VDR genotypes. These findings did not change after adjusting for environmental factors such as calcium intake and physical activity or age, weight, height, and changes in weight and height during the observation period. In conclusion, our data do not support the idea that VDR genotypes are related to BMD gain or to BMD at the forearm, hip, spine, and whole body in healthy boys and girls, aged 8-21 yr. VDR genotyping is probably of little use for the detection of individuals who would benefit from increased calcium and physical activity to increase their peak bone densities.

[Group sequential experiments. Short introduction and review]. / Gruppesekvensielle forsøksplanar. Kort innføring og oversikt.

Group sequential experiments are terminated when an interim statistical test turns out to be "significant", or when maximum study size is attained. To ensure a stipulated total level of significance the interim tests have to be performed at a stricter level of significance determined by the maximum number of interim tests. As for fixed size studies, it is possible to determine a study size leading to a stipulated power. This study size depends on expected effect of intervention, number of interim tests and level of significance. Tables and computer simulation programs have been developed to facilitate the design of such plans. If the intervention turns out to be about as effective as expected, a saving in study size of about 30% can be expected in the long run, relative to studies of fixed size. If the intervention is much more effective than expected, larger savings can be achieved.

The relationship between anthropometric measurements and fractures in women.

In a population-based, retrospective study involving postmenopausal women, we investigated the relation between fracture prevalence (risk) and present as well as previous body height and weight. A questionnaire was mailed to 46,353 postmenopausal women aged 50-80 years and there were 29,802 (64.3%) responses. Questions were asked about body height and weight and fractures after the age of 25 and at what year they had occurred. The fractures were grouped according to whether they had occurred within 5 years or 10 years prior to responding to the questionnaire. Main outcome was relative risk (RR) of having sustained a fracture of the hip, radius, or spine within 5 years or within 10 years prior to responding to the questionnaire. RRs for hip and spine fractures were negatively associated with current body mass index, current weight, and weight gain since the age of 25 years. Moreover, the RRs of these fractures were positively associated with current height, height at the age of 25, and height loss since the age of 25 years, with the exception of fracture of the spine and current height. RRs for radius fracture were negatively associated with current body mass index and height loss since the age of 25. Moreover, the RRs for radius fracture were positively associated with current weight and height, weight gain since the age of 25, and weight and height at the age of 25. Height at the age of 25 was a consistent risk factor for all fracture types. The RR of the highest quartile (greatest height) vs. the lowest was 2.5 for having a hip fracture during the past 5 years and 2.3 during the past 10 years, which corresponds to a RR of 1.4 for an increase in 1 SD (5.4 cm) in height at age 25. The RR for spine fracture increased about fivefold in women having sustained > or = 3 cm height reduction compared with those who had maintained height. We conclude that tall women have a greater relative risk of experiencing fragility fractures. By using height, women at risk of a later fracture can be selected already at the age of 25 years for later follow-up. Height loss, being strongly associated with fragility fractures, indicates the presence of an already existing osteoporotic condition that should receive evaluation and treatment.

[Conservative experimental groups in clinical comparative trials. Tables providing the minimum number of patients]. / Konservative forsøksgrupper ved samanliknande forsøk i klinisk medisin. Tabellar til beinveges avlesing.

To calculate the minimum size of sample required for clinical trials it is first necessary to decide the expected difference between the groups, and then the acceptable risk of wrongly declaring a significant result (alpha) or wrongly declaring a non-significant result (beta). Once these three parameters are set, simple tables can show the necessary sample sizes. Such tables are presented for classical comparative studies, survival studies, and group sequential plans. Sequential plans often entail large savings in sample size compared with fixed group plans.

Physical activity and dietary constituents as predictors of forearm cortical and trabecular bone gain in healthy children and adolescents: a prospective study.

We have prospectively studied forearm trabecular and cortical bone mineral density gain (delta BMD) in relation to nutrient intake, weight-bearing physical activity (WPA) and daylight exposure (DE) in 470 healthy boys and girls aged 8.2-16.5 years at the baseline. BMD was assessed using single photon absorptiometry (SPA). Cortical delta BMD peaked at the age of 14.0 +/- 0.3 and 16.0 +/- 0.3 (SD) years in girls and boys, respectively. Girls had achieved adult premenopausal values of trabecular BMD by the age of 15 years and cortical BMD values by the age of 16.5 years. WPA, BMD, body height, height gain, weight, weight gain, dietary polyunsaturated fat and sodium were correlated with delta BMD. WPA, predicting cortical as well as trabecular delta BMD, had the greatest effect on trabecular delta BMD in the presence of a high calcium intake in children below 11 years of age. In conclusion, our results indicate that physical activity and calcium intake should be encouraged at a prepubertal age in order to increase bone density.

Dietary calcium, saturated fat, fiber and vitamin C as predictors of forearm cortical and trabecular bone mineral density in healthy children and adolescents.

Diet, weight-bearing physical activity (WPA) and daylight hours spent outdoors (DE) were related to bone mineral density in the distal (BMDd) and ultradistal (BMDud) forearm of 495 healthy children (8-11 years) and adolescents (11-17 years). BMD was assessed by single photon absorptiometry. Using multiple regression, BMDd was predicted by saturated fat and BMDud by fiber in children. In adolescents, BMDd was predicted by saturated fat and vitamin C, and BMDud by calcium and vitamin C. WPA and DE were not related to BMD. In conclusion, our results showed that current intake of calcium, saturated fat, fiber and vitamin C were positively associated with forearm BMD in children and adolescents. These associations depended on age and bone type. If our findings are verified, dietary recommendations, especially when aimed at young people, may have to be reconsidered.

Assessment of coronary heart disease risk, II. A clinical multicentre study of general practitioners' risk assessment.

The objectives of the present study were: (i) to compare clinical assessment of coronary heart disease (CHD) risk with risk estimation faced with simulated, written case histories; (ii) to observe the risk assessment performed by general practitioners (GPs) in their clinical setting. Thirty-one GPs participating in a multicentre study were asked to invite 20 consecutive male patients aged 30-59 years to an opportunistic screening of CHD risk factors. They assessed the risk status of these patients and of 10 written case histories containing information about corresponding CHD risk factors. A composite 'infarction score' computed from epidemiologic data was used as a gold standard. Diagnostic performance in the clinical setting was compared with that in the simulated setting by Pearson's correlation. A weak, but statistically significant positive correlation was demonstrated when comparing correct estimation in the two settings. No correlation was found for over- and underestimation. Sensitivity was increased faced with clinical patients at the sacrifice of specificity compared to the simulated setting. The impact of a positive family history on clinical assessment parallels the epidemiological estimate. Due to lack of sensitivity, the other factors had a lower impact on risk estimation than an epidemiological estimate would presuppose. We advocate the application of a formal risk estimation to improve risk assessment accuracy. The synergistic effect of multiple risk factors should be emphasized in medical training to improve the clinical risk estimation.