γ-H2AX foci as in vivo effect biomarker in children emphasize the importance to minimize x-ray doses in paediatric CT imaging.

OBJECTIVES: Investigation of DNA damage induced by CT x-rays in paediatric patients versus patient dose in a multicentre setting. METHODS: From 51 paediatric patients (median age, 3.8 years) who underwent an abdomen or chest CT examination in one of the five participating radiology departments, blood samples were taken before and shortly after the examination. DNA damage was estimated by scoring γ-H2AX foci in peripheral blood T lymphocytes. Patient-specific organ and tissue doses were calculated with a validated Monte Carlo program. Individual lifetime attributable risks (LAR) for cancer incidence and mortality were estimated according to the BEIR VII risk models. RESULTS: Despite the low CT doses, a median increase of 0.13 γ-H2AX foci/cell was observed. Plotting the induced γ-H2AX foci versus blood dose indicated a low-dose hypersensitivity, supported also by an in vitro dose-response study. Differences in dose levels between radiology centres were reflected in differences in DNA damage. LAR of cancer mortality for the paediatric chest CT and abdomen CT cohort was 0.08 and 0.13 ‰ respectively. CONCLUSION: CT x-rays induce DNA damage in paediatric patients even at low doses and the level of DNA damage is reduced by application of more effective CT dose reduction techniques and paediatric protocols. .

A belgian multicenter prospective observational cohort study shows safe and efficient use of a composite mesh with incorporated oxidized regenerated cellulose in laparoscopic ventral hernia repair.

BACKGROUND: A variety of anti-adhesive composite mesh products have become available to use inside the peritoneal cavity. However, reimbursement of these meshes by the Belgian Governemental Health Agency (RIZIV/INAMI) can only be obtained after conducting a prospective study with at least one year of clinical follow-up. This -Belgian multicentric cohort study evaluated the experience with the use of Proceed®-mesh in laparoscopic ventral hernia repair. METHODS: During a 25 month period 210 adult patients underwent a laparoscopic primary or incisional hernia repair using an intra-abdominal placement of Proceed®-mesh. According to RIZIV/INAMI criteria recurrence rate after 1 year was the primary objective, while postoperative morbidity, including seroma formation, wound and mesh infections, quality of life and recurrences after 2 years were evaluated as secondary endpoints (NCT00572962). RESULTS: In total 97 primary ventral and 103 incisional hernias were repaired, of which 28 (13%) were recurrent. There were no conversions to open repair, no enterotomies, no mesh infections and no mortality. One year cumulative follow-up showed 10 recurrences (n = 192, 5.2%) and chronic discomfort or pain in 4.7% of the patients. Quality of life could not be analyzed due to incomplete data set. CONCLUSIONS: More than 5 years after introduction of this mesh to the market, this prospective multicentric study documents a favorable experience with the Proceed mesh in laparoscopic ventral hernia repair. However, it remains to be discussed whether reimbursement of these meshes in Belgium should be limited to the current strict criteria and therefore can only be obtained after at least 3-4 years of clinical data gathering and necessary follow-up.

Element specific atom counting for heterogeneous nanostructures: Combining multiple ADF STEM images for simultaneous thickness and composition determination.

In this paper, a methodology is presented to count the number of atoms in heterogeneous nanoparticles based on the combination of multiple annular dark field scanning transmission electron microscopy (ADF STEM) images. The different non-overlapping annular detector collection regions are selected based on the principles of optimal statistical experiment design for the atom-counting problem. To count the number of atoms, the total intensities of scattered electrons for each atomic column, the so-called scattering cross-sections, are simultaneously compared with simulated library values for the different detector regions by minimising the squared differences. The performance of the method is evaluated for simulated Ni@Pt and Au@Ag core-shell nanoparticles. Our approach turns out to be a dose efficient alternative for the investigation of beam-sensitive heterogeneous materials as compared to the combination of ADF STEM and energy dispersive X-ray spectroscopy.

Real-time simulations of ADF STEM probe position-integrated scattering cross-sections for single element fcc crystals in zone axis orientation using a densely connected neural network.

Quantification of annular dark field (ADF) scanning transmission electron microscopy (STEM) images in terms of composition or thickness often relies on probe-position integrated scattering cross sections (PPISCS). In order to compare experimental PPISCS with theoretically predicted ones, expensive simulations are needed for a given specimen, zone axis orientation, and a variety of microscope settings. The computation time of such simulations can be in the order of hours using a single GPU card. ADF STEM simulations can be efficiently parallelized using multiple GPUs, as the calculation of each pixel is independent of other pixels. However, most research groups do not have the necessary hardware, and, in the best-case scenario, the simulation time will only be reduced proportionally to the number of GPUs used. In this manuscript, we use a learning approach and present a densely connected neural network that is able to perform real-time ADF STEM PPISCS predictions as a function of atomic column thickness for most common face-centered cubic (fcc) crystals (i.e., Al, Cu, Pd, Ag, Pt, Au and Pb) along [100] and [111] zone axis orientations, root-mean-square displacements, and microscope parameters. The proposed architecture is parameter efficient and yields accurate predictions for the PPISCS values for a wide range of input parameters that are commonly used for aberration-corrected transmission electron microscopes.

A decade of atom-counting in STEM: From the first results toward reliable 3D atomic models from a single projection.

Quantitative structure determination is needed in order to study and understand nanomaterials at the atomic scale. Materials characterisation resulting in precise structural information is a crucial point to understand the structure-property relation of materials. Counting the number of atoms and retrieving the 3D atomic structure of nanoparticles plays an important role here. In this paper, an overview will be given of the atom-counting methodology and its applications over the past decade. The procedure to count the number of atoms will be discussed in detail and it will be shown how the performance of the method can be further improved. Furthermore, advances toward mixed element nanostructures, 3D atomic modelling based on the atom-counting results, and quantifying the nanoparticle dynamics will be highlighted.

Optimal experiment design for element specific atom counting using multiple annular dark field scanning transmission electron microscopy detectors.

This paper investigates the possible benefits for counting atoms of different chemical nature when analysing multiple 2D scanning transmission electron microscopy (STEM) images resulting from independent annular dark field (ADF) detector regimes. To reach this goal, the principles of statistical detection theory are used to quantify the probability of error when determining the number of atoms in atomic columns consisting of multiple types of elements. In order to apply this theory, atom-counting is formulated as a statistical hypothesis test, where each hypothesis corresponds to a specific number of atoms of each atom type in an atomic column. The probability of error, which is limited by the unavoidable presence of electron counting noise, can then be computed from scattering-cross sections extracted from multiple ADF STEM images. Minimisation of the probability of error as a function of the inner and outer angles of a specified number of independent ADF collection regimes results in optimal experimental designs. Based on simulations of spherical Au@Ag and Au@Pt core-shell nanoparticles, we investigate how the combination of two non-overlapping detector regimes helps to improve the probability of error when unscrambling two types of atoms. In particular, the combination of a narrow low angle ADF detector with a detector formed by the remaining annular collection regime is found to be optimal. The benefit is more significant if the atomic number Z difference becomes larger. In addition, we show the benefit of subdividing the detector regime into three collection areas for heterogeneous nanostructures based on a structure consisting of three types of elements, e.g., a mixture of Au, Ag and Al atoms. Finally, these results are compared with the probability of error resulting when one would ultimately use a pixelated 4D STEM detector and how this could help to further reduce the incident electron dose.

The surgeon and the law on patient's rights for minors.

The law of August 22nd, 2002 concerning patients' rights (LPR) gave a new dimension to the relationship between the physician and the patient. According to this law, it is up to the physician to judge if a patient is able to exercise his own rights or if the patient needs assistance from a representative. In the particular case of the patient being a minor, this often leads to a difficult situation because of the absence of validated criteria to evaluate the capacity of judgment of a minor patient. The triangular relationship physician-patient-parents might be hampered when the parents are involved in a divorce. In daily practice, there are many questions concerning the physicians' attitude towards the rights of the minor patient, particularly in cases of medical intervention. By means of case histories, we describe several problematic situations: the right of free choice of the physician, the right of the minor to obtain informational privacy, obtaining consent for a medical intervention. In cases where there is a divorce, the situation is even more difficult. Solutions are provided to act as effectively as possible in the minors' interests and to offer support to the physician. Note: According to article 388 of the Belgian Civil Code a minor is a person, either male or female, who has not attained the age of 18 years.

The atomic lensing model: New opportunities for atom-by-atom metrology of heterogeneous nanomaterials.

The atomic lensing model has been proposed as a promising method facilitating atom-counting in heterogeneous nanocrystals [1]. Here, image simulations will validate the model, which describes dynamical diffraction as a superposition of individual atoms focussing the incident electrons. It will be demonstrated that the model is reliable in the annular dark field regime for crystals having columns containing dozens of atoms. By using the principles of statistical detection theory, it will be shown that this model gives new opportunities for detecting compositional differences.

Influence of tumor site and histology on long-term survival in 193 children with extracranial germ cell tumors.

AIMS: Although germ cell tumors (GCT) supposedly share the same cell type of origin, their clinical course differs considerably depending on tumor site and histology. The aim of this work was to study long-term survival stratified for tumor site and tumor histology. MATERIALS AND METHODS: The medical records of 193 consecutive infants and children with extracranial GCT were studied. The GCT arose in the following anatomical sites: sacrococcygeal (n = 70), ovary (n = 66), testis (n = 20), retroperitoneum (n = 12), neck (n = 8), mediastinum (n = 7), and miscellaneous (n = 10). Histological analysis revealed 152 teratomas (mature: 115, immature: 37), 27 yolk sac tumors, 8 mixed tumors, 2 dysgerminomas, 2 gonadoblastomas, 1 choriocarcinoma and 1 embryonal carcinoma. RESULTS: Overall survival (OS) for the whole patient group was 0.91 +/- 0.02, and event-free survival (EFS) was 0.88 +/- 0.02 at ten years. Patients with gonadal GCT had a higher probability of OS than those with extragonadal GCT (p = 0.029). Patients with cervical and mediastinal tumors had a lower probability of EFS than those with gonadal, retroperitoneal or sacrococcygeal GCT (p = 0.018). Patients with choriocarcinoma, embryonal carcinoma, immature teratoma, yolk sac tumor and mixed GCT had a lower probability of EFS than patients with mature teratoma or gonadoblastoma (p < 0.001). CONCLUSIONS: Mortality in children with extracranial germ cell tumors is not only dictated by malignant histology, but also, as in the case of mature teratomas, by occurrence at certain sites.

A model of defect cluster creation in fragmented cascades in metals based on morphological analysis.

The impacts of ions and neutrons in metals cause cascades of atomic collisions that expand and shrink, leaving microstructure defect debris, i.e. interstitial or vacancy clusters or loops of different sizes. In De Backer et al (2016 Europhys. Lett. 115 26001), we described a method to detect the first morphological transition, i.e. the cascade fragmentation in subcascades, and a model of primary damage combining the binary collision approximation and molecular dynamics (MD). In this paper including W, Fe, Be, Zr and 20 other metals, we demonstrate that the fragmentation energy increases with the atomic number and decreases with the atomic density following a unique power law. Above the fragmentation energy, the cascade morphology can be characterized by the cross pair correlation functions of the multitype point pattern formed by the subcascades. We derive the numbers of pairs of subcascades and observed that they follow broken power laws. The energy where the power law breaks indicates the second morphological transition when cascades are formed by branches decorated by chaplets of small subcascades. The subcascade interaction is introduced in our model of primary damage by adding pairwise terms. Using statistics obtained on hundreds of MD cascades in Fe, we demonstrate that the interaction of subcascades increases the proportion of large clusters in the damage created by high energy cascades. Finally, we predict the primary damage of 500 keV Fe ion in Fe and obtain cluster size distributions when large statistics of MD cascades are not feasible.

Depth sectioning combined with atom-counting in HAADF STEM to retrieve the 3D atomic structure.

Aberration correction in scanning transmission electron microscopy (STEM) has greatly improved the lateral and depth resolution. When using depth sectioning, a technique during which a series of images is recorded at different defocus values, single impurity atoms can be visualised in three dimensions. In this paper, we investigate new possibilities emerging when combining depth sectioning and precise atom-counting in order to reconstruct nanosized particles in three dimensions. Although the depth resolution does not allow one to precisely locate each atom within an atomic column, it will be shown that the depth location of an atomic column as a whole can be measured precisely. In this manner, the morphology of a nanoparticle can be reconstructed in three dimensions. This will be demonstrated using simulations and experimental data of a gold nanorod.

How precise can atoms of a nanocluster be located in 3D using a tilt series of scanning transmission electron microscopy images?

In this paper, we investigate how precise atoms of a small nanocluster can ultimately be located in three dimensions (3D) from a tilt series of images acquired using annular dark field (ADF) scanning transmission electron microscopy (STEM). Therefore, we derive an expression for the statistical precision with which the 3D atomic position coordinates can be estimated in a quantitative analysis. Evaluating this statistical precision as a function of the microscope settings also allows us to derive the optimal experimental design. In this manner, the optimal angular tilt range, required electron dose, optimal detector angles, and number of projection images can be determined.

Atom-counting in High Resolution Electron Microscopy:TEM or STEM - That's the question.

In this work, a recently developed quantitative approach based on the principles of detection theory is used in order to determine the possibilities and limitations of High Resolution Scanning Transmission Electron Microscopy (HR STEM) and HR TEM for atom-counting. So far, HR STEM has been shown to be an appropriate imaging mode to count the number of atoms in a projected atomic column. Recently, it has been demonstrated that HR TEM, when using negative spherical aberration imaging, is suitable for atom-counting as well. The capabilities of both imaging techniques are investigated and compared using the probability of error as a criterion. It is shown that for the same incoming electron dose, HR STEM outperforms HR TEM under common practice standards, i.e. when the decision is based on the probability function of the peak intensities in HR TEM and of the scattering cross-sections in HR STEM. If the atom-counting decision is based on the joint probability function of the image pixel values, the dependence of all image pixel intensities as a function of thickness should be known accurately. Under this assumption, the probability of error may decrease significantly for atom-counting in HR TEM and may, in theory, become lower as compared to HR STEM under the predicted optimal experimental settings. However, the commonly used standard for atom-counting in HR STEM leads to a high performance and has been shown to work in practice.

Quantification by aberration corrected (S)TEM of boundaries formed by symmetry breaking phase transformations.

The present contribution gives a review of recent quantification work of atom displacements, atom site occupations and level of crystallinity in various systems and based on aberration corrected HR(S)TEM images. Depending on the case studied, picometer range precisions for individual distances can be obtained, boundary widths at the unit cell level determined or statistical evolutions of fractions of the ordered areas calculated. In all of these cases, these quantitative measures imply new routes for the applications of the respective materials.

Three-dimensional atomic models from a single projection using Z-contrast imaging: verification by electron tomography and opportunities.

In order to fully exploit structure-property relations of nanomaterials, three-dimensional (3D) characterization at the atomic scale is often required. In recent years, the resolution of electron tomography has reached the atomic scale. However, such tomography typically requires several projection images demanding substantial electron dose. A newly developed alternative circumvents this by counting the number of atoms across a single projection. These atom counts can be used to create an initial atomic model with which an energy minimization can be applied to obtain a relaxed 3D reconstruction of the nanoparticle. Here, we compare, at the atomic scale, this single projection reconstruction approach with tomography and find an excellent agreement. This new approach allows for the characterization of beam-sensitive materials or where the acquisition of a tilt series is impossible. As an example, the utility is illustrated by the 3D atomic scale characterization of a nanodumbbell on an in situ heating holder of limited tilt range.

Imaging of extraspinal musculoskeletal tuberculosis.

Tuberculosis (TB) is still a major cause of significant morbidity and mortality despite universal availability of effective chemotherapy. The emergence of multidrug-resistant mycobacteria along with a worldwide increase in HIV infection has led to a recent surge in the number of patients with TB. TB involves both pulmonary and extrapulmonary sites. Tuberculous spondylitis is the most common form of musculoskeletal TB and accounts for approximately 50% of cases. Extraspinal musculoskeletal TB is among the least common manifestations of TB. It shows a predilection for joints and para-articular areas while isolated soft tissue TB occurs extremely rare. A non-specific, often indolent clinical presentation in conjunction with its low prevalence constitutes obstacles for diagnosis. The differential diagnosis of extraspinal musculoskeletal TB consists of degenerative processes, inflammatory and infectious conditions, primary neoplasms, and metastatic lesions. Early diagnosis and treatment is of utmost importance to prevent serious joint and bone destruction. Radiological assessment of patients with musculoskeletal TB is often the key to adequate diagnosis and early treatment. The purpose of this manuscript is to review the imaging features of extraspinal musculoskeletal TB and to focus on the magnetic resonance imaging (MRI) characteristics of this pathology.

Mediastinal germ cell tumors: clinical aspects and outcomes in 7 children.

BACKGROUND: Mediastinal germ cell tumors presenting during childhood are extremely rare. Publications on this entity are very scarce. This paper reports on the clinical presentations, method(s) of treatment, complications, results and outcomes in a series of children with mediastinal germ cell tumors. METHODS: A retrospective chart review of 7 children treated between 1971 and 2001 for mediastinal germ cell tumor was carried out. Age at diagnosis and symptoms were recorded. Each patient's surgical treatment, peri- and postoperative complications, histological staging and final outcome were analysed. RESULTS: The median age of the 4 boys and 3 girls was 3 years (range 21 months-15 years). The most frequent symptoms were respiratory distress, persistent coughing, thoracic pain and anorexia/weight loss. Four patients had histologically benign tumors (mature teratoma). Their sole treatment consisted of complete surgical excision of the tumor and (part of) the thymus using either median sternotomy or left-sided thoracotomy. Recovery was uneventful. No recurrences have been observed. All four are alive with no evidence of disease, between 2.5 and 29 years after treatment. Malignant tumors were observed in three patients (1 yolk sac tumor, 1 choriocarcinoma and 1 malignant teratoma). Treatment consisted of either biopsy or debulking followed by chemotherapy (and radiotherapy in 1 case). Two of them died from uncontrollable metastatic disease. The patient with yolk sac tumor survived; he is now in remission, 4 years after diagnosis. CONCLUSIONS: Both this study and the literature review testify to the extreme rarity of mediastinal germ cell tumors in childhood. Children with this type of tumor usually are severely symptomatic. Histologically benign tumors carry an excellent prognosis provided surgical excision is complete. Histologically malignant tumors, on the other hand, have a worse prognosis. However, the use of platinum-based combination chemotherapy has considerably increased the survival rates.

Detecting and locating light atoms from high-resolution STEM images: The quest for a single optimal design.

In the present paper, the optimal detector design is investigated for both detecting and locating light atoms from high resolution scanning transmission electron microscopy (HR STEM) images. The principles of detection theory are used to quantify the probability of error for the detection of light atoms from HR STEM images. To determine the optimal experiment design for locating light atoms, use is made of the so-called Cramér-Rao Lower Bound (CRLB). It is investigated if a single optimal design can be found for both the detection and location problem of light atoms. Furthermore, the incoming electron dose is optimised for both research goals and it is shown that picometre range precision is feasible for the estimation of the atom positions when using an appropriate incoming electron dose under the optimal detector settings to detect light atoms.

StatSTEM: An efficient approach for accurate and precise model-based quantification of atomic resolution electron microscopy images.

An efficient model-based estimation algorithm is introduced to quantify the atomic column positions and intensities from atomic resolution (scanning) transmission electron microscopy ((S)TEM) images. This algorithm uses the least squares estimator on image segments containing individual columns fully accounting for overlap between neighbouring columns, enabling the analysis of a large field of view. For this algorithm, the accuracy and precision with which measurements for the atomic column positions and scattering cross-sections from annular dark field (ADF) STEM images can be estimated, has been investigated. The highest attainable precision is reached even for low dose images. Furthermore, the advantages of the model-based approach taking into account overlap between neighbouring columns are highlighted. This is done for the estimation of the distance between two neighbouring columns as a function of their distance and for the estimation of the scattering cross-section which is compared to the integrated intensity from a Voronoi cell. To provide end-users this well-established quantification method, a user friendly program, StatSTEM, is developed which is freely available under a GNU public license.

Optimal experimental design for nano-particle atom-counting from high-resolution STEM images.

In the present paper, the principles of detection theory are used to quantify the probability of error for atom-counting from high resolution scanning transmission electron microscopy (HR STEM) images. Binary and multiple hypothesis testing have been investigated in order to determine the limits to the precision with which the number of atoms in a projected atomic column can be estimated. The probability of error has been calculated when using STEM images, scattering cross-sections or peak intensities as a criterion to count atoms. Based on this analysis, we conclude that scattering cross-sections perform almost equally well as images and perform better than peak intensities. Furthermore, the optimal STEM detector design can be derived for atom-counting using the expression for the probability of error. We show that for very thin objects LAADF is optimal and that for thicker objects the optimal inner detector angle increases.