Search

Working from home during COVID-19: a descriptive study on the changes in working conditions and health. This study provides an overview of the changes in working conditions and health of home workers in the Netherlands between 2019 (pre COVID-19) and July 2020 (during the COVID-19 pandemic). Moreover, this descriptive study examined if these changes differ across different group of workers (i.e. gender, age, and taking care for (young) children). McNemar test, paired T-tests and a combination of T-tests and weighted deviation contrasts were used to examine differences between 2019 and 2020. In general, the results show a diverse pattern – with both some improvements as well as some deteriorations of working conditions and health – among home workers. First, compared to the pre-covid situation, during the pandemic respondents worked more overtime and less home workers experienced high autonomy. Furthermore, the majority of the home workers did not have an ergonomic workplace at home. The results also showed more sedentary behavior in 2020 compared to 2019. On the other hand, during the covid period, less respondents said to experience high workload or emotional job demands. Additionally, more home workers reported a good self-perceived general and physical health. Overall, the degree of burnout complaints, work-life imbalance and social support does not change between measurements. Personal characteristics seem to play a role in changes in health and working conditions. More women and workers with a temporary contract reported burn-out complaints during the covid-period than before, whereas the proportion of men reporting burn-out complaints slightly decreased. The proportion of women and parents with young children with high autonomy decreased. Additionally, more parents with young children experienced a work-life imbalance.

Samenvatting De COVID-19-pandemie en de daarmee getroffen maatregelen zorgden in maart 2020 direct voor grote veranderingen. Er zijn signalen dat deze veranderingen een negatief effect hebben op het welbevinden. Sommige onderzoeken spreken dit echter tegen, met name die onder de werkende bevolking. Mogelijk pakt de pandemie voor sommige groepen juist gunstig uit en voor andere groepen minder, waardoor het totaalbeeld vertekend wordt. In dit onderzoek focussen we ons op drie beroepsgroepen waarvan bekend is dat de COVID-19-pandemie en bijbehorende maatregelen direct een effect hebben op hun werktaken en hoeveelheid werkzaamheden: zorgpersoneel, onderwijspersoneel en verkopers. Met behulp van GEE-analyses onderzoeken we of er sprake is van een significante afname in welbevinden en een verandering in werkfactoren en in hoeverre de werkfactoren gerelateerd zijn aan het welbevinden. Uit de resultaten blijkt dat er slechts op beperkte schaal sprake is van een afname in welbevinden. Er wordt alleen een verslechtering in burn-outklachten gezien bij zorgpersoneel en verkopers. Werkfactoren laten vooral een verandering in gunstige richting zien, met uitzondering van autonomie. Die is in al de onderzochte groepen gedaald. Hoewel we wel een relatie vonden tussen de onderzochte werkfactoren en burn-outklachten, kunnen we de ontwikkelingen in het welbevinden niet verklaren door de verandering in werkfactoren.

The goal of this project is to investigate a new method for using list-mode data instead of binned projection data for single photon emission computed tomography (SPECT) reconstruction. List-mode acquisition was once standardly available for planar scintigraphy and is now becoming available for SPECT acquisition. The authors implemented maximum-likelihood iterative reconstruction with list-mode data for SPECT using a new projector/backprojector pair, which employs an intermediate stage to separate the source and camera specific components. In two dimensions, the intermediate stage is a circle surrounding the object. An emission radiance distribution is calculated at the circle from the estimate of the source distribution in the object. This leads to the probability that a photon, coming from the source distribution, leaves the circle surrounding the object at a certain point, going in a specific direction. The algorithm uses the emission radiance distribution to obtain the probabilities used in the iterative reconstruction method. The model takes into account distance-dependent resolution and nonuniform attenuation. Results illustrate how the individual steps of the algorithm work. The list-mode iterative reconstruction algorithm is compared to the standard MLEM iterative reconstruction method, which employs binned data. It is concluded that the finer sampling provided by list-mode data results in superior image quality. By using the intermediate stage, the authors obtained a structure that can very easily be adapted to different types of collimators and acquisition protocols.

The purpose of the study was to evaluate the resolution recovery in the list-mode iterative reconstruction algorithm (LMIRA) for SPECT. In this study we compare the performance of the proposed method with other iterative resolution recovery methods for different noise levels. We developed an iterative reconstruction method which uses list-mode data instead of binned data. The new algorithm makes use of a more accurate model of the collimator structure. We compared the SPECT list-mode reconstruction with MLEM, OSEM and RBI, all including resolution recovery. For the evaluation we used Gaussian shaped sources with different FWHM at three different locations and three noise levels. For these distributions we calculated the reconstructed images for a different number of iterations. The absolute error for the reconstructed images was used to evaluate the performance. The performance of all four methods is comparable for the sources located in the centre of the field of view. For the sources located out of the centre, the error of the list-mode method is significantly lower than that of the other methods. Splitting the system model into a separate object-dependent and detector-dependent module gives us a flexible reconstruction method. With this we can very easily adapt the resolution recovery to different collimator types.

Due to the limited resolution of single-photon emission computed tomography (SPECT) imaging devices, tissue interfaces are not well defined in the reconstructed image, even though resolution recovery techniques may be used during reconstruction. Therefore, segmentation of a particular region and quantification of the tracer uptake in that region is critical due to spillover effects, when based on the SPECT image only. In this study, we present two methods for quantification of tracer uptake in a SPECT image, defined by a matched high resolution structural magnetic resonance image. We show preliminary results of both techniques, when applied for quantifying regional uptake in the different compartments of a phantom simulating the basal ganglia. These results indicate that the quantification method, which takes into account the blurring by the SPECT imaging device, promises to be perform better in the presence of background activity.

This paper will review the recent advances and future developments in the field of coincidence imaging of positron emitters with a conventional Anger-type gamma camera. FDG imaging has shown high clinical importance in cardiology, neurology and especially oncology. Since access to full ring PET is mainly limited to university hospitals, there have been new developments allowing PET imaging on the standard Anger gamma camera. First the principles of coincidence imaging on a gamma camera will be reviewed. We will discuss the limitations of this technique, and the techniques used to partly overcome these limitations. The different configurations of the gamma camera operating in coincidence mode are pointed out. Different corrections for image degrading effects and reconstruction methods are evaluated in the final part.

A PACS (Picture Archiving and Communication System) is a system that is able to store, exchange, display and manipulate images and associated diagnoses from any modality within a hospital in a timely and cost-effective way. Several developments, such as the DICOM standard, fast and convenient networking, and new storage solutions for large amounts of data, make the setup of such a PACS system possible. As the information acquired with various imaging modalities is then available and often complementary, it is desirable for the clinician to have a point-by-point spatial co-registration of images from different modalities in order to enable a synergistic use of the multimodality imaging of a patient for increased diagnostic accuracy. Various types of algorithms are available for the matching of medical images from the same or from different modalities. Co-registration algorithms based on voxel properties consist of a similarity or dissimilarity measure and an iterative or non-iterative method minimizing the dissimilarity or maximizing the similarity between the two images by a transformation of one image relative to the other.

The Joint Analysis System (JAS) is a multi-sided, joint campaign-level simulation used by the Office of the Secretary of Defense/Director of Cost Assessment and Program Evaluation (OSD/CAPE) Simulation and Analysis Center (SAC) for theater-level strategic analysis to support and assist Department of Defense (DoD) decision-making. The need for a higher execution speed for JAS (400 times real-time) combined with a desire for the shortest possible time-to-solution has led to the application of high performance computers (HPCs) to support the JAS program goals. Previous work with JAS [previously called the Joint War fighting System (JWARS)] explored the viability of parallel execution of computationally-intensive simulation processes to shorten execution times. Further work was performed to port the "back-end" simulation code to the Linux® (Linus Torvalds) environment to take advantage of Linux-based HPC assets. Capabilities developed as part of the parallel processing effort are part of the JAS technical library, and the Linux porting is now part of baseline code. The US Army Research Laboratory (ARL) DoD Supercomputing Resource Center (DSRC) has recently added a 6,656 core SGI Altix® ICE 8200 system (called TOW) to its toolset. This new system offers the SAC an opportunity to further utilize the processing capabilities offered by HPCs. The focus of this paper is to discuss the challenges and lessons learned in adapting JAS for use on TOW.

Due to the rising interest in clinical PET imaging, some manufacturers adapt two-headed gamma cameras to work in coincidence mode. Recently, the use of three heads for coincidence imaging has been suggested. The three heads can be placed in different configurations to achieve optimal sensitivity profiles. Two of these configurations are U-shape and triangular. As the average angle of incidence of the photons will differ for each configuration, it is expected that the resolution properties will be different. Resolution will be degraded by angle of incidence effects, non-colinearity of the photons, and, for axial resolution, rebinning of the list mode data to two-dimensional projections. In this paper, we investigate the influence of camera configuration, detector radius and scatter medium on transaxial and axial resolution properties. FWHM and FWTM were measured for different values of these parameter, and compared with each other.

Gamma cameras used in PET mode are operating at high count rates, which leads to a high number of randoms in the acquired data. These data are often stored in listmode format to obtain more accurate reconstructions. We propose a randoms correction for an iterative list mode based reconstruction, which is based on the single photon distribution on each detector head. The method takes the spatial variation of the random coincidences into account. From the singles rates on each head the number of randoms in each voxel of the reconstruction is estimated. This is done by integrating the product of the singles over the solid angle formed by the voxel and both detectors. Camera rotation is taken Into account by integration this over all detector angles. This method only requires a quick singles scan prior or after the acquisition when there is unknown activity outside the FOV. When there is no activity outside the FOV or it is known the singles distribution on the detector head can be estimated from the reconstructed images. The randoms distribution can be subtracted after the reconstruction has been done.

In this study, the authors present two methods for quantification of tracer uptake in a SPECT image, guided by a matched high-resolution structural MR image. The authors show preliminary results of both techniques, when applied for quantifying regional uptake in the different compartments of a phantom simulating the basal ganglia. These results indicate that the quantification method, which takes into account the blurring by the SPECT imaging device, promises to be more performant in the presence of background activity.

A new projector/backprojector pair for iterative reconstruction using an intermediate stage is proposed. The aim was to separate the object-dependent and the detector-dependent characteristics into two separate modules. In two-dimensions (2D) the intermediate stage is a circle surrounding the object. An emission distribution is calculated at the circle from the initial estimate of the source distribution in the object. This leads to the probability that a photon, coming from the source distribution, leaves the circle surrounding the object at a certain point, going in a specific direction. Iterative reconstruction uses the total system sensitivity calculated from the integration over the distribution and the individual sensitivity for a given bin location, derived from the integration over a fraction of the distribution. The fraction is calculated from the geometry of the detection system. This information can be used in the forward and backprojection of an iterative reconstruction method to obtain a more accurate model of the processes involved. By using the intermediate stage the authors obtained a structure that can very easily be adapted to different types of collimators, taking into account the distance dependent resolution, and acquisition protocols. The method can even be used for list-mode reconstruction.

We developed an iterative reconstruction method for SPECT which uses list-mode data instead of binned data. It uses a more accurate model of the collimator structure. The purpose of the study was to evaluate the resolution recovery and to compare its performance to other iterative resolution recovery methods in the case of high noise levels The source distribution is projected onto an intermediate layer. Doing this we obtain the complete emission radiance distribution as an angular sinogram. This step is independent of the acquisition system. To incorporate the resolution of the system we project the individual list-mode events over the collimator wells to the intermediate layer. This projection onto the angular sinogram will define the probability a photon from the source distribution will reach this specific location on the surface of the crystal, thus being accepted by the collimator hole. We compared the SPECT list-mode reconstruction to MLEM, OSEM and RBI. We used Gaussian shaped point sources with different FWHM at different noise levels. For these distributions we calculated the reconstructed images at different number of iterations. The modeling of the resolution in this algorithm leads to a better resolution recovery compared to other methods, which tend to overcorrect.

A practical method for scatter compensation in SPECT imaging is the triple energy window technique (TEW) which estimates the fraction of scattered photons in the projection data pixel by pixel. This technique requires an acquisition of counts in three windows of the energy spectrum for each projection bin, which is not possible on every gamma camera. The aim of this study is to set up a scatter template for brain perfusion SPECT imaging by means of the scatter data acquired with the triple energy window technique. This scatter template can be used for scatter correction as follows: the scatter template is realigned with the acquired, by scatter degraded and reconstructed image by means of the corresponding emssion template, which also includes scatter counts. The ratios between the voxelvalues of this emission template and the acquired and reconstructed image are used to locally adjust the scatter template. Finally the acquired and reconstructed image is corrected for scatter by substracting the thus obtained scatter estimates. We compared the template based approach with the TEW scatter correction technique for data acquired with same gamma camera system and found a similar performance for both correction methods.

Gamma camera PET (Positron Emission Tomography) offers a low-cost alternative for dedicated PET scanners. However, sensitivity and count rate capabilities of dual-headed gamma cameras with PET capabilities are still limited compared to full-ring dedicated PET scanners. To improve the geometric sensitivity of these systems, triple-headed gamma camera PET has been proposed. As is the case for dual-headed PET, the sensitivity of these devices varies with the position within the field of view (FOV) of the camera. This variation should be corrected for when reconstructing the images. In earlier work, we calculated the two-dimensional sensitivity variation for any triple-headed configuration. This can be used to correct the data if the acquisition is done using axial filters, which effectively limit the axial angle of incidence of the photons, comparable to 2D dedicated PET. More recently, these results were extended to a fully 3D calculation of the geometric sensitivity variation. In this work, the results of these calculations are compared to the standard approach to correct for 3D geometric sensitivity variation. Current implementations of triple-headed gamma camera PET use two independent corrections to account for three-dimensional sensitivity variations: one in the transaxial direction and one in the axial direction. This approach implicitly assumes that the actual variation is separable in two independent components. We recently derived a theoretical expression for the 3D sensitivity variation, and in this work we investigate the separability of our result. To investigate the separability of the sensitivity variations, an axial and transaxial profile through the calculated variation was taken, and these two were multiplied, thus creating a separable function. If the variation were perfectly separable, this function would be identical to the calculated variation. As a measure of separability, we calculated the percentual deviation of the separable function to the original variation. We investigated the separability for several camera configurations and rotation radii. We found that, for all configurations, the variation is not separable , and becomes less separable as the rotation radius tends to smaller values. This indicates that in this case, our sensitivity correction will give better results than the separable correction now applied.

This overview takes a look at different correction techniques for Single Photon Emission Computed Tomography (SPECT). We discuss the influence of the detection system followed by the scatter and attenuation caused by the object of investigation. When possible we describe how the correction methods for the different physical effects can be incorporated in the reconstruction method, being either filtered backprojection or iterative reconstruction.

Nonuniform attenuation correction in brain SPECT can be done routinely by means of additional gamma transmission CT (TCT) measurements, using different commercially available line-source isotopes, 201Tl, 153Gd, and 99mTc are among the most commonly used isotopes, depending on practical and cost-effectiveness issues. We have measured additional radiation burden from static uncollimated brain SPECT transmission sources for these isotopes. The influence of the transmission isotope on brain quantification was also measured and compared with uniform attenuation correction for phantom and human data. Full iterative transmission and emission reconstruction were compared with filtered backprojection techniques.Rod sources with 201Tl, 153Gd, and 99mTc were used on a triple-head gamma camera. Dosimetry was performed using LiF TLD-100 pellets and an anthropomorphic RANDO phantom. Effective dose equivalents were calculated on the basis of measured and extrapolated absorbed doses. For brain activity measurements, a Hoffman phantom was used. Images were corrected for scatter (triple-energy window) and were reconstructed by Chang attenuation correction and filtered backprojection as well as full iterative reconstruction (ordered-subsets expectation maximization [OSEM]). To study the effect of inhomogeneous bone attenuation, realistic measurements were performed on 10 young, healthy volunteers with 153Gd TCT. After stereotactic image realignment, a volume-of-interest analysis normalized to total counts was performed.Brain SPECT-TCT using 201Tl, 153Gd, and 99mTc produced total effective dose-rate equivalents of 50.3 +/- 11.2, 32.0 +/- 2.7, and 71.1 +/- 7.1 microSv/GBq x h, respectively, representing dose equivalents of 18.6, 11.9, and 26.3 microSv for a typical 20-min brain SPECT scan at maximal used source strength. Standardized quantification resulted in insignificant differences between the isotopes and methods (Chang versus OSEM) used for nonuniform correction. Iterative reconstruction enhanced image contrast and provided more accurate gray-to-white matter ratios. Between nonuniform and uniform attenuation with an optimized attenuation coefficient, slight central discrepancies were found for volunteer studies. Significantly lower intersubject variation was found for nonuniform corrected values in infratentorial and posterior brain regions.Brain transmission scanning using 201Tl, 153Gd, or 99mTc results in limited effective radiation dose equivalents compared with the typical radiation burden. Relative brain perfusion quantification is not significantly different for the various nonuniform TCT isotopes. Iterative reconstruction improves gray-to-white contrasts but has no significant influence on brain perfusion semiquantification. Nonuniform attenuation correction decreases intersubject variability in the posterior brain regions that were compared, which may lead to improved sensitivity toward clinical applications.

Iterative reconstruction algorithms produce accurate images without streak artifacts as in filtered backprojection. They allow improved incorporation of important corrections for image degrading effects, such as attenuation, scatter and depth-dependent resolution. Only some corrections, which are important for accurate reconstruction in positron emission tomography and single photon emission computed tomography, can be applied to the data before filtered backprojection. The main limitation for introducing iterative algorithms in nuclear medicine has been computation time, which is much longer for iterative techniques than for filtered backprojection. Modern algorithms make use of acceleration techniques to speed up the reconstruction. These acceleration techniques and the development in computer processors have introduced iterative reconstruction in daily nuclear medicine routine. We give an overview of the most important iterative techniques and discuss the different corrections that can be incorporated to improve the image quality.

In the near future, it will be possible to perform coincidence detection on a gamma camera with three heads, which increases the geometric sensitivity of the system. Different geometric configurations are possible, and each configuration yields a different geometric sensitivity. The purpose of this work was to calculate the sensitivities for different three-headed configurations as a function of the position in the field of view, the dimensions of the detector heads and the distance of the heads from the center of the field of view. The configurations that were compared are: a regular two headed configuration (180 deg. opposed), a triple-headed configuration with the three heads in an equilateral triangle (120 deg.), and a triple-headed configuration with two heads in a regular two headed configuration, and the third perpendicular between the first two, which makes a U-shaped configuration. An expression was derived for any planar detector configuration to calculate the geometric sensitivity for each Line Of Response (LOR). This sensitivity was integrated to get the sensitivity profile, which gives the geometric sensitivity at a certain distance from the center of rotation. We found that the triangular configuration gave the best sensitivities when placed very near to each other (nearly full ring configuration), but for larger fields of view, the U-shaped configuration performed better.

Enteroviruses may be involved in the pathogenesis of insulin-dependent diabetes mellitus, either through direct beta-cell infection or as triggers of autoimmunity. In the present study we investigated the patterns of infection in adult human islet cell preparations (consisting of 56+/-14% beta-cells) by several coxsackieviruses. The cells were infected with prototype strains of coxsackievirus B (CBV) 3, 4, and 5 as well as coxsackievirus A9 (CAV-9). The previously characterized diabetogenic strain of coxsackievirus B4 (CBV-4-E2) was used as a reference. All viruses replicated well in beta-cells, but only CBVs caused cell death. One week after infection, the insulin response of the beta-cells to glucose or glucose plus theophylline was most severely impaired by CBV-3 and CBV-5 infections. CBV-4 also caused significant functional impairment, whereas CAV-9-infected cells responded like uninfected controls. After 2 days of infection, about 40% of CBV-5-infected cells had undergone morphological changes characteristic of pyknosis, i.e. highly distorted nuclei with condensed but intact chromatin. Both mitochondria and plasma membrane were intact in these cells. DNA fragmentation was found in 5.9+/-1.1% of CBV-5-infected beta-cell nuclei (2.1+/-0.3% in controls; P0.01). CAV-9 infection did not induce DNA fragmentation. One week after infection the majority of infected cells showed characteristics of secondary necrosis. Medium nitrite and inducible nitric oxide synthase messenger ribonucleic acid levels were not significantly up-regulated by CBV infection. These results suggest that several enteroviruses may infect human beta-cells. The infection may result in functional impairment or death of the beta-cell or may have no apparent immediate adverse effects, as shown here for CAV-9. Coxsackie B viruses cause functional impairment and beta-cell death characterized by nuclear pyknosis. Apoptosis appears to play a minor role during a productive CBV infection in beta-cells.

Surface major histocompatibility complex (MHC) class I and class II expression by pancreatic islet cells is considered a local initiator or regulator of immune processes that can lead to diabetes. Locally released cytokines, in particular interferon-gamma, are known to stimulate MHC antigen expression by islet cells. The present study quantifies MHC expression in cultured pancreatic beta- and non-beta-cells from both rat and human organs. Interferon-gamma increased MHC class I expression in endocrine beta- and non-beta-cells as well as in pancreatic ductal cells. The cytokine induced a 6-fold increase in the MHC class I messenger ribonucleic acid levels in pancreatic beta-cells; this effect was 2-fold amplified in the presence of elevated glucose levels (20 mmol/L instead of 6 mmol/L). No MHC class II expression was observed in endocrine beta- or non-beta-cells; human, but not rat, ductal cells exhibited MHC class II expression that increased in the presence of interferon-gamma. These data indicate that the increase in beta-cell MHC class I expression described in the pancreata of diabetic patients may result from stimulated transcription after exposure to locally released interferon-gamma and/or to a hyperglycemic state. The association of human islets with ductal cells in which MHC class II expression is stimulated by interferon-gamma makes these cells potential participants in the autoimmune process in diabetes.

Endocrine and exocrine pancreatic morphogenesis is known to occur from ductal epithelium, but the factors that regulate this process are unknown. Vascular endothelial growth factor (VEGF)/vascular permeability factor has recently been reported to affect fetal islet ontogenesis. VEGF is an angiogenic factor with a growth-promoting effect that is thought to be restricted to vascular endothelial cells. We demonstrated that VEGF is also a mitogen for adult rat pancreatic duct epithelial cells in primary culture. VEGF supplementation to a serum-free culture medium increased the 5-bromo-2'-deoxyuridine-pulse labeling index of ductal cells more than 2-fold. Immunohistochemical staining and protein blots revealed that pancreatic duct cells express fetal liver kinase-1 high-affinity receptors for VEGF. In pancreatic tissue, immunohistochemistry shows that VEGF peptide is expressed in normal pancreatic islet cells. In duct ligation-induced acute pancreatitis, numerous inflammatory leukocytes containing VEGF were seen to infiltrate between hyperplastic ducts. In the latter model, islet neogenesis has previously been observed. Our data indicate the possibility that VEGF plays a role in the paracrine regulation of ductal growth and differentiation in vivo, eg, in pancreatitis. In vitro, however, VEGF did not induce endocrine differentiation of ductal cells, indicating that it is not the only factor required for the activation of islet neogenesis.

Methods are now available to characterize Kupffer cells both in vivo and in vitro. They can be isolated and purified from the liver and their functional activities studied in maintenance culture. Kupffer cells are not merely phagocytic cells or scavengers but they can also produce and secrete a variety of substances that can regulate the functions of other cells. They can also regulate the immune system and be directly cytotoxic to tumor cells and parasites. In the light of these reported functions, the clinical importance of Kupffer cells in a variety of liver diseases deserves to be better explored. Although the origin and cytokinetics of Kupffer cells, and specially their relation to the Mononuclear Phagocyte System (MPS), are still not completely understood, it has now become clear that Kupffer cells are not end-cells incapable of self-proliferation. Under various experimental conditions Kupffer cells have been shown to respond to activation by strong mitotic proliferation. On the other hand, bone marrow-derived cells can migrate to the liver under certain conditions and differentiate into liver macrophages, thus becoming Kupffer cells.

The four types of non-parenchymal sinusoid lining cells can be identified in situ and can be isolated for in vitro studies: the fenestrated endothelial cells, the phagocytic Kupffer cells, the fibroblast-like fat-storing cells, and the 'natural killer' pit cells. In situ the last three sinusoidal cell types can be seen to proliferate and increase in number in experimental models of liver pathology, such as inflammations and fibrosis. The understanding of the population dynamics of these cells--their mitotic activity, turnover time, and migration--may therefore have clinical applications. In the present article our data concerning the proliferation kinetics of Kupffer and pit cells in rat liver are reviewed.