Correcting B0 inhomogeneity-induced distortions in whole-body diffusion MRI of bone

Diffusion-weighted magnetic resonance imaging (DWI) of the musculoskeletal system has various applications, including visualization of bone tumors. However, DWI acquired with echo-planar imaging is susceptible to distortions due to static magnetic field inhomogeneities. This study aimed to estimate spatial displacements of bone and to examine whether distortion corrected DWI images more accurately reflect underlying anatomy. Whole-body MRI data from 127 prostate cancer patients were analyzed. The reverse polarity gradient (RPG) technique was applied to DWI data to estimate voxel-level distortions and to produce a distortion corrected DWI dataset. First, an anatomic landmark analysis was conducted, in which corresponding vertebral landmarks on DWI and anatomic T2-weighted images were annotated. Changes in distance between DWI- and T2-defined landmarks (i.e., changes in error) after distortion correction were calculated. In secondary analyses, distortion estimates from RPG were used to assess spatial displacements of bone metastases. Lastly, changes in mutual information between DWI and T2-weighted images of bone metastases after distortion correction were calculated. Distortion correction reduced anatomic error of vertebral DWI up to 29 mm. Error reductions were consistent across subjects (Wilcoxon signed-rank p < 10–20). On average (± SD), participants’ largest error reduction was 11.8 mm (± 3.6). Mean (95% CI) displacement of bone lesions was 6.0 mm (95% CI 5.0–7.2); maximum displacement was 17.1 mm. Corrected diffusion images were more similar to structural MRI, as evidenced by consistent increases in mutual information (Wilcoxon signed-rank p < 10–12). These findings support the use of distortion correction techniques to improve localization of bone on DWI.

Posture Assessment in Dentistry for Different Visual Aids Using 2D Markers

Attention and awareness towards musculoskeletal disorders (MSDs) in the dental profession has increased considerably in the last few years. From recent literature reviews, it appears that the prevalence of MSDs in dentists concerns between 64 and 93%. In our clinical trial, we have assessed the dentist posture during the extraction of 90 third lower molars depending on whether the operator performs the intervention by the use of the operating microscope, surgical loupes, or with the naked eye. In particular, we analyzed the evolution of the body posture during different interventions evaluating the impact of visual aids with respect to naked eye interventions. The presented posture assessment approach is based on 3D acquisitions of the upper body, based on planar markers, which allows us to discriminate spatial displacements up to 2 mm in translation and 1 degree in rotation. We found a significant reduction of neck bending in interventions using visual aids, in particular for those performed with the microscope. We further investigated the impact of different postures on MSD risk using a widely adopted evaluation tool for ergonomic investigations of workplaces, named (RULA) Rapid Upper Limb Assessment. The analysis performed in this clinical trial is based on a 3D marker tracker that is able to follow a surgeon’s upper limbs during interventions. The method highlighted pros and cons of different approaches.

Performance Evaluation of Low-Cost Multi-Frequency GNSS Receivers and Antennas for Displacement Detection

Low-cost Global Navigation Satellite System (GNSS) receivers are currently used in various engineering applications. These low-cost devices are regarded as suitable sensors for applications in areas with a high risk of instrument damage. The main objectives of this research were to identify the size of displacements that can be detected in relative and absolute positioning modes by low-cost GNSS instruments and to compare the results of selected antennas. Additionally, geodetic and low-cost GNSS instruments were compared in the level of observations. For this study, low-cost SimpleRTK2B V1 boards, which house ZED-F9P GNSS chips, and three low-cost antennas, namely, Survey, Tallysman TW3882, and Survey Calibrated, were selected. While antenna calibration parameters are known for the last antenna, this is not the case for the first two. For testing purposes, a geodetic network consisting of four points was established; horizontal and vertical movements were imposed by a special mechanism with high accuracy. In relative positioning mode, the results indicate that the Survey Calibrated antenna can detect horizontal and vertical displacements with sizes of 4 mm, and 6 mm, respectively. In the detection of horizontal displacements, the performance of the Survey antenna was not as good as that of Tallysman, and the sizes of detected displacements were 6 mm and 4 mm for the first, and second antennas, respectively. Vertical displacements of 9 mm were detected using both Survey and Tallysman antennas. In absolute positioning mode, Survey Calibrated also had better performance than the Tallysman antenna, and spatial displacements of 20 mm or greater were detected by low-cost GNSS instruments. The observations made with low-cost and geodetic GNSS instruments were compared, and the latter showed better performance. However, the differences in cycle slips and the noise of phase observations were inferior. Considering their cost and proven performance, it can be concluded that such sensors can be considered for setting up a highly accurate but low-cost geodetic monitoring system.

Urban paradox and the rise of the neoliberal city: Case study of Lagos, Nigeria

In a bid to actualise the vision of transforming Lagos into Africa’s model megacity and global economic and financial hub, the state government has embarked on and/or supported various urban development projects. Drawing on the theoretical underpinnings of neoliberalism, we argue that governance practices in Lagos are transforming the city in a manner that is paradoxical to the intents of the city’s development plan. This paper, therefore, explores how government practices have shaped the city, and the socio-spatial consequences of the recent Lagos state government-supported developments. Of interest are projects from the Lagos State Development plan (2012–2025) which have resulted in significant spatial displacements – hence the selected case studies of Lekki Free Trade Zone and Badia-East Housing Estate. The study reveals that the Lagos state development policy results in creative destruction largely due to the uncritical embrace of market logic over social logic, thereby entrenching urban discontent and socio-spatial fragmentation across the city.

Meaning-forming functions of the spatial coordinate of culture in Foucault's philosophical concept

The article is devoted to the study of understanding the meaning-forming functions of culture, determined by its spatial characteristics in the philosophical work of Michel Foucault. He puts forward the thesis about the decisive role of space in social practice, the growth of complication of its organization from planar to three-dimensional, and opens up virtual spaces of cultural thinking. Space is understood not only geographically, but as the initial impulse and attribute of culture. The comparison method makes it possible to study the evolution of the thinker’s views from focusing on social aspects, through awareness of the problems of individual consciousness to understanding the deep dynamics of culture as a semiotic, ethical and aesthetic phenomenon. Striving for generalization, the author relies on such notions of M. Foucault as episteme, “spaces of disagreement”, and “heterotopic” spaces. The concept of “individuation of spatial vision” is introduced, and the principle of “multiplicity of spatial levels” is included in the scientific circulation. As a result of the analysis, a conclusion is made about the discovery of the cultural relativity of spatial meanings in the context of the historical comprehension of the topos, the dynamics of its points and the branching of spatial levels. This article is an attempt to reveal the mechanism of spatial displacements outlined by Foucault, which will become the basis for understanding the new possibilities of creativity in art and culture.

Deformation calculation and stability of rod elements of steel structures with an asymmetric cross-section

To develop practical recommendations for calculating the stability of rod elements of steel structures with an asymmetric cross-section, which is formed as a result of uneven corrosion damage, strengthening or reduction of the cross-section, there is proposed a numerical and analytical solution of the deformation problem, taking into account physical and geometric (according to the spatially deformed scheme) nonlinearities. It allows reducing the calculation time by several orders of magnitude as compared to the existing numerical solutions. The analytical solution of the deformation problem of elastic rods compressed-bent in two planes is based on the qualitative proximity of bending forms of deformation under central compression, namely, sinusoids with corresponding forms obtained by non-deformational calculation, on a square parabola. The latter was replaced by a sinusoid, which allowed obtaining a general solution. The manifestations of physical nonlinearity are compensated by additional loading of the elastic rod with a fictitious force with biaxial eccentricities, which is assessed using the «section» algorithm in the most loaded section, taking into account its spatial displacements. As a result, there was obtained a system of numerical-analytical equilibrium equations in dimensionless parameters, the solutions of which, as the load increases, allow assessing the coefficient of loss of spatial stability.

A Formal Account of Structuring Motor Actions With Sensory Prediction for a Naive Agent

For naive robots to become truly autonomous, they need a means of developing their perceptive capabilities instead of relying on hand crafted models. The sensorimotor contingency theory asserts that such a way resides in learning invariants of the sensorimotor flow. We propose a formal framework inspired by this theory for the description of sensorimotor experiences of a naive agent, extending previous related works. We then use said formalism to conduct a theoretical study where we isolate sufficient conditions for the determination of a sensory prediction function. Furthermore, we also show that algebraic structure found in this prediction can be taken as a proxy for structure on the motor displacements, allowing for the discovery of the combinatorial structure of said displacements. Both these claims are further illustrated in simulations where a toy naive agent determines the sensory predictions of its spatial displacements from its uninterpreted sensory flow, which it then uses to infer the combinatorics of said displacements.

Correcting B0 inhomogeneity-induced distortions in whole-body diffusion MRI of bone metastases

BackgroundAccurate imaging of bone metastases is necessary for treatment planning and assessing treatment response. Diffusion-weighted magnetic resonance imaging (DWI) can detect bone metastases, but DWI acquired with echo-planar imaging is susceptible to distortions due to static magnetic field inhomogeneities.PurposeEstimate spatial displacements of bone lesions on DWI. Examine whether distortion-corrected DWI more accurately reflects underlying anatomy.Study TypeRetrospective.Subjects18 patients with prostate cancer bone metastases.Field Strength/Sequence3.0 T; DWI and T2-weighted imaging.AssessmentWe first applied the reverse polarity gradient (RPG) technique to estimate spatial displacements of bone metastasis on DWI. Next, we calculated changes in mutual information (MI) between DWI and T2-weighted images after RPG distortion correction. Further, we annotated skeletal landmarks on DWI and T2-weighted images. RPG was again used to estimate displacements of these landmarks. Lastly, we calculated changes in distance between DWI- and T2-defined landmarks (i.e., changes in error) after RPG distortion correction.Statistical TestsMean and bootstrap-derived confidence intervals were used to summarize variables that estimate bone lesion distortions. Wilcoxon signed-rank tests were used to assess change in MI between DWI and T2-weighted images after RPG.ResultsMean (95% CI) displacement of bone lesions was 5.6 mm (95% CI: 4.8-6.5); maximum displacement was 17.1 mm. Corrected diffusion images were more similar to structural MRI, as evidenced by consistent increases in MI after applying RPG (Wilcoxon signed-rank p<10−13). Like bone metastases, our annotated skeletal landmarks also underwent substantial displacement (average, 6.3 mm). Lastly, RPG led to consistent error reductions between DWI and T2 for each skeletal landmark (mean, [95% CI]): thoracic vertebrae (−3.8 mm, [-4.3,-3.3]), abdominal vertebrae (−1.0 mm, [-1.2,-0.71]), pelvic vertebrae (−0.6 mm, [-1.0,-0.17]), and femoral head (−1.2 mm, [-2.1,-0.4]).Data ConclusionsThese findings support the use of distortion correction techniques to improve localization of bone metastases on DWI.Grant SupportThis work was supported by NIH/NIBIB #K08EB026503, American Society for Radiation Oncology, and the Prostate Cancer Foundation. This work was further supported by the National Institute on Aging T35 grant AG26757 (PI: Dilip V. Jeste, MD, and Alison Moore, MD, MPH), and the Stein Institute for Research on Aging and the Center for Healthy Aging at the University of California, San Diego.

A set of non-destructive testing methods used for diagnosing the foundations of pumping units

Technical re-equipment of oil pumping stations often involves changing the power and weight of pumping equipment. In this regard, it is important to assess whether the replacement of a pumping unit foundation is feasible and, namely, whether the further use of existing facilities is possible, since the costs of replacing the foundations often exceed the costs of adapting existing structures to new equipment. The authors have developed a technology for examining pumping unit foundations to determine the possibility of increasing the load while replacing the equipment. Previously, no such survey has been conducted. The article presents the composition of the recommended diagnostic work, while describing the specifics and limitations of the methods used with some survey results given regarding more than 100 pump foundations. The average age of the samples was 44.9 years. As a result of geodetic measurements, the tilt and settlement values of the foundations were actually found to be free of changes over recent decades and complied with modern regulatory requirements, while the results of engineering and geological surveys have confirmed no serious risks of spatial displacements occurred. It was determined that during diagnostics it is necessary to control the following parameters: the existence of foundation waterproofing, concrete protective layer status, concrete strength and reinforced metal hardness, and whether the location of the reinforcement bars complies with the requirements of the design and/or regulatory and technical documentation. It is also necessary to make sure that there are no unacceptable corrosion damages to metal structures, with fastening and anchor bolt sizes being in compliance with the design and/or regulatory and technical documentation. The data on detected defects of various types are given taking into account the operating period and conditions of the foundations.