Use Of Voxels Research Articles

Differential grey matter structure in women with premenstrual dysphoric disorder: evidence from brain morphometry and data-driven classification

Premenstrual dysphoric disorder (PMDD) is a female-specific condition classified in the Diagnostic and Statical Manual—5th edition under depressive disorders. Alterations in grey matter volume, cortical thickness and folding metrics have been associated with a number of mood disorders, though little is known regarding brain morphological alterations in PMDD. Here, women with PMDD and healthy controls underwent magnetic resonance imaging (MRI) during the luteal phase of the menstrual cycle. Differences in grey matter structure between the groups were investigated by use of voxel- and surface-based morphometry. Machine learning and multivariate pattern analysis were performed to test whether MRI data could distinguish women with PMDD from healthy controls. Compared to controls, women with PMDD had smaller grey matter volume in ventral posterior cortices and the cerebellum (Cohen’s d = 0.45–0.76). Region-of-interest analyses further indicated smaller volume in the right amygdala and putamen of women with PMDD (Cohen’s d = 0.34–0.55). Likewise, thinner cortex was observed in women with PMDD compared to controls, particularly in the left hemisphere (Cohen’s d = 0.20–0.74). Classification analyses showed that women with PMDD can be distinguished from controls based on grey matter morphology, with an accuracy up to 74%. In line with the hypothesis of an impaired top-down inhibitory circuit involving limbic structures in PMDD, the present findings point to PMDD-specific grey matter anatomy in regions of corticolimbic networks. Furthermore, the results include widespread cortical and cerebellar regions, suggesting the involvement of distinct networks in PMDD pathophysiology.

Understanding Lateral Marsh Edge Erosion with Terrestrial Laser Scanning (TLS)

Coastal wetlands are a crucial buffer zone between land and sea but lateral erosion threatens their long-term sustainability. Better understanding of the forces leading to lateral marsh retreat will benefit the assessment of management options applied to mitigate the erosion. Terrestrial Laser Scanning (TLS), Light Detection and Ranging (lidar), and associated technologies are increasingly being used to assess this erosion. The central objective of this study was to identify a methodology for measuring marsh edge erosion with a TLS and correlate that erosion with exposed roots and incident wave energy. We quantified edge erosion across multiple temporal and spatial scales using a TLS, showing greater than one meter of lateral erosion over a 318-day period. We then evaluated the relationships between the erosion and incident wave energy along with erosion and vegetation roots. Wave height and erosion was strongly related (r2 = 0.99), while vegetation roots did not show an apparent effect. We discuss the challenges that arise from using TLS equipment, TLS data sets, and the use of voxels to measure marsh edge erosion.

Dosimetry for nonuniform activity distributions: A method for the calculation of 3D absorbed‐dose distribution without the use of voxel S‐values, point kernels, or Monte Carlo simulations

Nonuniform activity within the target lesions and the critical organs constitutes an important limitation for dosimetric estimates in patients treated with tumor-seeking radiopharmaceuticals. The tumor control probability and the normal tissue complication probability are affected by the distribution of the radionuclide in the treated organ/tissue. In this paper, a straightforward method for calculating the absorbed dose at the voxel level is described. This new method takes into account a nonuniform activity distribution in the target/organ. The new method is based on the macroscopic S-values (i.e., the S-values calculated for the various organs, as defined in the MIRD approach), on the definition of the number of voxels, and on the raw-count 3D array, corrected for attenuation, scatter, and collimator resolution, in the lesion/organ considered. Starting from these parameters, the only mathematical operation required is to multiply the 3D array by a scalar value, thus avoiding all the complex operations involving the 3D arrays. A comparison with the MIRD approach, fully described in the MIRD Pamphlet No. 17, using S-values at the voxel level, showed a good agreement between the two methods for (131)I and for (90)Y. Voxel dosimetry is becoming more and more important when performing therapy with tumor-seeking radiopharmaceuticals. The method presented here does not require calculating the S-values at the voxel level, and thus bypasses the mathematical problems linked to the convolution of 3D arrays and to the voxel size. In the paper, the results obtained with this new simplified method as well as the possibility of using it for other radionuclides commonly employed in therapy are discussed. The possibility of using the correct density value of the tissue/organs involved is also discussed.

Large Eddy Simulations of 2D and Open-tip Airfoils Using Voxel Meshes

This paper presents Large Eddy simulations of flow and acoustic computations around 2D and 3D airfoils using a novel type of mesh called voxel mesh. Voxel mesh refers to the mesh that has different number of nodes in the neighbouring cell layers. Voxel mesh has many advantages such as creating cells with minimum skewness, automatic mesh generation and uniformity in cell shapes and sizes. The voxel meshes aren’t yet validated in boundary layer computations. In this paper we validate the use of voxel meshes in boundary layer computations in 2D and 3D airfoils. Six cases were tried out in the research three 2D meshes and three 3D cases were tried out. Each case was simulated at Reynolds number 2.83×105 and attack angle of 90. Flow field computation was done by FrontFlowBlue-7.2 software the acoustic computation was done by using FrontFlowBlue-Acoustic2.2 software. The results obtained from the simulations were compared with the experimental values. The use of voxel meshes to resolve the boundary layer in turbulent fluid flows could be validated using 2D airfoils. Therefore voxel meshes were used in 3D airfoil flow computations. After successful flow computations the source fluctuations in the flow was used for the acoustic computations. The sound pressure levels computed from the acoustic computations were compared with the experimental values. Some oscillation in the pressure could be observed due to the step like structure at the surface of voxel mesh but these variations were less apparent in meshes that had smaller cells.

An analytical method for computing voxel S values for electrons and photons

The use of voxel S values (VSVs) is perhaps the most common approach to radiation dosimetry for nonuniform distributions of activity within organs or tumors. However, VSVs are currently available only for a limited number of voxel sizes and radionuclides. The objective of this study was to develop a general method to evaluate them for any spectrum of electrons and photons in any cubic voxel dimension of practical interest for clinical dosimetry in targeted radionuclide therapy. The authors developed a Monte Carlo simulation in Geant4 in order to evaluate the energy deposited per disintegration (E(dep)) in a voxelized region of soft tissue from monoenergetic electrons (10-2000 keV) or photons (10-1000 keV) homogeneously distributed in the central voxel, considering voxel dimensions ranging from 3 mm to 10 mm. E(dep) was represented as a function of a dimensionless quantity termed the "normalized radius," R(n) = R∕l, where l is the voxel size and R is the distance from the origin. The authors introduced two parametric functions in order to fit the electron and photon results, and they interpolated the parameters to derive VSVs for any energy and voxel side within the ranges mentioned above. In order to validate the results, the authors determined VSV for two radionuclides ((131)I and (89)Sr) and two voxel dimensions and they compared them with reference data. A validation study in a simple sphere model, accounting for tissue inhomogeneities, is presented. The E(dep)(R(n)) for both monoenergetic electrons and photons exhibit a smooth variation with energy and voxel size, implying that VSVs for monoenergetic electrons or photons may be derived by interpolation over the range of energies and dimensions considered. By integration, S values for continuous emission spectra from β(-) decay may be derived as well. The approach allows the determination of VSVs for monoenergetic (Auger or conversion) electrons and (x-ray or gamma-ray) photons by means of two functions whose parameters can be interpolated from tabular data provided. Through integration, it is possible to generalize the method to any continuous (beta) spectrum, allowing to calculate VSVs for any electron and photon emitter in a voxelized structure.

Novel 3D modeling methods for virtual fabrication and EDA compatible design of MEMS via parametric libraries

This paper provides a brief summary of the state-of-the-art of MEMS-specific modeling techniques and describes the validation of new models for a parametric component library. Two recently developed 3D modeling tools are described in more detail. The first one captures a methodology for designing MEMS devices and simulating them together with integrated electronics within a standard electronic design automation (EDA) environment. The MEMS designer can construct the MEMS model directly in a 3D view. The resulting 3D model differs from a typical feature-based 3D CAD modeling tool in that there is an underlying behavioral model and parametric layout associated with each MEMS component. The model of the complete MEMS device that is shared with the standard EDA environment can be fully parameterized with respect to manufacturing- and design-dependent variables. Another recent innovation is a process modeling tool that allows accurate and highly realistic visualization of the step-by-step creation of 3D micro-fabricated devices. The novelty of the tool lies in its use of voxels (3D pixels) rather than conventional 3D CAD techniques to represent the 3D geometry. Case studies for experimental devices are presented showing how the examination of these virtual prototypes can reveal design errors before mask tape out, support process development before actual fabrication and also enable failure analysis after manufacturing.

Pixel Patterns for Voxels in Contact-Type Three Dimensional Imaging Systems

A three dimensional image (3-D) is synthesized with the use of voxels with known coordinates. Each of these voxels has a corresponding pixel pattern in the display panel. The pattern is found in the optical geometry of the defined viewing zone in contact-type 3-D imaging systems based on a point light source array by assuming that each of the voxels can be seen at any place in the zone. This geometry provides that voxels are aligned in known planes parallel to the array plane. Since each of these voxels is made of rays from specific point light sources, which pass specific pixels in the display panel, the pixel pattern for each voxel is determined as that of the pixels that enable the sources to be seen in the viewing zone through them. The resulting pixel pattern creates a good 3-D image.

Evaluation of task-oriented performance of several fully 3D PET reconstruction algorithms

The relative performance of 5 fully 3D PET reconstruction algorithms is evaluated. The algorithms are a filtered backprojection (FBP) method and 2 variants each of the EM-ML and ART iterative methods. For each of the iterative methods, 1 variant makes use of voxels and the other makes use of 'blobs' (spherically symmetric functions smoothly decaying to zero at their boundaries) as basis functions in its discrete reconstruction model. The methods are evaluated from the point of view of the efficacy of the reconstructions produced by them for 3 typical medical tasks - estimation of the average activity inside specific regions of interest, hot spots detection, and cold spots detection. A free parameter is allowed in the description of each of the 5 algorithms; the parameters are determined by a training process during which a value of the free parameter is selected which (nearly) maximizes a technical figure of merit. Such training and the actual comparative evaluation is done by making use of randomly generated phantoms and their projection data. The methodology allows assignation of levels of statistical significance to claims of the relative superiority of 1 algorithm over another for a particular task. It is found that using blobs as basis functions in the iterative algorithms is definitely advantageous over using voxels. This result has high statistical significance. (A visual illustration of it is given.) Comparing FBP, EM-ML using blobs, and ART using blobs, the authors do not find a clear difference in the overall performance of the investigated variants of the methods. If anything, their results suggest that ART using blobs may be the most efficacious of the 3.