Area Distortion Research Articles

Experimental Assessment of Magnetic Resonance Imaging Distortion for Radiation Therapy Planning

MRI is widely used in radiation therapy planning, particularly in stereotactic radiosurgery for brain metastases. The article addresses the geometric distortion of MRI images, which can lead to errors in radiation therapy planning. A series of experiments with a simple phantom were conducted on two MRI scanners with 0.5 T and 1.5 T magnetic fields. Deviations in the positions of the phantom objects from their actual locations were observed. The detected deviations can reach up to 5 mm. A theoretical dependence of the magnetic field gradient on the distance to the center of homogeneity was calculated, which agrees well with the approximation of experimental data. An assessment was made of the dependence of the image area distortion of objects located at the center of the field homogeneity on their actual sizes. It was found that the area deviation can reach up to 20%.

3D textured mesh scene data fusion method considering multiple scales and resolutions

ABSTRACT The fusion of 3D textured mesh scene data can effectively and seamlessly integrate multiple spatially related 3D geographical scene models into larger and more comprehensive datasets. Existing methods usually have different degrees of texture distortion and unreduced texture problems in the splicing area, and these methods do not consider the current situation of Level of Detail(LoD) data organisation in the 3D textured mesh model. We propose a 3D textured mesh scene data fusion method considering multiple scales and resolutions. First, seamless extraction of splicing areas was achieved based on spatial relationship constraints and orthogonal inverse projection principles. Second, the sparse scene structure concept was employed to generate sparse summary scene images. Finally, a dual simplification operator for both mesh and texture was proposed to construct multi-resolution 3D textured mesh models, simultaneously reconstructing triangular facets and textures within the splicing regions. We used multiple 3D textured mesh data constructed from aerial obliques to conduct data fusion experimental verification. The results indicate that our method exhibits minimal texture distortion during grid reconstruction in splicing areas and model simplification, effectively reducing the amount of simplified texture data. Additionally, our method adeptly addresses multilevel detailed 3D textured mesh models, demonstrating good feasibility and advancement.

Long-Term Comparison of Esthetic Outcomes Between Hatchet and Transposition Flaps in Facial-Defect Reconstruction.

Transposition flaps are commonly used for facial-defect repair after wide excision of skin cancers. However, such repair often causes excessive tension at the donor site that can result in distortion of the adjacent area. The hatchet flap, a rotation-advancement flap, can prevent distortion by redistributing the donor site tension evenly to the recipient site. This study aims to compare the esthetic outcomes of the hatchet flap and transposition flap in facial-defect reconstruction. We retrospectively included 50 patients who underwent facial reconstruction with the hatchet flap or transposition flap after excision of skin cancer. They were followed up for more than 6months. At the last follow-up visit, the esthetic outcome was evaluated by subjective and objective assessments using the patients and observer scar assessment scale and Manchester scar scale. Thirty patients and 20 patients underwent reconstruction using the hatchet flap and the transposition flap, respectively. The total score from the patient and observer scar assessment scale was significantly lower in the hatchet flap group compared with the transposition flap group (p = 0.009). The Manchester scar scale showed a total score of 7.67 ± 2.2 for the hatchet flap and 9.95 ± 1.99 for the transposition flap: in the color (p < 0.001), distortion (p < 0.001), and texture (p < 0.02) categories, the hatchet flap yielded significantly better outcomes than the transposition flap. The hatchet flap had good esthetic outcome for facial reconstruction and could be a valuable option for reconstructing facial defects. This journal requires that authors assign a level of evidence to each article. For a full description of these evidence-based medicine ratings, please refer to Table of Contents or online Instructions to Authors www.springer.com/00266.

Evaluation and comparison of functional and esthetic outcomes of pectoralis major myocutaneous flap with or without removal of sternocleidomastoid muscle following neck dissection in patients being operated for oral squamous cell carcinoma

India comprising the burden of oral squamous cell carcinoma which grow locally and then spreads to the cervical lymph nodes. Neck dissection is a beneficial procedure for addressing metastases in the neck arising from head and neck cancers. This surgical technique aims to remove lymph nodes on one side of the neck where cancer cells may have spread. However, this procedure can significantly impact a patient's appearance and cause distortion in the cervical area, particularly when it involves the removal of the sternocleidomastoid muscle, leading to a flattening effect in the lateral neck area. Reconstructing tissue defects following extensive surgeries in the head and neck region presents a distinct challenge for surgeons. They have the option to use either pedicled or free tissue transfer for this purpose. We compared and evaluated functional and esthetics outcomes of pectoralis major myocutaneous flap with or without removal of sternocleidomastoid muscle following neck dissection. We concluded that lack of notable distinction between the MRND type II and III groups. Both groups exhibited restricted range of motion in flexion, abduction, and external rotation. Notably, there was a significant impact on neck circumference, while shoulder functionality demonstrated gradual improvement over time. Interestingly, no substantial variances were observed between the groups in terms of drainage and wound healing. The quality of life reported by participants was generally favorable, with composite scores, social-emotional sub-scores, and average physical function aligning with acceptable standards. It's important to note that achieving a more substantial sample size is imperative to obtain results of greater significance and reliability.

Research on Image Stitching Algorithm Based on Point-Line Consistency and Local Edge Feature Constraints.

Image stitching aims to synthesize a wider and more informative whole image, which has been widely used in various fields. This study focuses on improving the accuracy of image mosaic and proposes an image mosaic method based on local edge contour matching constraints. Because the accuracy and quantity of feature matching have a direct influence on the stitching result, it often leads to wrong image warpage model estimation when feature points are difficult to detect and match errors are easy to occur. To address this issue, the geometric invariance is used to expand the number of feature matching points, thus enriching the matching information. Based on Canny edge detection, significant local edge contour features are constructed through operations such as structure separation and edge contour merging to improve the image registration effect. The method also introduces the spatial variation warping method to ensure the local alignment of the overlapping area, maintains the line structure in the image without bending by the constraints of short and long lines, and eliminates the distortion of the non-overlapping area by the global line-guided warping method. The method proposed in this paper is compared with other research through experimental comparisons on multiple datasets, and excellent stitching results are obtained.

ACCURATE REGISTRATION BETWEEN ULTRA-WIDE-FIELD AND NARROW ANGLE RETINA IMAGES WITH 3D EYEBALL SHAPE OPTIMIZATION.

The Ultra-Wide-Field (UWF) retina images have attracted wide attentions in recent years in the study of retina. However, accurate registration between the UWF images and the other types of retina images could be challenging due to the distortion in the peripheral areas of an UWF image, which a 2D warping can not handle. In this paper, we propose a novel 3D distortion correction method which sets up a 3D projection model and optimizes a dense 3D retina mesh to correct the distortion in the UWF image. The corrected UWF image can then be accurately aligned to the target image using 2D alignment methods. The experimental results show that our proposed method outperforms the state-of-the-art method by 30%.

Extra-conventional strengthening mechanisms in non-recrystallized grains of an extruded Mg-Gd-Zr alloy

Mg-RE (RE = rare earth) based alloys generally exhibit outstanding mechanical properties. However, their high-strength seems to be unexplained using classic strengthening mechanisms in some cases. Herein, a Mg-13Gd-0.4Zr (wt%) alloy that was fabricated by a conventional differential thermal extrusion plus artificial aging treatment exhibits ultra-high yield strength over 510 MPa in both tension and compression. Characterizations using Cs-corrected scanning transmission electron microscopy (STEM) show two unusual microstructures in non-recrystallized grains as: a large density of basal stacking faults (SFs) and profuse distortion areas (DAs). Atomic-resolution STEM imaging indicates that basal SFs are consisted of two types of intrinsic SFs, namely I1 and I2, and DAs are self-assembled by 〈c〉 and 〈c + a〉 screw partials. Their strengthening mechanisms are analogous to grain boundary strengthening and dispersion strengthening, respectively, contributing satisfactory yield-strength increments of ∼46 MPa and ∼76 MPa, respectively. Moreover, DAs improved aging hardening by inducing novel clusters at DA-related boundaries, or increasing the number density of βH’ precipitate and promoting their distribution along a certain direction. This work supplements the strengthening mechanisms in traditional high-strength Mg-RE(-Zr) based alloys and provides novel insights in the development of ultra-high-strength Mg alloys.

Simultaneous Boundary and Interior Parameterization of Planar Domains Via Deep Learning

In isogeometric analysis (IGA), domain parameterization plays a crucial role as it significantly impacts the results of subsequent numerical analyses. Previous literature has often treated domain parameterization as two separate processes: boundary correspondence and interior parameterization. However, this division tends to decrease the quality of the final parameterization. To address this issue, this article proposes a learning-based method that simultaneously parameterizes the boundary and interior of a simply connected planar computational domain using a deep neural network. In our approach, we train a neural network to represent the inverse parameterization, which maps the computational domain to the parametric domain, based on the given boundary curve of the planar computational domain. The key component of our neural network is a Multilayer Perceptron (MLP), which takes the coordinates of a point in the computational domain as input and outputs the corresponding parametric values. The loss function of our method comprises three terms. First, it considers the area distortion and angular distortion of the parameterization, which are determined by the Jacobian matrix of the parameterization. Second, it incorporates the boundary difference, quantified by the Hausdorff distance between the boundary of the parametric domain and the image of the inverse mapping of the computational boundary. By optimizing this loss function, we achieve a robust parameterization. Once the network is trained, we employ a tensor-product B-spline function to fit the mapping from the parametric domain to the computational domain. To evaluate the effectiveness of our method, we conduct experiments on the MPEG-7 dataset. The experimental results demonstrate that our approach yields parameterization results with lower distortion and higher bijectivity ratio compared to state-of-the-art approaches.

Effect of the Cryogenically Treated Copper Nozzle Used in Plasma Arc Machining of S235 Steel

The investigation was carried out by making use of the design of experiments method in order to achieve its objective, which was to study wear analysis in relation to a cryogenically treated nozzle that was utilized in plasma arc machining. Kerf width and surface roughness are two output characteristics that are key variables in deciding the quality of the cut and the efficiency of the operation. Both of these metrics are outputted by the process. While machining S235 steel, an investigation into the impact that nozzle treatment has on various quality metrics is currently under way. The examination is carried out with the arc voltage, the cutting speed, and the gas pressure, all serving as important components. A cryogenic treatment of the nozzle material using liquid nitrogen at a temperature of −194°C has been attempted in an effort to increase the life of the nozzle. Machining is performed using two different nozzle conditions, such as cryogenically treated and cryogenically untreated, with regard to the input parameter combinations that have been selected. To have a better understanding of the wear behavior of nozzles, an image from a scanning electron microscope is studied. Because of the treatment, the production of wear tracks in the direction that gas flow takes has been drastically decreased. This, in turn, has increased the cutting efficiency by decreasing the amount of arc current that was necessary. In addition, a grey relational analysis is carried out in order to find the best possible machining settings in both conditions. The parameters that were optimized for a nozzle that had been cryogenically treated were 6 bar of gas pressure, 120 amperes of arc current, and 1800 of cutting speed per minute. The use of cryogenic treatment resulted in a reduction of surface roughness by 0.4670 µm and a narrowing of the kerf width by 0.96 mm. It is clear from the SEM pictures of untreated and cryogenically treated nozzles that thermal distortion and wear in the nozzle tip area are minimized to a greater extent in the treated nozzle. This is evidenced by the fact that the treated nozzle has a more uniform appearance.

Fundamental Theory and R-linear Convergence of Stretch Energy Minimization for Spherical Equiareal Parameterization

Abstract Here, we extend the finite distortion problem from bounded domains in ℝ2 to closed genus-zero surfaces in ℝ3 by a stereographic projection. Then, we derive a theoretical foundation for spherical equiareal parameterization between a simply connected closed surface M and a unit sphere 𝕊2 by minimizing the total area distortion energy on ̅ℂ. After the minimizer of the total area distortion energy is determined, it is combined with an initial conformal map to determine the equiareal map between the extended planes. From the inverse stereographic projection, we derive the equiareal map between M and 𝕊2. The total area distortion energy is rewritten into the sum of Dirichlet energies associated with the southern and northern hemispheres and is decreased by alternatingly solving the corresponding Laplacian equations. Based on this foundational theory, we develop a modified stretch energy minimization function for the computation of spherical equiareal parameterization between M and 𝕊2. In addition, under relatively mild conditions, we verify that our proposed algorithm has asymptotic R-linear convergence or forms a quasi-periodic solution. Numerical experiments on various benchmarks validate that the assumptions for convergence always hold and indicate the efficiency, reliability, and robustness of the developed modified stretch energy minimization function.

Holomorphic motions, dimension, area and quasiconformal mappings

We describe the variation of the Minkowski, packing and Hausdorff dimensions of a set moving under a holomorphic motion, as well as the variation of its area. Our method provides a new, unified approach to various celebrated theorems about quasiconformal mappings, including the work of Astala on the distortion of area and dimension under quasiconformal mappings and the work of Smirnov on the dimension of quasicircles.

Evaluation of Distortion in the Posterior Palatal Seal Area of Maxillary Cast by Different Adaptation Techniques of Denture Bases.

To evaluate and compare the amount of distortion in the posterior palatal seal area in V-shaped and U-shaped palatal form of maxillary cast by different adaptation techniques of maxillary denture bases. A total of 60 stone casts were made, out of which 30 identical stone casts of U-shaped palatal form and 30 identical stone casts of V-shaped palatal form of maxillary casts were prepared. The 30 stone casts of U-shaped palatal form and 30 stone casts of V-shaped palatal forms were divided into three groups for measurements to be done. Data were statistically analyzed by using two-way analysis of variance (ANOVA) without replication. Discrepancies of fit of dentures on U-shaped casts and V-shaped casts of Groups 1, 2, and 3 in transverse and sagittal sections were measured, and comparative statistical analysis between Group 1&2, Group 1&3, and Group 2&3 was done for statistical significant values. Discrepancy in the central region was maximum, and the anchoring methods Group 2 and Group 3 produced a significantly better adaptation than the conventional method (Group 1). The adaptations for V-shaped palate were better when compared with U-shaped palate in the central region.

Electric field distribution and performance optimization of high-speed train cable terminal with internal defects

High voltage cable terminal of high-speed electric multiple units (EMU) is an important part of on-board high voltage equipment. As the weak link of the cable assembly, the cable terminal is prone to penetrability discharge and resulting in insulation failure, which seriously affects the EMU’s safety and reliability. The electric field intensity distribution of high-voltage cable terminal with internal defects such as air gaps, moisture, semiconductors and carbons are simulated and studied. At the same time, in order to improve the distortion of the internal electric field intensity of the EMU cable terminal, nonlinear materials and high dielectric materials are used to replace the stress tube respectively, and the optimization effects of the two materials on the internal distortion electric field of the cable terminal are studied. The results show that the defects are closer to the multi-layer combination area among main insulation layer, stress tube layer and outer semiconducting layer of the cable terminal, the electric field distortion of multi-layer combination area become greater. With the increasing of defect size, the electric field intensity also gradually increases. However, the inner defect location and size have less effect on the electric field intensity along the cable terminal umbrella skirt. It is found that both nonlinear materials and high dielectric materials can effectively optimize the electric field intensity of cable terminal and improve the electric field distortion. This work can be helpful for operation and design of high-speed EMU’s cable terminal.

A new method of joining stainless steels using Ni micro-plating bonding and the mechanical properties of the joint

Stainless steel is applied in a wide range of fields as a material with high heat and corrosion resistance. Welding, brazing, and solid-phase bonding are the most common joining techniques for stainless steel. Conventional joining methods have issues such as local thermal distortion of the joining area and the need for high-temperature heat treatment at 800–1000 °C. In this paper, we investigated a new joining technique for stainless steel. With the aim of establishing a new joining technology for stainless steel, we joined stainless steel using the Ni Micro-Plating Bonding method (NMPB) and evaluated the shear stress and the tensile stress of the joints. The joining process is performed at about 55 °C, followed by heat treatment at a relatively low temperature of 300 °C or higher. Shear and tensile tests were conducted on the NMPB joined SUS304, and the results showed that the shear stress was 114 MPa and the tensile stress was 77 MPa without annealing. After heat treatment at 300–400 °C for 1.5h, the shear stress of 200 MPa and the tensile stress of 240 MPa were obtained. In addition, the heat treatment at 600–800 °C for 1.5h resulted in the shear stress of 230 MPa and the tensile stress of 400 MPa. The plating crystallographic structure before heat treatment showed preferential orientation to <001>, but after heat treatment, recrystallization progressed beyond the boundary interface at 400 °C or higher, and a non-oriented crystalline was observed.

Spatial Distribution Analysis of Landslide Deformations and Land-Use Changes in the Three Gorges Reservoir Area by Using Interferometric and Polarimetric SAR

Landslides are geological events that frequently cause major disasters. Research on landslides is essential, but current studies mostly use historical landslide data and do not reflect dynamic, real-time research results. In this study, landslide deformations and land-use changes were used to analyze the landslide distribution in Fengjie County and Wushan County in the Three Gorges Reservoir Area (TGRA) by using interferometric and polarimetric SAR. In this study, the mean annual rate of landslide deformations was obtained using the small baseline subset interferometric synthetic aperture radar (SBAS-InSAR) for the ALOS-2 (2014–2019) data. Land-use changes were based on the 2007 and 2017 land-use results from dual-polarization ALOS-1 and ALOS-2 data, respectively. To address the problem of classification accuracy reduction caused by geometric distortion in mountainous areas, we first used texture maps and pseudocolor maps synthesized with dual-polarization intensity maps to perform classification with random forest (RF), and then we used coherence and slope maps to run the K-Means algorithm (KMA). We named this the secondary classification method. It is an improvement on the single classification method, exhibiting a 94% classification accuracy, especially in rugged areas. Combined with land-use changes, GIS spatial analysis was used to analyze the spatial distribution of landslides, and it was found that the landslide rate was significantly correlated with the type after change, with a correlation coefficient of 0.7. In addition, land-use types associated with human activities, such as cultivated vegetation, were more likely to cause landslide deformation, which can be used to guide local land-use planning.

Adaptive dewarping of severely warped camera-captured document images based on document map generation.

Automated dewarping of camera-captured handwritten documents is a challenging research problem in Computer Vision and Pattern Recognition. Most available systems assume the shape of the camera-captured image boundaries to be anywhere between trapezoidal and octahedral, with linear distortion in areas between the boundaries for dewarping. The majority of the state-of-the-art applications successfully dewarp the simple-to-medium range geometrical distortions with partial selection of control points by a user. The proposed work implements a fully automated technique for control point detection from simple-to-complex geometrical distortions in camera-captured document images. The input image is subject to preprocessing, corner point detection, document map generation, and rendering of the de-warped document image. The proposed algorithm has been tested on five different camera-captured document datasets (one internal and four external publicly available) consisting of 958 images. Both quantitative and qualitative evaluations have been performed to test the efficacy of the proposed system. On the quantitative front, an Intersection Over Union (IoU) score of 0.92, 0.88, and 0.80 for document map generation for low-, medium-, and high-complexity datasets, respectively. Additionally, accuracies of the recognized texts, obtained from a market leading OCR engine, are utilized for quantitative comparative analysis on document images before and after the proposed enhancement. Finally, the qualitative analysis visually establishes the system's reliability by demonstrating improved readability even for severely distorted image samples.

Using Optimal Transport to Improve Spherical Harmonic Quantification of Complex Biological Shapes.

The knowledge of the anatomical shape of both gross and microscopic structures is the key to understanding the effects of disease processes on cellular structure. Geometric morphometric methods, such as Procrustes superimposition, and Spherical Harmonics (SPHARM), have been used to capture the biological shape variation and group differences in morphology. Previous SPHARM-MAT techniques use the CALD algorithm to parameterize the mesh surface. It starts from initial mapping and performs local and global smoothing methods alternately to control the area and length distortions simultaneously. However, this parameterization may not be sufficient in complex morphological cases. To bridge this gap, we propose SPHARM-OT, an enhanced SPHARM surface modeling method using optimal transport (OT) for spherical parameterization. First, the genus 0 3D objects are conformally mapped onto a sphere. Then the optimal transport theory via spherical power diagram is introduced to minimize the area distortion. This new algorithm can effectively reduce the area distortion and lead to a better reconstruction result. We demonstrate the effectiveness of the method by applying it to the human sphenoidal paranasal sinuses.

Improved color image defogging algorithm based on dark channel prior

An improved algorithm of image defogging was proposed based on dark channel prior in order to solve the low efficiency and color distortion in the bright area using original algorithm. If the image contains large areas of bright areas such as sky, white clouds or partial white objects and water surface, we can know that the dark channel prior theory does not apply to these areas. Firstly, it is necessary to clear the bright area of the image. According to principle that he adjacent pixel attributes have similarity, the image transmittance of the local region also has similarity, Block function is Consruted. Applied the dark channel prior, judging whether each block includes a bright area by the absolute value of difference of atmospheric intensity and dark channel, the dark and bright areas of the image are obtained. So the estimation value of the adaptive space transmittance are also obtained. Secondly, the transmittance of bright region is small and it causes deviation, so the enhancement formula is used to modify it dynamically. In order to preserve the edge details after image restoration, for bright areas, using texture function to optimize transmittance independently, for others, using gradient and texture function together. Finally, it restored the fog-free image applying the atmospheric scattering model. The experimental results showed that the restored image had obvious details and rich color and fast processing speed through the proposed algorithm. The algorithm can also be applied to outdoor visual systems, such as video surveillance, intelligent traffic and so on.

Abnormal hardening and amorphization in an FCC high entropy alloy under extreme uniaxial tension

Ever more extreme environments in advancing industrial applications motivate efforts to design new generation of alloys with excellent mechanical properties. High entropy alloys (HEAs) are considered as promising candidates for bearing extreme loadings. However, the reported results of correspondence between extremely mechanical behaviors and micromechanisms are still in infancy. Here we showed mechanical responses over wide strain rate and temperature ranges and microscopic observations recovered from dynamic uniaxial tension of face-centered cubic (FCC) HEA to reveal plasticity mechanisms transition under various loading conditions. In particular, with an increasing strain during the extreme dynamic tension a sequence of mechanisms, including twinning, detwinning-induced localization, nanoscale body-centered cubic (BCC) phase transformation and symbiotic amorphization, were progressively activated for continued plasticity. At strains over 35%, twin boundaries hindrance to localized band propagation and more dislocations emitting from BCC phases even collectively caused a second sharp rise in hardening. Additionally, the plasticity kept increasing during crystal to amorphization transition, which should be promoted by severe lattice distortion in super-dense dislocations areas. By combining large scale molecular dynamic simulations, the causes of phase transition to BCC lattice structure or even to amorphous bands were explained in depth. The thorough uncovering of these brand-new mechanisms can help understand the plasticity and amorphization of HEAs under the extreme loadings.

Low-Altitude Photogrammetry and Remote Sensing in UAV for Improving Mapping Accuracy

The low-altitude photogrammetry technology of unmanned aerial vehicles (UAVs) is widely used in many fields, but the absence of analysis and research affects the accuracy of its data products. At the same time, low-altitude photogrammetry faces the problem of low elevation positioning accuracy. The network space triangulation adjustment in the beam technique region is considered to eliminate perspective distortion in non-overlapping areas. This paper explains the key technologies of low-altitude photography and remote sensing mapping of UAVs, rectifies the distortion difference of remote sensing images, and then carries out grid division on the image according to the improved APAP (as-projective-as-possible warp) matching method. Next, it solves each grid homography matrix, linearizes the homography matrix, and carries out image matching according to the linearized homography matrix, which can effectively weaken the ghosting phenomenon during image matching. The network space triangulation adjustment in the beam technique region is considered to eliminate perspective distortion in non-overlapping areas. The two measurement areas’ accuracy level is analyzed using digital line drawing and digital orthophoto images (DOIs). Finally, the experimental results indicate that the image matching algorithm proposed in this paper has strong reliability and can substantially increase photogrammetric elevation positioning.