Medial Axis Research Articles

Molecular Methods for Assessing the Morphology, Topology, and Performance of Polyamide Membranes.

The molecular-scale morphology and topology of polyamide composite membranes determine the performance characteristics of these materials. However, molecular-scale simulations are computationally expensive and morphological and topological characterization of molecular structures are not well developed. Molecular dynamics simulation and analysis methods for the polymerization, hydration, and quantification of polyamide membrane structures were developed and compared to elucidate efficient approaches for producing and analyzing the polyamide structure. Polymerization simulations that omitted the reaction-phase solvent did not change the observed hydration, pore-size distribution, or water permeability, while improving the simulation efficiency. Pre-insertion of water into the aggregate pores (radius ≈ 4 Å) of dry domains enabled shorter hydration simulations and improved simulation scaling, without altering pore structure, properties, or performance. Medial axis and Minkowski functional methods were implemented to identify permeation pathways and quantify the polyamide morphology and topology, respectively. Better agreement between simulations and experimentally observed systems was accomplished by increasing the domain size rather than increasing the number of ensemble realizations of smaller systems. The largest domain hydrated was an order of magnitude larger by volume than the largest domain previously reported. This work identifies methods that can enable more efficient and meaningful fundamental modeling of membrane materials.

Tibial and Femoral Bone Tunnel Position after Arthroscopic Reconstruction of the Anterior Cruciate Ligament: A Retrospective Study

Aim: To assess the tibial and femoral bone tunnel position after arthroscopic reconstruction of the anterior cruciate ligament Study design: Retrospective study Place and duration: This Study was conducted at ZKS Catogary C Hospital Matta Swat Pakistan from January 2020 to Januray 2021. Methodology: In this study, total 52 patients were included. The tunnel position after anterior cruciate ligament (ACL) reconstruction was determined using a three-dimensional CT scan. SPSS software version 23 used to identify the relation between tunnel positions and ACL reconstruction outcomes. Results: The radiological evaluation indicated that the average length of the femoral tunnel is 43.75 ± 3.2 mm, and the tibial tunnel is 23 ± 4.6 mm. All the bones were anatomically positioned. The coronal and sagittal angles of the tibial and femoral tunnel were 24.7 ± 3.4; 53.2 ± 2.9 degrees and 28.7 ± 3.3; 42.6 ± 2.8 degrees respectively. The X- and Y-axis values of the femoral and tibial tunnel were 26.7 ± 3.8 mm; 43.6 ± 6.5 mm and 46.7 ± 2.8 mm; 32.2 ± 4.6 mm respectively. Conclusion: There was a significant positive correlation between the sagittal angle of the tibial tunnel to the medial axis and femoral tunnel to the Y-axis indicating that the tibial sagittal angle is a correspondent of the intra-articular femoral tunnel behind the resident’s ridge. In conclusion, these findings may lead to a better and safe surgical procedure with improved clinical outcomes in terms of knee kinematics and risk of complications. Keywords: femoral bone tunnel position, anterior cruciate ligament, arthroscopic reconstruction

Dynamic-MRI quantification of abdominal wall motion and deformation during breathing and muscular contraction

Background and ObjectiveBiomechanical assessment of the abdominal wall represents a major prerequisite for a better understanding of physiological and pathological situations such as hernia, post-delivery recovery, muscle dystrophy or sarcopenia. Such an assessment is challenging and requires muscular deformations quantification which have been very scarcely reported in vivo. In the present study, we intended to characterize abdominal wall deformations in passive and active conditions using dynamic MRI combined to a semiautomatic segmentation procedure. MethodsDynamic deformations resulting from three complementary exercises i.e. forced breathing, coughing and Valsalva maneuver were mapped in a transversal abdominal plane and so for twenty healthy volunteers. Real-time dynamic MRI series were acquired at a rate of 182 ms per image, then segmented semi-automatically to follow muscles deformation through each exercise. Circumferential and radial strains of each abdominal muscle were computed from the geometrical characteristics’ quantification, namely the medial axis length and the thickness. Muscular radial displacement maps were computed using image registration. ResultsLarge variations in circumferential and radial strains were observed for the lateral muscles (LM) but remained low for the rectus abdominis muscles (RA). Contraction phases of each exercise led to LM muscle shortening down to -9.6 ± 5.9% during Valsalva maneuver with a 16.2 ± 9.6% thickness increase. Contraction also led to inward radial displacement of the LM up to 9.9 ± 4.1 mm during coughing. During maximal inhalation, a significant 10.0 ± 6.6% lengthening was quantified for LM while a significant thickness decrease was computed for the whole set of muscles (-14.7 ± 6.6% for LM and -7.3 ± 6.5% for RA). The largest displacement was observed for the medial part of RA (17.9 ± 8.0 mm) whereas the posterior part of LM underwent limited motion (2.8 ± 2.3 mm). Displacement rate and correlation between muscle thickness and medial axis length during each exercise provided insights regarding subject-specific muscle function. ConclusionsDynamic MRI is a promising tool for the assessment of the abdominal wall motion and deformations. The corresponding metrics which have been continuously recorded during the exercises provided global and regional quantitative information. These metrics offer perspectives for a genuine clinical evaluation tool dedicated to the assessment of abdominal muscles function in both healthy subjects and patients.

Bone histology on Koreaceratops hwaseongensis (Dinosauria: Ceratopsia) from the Lower Cretaceous of South Korea

Koreaceratops hwaseongensis is a basal ceratopsian dinosaur found in the Lower Cretaceous Sihwa Formation (Albian), South Korea. It was found only with the lower part of the body. The right tibia and fibula exhibit poor histological preservation due to microbial degradation. They are characterized by signs of extensive tunneling by microorganisms, which rendered the bone cortex into an amalgam of microscopical globules and foci. Such signs of biodegradation may support the hypothesis that the Lower Cretaceous Korean peninsula had a semi-arid and seasonal wet-dry climate. However, a few remaining traces of histological features like the vasculature and absence/presence of growth marks indicate that the growth pattern of Koreaceratops is very similar to that of a subadult Protoceratops andrewsi. Both species exhibit zonation with some bone remodeling in their tibiae and lines of arrested growth with an extensive bone remodeling in their fibulae. The only histological similarity between Koreaceratops and the more basal ceratopsians Psittacosaurus is the longitudinal and reticular vasculature in their fibulae. These suggest that Koreaceratops is much closer to Protoceratops than Psittacosaurus in terms of phylogeny. The fibula of Koreaceratops shows a constant osseous drift that initially drifted toward the medial axis but abruptly changed to the anterior axis in the final growth interval. In addition, the right tibia's final growth exhibiting an anteromedial osseous drift suggests that Koreaceratops experienced a change in its right hindlimb's biomechanics before death. The number of growth zones in the tibia indicates that Koreaceratops was approximately eight years old when it died.

Controlling camera movement in VR colonography

Immersive Colonography allows medical professionals to navigate inside the intricate tubular geometries of subject-specific 3D colon images using Virtual Reality displays. Typically, camera travel is performed via Fly-Through or Fly-Over techniques that enable semi-automatic traveling through a constrained, well-defined path at user-controlled speeds. However, Fly-Through is known to limit the visibility of lesions located behind or inside haustral folds. At the same time, Fly-Over requires splitting the entire colon visualization into two specific halves. In this paper, we study the effect of immersive Fly-Through and Fly-Over techniques on lesion detection and introduce a camera travel technique that maintains a fixed camera orientation throughout the entire medial axis path. While these techniques have been studied in non-VR desktop environments, their performance is not well understood in VR setups. We performed a comparative study to ascertain which camera travel technique is more appropriate for constrained path navigation in Immersive Colonography and validated our conclusions with two radiologists. To this end, we asked 18 participants to navigate inside a 3D colon to find specific marks. Our results suggest that the Fly-Over technique may lead to enhanced lesion detection at the cost of higher task completion times. Nevertheless, the Fly-Through method may offer a more balanced trade-off between speed and effectiveness, whereas the fixed camera orientation technique provided seemingly inferior performance results. Our study further provides design guidelines and informs future work.

On an old theorem of Erd

Erdős proved in 1946 that if a set $E\subset \mathbb R ^n$ is closed and non-empty, then the set, called ambiguous locus or medial axis, of points in $\mathbb R ^n$ with the property that the nearest point in $E$ is not unique, can be covered by countably

A Cutter Selection Method for 2 1/2-Axis Trochoidal Milling of the Pocket Based on Optimal Skeleton

The trochoidal toolpath is generated based on skeleton. However, several different skeletons can be extracted from one pocket. To improve the efficiency of trochoidal rough milling, a cutter selection method basing the optimal skeleton is proposed. Firstly, for a pocket, preliminary skeleton curves and nodes are extracted according to the principle of medial axis transformation. A skeleton extraction method is given that the skeleton is a combination of skeleton curves generated by randomly connecting the preliminary skeleton curves under nodes constraint. A set of skeletons can be obtained by repeatedly extracting skeleton. Furthermore, an optimization model based on the shortest machining time is established, and then the optimization model is solved by the Genetic Algorithm to determine the optimal tool combination and skeleton. The developed approach is validated in trochoidal milling a pocket for cutter selection. The experimental results show that the method can significantly improve the processing efficiency.

Continuous collision detection with medial axis transform for rigid body simulation

Continuous collision detection with medial axis transform for rigid body simulation

Is Proximal Tibia Sufficient for Accurate Measurement of Tibial Slope Angles on Three-dimensional Tomography-based Anatomical Models?

Tibial slope measurements performed using only the proximal part of tibia ignore the native tibial anatomical axis. Our first aim is to measure the native medial, lateral and total tibial slope angles of gender groups using the whole tibial anatomical axis on computerized tomography-based three-dimensional anatomical models. The second aim is to determine the correlation between proximal and whole tibial anatomical axis for measurement of medial, lateral, and total tibial slope angles. We randomly selected 100 females and 100 males between 18-60 years of age. Three-dimensional anatomical models of right and left tibia were created. The gender-specific differences of medial, lateral, and total tibial slope angles according to proximal and whole tibial anatomical axis were measured. Correlation coefficients (r) of medial, lateral, and total tibial slope angles measured with proximal and whole tibial anatomical axis were calculated. The mean age was 47.1 years. A statistically significant difference was observed between female (7.1 ± 3) and male (8.2 ± 2.5) groups in terms of mean lateral tibial slope angles according to the whole tibial anatomical axis (p=0.008). A strong correlation between proximal and whole tibial anatomical axis for all tibial slope angle measurements was detected. The method we determined for 3D measurement of medial, lateral and total tibial slope angles using proximal tibial anatomical axis has a strong correlation with slope angles measured in accordance with the whole tibial anatomical axis. Our 3D tibial slope angle measurement method on the proximal tibia has high reliability and could be used in the daily practice.

İç mekân navigasyonu ağ modelleri: Karşılaştırmalı bir inceleme

Nowadays, the use of outdoor navigation applications is quite common. For indoor navigation, this case is still an emerging application due to the lack of use of a standardised positioning equipment, higher costs, accuracy issues, the more complex structure of indoor spaces and the fact that a comprehensive network model to support indoor navigation for floor-level paths and non-level paths and the studies on the computation of routes are not fully developed yet. Due to the degree of complexity of indoor spaces vary depending on the non-standard structures of buildings and the freedom of movement capability is in a wide spectrum, different navigation networks can be generated. In this study, the Medial Axis Transform (MAT) based methods and the Visibility Graph (VG) based network model that originates from isovists theory which are the prominent navigation network models in the literature are generated in the building information modelling of Yildiz Technical University Civil Engineering Faculty building by utilizing the two-dimensional floor plans of the building and a new approach is proposed based on the VG model by restricting the line of sight between sub-corridors of indoor space and combining it with the MAT. The usability of these navigation network models is compared in terms of the shortest distance and the fewest turns made on the route. The findings of the experimental study showed that the VG based network model which is shown in previous studies to be correlated with human perception enables a mean of 1.17 m shorter distances and 0.20 times fewer turns than the compared routes compared to closest network model. The statistical tests demonstrated that the proposed hybrid approach does not differ significantly from VG thus can be used instead of VG based model for various scenarios.

Digital analysis of external fixation area of proximal humerus fractures in elderly patients

IntroductionThe purpose is based on anatomical basis, combined with three-dimensional measurement, to guide the clinical repositioning of proximal humeral fractures, select the appropriate pin entry point and angle, and simulate surgery.Methods11 fresh cadaveric specimens were collected, the distance of the marked points around the shoulder joint was measured anatomically, and the vertical distance between the inferior border of the acromion and the superior border of the axillary nerve, the vertical distance between the apex of the humeral head and the superior border of the axillary nerve, the vertical distance between the inferior border of the acromion and the superior border of the anterior rotator humeral artery, and the vertical distance between the apex of the humeral head and the superior border of the anterior rotator humeral artery were marked on the 3D model based on the anatomical data to find the relative safety zone for pin placement.ResultsContralateral data can be used to guide the repositioning and fixation of that side of the proximal humerus fracture, and uniform data cannot be used between male and female patients. For lateral pining, the distance of the inferior border of the acromion from the axillary nerve (5.90 ± 0.43) cm, range (5.3-6.9) cm, was selected for pining along the medial axis of the humeral head, close to the medial cervical cortex, and the pining angle was measured in the coronal plane (42.84 ± 2.45)°, range (37.02° ~ 46.31°), and in the sagittal plane (28.24 ± 2.25)°, range (19.22° ~ 28.51°). The pin was advanced laterally in front of the same level of the lateral approach point to form a cross-fixed support with the lateral pin, and the pin angle was measured in the coronal plane (36.14 ± 1.75)°, range (30.32° ~ 39.61°), and in the sagittal plane (28.64 ± 1.37)°, range (22.82° ~ 32.11°). Two pins were taken at the greater humeral tuberosity for fixation, with the proximal pin at an angle (159.26 ± 1.98) to the coronal surface of the humeral stem, range (155.79° ~ 165.08°), and the sagittal angle (161.76 ± 2.15)°, with the pin end between the superior surface of the humeral talus and the inferior surface of the humeral talus. The distal needle of the greater humeral tuberosity was parallel to the proximal approach trajectory, and the needle end was on the inferior surface of the humeral talus.ConclusionBased on the anatomical data, we can accurately identify the corresponding bony structures of the proximal humerus and mark the location of the pin on the 3D model for pin placement, which is simple and practical to meet the relevant individual parameters.

Manifestation of lattice topology data model for indoor navigation path based on the 3D building environment

Abstract Navigation, also known as discovering one’s direction, is a complex human activity. To produce effective routes, it relies on knowledge of the surroundings’ precise geometry and semantic information. Complex geometrical data can be precisely delineated with the improvement of 3D geometric models. A precise 3D geometric model containing a specifically built-in Building Information Modelling (BIM) environment can be integrated into the Geographical Information System platform for indoor path generation to satisfy the requirements of indoor location-based services. Therefore, this paper proposes an approach to evaluate a 3D indoor topology network called a lattice topology data model (LTDM) for the floor-level paths in a 3D multipatch-based model. The LTDM requires the geometric information of the integrated BIM model to identify the indoor space and bounding lines for indoor network generation. The novelty of this study is in the application of the replacement of cell values into vector length for pathfinding through a combination of the Poincaré duality theorem and Dijkstra’s algorithm. The Campus Infrastructure Building model was chosen to validate the proposed method. Multiple space centroid pairs within the floor level were randomly selected to identify the shortest path using the LTDM principle. Paths drawn from the Medial Axis Transformation were compared with LTDM-generated paths for availability testing. The average floor-level path availability was 112% due to the generation of extra paths reflecting real-life situations. The LTDM paths were compared with on-site measurements for accuracy tests, and the average error rate was 3.18%. The results show that the implementation of the LTDM generates an excellent topology data network.

Stress myocardial blood flow reduced after severe COVID-19, not related to symptoms

Abstract Introduction Persistent cardiopulmonary symptoms after COVID-19 are reported in a large number of patients and the underlying pathology is still poorly understood. (1) Histopathologic studies revealed myocardial macrophage infiltrates in deceased patients, likely an unspecific finding of severe illness, and increased prevalence of micro- and macrovascular thrombi. (2) We examined whether microvascular perfusion, measured by quantitative cardiac magnetic resonance under vasodilator stress, was altered post COVID-19. Methods Our population consisted of 12 patients from the Pa-COVID-19-Study of the Charité Berlin, which received a cardiac MRI as part of a systematic follow up post discharge, 10 patients that presented at the German Heart Center Berlin with persistent cardiac symptoms post COVID-19 and 12 patients from the Kings College London referred for stress MRI and previous COVID-19. The scan protocol included standard functional, edema and scar imaging and quantitative stress and rest perfusion to assess both macro- and microvascular coronary artery disease. The pharmacological stress agent was regadenosone in 20 and adenosine in 13 of the patients. To control for the higher heart rate increase under regadenosone compared to adenosine, we calculated the myocardial blood flow per heartbeat (MBF_HRi) under stress. Results The median time between first positive PCR for COVID-19 and the CMR exam was 2 months (Range 0 to 12). None of the 33 patients exhibited signs of myocardial edema. One patient with a previous history of myocarditis had focal fibrosis. Three patients with known coronary artery disease showed ischemic Late Enhancement. Five patients had a small pericardial effusion; one of these four patients showed slight focal pericardial edema and LGE, consistent with mild focal pericarditis. Five Patients had a stress-induced focal perfusion deficit. Mean Stress MBF_HRi was 32.5±6.5 μl/beat/g. Stress MBF_HRi was negatively correlated with COVID-19 severity (rho=−0.361, P=0.039) and age (r=−0.452, P=0.009). The correlation with COVID-19 severity remained significant after controlling for age (rho=−0.390, P=0.027). There was no apparent difference in stress MBF_HRi between patients with and without persistent chest pain (34.5 vs. 31.5 μl/beat/g, P=0.229) Conclusion While vasodilator-stress myocardial blood flow after COVID-19 was negatively correlated to COVID-19 severity, it was not correlated to the presence of chest pain. The etiology of persistent cardiac symptoms after COVID-19 remains unclear. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): Philips Figure 1. A) Quantitative regadenosone stress myocardial blood flow (MBF) map, medial short axis slice, in a patient with persistent cardiac symptoms after COVID-19. B) Boxplot of stress MBF per heart beat by COVID-19 severity, showing decreasing MBF with increasing COVID-19 severity.

Registration of Regeneration in Planarians from Photographic Images

In this study, an approach to constructing a mathematical model for quantifying the dynamics of regeneration of planarian flatworms in biological experiments is considered, based on an analysis of a series of digital microscopic images. A method is proposed to describe the body shape of a planarian using a continuous morphological model, based on the concept of a medial representation of the worm’s silhouette. The silhouette in this case is a polygon approximating the contours of the planarian’s body. The medial representation of the figure includes a medial axis and a radial function that describes the width of the figure relative to the medial axis. We propose a set of morphological criteria for assessing the dynamics of regeneration based on a continuous morphological model and present the results of computational experiments.

A unifying parametric language and a toolbox for future investigations of the role of the medial axis parameters in human vision.

A unifying parametric language and a toolbox for future investigations of the role of the medial axis parameters in human vision.

Medial IPC

We propose a framework of efficient nonlinear deformable simulation with both fast continuous collision detection and robust collision resolution. We name this new framework Medial IPC as it integrates the merits from medial elastics, for an efficient and versatile reduced simulation, as well as incremental potential contact, for a robust collision and contact resolution. We leverage medial axis transform to construct a kinematic subspace. Instead of resorting to projective dynamics, we use classic hyperelastics to embrace real-world nonlinear materials. A novel reduced continuous collision detection algorithm is presented based on the medial mesh. Thanks to unique geometric properties of medial axis and medial primitives, we derive closed-form formulations for identifying between-primitive collision within the reduced medial space. In the meantime, the implicit barrier energy that generates necessary repulsion forces for collision resolution is also formulated with the medial coordinate. In other words, Medial IPC exploits a universal reduced coordinate for simulation, continuous self-/collision detection, and IPC-based collision resolution. Continuous collision detection also allows more aggressive time stepping. In addition, we carefully implement our system with a heterogeneous CPU-GPU deployment such that massively parallelizable computations are carried out on the GPU while few sequential computations are on the CPU. Such implementation also frees us from generating training poses for selecting Cubature points and pre-computing their weights. We have tested our method on complicated deformable models and collision-rich simulation scenarios. Due to the reduced nature of our system, the computation is faster than fullspace IPC or other fullspace methods using continuous collision detection by at least one order. The simulation remains high-quality as the medial subspace captures intriguing and local deformations with sufficient realism.

Can humans perform mental regression on a graph? Accuracy and bias in the perception of scatterplots

Despite the widespread use of graphs, little is known about how fast and how accurately we can extract information from them. Through a series of four behavioral experiments, we characterized human performance in “mental regression”, i.e. the perception of statistical trends from scatterplots. When presented with a noisy scatterplot, even as briefly as 100 ms, human adults could accurately judge if it was increasing or decreasing, fit a regression line, and extrapolate outside the original data range, for both linear and non-linear functions. Performance was highly consistent across those three tasks of trend judgment, line fitting and extrapolation. Participants’ linear trend judgments took into account the slope, the noise, and the number of data points, and were tightly correlated with the t-test classically used to evaluate the significance of a linear regression. However, they overestimated the absolute value of the regression slope. This bias was inconsistent with ordinary least squares (OLS) regression, which minimizes the sum of square deviations, but consistent with the use of Deming regression, which treats the x and y axes symmetrically and minimizes the Euclidean distance to the fitting line. We speculate that this fast but biased perception of scatterplots may be based on a “neuronal recycling” of the human visual capacity to identify the medial axis of a shape.

Automatically quantifying evolution of retrogressive thaw slumps in Beiluhe (Tibetan Plateau) from multi-temporal CubeSat images

Retrogressive thaw slumps (RTSs) are among the most dynamic landforms resulting from the thawing of ice-rich permafrost. However, RTS distribution and evolution are poorly quantified because most of them occur in remote and inaccessible areas. In this study, we propose a method that integrates deep learning, change detection, and medial axis transform, aiming to automatically quantify the RTS development on multi-temporal images in the Beiluhe region on the Tibetan Plateau from 2017 to 2019. The images are taken by the Planet CubeSat constellation with high spatial and temporal resolution. The experiments show that automatic delineation based on deep learning can produce similar results to manual delineation, providing the potential of using these results to quantify the changes of RTS boundaries in different years. Our method reveals that among manually-delineated 342 RTSs in the Beiluhe region, 83% and 76% of them expanded from 2017 to 2018 and 2018 to 2019, respectively. For the expansion from 2017 to 2018, the average and maximum expanding areas are 0.20 ha and 1.47 ha, while the average and maximum retreat distances are 21.3 m and 91 m, respectively. For 2018 to 2019 the average and maximum expansion areas and retreat distances are 0.22 ha, 2.53 ha, 25.0 m, and 212 m, respectively. The results show that the method can quantify RTS development automatically on multi-temporal images but may miss some small and subtle RTSs. Moreover, this study provides the very first quantitative report on RTS development on the Tibetan Plateau, which helps to advance the understanding of permafrost degradation.

Spline-based medial axis transform representation of binary images

Medial axes are well-known descriptors used for representing, manipulating, and compressing binary images. In this paper, we present a full pipeline for computing a stable and accurate piece-wise B-spline representation of Medial Axis Transforms (MATs) of binary images. A comprehensive evaluation on a benchmark shows that our method, called Spline-based Medial Axis Transform (SMAT), achieves very high compression ratios while keeping quality high. Compared with the regular MAT representation, the SMAT yields a much higher compression ratio at the cost of a slightly lower image quality. We illustrate our approach on a multi-scale SMAT representation, generating super-resolution images, and free-form binary image deformation.

Design Considerations for a Steerable Needle Robot to Maximize Reachable Lung Volume.

Steerable needles that are able to follow curvilinear trajectories and steer around anatomical obstacles are a promising solution for many interventional procedures. In the lung, these needles can be deployed from the tip of a conventional bronchoscope to reach lung lesions for diagnosis. The reach of such a device depends on several design parameters including the bronchoscope diameter, the angle of the piercing device relative to the medial axis of the airway, and the needle's minimum radius of curvature while steering. Assessing the effect of these parameters on the overall system's clinical utility is important in informing future design choices and understanding the capabilities and limitations of the system. In this paper, we analyze the effect of various settings for these three robot parameters on the percentage of the lung that the robot can reach. We combine Monte Carlo random sampling of piercing configurations with a Rapidly-exploring Random Trees based steerable needle motion planner in simulated human lung environments to asymptotically accurately estimate the volume of sites in the lung reachable by the robot. We highlight the importance of each parameter on the overall system's reachable workspace in an effort to motivate future device innovation and highlight design trade-offs.