Full Displacement Research Articles

Left ventricle segment-specific motion assessment for cardiac-gated radiosurgery.

Purpose.Cardiac radiosurgery is a non-invasive treatment modality for ventricular tachycardia, where a linear accelerator is used to irradiate the arrhythmogenic region within the heart. In this work, cardiac magnetic resonance (CMR) cine images were used to quantify left ventricle (LV) segment-specific motion during the cardiac cycle and to assess potential advantages of cardiac-gated radiosurgery.Methods.CMR breath-hold cine images and LV contour points were analyzed for 50 controls and 50 heart failure patients with reduced ejection fraction (HFrEF, EF < 40%). Contour points were divided into anatomic segments according to the 17-segment model, and each segment was treated as a hypothetical treatment target. The optimum treatment window (one fifth of the cardiac cycle) was determined where segment centroid motion was minimal, then the maximum centroid displacement and treatment area were determined for the full cardiac cycle and for the treatment window. Mean centroid displacement and treatment area reductions with cardiac gating were determined for each of the 17 segments.Results.Full motion segment centroid displacements ranged between 6-14 mm (controls) and 4-11 mm (HFrEF). Full motion treatment areas ranged between 129-715 mm2(controls) and 149-766 mm2(HFrEF). With gating, centroid displacements were reduced to 1 mm (controls and HFrEF), while treatment areas were reduced to 62-349 mm2(controls) and 83-393 mm2(HFrEF). Relative treatment area reduction ranged between 38%-53% (controls) and 26%-48% (HFrEF).Conclusion.This data demonstrates that cardiac cycle motion is an important component of overall target motion and varies depending on the anatomic cardiac segment. Accounting for cardiac cycle motion, through cardiac gating, has the potential to significantly reduce treatment volumes for cardiac radiosurgery.

Material point method simulations of displacement pile and CPT penetration in sand considering the effects of grain breakage

Full displacement installation dramatically alters the stress and strain fields applying around piles and Cone Penetrometer (CPT) probes at sand sites. Calibration chamber tests have indicated that severe particle crushing occurs near to the pile or cone tips and a distinct shear zone may develop that leaves crushed sand adhering to the pile or cone shaft. It is therefore important to investigate how particle breakage affects the stress and deformation fields developed as this process occurs. In this study, installation by monotonic jacking of conically tipped model piles or CPT probes into silica sand is simulated by material point method (MPM) analyses. A thermodynamically consistent model which considers competing grain crushing and dilation is employed to model the sand behavior, while an MPM approach is adopted to cater for the large deformations involved in the penetration process. Particle crushing is predicted beneath the pile tip and around the pile shaft. The numerical results are compared to directly related instrumented pile calibration chamber tests. The numerical results show that the computed stress and displacement fields match key aspects of the experimental results well, especially in reproducing the volumetric compression observed experimentally. The results confirm that combining MPM with suitably sophisticated constitutive models creates new capabilities for analyzing large-deformation problems.

Prediction of the Proximal Humerus Morphology Based on a Statistical Shape Model with Two Parameters: Comparison to Contralateral Registration Method.

(1) Background: Complex proximal humerus fractures often result in complications following surgical treatment. A better understanding of the full 3D displacement would provide insight into the fracture morphology. Repositioning of fracture elements is often conducted by using the contralateral side as a reconstruction template. However, this requires healthy contralateral anatomy. The purpose of this study was to create a Statistical Shape Model (SSM) and compare its effectiveness to the contralateral registration method for the prediction of the humeral proximal segment; (2) Methods: An SSM was created from 137 healthy humeri. A prediction for the proximal segment of the left humeri from eight healthy patients was made by combining the SSM with parameters. The predicted proximal segment was compared to the left proximal segment of the patients. Their left humerus was also compared to the contralateral (right) humerus; (3) Results: Eight modes explained 95% of the variation. Most deviations of the SSM prediction and the contralateral registration method were below the clinically relevant 2 mm distance threshold.; (4) Conclusions: An SSM combined with parameters is a suitable method to predict the proximal humeral segment when the contralateral CT scan is unavailable or the contralateral humerus is unhealthy, provided that the fracture pattern allows measurements of these parameters.

Making use of Digital Image Correlation to identify the true character of the applied load

Digital Image Correlation became one of the dominant optical full-field techniques used in experimental mechanics. It does not require sophisticated equipment to evaluate the full displacement vector field of the specimen under test with great accuracy. In this paper, we would like to put the reader's attention to the DIC technique as a solution that may identify the genuine character of the load applied to the object under test. Our experience with testing wind turbine blades using DIC proves that possibility. Full Text: PDF References E.M.C Jones, M.A. Iadicola, "A good practises guide for digital image correlation" International Digital Image Correlation Society, (2018), CrossRef B. Pan, "Digital image correlation for surface deformation measurement: historical developments, recent advances and future goals", Meas. Sci. Technol. 29, 082001 (2018), CrossRef B. Pan, L.P. Yu, Q.B. Zhang, "Review of single-camera stereo-digital image correlation techniques for full-field 3D shape and deformation measurement", Sci. China Technol. Sci. 61, 2 (2018), CrossRef S. Sharma, N. Iniyan Thiruselvam, S.J. Subramanian, G.S. Kumar, "Computation of strains from stereo digital image correlation using principal component analysis", Meas. Sci. Technol. 32, 105201 (2021), CrossRef IEC 61400-5:2020 Wind energy generation systems - Part 5: Wind turbine, DirectLink IEC 61400-23:2014 Wind turbines - Part 23: Full-scale structural testing of rotor blades, DirectLink

Flexural toughness of extruded fiber-reinforced mortar with preferentially aligned fibers

This study explored the flexural toughness properties of polyvinyl alcohol (PVA) fiber-reinforced concrete (FRC) using a modified ASTM C1609 third-point bending test, and it established a comparative study between two methods of casting: traditional casting and pump-driven extrusion. The primary hypothesis posited that the extrusion process would promote fiber alignment parallel to the tensile stresses, thereby enhancing the flexural performance of the concrete. The study corroborated previous research findings that introducing fibers enhances the ductility and post-peak performance of the concrete. Moreover, this research introduced a unique observation that strategic fiber alignment through extrusion could serve to further enhance the concrete's flexural performance. The research employed digital image correlation to capture the full displacement field during testing, facilitating an examination of the crack propagation process and strain localization. The findings showed that the extrusion-based casting method improved the residual strengths by an average of 39% and 87% compared to conventional cast method for the 0.5% and 1% fiber volume specimens, respectively. Additionally, the base of the extruded specimens exhibited a greater incidence of crack initiation and displayed enhanced energy absorption through multiple cracking events. These observations underscore the concept that fiber alignment, when facilitated by extrusion, plays a significant role in influencing crack propagation and, consequently, in improving the flexural properties of the composite material.

Study on Large Deformation Characteristics and Secondary Lining Supporting Time of Tunnels in Carbonaceous Schist Stratum under High Geo-Stress

The deformation characteristics and the timing for secondary lining support in high geo-stress soft rock tunnels have drawn significant attention. In carbonaceous shale formations, tunnel construction deformations are very pronounced under construction disturbances due to the development of joints, dense fractures, and poor interlayer bonding. With the Xishuangbanna tunnel as our research backdrop, this study meticulously analyzed the deformation patterns and characteristics inherent to high geo-stress tunnels constructed within carbonaceous schist formations. Employing a comprehensive approach involving full displacement analysis and on-site construction mechanics testing, we utilized the displacement release rate and structural safety factors as key indicators to determine the secondary lining supporting time. Employing this innovative approach, we successfully identified the ideal junctures for implementing secondary lining support in tunnels excavated through high geo-stress carbonaceous schist. The research findings indicate that the primary damage modes in high geo-stress carbonaceous schist tunnels are initial support failure and extensive early support deformation. These vulnerabilities are primarily attributed to weak and fragmented strata, elevated ground stress levels, and inadequate support strength. During the early stages of tunnel construction, substantial deformations are observed, exhibiting high rates of change. Horizontal convergence, notably, significantly surpasses the settlement at the tunnel’s crown. When employing the three-bench method for construction, the deformation occurring before the excavation of the middle bench contributes the most to the total deformation monitored, whereas the deformation generated after the excavation of the inverted arch constitutes a minor proportion. The tunnel’s crown and invert experience tension while the secondary lining undergoes compression. The internal forces are most significant at the tunnel’s hance and knee, with the left tunnel knee being the weakest section of the secondary lining. The findings of our study are poised to guide the design and execution of tunnels constructed within high geo-stress carbonaceous schist formations.

Adaptive MOR techniques for non‐linear FE simulations of unit cells

AbstractThis work shows an adaptive Model Order Reduction (MOR) scheme for the computation of unit cells with non‐linear material behavior. A reduction of dimensionality and computational cost is achieved by projecting the high‐fidelity system of equations (SOE) from the full vector space to a lower dimensional subspace. An adaptive algorithm updates the projection operator, which is initially gained from a Proper Orthogonal Decomposition (POD), to ensure convergence and optimal size control of the reduced problem. Numerical examples show a comparison between the discretization of full displacements and fluctuations of a hexagonal unit cell, which show the independence of the MOR basis from the macroscopic displacements.

TWO LIFE STRATEGIES IN COPEPOD CRYPTIC SPECIES: COEXISTENCE AND DISPLACEMENT

Among invasive species there is a special group so named cryptic species for which morphological identification is very difficult. This review is devoted to analysis of the dispersal routes of two copepod cryptic species complexes into aquatic ecosystems. Eurytemora carolleeae introduction was revealed in 2007 with bar-code. The species was described as a new taxon; its distribution was also studied using morphology. Biological invasions of two other Copepod species Acanthocyclops americanus and Eurytemora caspica were mainly studied using morphological methods since the species have already been described. At the same time, to confirm their distinctions from local forms, molecular genetic tools were also used. Two scenarios resulting from cryptic species’ invasions and their competitions with native species were the partly ( E. carrolleeae ) or full displacement ( A. americanus ). Example: the invasion of Eurytemora carolleeae into the Baltic Sea and the Atlantic coast of Europe. When assessing the possible negative impact of invasive species on competitors, the most attention should be paid to predator species. Identification of cryptic species significantly complicates the situation with the assessment of bioinvasion and needs the use of molecular methods.

(Invited) Kinetics of SWCNT Coating Displacement By ssDNA Depends on SWCNT Structure

Non-covalent hybrids formed by suspending single-wall carbon nanotubes (SWCNTs) in single-stranded DNA (ssDNA) present novel phenomena and suggest potential applications in biomedicine and nanotube sorting. Although the structures of these hybrids have been simulated using molecular dynamics calculations, much more experimental research is needed to understand their properties. In this study, selective interactions between SWCNTs and ssDNA are probed by measuring the kinetics by which ssDNA displaces SDS (sodium dodecyl sulfate) coatings on the nanotube surfaces. We used samples initially suspended in a low concentration of SDS to allow the coating displacement to occur and to suppress formation of free SDS micelles. The displacement process was monitored by time-dependent measurements of SWCNT fluorescence intensities and wavelengths. Our experiments showed very smooth decreases in fluorescence intensity and red-shifts in fluorescence wavelengths during the displacement process. Through a series of measurements, we found that ssDNA sequences with repeated guanine (G) and thymine (T) bases showed systematic patterns in the coating displacement kinetics. One result is that SDS displacement depends strongly on oligo length, with (GT)3 showing an initial rate constant 500 times greater than that of (GT)20. For shorter oligos in the (GT) n series, we observe an inverse dependence of initial rate constant on SWCNT diameter, with SDS displacement from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is not present for (GT) n oligos with n greater than 6. We also find a distinct and systematic dependence of initial rate constant on nanotube chiral angle for (GT)5 and (GT)6. This effect gives a factor of ~3 difference between (9,1) and (6,5) despite their identical diameters. We empirically find these initial rate constants to vary as (SWCNT diameter)-4(cos 3θ)-y with y = -1/2 for (GT)5 and -1 for (GT)6. In addition, the full displacement kinetic traces are well fitted by double exponential kinetics, with rate constants and amplitudes dependent on SWCNT diameter. A two-step kinetic model for the displacement process will be presented to account for these findings.

Rapid response mechanism in conflict-affected settings of Cameroon: lessons learned from a multisector intervention for internally displaced persons

The Northwest and Southwest regions of Cameroon have experienced armed conflict over the last seven years, characterized by mass displacement and limited access to health care and social amenities. In response, an emergency intervention programme called “rapid response mechanism” (RRM) was initiated to provide lifesaving services to internally displaced persons. The intervention was multisectoral and included a health component, nutrition, water hygiene and sanitation, and child protection. RRM served communities of Ekondo Titi district, marked with high levels of insecurity, poor telecommunication networks and limited geographical access. Although the RRM was designed to provide rapid and lifesaving interventions to the affected populations; the RRM, in this case, was only initiated one year after the conflict escalated. Key benefits of the RRM included: (i) increased access to health care services through its integrated community case management approach, (ii) development of full displacement map within the health district, further strengthening the health system by establishing a community-based surveillance and response system through community health workers, and (iii) assisting the health district team in mass vaccination campaigns in seven of the nine health areas, which were otherwise completely inaccessible. The RRM model was largely primary health care focused compared to other RRMs in conflict-affected countries. It is important for RRM benefit packages to be harmonized to enable better preparedness and responses in conflicts. There is also a need for better coordination among sectoral partners to ensure improved response in crises.

Characterizing the Adhesion Between Thin Films and Rigid Substrates Using Digital Image Correlation-Informed Inverse Finite Elements and the Blister Test

Abstract Characterizing the adhesion between thin films and rigid substrates is crucial in engineering applications. Still, existing standard methods suffer from issues such as poor reproducibility, difficulties in quantifying adhesion parameters, or overestimation of adhesion strength and fracture energy. Recent studies have shown that the blister test (BT) is a superior method for characterizing adhesion, as it provides a quantifiable measurement of mix-mode fracture energy, and it is highly reproducible. In this paper, we present a novel method to characterize mechanical mix-mode adhesion between thin films and rigid substrates using the BT. Our method combines the full triaxial displacement field obtained through digital image correlation with inverse finite element method simulations using cohesive zone elements. This approach eliminates the need for making any mechanistic or kinematic assumptions of the blister formation and allows the characterization of the full traction-separation law governing the adhesion between the film and the substrate. To demonstrate the efficacy of this methodology, we conducted a case study analyzing the adhesion mechanics of a polymeric pressure-sensitive adhesive on an aluminum substrate. Our results indicate that the proposed technique is a reliable and effective method for characterizing the mix-mode traction-separation law governing the mechanical behavior of the adhesive interface and could have broad applications in the field of materials science and engineering. Also, by providing a comprehensive understanding of the adhesion mechanics between thin films and rigid substrates, our method can aid in the design and optimization of adhesively bonded structures.

Inferring displacement fields from sparse measurements using the statistical finite element method

Nowadays, strain and displacement can be measured using techniques such as electronic speckle pattern interferometry and digital image correlation. However, usually, only some part of the domain of interest is accessible for measurement devices. In order to assess also inaccessible areas of the structure, a fundamental task for structural health monitoring is the inference of full-field displacements from sparse measurements. Another important task is the inference of mechanical stress from displacement or strain data. In computational mechanics, the link between such data and stress is established via constitutive models.A well-established approach for inferring full displacement and stress fields from possibly sparse data is to calibrate the parameter of a given constitutive model using a Bayesian update. After calibration, a (stochastic) forward simulation is conducted with the identified model parameters to resolve physical fields in regions that were not accessible to the measurement device. A shortcoming of model calibration is that the model is deemed to best represent reality, which is only sometimes the case, especially in the context of the aging of structures and materials. While this issue is often addressed with repeated model calibration, a different approach is followed in the recently proposed statistical Finite Element Method (statFEM). Instead of using Bayes’ theorem to update model parameters, the displacement is chosen as the stochastic prior and updated to fit the measurement data more closely. For this purpose, the statFEM framework introduces a so-called model-reality mismatch, parametrized by only three hyperparameters. This makes the inference of full-field data computationally efficient in an online stage: If the stochastic prior can be computed offline, solving the underlying partial differential equation (PDE) online is unnecessary. Compared to solving a PDE, identifying only three hyperparameters and conditioning the state on the sensor data requires much fewer computational resources. Computational efficiency is an essential requirement for online applications. It is noted that conditioning a model-based prior field on sensor data represents a variant of physics-based regression.This paper presents two contributions to the existing statFEM approach: First, we use a non-intrusive polynomial chaos method to compute the prior, enabling the use of complex mechanical models in deterministic formulations. Second, we examine the influence of prior material models (linear elastic and St.Venant Kirchhoff material with uncertain Young’s modulus) on the updated solution. We present statFEM results for 1D and 2D examples, while an extension to 3D is straightforward.

Parallel Implementation of Nonadditive Gaussian Process Potentials for Monte Carlo Simulations.

A strategy is presented to implement Gaussian process potentials in molecular simulations through parallel programming. Attention is focused on the three-body nonadditive energy, though all algorithms extend straightforwardly to the additive energy. The method to distribute pairs and triplets between processes is general to all potentials. Results are presented for a simulation box of argon, including full box and atom displacement calculations, which are relevant to Monte Carlo simulation. Data on speed-up are presented for up to 120 processes across four nodes. A 4-fold speed-up is observed over five processes, extending to 20-fold over 40 processes and 30-fold over 120 processes.

Magnetic Resonance Elastography-Based Technique to Assess the Biomechanics of the Skull-Brain Interface: Repeatability and Age-Sex Characteristics.

Increasing concerns have been raised about the long-term negative effects of subconcussive repeated head impact (RHI). To elucidate RHI injury mechanisms, many efforts have studied how head impacts affect the skull-brain biomechanics and have found that mechanical interactions at the skull-brain interface dampen and isolate brain motions by decoupling the brain from the skull. Despite intense interest, in vivo quantification of the functional state of the skull-brain interface remains difficult. This study developed a magnetic resonance elastography (MRE) based technique to non-invasively assess skull-brain mechanical interactions (i.e., motion transmission and isolation function) under dynamic loading. The full MRE displacement data were separated into rigid body motion and wave motion. The rigid body motion was used to calculate the brain-to-skull rotational motion transmission ratio (Rtr) to quantify skull-brain motion transmissibility, and the wave motion was used to calculate the cortical normalized octahedral shear strain (NOSS) (calculated based on a partial derivative computing neural network) to evaluate the isolation capability of the skull-brain interface. Forty-seven healthy volunteers were recruited to investigate the effects of age/sex on Rtr and cortical NOSS, and 17 of 47 volunteers received multiple scans to test the repeatability of the proposed techniques under different strain conditions. The results showed that both Rtr and NOSS were robust to MRE driver variations and had good repeatability, with intraclass correlation coefficient (ICC) values between 0.68 and 0.97 (fair to excellent). No age or sex dependence were observed with Rtr, whereas a significant positive correlation between age and NOSS was found in the cerebrum, frontal, temporal, and parietal lobes (all p < 0.05), but not in the occipital lobe (p = 0.99). The greatest change in NOSS with age was found in the frontal lobe, one of the most frequent locations of traumatic brain injury (TBI). Except for the temporal lobe (p = 0.0087), there was no significant difference in NOSS between men and women. This work provides motivation for utilizing MRE as a non-invasive tool for quantifying the biomechanics of the skull-brain interface. It evaluated the age and sex dependence and may lead to a better understanding of the protective role and mechanisms of the skull-brain interface in RHI and TBI, as well as improve the accuracy of computational models in simulating the skull-brain interface.

Interfacial fracture performance of engineered cementitious composites and fire-damaged concrete

This study investigated the interfacial fracture properties of engineered cementitious composites (ECC) and fire-damaged concrete using bi-material wedge splitting specimens. The full load versus crack mouth opening displacement (CMOD) curves of the bi-material specimens were obtained using wedge splitting tests, and the fracture toughness and fracture energy were calculated. The effects of the maximum temperature experienced by the concrete (20–700 °C) and the interfacial roughness (0–5 mm) on the interfacial damage mode, fracture toughness, and fracture energy were studied. The results indicated that when the maximum temperature experienced by the concrete was lower than 400 ℃ or the interface was smooth, the damage mode of the specimens was primarily adhesive failure. However, when the maximum temperature experienced by the concrete was equal to or greater than 400 °C and the interface was rough, cohesive failure often occurred in the specimens. Owing to the change in the damage mode, the bi-material specimens had the highest values of the fracture toughness and fracture energy at 400 °C. When the maximum temperature experienced by the concrete exceeded 400 °C, both the fracture toughness and fracture energy decreased with the increasing temperature. In this study, the fracture toughness and fracture energy of the bi-material specimens first increased and subsequently decreased with the increaseing roughness, and the maximum fracture toughness and fracture energy values were obtained when the interface roughness was 3 mm. The study results would provide a reference for the surface treatment when ECC was used in the strenthening of fire damaged concrete.

The Formation of a Unique 2D Isonicotinate Polymer Driven by Cu(II) Aerobic Oxidation.

The isolation and structural characterization of a unique Cu(II) isonicotinate (ina) material with 4-acetylpyridine (4-acpy) is provided. The formation of [Cu(ina)2(4-acpy)]n (1) is triggered by the Cu(II) aerobic oxidation of 4-acpy using O2. This gradual formation of ina led to its restrained incorporation and hindered the full displacement of 4-acpy. As a result, 1 is the first example of a 2D layer assembled by an ina ligand capped by a monodentate pyridine ligand. The Cu(II)-mediated aerobic oxidation with O2 was previously demonstrated for aryl methyl ketones, but we extend the applicability of this methodology to heteroaromatic rings, which has not been tested so far. The formation of ina has been identified by 1H NMR, thus demonstrating the feasible but strained formation of ina from 4-acpy in the mild conditions from which 1 was obtained.

In situ synchrotron radiation µCT indentation of cortical bone: Anisotropic crack propagation, local deformation, and fracture

The development of treatment strategies for skeletal diseases relies on the understanding of bone mechanical properties in relation to its structure at different length scales. At the microscale, indention techniques can be used to evaluate the elastic, plastic, and fracture behaviour of bone tissue. Here, we combined in situ high-resolution SRµCT indentation testing and digital volume correlation to elucidate the anisotropic crack propagation, deformation, and fracture of ovine cortical bone under Berkovich and spherical tips. Independently of the indenter type we observed significant dependence of the crack development due to the anisotropy ahead of the tip, with lower strains and smaller crack systems developing in samples indented in the transverse material direction, where the fibrillar bone ultrastructure is largely aligned perpendicular to the indentation direction. Such alignment allows to accommodate the strain energy, inhibiting crack propagation. Higher tensile hoop strains generally correlated with regions that display significant cracking radial to the indenter, indicating a predominant Mode I fracture. This was confirmed by the three-dimensional analysis of crack opening displacements and stress intensity factors along the crack front obtained for the first time from full displacement fields in bone tissue. The X-ray beam significantly influenced the relaxation behaviour independent of the tip. Raman analyses did not show significant changes in specimen composition after irradiation compared to non-irradiated tissue, suggesting an embrittlement process that may be linked to damage of the non-fibrillar organic matrix. This study highlights the importance of three-dimensional investigation of bone deformation and fracture behaviour to explore the mechanisms of bone failure in relation to structural changes due to ageing or disease. Statement of significanceCharacterising the three-dimensional deformation and fracture behaviour of bone remains essential to decipher the interplay between structure, function, and composition with the aim to improve fracture prevention strategies. The experimental methodology presented here, combining high-resolution imaging, indentation testing and digital volume correlation, allows us to quantify the local deformation, crack propagation, and fracture modes of cortical bone tissue. Our results highlight the anisotropic behaviour of osteonal bone and the complex crack propagation patterns and fracture modes initiating by the intricate stress states beneath the indenter tip. This is of wide interest not only for the understanding of bone fracture but also to understand other architectured (bio)structures providing an effective way to quantify their toughening mechanisms in relation to their main mechanical function.

Bile acid interactions with neurotransmitter transporters.

Synthesized in the liver from cholesterol, the bile acids (BAs) primary role is emulsifying fats to facilitate their absorption. BAs can cross the blood-brain barrier (BBB) and be synthesized in the brain. Recent evidence suggests a role for BAs in the gut-brain signaling by modulating the activity of various neuronal receptors and transporters, including the dopamine transporter (DAT). In this study, we investigated the effects of BAs and their relationship with substrates in three transporters of the solute carrier 6 family. The exposure to obeticholic acid (OCA), a semi-synthetic BA, elicits an inward current (IBA) in the DAT, the GABA transporter 1 (GAT1), and the glycine transporter 1 (GlyT1b); this current is proportional to the current generated by the substrate, respective to the transporter. Interestingly, a second consecutive OCA application to the transporter fails to elicit a response. The full displacement of BAs from the transporter occurs only after exposure to a saturating concentration of a substrate. In DAT, perfusion of secondary substrates norepinephrine (NE) and serotonin (5-HT) results in a second OCA current, decreased in amplitude and proportional to their affinity. Moreover, co-application of 5-HT or NE with OCA in DAT, and GABA with OCA in GAT1, did not alter the apparent affinity or the Imax, similar to what was previously reported in DAT in the presence of DA and OCA. The findings support the previous molecular model that suggested the ability of BAs to lock the transporter in an occluded conformation. The physiological significance is that it could possibly avoid the accumulation of small depolarizations in the cells expressing the neurotransmitter transporter. This achieves better transport efficiency in the presence of a saturating concentration of the neurotransmitter and enhances the action of the neurotransmitter on their receptors when they are present at reduced concentrations due to decreased availability of transporters.

A Deep Learning Framework to Estimate Elastic Modulus from Ultrasound Measured Displacement Fields.

Ultrasound (US) elastography is a technique that enables non-invasive quantification of material properties, such as stiffness, from ultrasound images of deforming tissue. The displacement field is measured from the US images using image matching algorithms, and then a parameter, often the elastic modulus, is inferred or subsequently measured to identify potential tissue pathologies, such as cancerous tissues. Several traditional inverse problem approaches, loosely grouped as either direct or iterative, have been explored to estimate the elastic modulus. Nevertheless, the iterative techniques are typically slow and computationally intensive, while the direct techniques, although more computationally efficient, are very sensitive to measurement noise and require the full displacement field data (i.e., both vector components). In this work, we propose a deep learning approach to solve the inverse problem and recover the spatial distribution of the elastic modulus from one component of the US measured displacement field. The neural network used here is trained using only simulated data obtained via a forward finite element (FE) model with known variations in the modulus field, thus avoiding the reliance on large measurement data sets that may be challenging to acquire. A U-net based neural network is then used to predict the modulus distribution (i.e., solve the inverse problem) using the simulated forward data as input. We quantitatively evaluated our trained model with a simulated test dataset and observed a 0.0018 mean squared error (MSE) and a 1.14% mean absolute percent error (MAPE) between the reconstructed and ground truth elastic modulus. Moreover, we also qualitatively compared the output of our U-net model to experimentally measured displacement data acquired using a US elastography tissue-mimicking calibration phantom.

Simultaneous acquisition of vibration and diffusion by multifrequency diffusion tensor imaging-magnetic resonance elastography (mDTI-MRE)

Magnetic Resonance Elastography (MRE) and Diffusion Tensor Imaging (DTI) are MRI techniques that provide complementary diagnostic information and utilize motion-sensitive magnetic field gradients. In MRE, tissue vibrations are encoded into the MRI signal phase, while in DTI the diffusive motion of water molecules is assessed by means of the MRI signal magnitude. Careful consideration of the motion-encoding gradient timing conditions and the mechanical frequencies allows the simultaneous acquisition of vibration and diffusion data without observable mutual interferences. We propose a multifrequency Diffusion Tensor Imaging-Magnetic Resonance Elastography (mDTI-MRE) protocol that measures the diffusive behavior along 24 directions and the full 3D displacement field at two mechanical frequencies. Using this method, mDTI-MRE provides information about the mechanical wave field and about a preferred direction, which may facilitate the accurate mechanical characterization of anisotropic biological tissues, such as brain white matter and skeletal muscle.