Objective: The study aimed to assess the cumulative radiation exposure from preoperative, periprocedural, and follow-up imaging to patients who underwent common endovascular deep venous interventions for acute and chronic central venous outflow obstructive diseases; namely, deep vein thrombosis (DVT) thrombolysis, unilateral chronic iliofemoral venous stenting, and inferior vena cava (IVC) reconstruction in a single center. Methods: Patients who had DVT thrombolysis of upper extremity (UE) DVT and lower extremity (LE) DVT, unilateral chronic iliofemoral venous stenting, and endovascular IVC reconstruction between May 1, 2012, and July 31, 2017, in a single unit were retrospectively reviewed. Demographic data, anatomic DVT, imaging, technical details of the index procedure, follow-up, and radiation exposure measured in dose-length product, dose-area product (DAP), and fluoroscopy time (FT) from related computed tomography scans and interventions were analyzed. Mann-Whitney U tests were performed to assess for significance of differences between subgroups. A P value of less than .05 was considered significant. Results: In total, 20 UE DVT thrombolysis, 91 LE DVT thrombolysis, 56 unilateral chronic iliofemoral venous stenting, and 39 endovascular IVC reconstruction patients were included in the study, with the following median ages: 39 years (range, 20-67 years), 44 years (range, 15-78 years), 45 years (range, 20-80 years), and 35 years (range, 18 -73 years), respectively. The median cumulative DAP for the index DVT thrombolysis was 9.2 Gycm(2) (range, 0.2-176.0 Gycm(2)) for LE DVT and 2.0 Gycm(2) (range, 0.1-11.7 Gycm(2)) for UE DVT (P<.0001). The median cumulative FT for the index thrombolysis was 981 seconds (range, 20-4890 seconds) and 837 seconds (range, 19-2895 seconds) for LE DVT and UE DVT, respectively (P=.18). For unilateral chronic iliofemoral venous stenting, the median cumulative DAP and FT were 32.4 Gycm(2) (range, 0.1-289.6 Gycm(2)) and 660 seconds (range, 246-4200 seconds), respectively. Meanwhile, the median cumulative DAP and FT for the endovascular IVC reconstruction were 60.8 Gycm(2) (range, 2.5-269.1 Gycm(2)) and 2846 seconds (range, 83611682 seconds), respectively. The median DAP for secondary procedures during follow-up was 6.6 Gycm(2) (range, 0.8 186.5 Gycm(2)), 1.9 Gycm(2) (range, 0.2-111.7 Gycm(2)), and 24.3 Gycm(2) (range, 0.2-157.5 Gycm(2)) for LE DVT thrombolysis, unilateral chronic iliofemoral venous stenting, and endovascular IVC reconstruction, respectively. Conclusions: Patient radiation exposure for endovascular deep venous interventions for central venous outflow obstruction measured in DAP and FT seemed to be less than and at most similar to anatomically comparable arterial interventions in the literature. However, these patients were usually much younger than those with arterial diseases and may need secondary interventions involving further radiation exposure in their lifetime.

We note with disappointment Doss’s suggestion that occupational radiation exposure should be considered as potentially beneficial. This comes at a time when the entire interventionist community is trying to impress on their young trainees, many of whom will be exposed to radiation several times a week, performing in some cases lengthy fluoroscopically guided procedures over a 40-year career, the importance of protecting against this exposure. We are aware that Doss and his group extol the virtues of not sparing irradiation to ensure proper screening, diagnosis, and treatment of patients. Although we would not advocate avoiding the use of radiation …

We note with disappointment Doss’s suggestion that occupational radiation exposure should be considered as potentially beneficial. This comes at a time when the entire interventionist community is trying to impress on their young trainees, many of whom will be exposed to radiation several times a week, performing in some cases lengthy fluoroscopically guided procedures over a 40-year career, the importance of protecting against this exposure. We are aware that Doss and his group extol the virtues of not sparing irradiation to ensure proper screening, diagnosis, and treatment of patients. Although we would not advocate avoiding the use of radiation …

Catheter thrombolysis of acute deep venous thrombosis (DVT) of the upper extremity (UE) and lower extremity (LE) is being increasingly carried out following emerging evidence to support that it reduces the risk for development of post-thrombotic syndrome. Such intervention and its potential secondary procedures may expose the patients to significant cumulative radiation over time. Furthermore, these patients are often relatively younger than those with arterial diseases. The study aimed to assess the cumulative radiation exposure to patients who had thrombolysis for acute DVT of the LE and UE.

Endovenous stents can be used for deep venous reconstruction to treat patients with post-thrombotic syndrome. Guidelines on iliocaval stenting suggest that stenting across the inguinal ligament should be avoided. However, stenting from a normal peripheral inflow segment is more important; therefore, stenting across the ligament may be necessary. There are limited data on the outcomes of nitinol venous stents placed across the inguinal ligament for patients with occlusive post-thrombotic disease, but it is thought that this procedure is associated with early stent thrombosis because of the extensive nature of the disease.

Background: Radiation exposure during fluoroscopically guided interventions such as endovascular aortic repair (EVAR) is a growing concern for operators. This study aimed to measure DNA damage/repair markers in operators perfoming EVAR. Methods: Expression of the DNA damage/repair marker, γ-H2AX and DNA damage response marker, phosphorylated ataxia telangiectasia mutated (pATM), were quantified in circulating lymphocytes in operators during the peri-operative period of endovascular (infrarenal, branched, and fenestrated) and open aortic repair using flow cytometry. These markers were separately measured in the same operators but this time wearing leg lead shielding in addition to upper body protection and compared with those operating with unprotected legs. Susceptibility to radiation damage was determined by irradiating operators’ blood in vitro. Results: γ-H2AX and pATM levels increased significantly in operators immediately after branched endovascular aortic repair/fenestrated endovascular aortic repair ( P <0.0003 for both). Only pATM levels increased after infrarenal endovascular aortic repair ( P <0.04). Expression of both markers fell to baseline in operators after 24 hours ( P <0.003 for both). There was no change in γ-H2AX or pATM expression after open repair. Leg protection abrogated γ-H2AX and pATM response after branched endovascular aortic repair/fenestrated endovascular aortic repair. The expression of γ-H2AX varied significantly when operators’ blood was exposed to the same radiation dose in vitro ( P <0.0001). Conclusions: This is the first study to detect an acute DNA damage response in operators performing fluoroscopically guided aortic procedures and highlights the protective effect of leg shielding. Defining the relationship between this response and cancer risk may better inform safe levels of chronic low-dose radiation exposure.

Introduction: Cell therapy using unselected mononuclear cell populations has had modest benefits in patients with critical limb ischemia (CLI). We hypothesized that tissue-remodeling monocytes, identified by their expression of CD16 (CD16+ Mo), may be a novel cellular therapy for CLI. Methods and Results: Flow cytometry showed that the proportion of circulating CD16+ Mo was greater in CLI patients (n=25) compared with matched controls (n=15, P<0.0001). Removal of ischemia following revascularization or amputation resulted in a fall in CD16+ Mo to control levels (P<0.05). CLI CD16+ Mo expressed higher levels of the adhesive proteins VLA, ICAM-1 and CD11c compared with controls (P<0.05). Conditioned media from these cells contained higher levels of HB-EGF, PlGF, endoglin, VEGF-C and VEGF-D (P<0.05) and induced greater endothelial cell tubule formation (P<0.05) compared with CD16- Mo from the same patients (n=9). CD16+ Mo preferentially migrated towards ischemic muscle supernatants isolated from CLI patients (n=7, P<0.02). CD16+ and CD16- Mo were isolated from 12 CLI patients and 1x10 6 cells injected into the adductor muscles of nude athymic mice following femoral artery excision. More ischemic hindlimbs were salvaged when treated with CD16+ compared with CD16- Mo (83% [10/12] vs 17% [2/12] limbs, P<0.05) and this was associated with enhanced arteriogenesis (αSMA-stained vessels, P<0.05). Conclusion: Circulating CD16+ Mo from CLI patients have increased expression of adhesion markers, are preferentially retained within ischemic muscle and promote robust arteriogenesis and limb salvage in experimental HLI. This monocyte subset may be an effective cellular therapy for CLI.

A variational multiscale constitutive model that accounts for strain rate dependent ductility of nanocrystalline materials during intergranular failure has been presented. The presented model is an extension of the previous work [1], in which a nanocrystalline material is modelled as two-phase with grain interior being modelled using crystal plasticity theory while grain boundary affected zone using porous plasticity model which accounts for ductile damage due to void growth and coalescence. The model capability of capturing the strain rate dependent deformation and failure has been demonstrated through validations against uniaxial test data taken from literature. The validated results show a good agreement between experimental and simulated response.

Here, we propose a damage model that describes the degradation of the material properties of indium-tin-oxide (ITO) thin films deposited on polymer substrates under cyclic loading. We base this model on our earlier tensile test model and show that the new model is suitable for cyclic loading. After calibration with experimental data, we are able to capture the stress-strain behavior and changes in electrical resistance of ITO thin films. We are also able to predict the crack density using calibrations from our previous model. Finally, we demonstrate the capabilities of our model based on simulations using material properties reported in the literature. Our model is implemented in the commercially available finite element software ABAQUS using a user subroutine UMAT.

We have studied the void growth problem by employing the Taylor-based strain gradient plasticity theories, from which we have chosen the following three, namely, the mechanism-based strain gradient (MSG) plasticity (Gao et al 1999 J. Mech. Phys. Solids 47 1239, Huang et al 2000 J. Mech. Phys. Solids 48 99-128), the Taylor-based nonlocal theory (TNT; 2001 Gao and Huang 2001 Int. J. Solids Struct. 38 2615) and the conventional theory of MSG (CMSG; Huang et al 2004 Int. J. Plast. 20 753). We have addressed the following three issues which occur when plastic deformation at the void surface is unconstrained. (1) Effects of elastic deformation. Elasticity is essential for cavitation instability. It is therefore important to guarantee that the gradient term entering the Taylor model is the effective plastic strain gradient instead of the total strain gradient. We propose a simple elastic-plastic decomposition method. When the void size approaches the minimum allowable initial void size related to the maximum allowable geometrically necessary dislocation density, overestimation of the flow stress due to the negligence of the elastic strain gradient is on the order of l epsilon Y/R-0 near the void surface, where l, epsilon(Y) and R-0 are, respectively, the intrinsic material length scale, the yield strain and the initial void radius. (2) MSG intrinsic inconsistency, which was initially mentioned in Gao et al (1999 J. Mech. Phys. Solids 47 1239) but has not been the topic of follow-up studies. We realize that MSG higher-order stress arises due to the linear-strain-field approximation within the mesoscale cell with a nonzero size, l(epsilon). Simple analysis shows that within an MSG mesoscale cell near the void surface, the difference between microscale and mesoscale strains is on the order of (l epsilon/R-0)(2), indicating that when l(epsilon)/R-0 similar to 1.0, the higher-order stress effect can make the MSG result considerably different from the TNT or CMSG results. (3) Critical condition for cavitation instability. When Taylor plasticity replaces classical plasticity as the flow rule, the critical cavitation condition, appearing when the derivative of the externally imposed mean stress with respect to the current void radius becomes zero, is rewritten analytically according to the Leibniz relation and found to be very different from the classical counterpart.

In this paper the texture evolution in nano-indentation experiments was investigated numerically. To achieve this, a three-dimensional implicit finite-element model incorporating a strain-gradient crystal-plasticity theory was developed to represent accurately the deformation of a body-centred cubic metallic material. A hardening model was implemented to account for strain hardening of the involved slip systems. The surface topography around indents in different crystallographic orientations was compared to corresponding lattice rotations. The influence of strain gradients on the prediction of lattice rotations in nano-indentation was critically assessed.

The evolution of defects or voids, generally recognized as the basic failure mechanism in most metals and alloys, has been intensively studied. Most investigations have been limited to spatially periodic cases with non-random distributions of the radii of the voids. In this study, we use a new form of the incompressibility of the matrix to propose the formula for the volumetric plastic energy of a void inside a porous medium. As a consequence, we are able to account for the weakening effect of the surrounding voids and to propose a general model for the distribution and interactions of multi-sized voids. We found that the single parameter in classical Gurson-type models, namely void volume fraction is not sufficient for the model. The relative growth rates of voids of different sizes, which can in principle be obtained through physical or numerical experiments, are required. To demonstrate the feasibility of the model, we analyze two cases. The first case represents exactly the same assumption hidden in the classical Gurson’s model, while the second embodies the competitive mechanism due to void size differences despite in a much simpler manner than the general case. Coalescence is implemented by allowing an accelerated void growth after an empirical critical porosity in a way that is the same as the Gurson–Tvergaard–Needleman model. The constitutive model presented here is validated through good agreements with experimental data. Its capacity for reproducing realistic failure patterns is shown by simulating a tensile test on a notched round bar.

We present unified predictions for the crack onset strain, evolution of crack density, and changes in electrical resistance in indium tin oxide/polymer thin films under tensile loading. We propose a damage mechanics model to quantify and predict such changes as an alternative to fracture mechanics formulations. Our predictions are obtained by assuming that there are no flaws at the onset of loading as opposed to the assumptions of fracture mechanics approaches. We calibrate the crack onset strain and the damage model based on experimental data reported in the literature. We predict crack density and changes in electrical resistance as a function of the damage induced in the films. We implement our model in the commercial finite element software ABAQUS using a user subroutine UMAT. We obtain fair to good agreement with experiments.

When the brittle heterogeneous material is simulated via lattice models, the quasi-static failure depends on the relative magnitudes of [Formula: see text], the characteristic releasing time of the internal forces of the broken elements and [Formula: see text], the characteristic relaxation time of the lattice, both of which are infinitesimal compared with [Formula: see text], the characteristic loading period. The load–unload (L–U) method is used for one extreme, T elem ≪ T lattice , whereas the force–release (F–R) method is used for the other, T elem ≫ T lattice . For cases between the above two extremes, we develop a new algorithm by combining the L–U and the F–R trial displacement fields to construct the new trial field. As a result, our algorithm includes both L–U and F–R failure characteristics, which allows us to observe the influence of the ratio of [Formula: see text] to [Formula: see text] by adjusting their contributions in the trial displacement field. Therefore, the material dependence of the snap-back instabilities is implemented by introducing one snap-back parameter γ. Although in principle catastrophic failures can hardly be predicted accurately without knowing all microstructural information, effects of γ can be captured by numerical simulations conducted on samples with exactly the same microstructure but different γs. Such a same-specimen-based study shows how the lattice behaves along with the changing ratio of the L–U and F–R components.

Deriving bulk materials with ultra-high mechanical strength from nanometer-sized single metalic crystals depends on the consolidation procedure. We present an accurate molecular dynamics study to quantify microstructure responses to consolidation. Aluminum single crystals with an average size up to 10.7nm were hydrostatically compressed at temperatures up to 900K and pressures up to 5GPa. The consolidated material developed an average grain size that grew exponentially with the consolidation temperature, with a growth rate dependent on the starting average grain size and the consolidation pressure. The evolution of the microstructure was accompanied by a significant reduction in the concentration of defects. The ratio of vacancies to dislocation cores decreased with the average grain size and then increased after reaching a critical average grain size. The deformation mechanisms of poly-crystalline metals can be better understood in the light of the current findings.

In most metals and alloys, the evolution of voids has been generally recognized as the basic failure mechanism. Furthermore, stress triaxiality has been found to influence void growth dramatically. Besides strain intensity, it is understood to be the most important factor that controls the initiation of ductile fracture. We include sensitivity of stress triaxiality in a variational porous plasticity model, which was originally derived from hydrostatic expansion. Under loading conditions rather than hydrostatic deformation, we allow the critical pressure for voids to be exceeded so that the growth due to plasticity becomes dependent on the stress triaxiality. The limitations of the spherical void growth assumption are investigated. Our improved constitutive model is validated through good agreements with experimental data. Its capacity for reproducing realistic failure patterns is also indicated by a numerical simulation of a compact tensile (CT) test.

A micro-machining process becomes increasingly important with the continuous miniaturization of components used in various fields from military to civilian applications. To characterise underlying micromechanics, a 3D finite-element model of orthogonal micro-machining of f.c.c. single crystal copper was developed. The model was implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine VUMAT. Strain-gradient crystal-plasticity and conventional crystal-plasticity theories were used to demonstrate the influence of pre-existing and evolved strain gradients on the cutting process for different combinations of crystal orientations and cutting directions.

We present a variational multiscale constitutive model that accounts for intergranular failure in nanocrystalline fcc metals due to void growth and coalescence in the grain boundary region. Following previous work by the authors, a nanocrystalline material is modeled as a two-phase material consisting of a grain interior phase and a grain boundary affected zone (GBAZ). A crystal plasticity model that accounts for the transition from partial dislocation to full dislocation mediated plasticity is used for the grain interior. Isotropic porous plasticity model with further extension to account for failure due to the void coalescence was used for the GBAZ. The extended model contains all the deformation phases, i.e. elastic deformation, plastic deformation including deviatoric and volumetric plasticity (void growth) followed by damage initiation and evolution due to void coalescence. Parametric studies have been performed to assess the model's dependence on the different input parameters. The model is then validated against uniaxial loading experiments for different materials. Lastly we show the model's ability to predict the damage and fracture of a dog-bone shaped specimen as observed experimentally.

A hybrid parallelization method composed of a coarse-grained genetic algorithm (GA) and fine-grained objective function evaluations is implemented on a heterogeneous computational resource consisting of 16 IBM Blue Gene/P racks, a single x86 cluster node and a high-performance file system. The GA iterator is coupled with a finite-element (FE) analysis code developed in house to facilitate computational steering in order to calculate the optimal impact velocities of a projectile colliding with a polyurea/structural steel composite plate. The FE code is capable of capturing adiabatic shear bands and strain localization, which are typically observed in high-velocity impact applications, and it includes several constitutive models of plasticity, viscoelasticity and viscoplasticity for metals and soft materials, which allow simulation of ductile fracture by void growth. A strong scaling study of the FE code was conducted to determine the optimum number of processes run in parallel. The relative efficiency of the hybrid, multi-level parallelization method is studied in order to determine the parameters for the parallelization. Optimal impact velocities of the projectile calculated using the proposed approach, are reported.

In this work, we present a variational multiscale model for grain growth in face-centered cubic nanocrystalline (nc) metals. In particular, grain-growth-induced stress softening and the resulting relaxation phenomena are addressed. The behavior of the polycrystal is described by a conventional Taylor-type averaging scheme in which the grains are treated as two-phase composites consisting of a grain interior phase and a grain boundary-affected zone. Furthermore, a grain-growth law that captures the experimentally observed characteristics of the grain coarsening phenomena is proposed. To this end, the grain size is not taken as constant and varies according to the proposed stress-driven growth law. Several parametric studies are conducted to emphasize the influence of the grain-growth rule on the overall macroscopic response. Finally, the model is shown to provide a good description of the experimentally observed grain-growth-induced relaxation in nc-copper.