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Phase‐field methods are attractive for simulating the mechanical failure of geometrically complex porous microstructures described by 2D/3D x‐ray μ$$ \mu $$CT images in subsurface (e.g., CO 2$$ {}_2 $$ storage) and manufacturing (e.g., Li‐ion battery) applications. They capture the nucleation, growth, and branching of fractures without prior knowledge of the propagation path or having to remesh the domain. Their drawback lies in the high computational cost for the typical domain sizes encountered in practice. We present a multiscale preconditioner that significantly accelerates the convergence of Krylov solvers in computing solutions of linear(ized) systems arising from the sequential discretization of the momentum and crack‐evolution equations in phase‐field methods. The preconditioner is an algebraic reformulation of a recent pore‐level multiscale method (PLMM) by the authors and consists of a global preconditioner MG$$ {\mathrm{M}}_{\mathrm{G}} $$ and a local smoother ML$$ {\mathrm{M}}_{\mathrm{L}} $$. Together, MG$$ {\mathrm{M}}_{\mathrm{G}} $$ and ML$$ {\mathrm{M}}_{\mathrm{L}} $$ attenuate low‐ and high‐frequency errors simultaneously. The proposed MG$$ {\mathrm{M}}_{\mathrm{G}} $$, used in the momentum equation only, is a simplification of a recent variant proposed by the authors that is much cheaper and easier to deploy in existing solvers. The smoother ML$$ {\mathrm{M}}_{\mathrm{L}} $$, used in both the momentum and crack‐evolution equations, is built such that it is compatible with MG$$ {\mathrm{M}}_{\mathrm{G}} $$ and more robust and efficient than black‐box smoothers like ILU(k$$ k $$). We test MG$$ {\mathrm{M}}_{\mathrm{G}} $$ and ML$$ {\mathrm{M}}_{\mathrm{L}} $$ systematically for static‐ and evolving‐crack problems on complex 2D/3D porous microstructures, and show that they outperform existing algebraic multigrid solvers. We also probe different strategies for updating MG$$ {\mathrm{M}}_{\mathrm{G}} $$ as cracks evolve and show the associated cost can be minimized if MG$$ {\mathrm{M}}_{\mathrm{G}} $$ is updated adaptively and infrequently. Both MG$$ {\mathrm{M}}_{\mathrm{G}} $$ and ML$$ {\mathrm{M}}_{\mathrm{L}} $$ are scalable on parallel machines and can be implemented non‐intrusively in existing codes. [ABSTRACT FROM AUTHOR]

To explore the correlation between the typical findings of dynamic contrast-enhanced computed tomography (DCE-CT) and tumoral angiogenesis (microvessel density [MVD] and vascular endothelial growth factor [VEGF]) in adenomas and nonadenomas such that the enhancement mechanism of DCE-CT in adrenal masses can be explained more precisely. Forty-two patients with 46 adrenal masses confirmed by surgery and pathology were included in the study; these masses included 23 adenomas, 18 nonadenomas, and 5 hyperplastic nodules. The findings of DCE-CT and angiogenesis in adrenal masses were studied. The features of DCE-CT in adenomas and nonadenomas were evaluated to determine whether the characteristics of DCE-CT in adrenal masses were closely correlated with tumoral angiogenesis. Adrenal adenomas were significantly different from nonadenomas in the time density curve and the mean percentage of enhancement washout at the 7-minute delay time in DCE-CT. The mean MVD and VEGF expression exhibited significant differences between the rapid washout group (types A and C) and the slow washout group (types B, D, and E) and between the relative washout (Washr) ≥34% and the absolute washout (Washa) ≥43% on the 7-minute enhanced CT scans (P=0.000). Adenomas were suggested when adrenal masses presented as types A and C, and/or the Washr ≥34%, and/or the Washa ≥43%, and the opposite was suggested for nonadenomas. These results showed a close correlation between the characteristics of DCE-CT and both MVD and VEGF expression in adrenal masses. There was also a significant difference in MVD and VEGF expression between adenomas and nonadenomas. In conclusion, MVD and VEGF expression are two important pathological factors that play important roles in the characterization of DCE-CT in adrenal masses because they cause different time density curve types, the Washr and the Washa for adrenal adenomas and nonadenomas.

This study was performed to evaluate the findings including the time density curve (TD curve), the relative percentage of enhancement washout (Washr) and the absolute percentage of enhancement washout (Washa) at dynamic contrast-enhanced computed tomography (DCE-CT) in 70 patients with 79 adrenal masses (including 44 adenomas and 35 nonadenomas) confirmed histopathologically and/or clinically. The results demonstrated that the TD curves of adrenal masses were classified into 5 types, and the type distribution of the TD curves was significantly different between adenomas and nonadenomas. Types A and C were characteristic of adenomas, whereas types B, D and E were features of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma based on the TD curves were 93%, 80% and 87%, respectively. Furthermore, when myelolipomas were excluded, the specificity and accuracy for adenoma were 90% and 92%, respectively. The Washr and the Washa values for the adenomas were higher than those for the nonadenomas. The diagnostic efficiency for adenoma was highest at 7-min delay time at DCE-CT; Washr was more efficient than Washa. Washr ≥34% and Washa ≥43% were both suggestive of adenomas and, on the contrary, suspicious of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma were 84%, 77% and 81%, respectively. When myelolipomas were precluded, the diagnostic specificity and accuracy were 87% and 85%, respectively. Therefore, DCE-CT aids in characterization of adrenal tumors, especially for lipid-poor adenomas which can be correctly categorized on the basis of TD curve combined with the percentage of enhancement washout.

AimTo investigate cyclo (Arg-Gly-Asp-D-Phe-Lys) peptide (RGD)-modified PEGylated dendrimer-entrapped gold nanoparticles (PEGylated Au DENPs-RGD) for targeted computed tomography (CT) imaging of breast carcinomas.Materials & methodsPEGylated Au DENPs-RGD were synthesized and characterized. Then, the PEGylated Au DENPs-RGD for targeted CT imaging were investigated using the MDA-MB-435 cell line, an integrin-rich breast carcinoma cells, and mice with MDA-MB-435 xenograft tumors. Finally, silver enhancement staining and integrin αvβ3 immunohistochemistry of the tumors were performed.ResultsThe synthesized PEGylated Au DENPs-RGD were spherical, water dispersible and biocompatible nanoprobes with a gold nanoparticle core size of 2.8 nm. Due to the presence of the Au nanoparticles, the PEGylated Au DENPs-RGD displayed a higher x-ray attenuation intensity than Omnipaque at the same Au or I concentrations. The conjugated RGD ligand can specifically identify and target overexpressed integrin receptors on MDA-MB-435 cells. After intravenous injection, these nanoprobes accumulated in the targeted area of mice with MDA-MB-435 xenograft tumors, which enabled the tumor to be detected by CT imaging. The histological results confirmed the imaging results.ConclusionThe PEGylated Au DENPs-RGD can be used as targeted nanoprobes with good biocompatibility for targeted CT imaging and diagnosis of integrin-positive tumors.

PurposeMagnetization transfer (MT) MRI can be effective for the diagnosis of a broad range of fibrotic diseases, including liver fibrosis. However, respiratory motion, a major source of artifacts in thoracic and abdominal MR imaging, can obscure important anatomic structures, making diagnosis difficult. In this study, we explored the potential to combine free-breathing (FB) respiratory self-gating (RSG) methods with MT saturation for FB MT ratio (MTR) measurements of abdominal organs.MethodsA respiratory self-gated multiple-gradient recalled echo sequence with MT presaturation (RSG-MT GRE) was developed and applied in a series of seven normal volunteers. We compared the MTR values of liver, pancreas, kidney, spleen, and posterior paraspinal muscle measured using our RSG-MT GRE sequence and a conventional MT GRE sequence.ResultsRSG consistently reduced motion artifacts within MT-weighted images acquired during FB, improved the accuracy of FB MTR measurements, and produced comparable MTRs to breath-holding MTR measurements.ConclusionRSG approaches may offer to improve the utility of MT-weighted imaging methods for the assessment of fibrotic diseases and tumor desmoplasia in abdominal organs.

AimTo test the hypothesis that MRI can monitor intraportal vein (IPV) transcatheter delivery of clinically applicable heparin-protamine-ferumoxytol (HPF) nanocomplex-labeled natural killer (NK) cells to liver tumor.Materials & methodsLiver tumor rat models underwent catheterization for IPV infusion of HPF-labeled NK cells (NK-92MI cell line). MRI measurements within tumor and adjacent liver tissues were compared pre- and post-NK cell infusion. Histology studies were used to identify NK cells in the target tumors.ResultsFor first time, we demonstrated that MRI tracks HPF-labeled NK cells migration within liver following IPV delivery.ConclusionIPV transcatheter infusion permitted selective delivery of NK cells to liver tissues and MRI allowed tracking NK cell biodistributions within the tumors.

Selective laser melted (SLMed) AlSi10Mg alloys usually fail before necking during tensile tests, which results in inadequate ductility. To overcome this problem, here we introduced Al4C3 nanorods into the primary Al cells of SLMed AlSi10Mg via in-situ chemical reaction. Tensile tests revealed that those in-cell Al4C3 nanorods not only increased the strain-hardening ability of SLMed AlSi10Mg but also delayed the fracture beyond necking. Consequently, 15% of tensile strength increase and 78% of ductility increase were achieved simultaneously. Post-tensile TEM analysis revealed that those in-cell Al4C3 nanorods pinned and accumulated dislocations within cells and thus alleviated stress concentration along cell boundaries. Al4C3 nanorods were introduced into the primary Al cells of selective laser melted AlSi10Mg via in-situ chemical reaction, which enhanced tensile strength and ductility simultaneously. [ABSTRACT FROM AUTHOR]

The shifted fracture method (SFM) is an embedded method that enables sharp crack representations while using mesh‐fitted data structures. In the SFM, the true crack is embedded in the computational grid, but the crack interface conditions are approximated by, or shifted to, a surrogate crack composed of element boundaries (i.e., edges/faces in two/three dimensions). This avoids enriched degrees‐of‐freedom and cut elements, so that data structures and geometrical treatment are much simpler, while still maintaining mesh‐independent and accurate crack approximations. This article presents a continuous‐discontinuous model of fracture based on blending a phase‐field (PF) model with the SFM. The PF tracks the evolution of cracks inside a numerical fracture processing zone: diffuse cracks initiate, propagate, branch, and merge according to the field equations of energy minimization; no ad‐hoc criteria are needed. The PF damage variable is then used to define the geometry of the true crack. With computational efficiency in mind, the PF model is only solved in subdomains where additional crack growth is expected and the SFM representation is used elsewhere. The efficiency and accuracy of the proposed approach in capturing complex crack patterns are illustrated by a representative set of two‐dimensional numerical examples. [ABSTRACT FROM AUTHOR]

Summary: We propose a new embedded finite element method to simulate partial differential equations over domains with internal interfaces. Our approach belongs to the family of surrogate/approximate interface methods and relies on the idea of shifting the location and value of jump interface conditions. This choice has the goal of preserving optimal convergence rates while avoiding small cut cells and related problematic issues, typical of traditional embedded methods. The proposed approach is accurate, robust, efficient, and simple to implement. We apply this concept to internal interface computations in the context of the mixed Poisson problem, also known as the Darcy flow problem. An extensive set of numerical tests is provided to demonstrate the performance of the proposed approach. [ABSTRACT FROM AUTHOR]

Background: Breast diffusion kurtosis imaging (DKI) is a novel MRI technique to assess breast cancer but the effectivity still remains to be improved.Purpose: To investigate the performance of whole-volume histogram parameters derived from a DKI model for differentiating benign and malignant breast lesions.Study Type: Retrospective.Population: In all, 120 patients with breast lesions (62 malignant, 58 benign).Sequence: DKI sequence with seven b-values (0, 500, 1000, 1500, 2000, 2500, and 3000 s/mm2 ) and DWI sequence with two b-values (0 and 1000 s/mm2 ) on 3.0T MRI.Assessment: Histogram parameters of the DKI model (K and D) and the DWI model (ADC), including the minimum, maximum, mean, percentile values (25th, 50th, 75th, and 95th), standard deviation, kurtosis and skewness, were calculated by two radiologists for the whole lesion volume.Statistical Tests: Student's t-test was used to compare malignant and benign lesions. The diagnostic performances were evaluated by receiver operating characteristic (ROC) analysis.Results: Kmax , Dmin , and ADCmin had the highest area under the curve (AUC) (0.875, 0.830, and 0.847, respectively), sensitivity (85.5%, 74.2%, and 77.4%, respectively), and accuracy (85.0%, 79.2%, and 81.7%, respectively) in their individual histogram parameter groups, and Kmax was found to outperform Dmin and ADCmin . ADC histogram parameters (from ADCmin to ADCsd ) were significantly lower than D histogram parameters in all groups.Data Conclusion: Kmax , Dmin , and ADCmin were found to be better metrics than the corresponding average values for differentiating benign from malignant tumors. Histogram parameters derived from the DKI model provided more information and had better diagnostic performance than ADC parameters derived from the DWI model.Level Of Evidence: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:627-634. [ABSTRACT FROM AUTHOR]