Constraining OCT with Knowledge of Device Design Enables High Accuracy Hemodynamic Assessment of Endovascular Implants

Background

Stacking cross-sectional intravascular images permits three-dimensional rendering of endovascular implants, yet introduces between-frame uncertainties that limit characterization of device placement and the hemodynamic microenvironment. In a porcine coronary stent model, we demonstrate enhanced OCT reconstruction with preservation of between-frame features through fusion with angiography and a priori knowledge of stent design.

Methods and Results

Strut positions were extracted from sequential OCT frames. Reconstruction with standard interpolation generated discontinuous stent structures. By computationally constraining interpolation to known stent skeletons fitted to 3D ‘clouds’ of OCT-Angio-derived struts, implant anatomy was resolved, accurately rendering features from implant diameter and curvature (n = 1 vessels, r² = 0.91, 0.90, respectively) to individual strut-wall configurations (average displacement error ~15 μm). This framework facilitated hemodynamic simulation (n = 1 vessel), showing the critical importance of accurate anatomic rendering in characterizing both quantitative and basic qualitative flow patterns. Discontinuities with standard approaches systematically introduced noise and bias, poorly capturing regional flow effects. In contrast, the enhanced method preserved multi-scale (local strut to regional stent) flow interactions, demonstrating the impact of regional contexts in defining the hemodynamic consequence of local deployment errors.

Conclusion

Fusion of planar angiography and knowledge of device design permits enhanced OCT image analysis of in situ tissue-device interactions. Given emerging interests in simulation-derived hemodynamic assessment as surrogate measures of biological risk, such fused modalities offer a new window into patient-specific implant environments.     

Future challenges in coupled C–N–P cycle models for terrestrial ecosystems under global change: a review

Climate change has consequences for terrestrial functioning, but predictions of plant responses remain uncertain because of the gaps in the representation of nutrient cycles and C–N–P interactions in ecosystem models. Here, we review the processes that are included in ecosystem models, but focus on coupled C–N–P cycle models. We highlight important plant adjustments to climate change, elevated atmospheric CO₂, and/or nutrient limitations that are currently not—or only partially—incorporated in ecosystem models by reviewing experimental studies and compiling data. Plant adjustments concern C:N:P stoichiometry, photosynthetic capacity, nutrient resorption rates, allocation patterns, symbiotic N₂ fixation and root exudation (phosphatases, carboxylates) and the effect of root exudation on nutrient mobilization in the soil rhizosphere (P solubilization, biochemical mineralization of organic P and priming effect). We showed that several plant adjustments could be formulated and calibrated using existing experimental data in the literature. Finally, we proposed a roadmap for future research because improving ecosystem models necessitate specific data and collaborations between modelers and empiricists.     

Intermediate habitat associations by hybrids may facilitate genetic introgression in a songbird

Hybridization or the interbreeding of genetically discrete populations or species can occur where ranges of genetically distinct units overlap. Golden‐winged warblers Vermivora chrysoptera, a species that has been in steady decline for decades, highlight the potential population‐level consequences of hybridization. A major factor implicated in their decline is hybridization with their sister species, the blue‐winged warbler Vermivora cyanoptera, which has likely been exacerbated by historic and current land‐use practices. We examined habitat associations of golden‐winged and blue‐winged warblers, phenotypic hybrids, and cryptic hybrids (i.e. mismatch between plumage phenotype and genotype as identified by mitochondrial DNA) in an area of relatively recent range overlap and hybridization in northern New York, USA. To explore the robustness of these results, we then compared the patterns from New York with habitat associations from the central Pennsylvanian Appalachian Mountains where blue‐winged warblers either do not occur or are in very low abundance, yet cryptic golden‐winged warbler hybrids are present. From 2008 to 2011, we captured 122 birds in New York and 28 in Pennsylvania and collected blood samples, which we used to determine maternal ancestry. For each bird captured, we measured territory‐level (50‐m radius circles) habitat, and later used remote‐sensing data to quantify habitat on the territories and in surrounding areas (100‐, 250‐, and 500‐m radius circles). In New York, golden‐winged warblers occupied structurally heterogeneous territories surrounded by homogeneously structured, contiguous deciduous forest, far from urban areas. Blue‐winged warblers showed opposite associations, and hybrids’ habitat associations were typically intermediate. In Pennsylvania, the habitat associations of golden‐winged warblers and their cryptic hybrids were remarkably similar to those in New York. These findings suggest that patterns of habitat occupancy by hybrids may promote contact with golden‐winged warblers and thus likely facilitate genetic introgression, even in areas where the parental species are not sympatric.     

Can the modeling for simplification of a dental implant surface affect the accuracy of 3D finite element analysis?

The aim of this study was to assess stress/strain of different implant modeling simplifications by 3D-FEA. Three variation of external hexagon implant (Ø3.75?×?10 mm) supporting one molar crown were simulated: A (no threads); B (slightly threads simplification); C (original design). 200 N (axial) and 100 N (oblique) were applied. Cortical bone was evaluated by maximum principal stress and microstrain qualitatively and quantitatively (ANOVA and Tukey post hoc (p < 0.05)). Higher stress levels (p < 0.05) were observed in model A. Models B and C presented similar stress transmission. It was possible to conclude that slightly simplification should be used for studies evaluating stress transferring for bone tissue.