Purpose To study the feasibility of high-frame-rate (HFR) contrast material-enhanced (CE) ultrasound particle image velocimetry (PIV), or echo PIV, in the abdominal aorta. Materials and Methods Fifteen healthy participants (six men; median age, 23 years [age range, 18-34 years]; median body mass index, 20.3 kg/m [range, 17.3-24.9 kg/m]) underwent HFR CE US. US microbubbles were injected at incremental doses (0.25, 0.5, 0.75, and 1.5 mL), with each dose followed by US measurement to determine the optimal dosage. Different US mechanical index values were evaluated (0.09, 0.06, 0.03, and 0.01) in a diverging wave acquisition scheme. PIV analysis was performed via pairwise cross-correlation of all captured images. Participants also underwent phase-contrast MRI. The echo PIV and phase-contrast MRI velocity profiles were compared via calculation of similarity index and relative difference in peak velocity. Results Visualization of the aortic bifurcation with HFR CE US was successful in all participants. Optimal echo PIV results were achieved with the lowest contrast agent dose of 0.25 mL in combination with the lowest mechanical indexes (0.01 or 0.03). Substantial bubble destruction occurred at higher mechanical indexes (≥0.06). Flow patterns were qualitatively similar in the echo PIV and MR images. The echo PIV and MRI velocity profiles showed good agreement (similarity index, 0.98 and 0.99; difference in peak velocity, 8.5% and 17.0% in temporal and spatial profiles, respectively). Conclusion Quantification of blood flow in the human abdominal aorta with US particle image velocimetry (echo PIV) is feasible. Use of echo PIV has potential in the clinical evaluation of aortic disease. © RSNA, 2018 Online supplemental material is available for this article.
Porosity, pore size and pore interconnectivity are critical factors for cellular infiltration into electrospun scaffolds. This study utilized dual electrospinning with sacrificial fiber extraction to produce scaffolds with engineered porosity and mechanical properties. Subsequently, scaffolds were covalently grafted with heparin, a known anti-coagulant with growth-factor binding properties. We hypothesized that the tissue ingrowth would correlate positively with the porosity of the scaffolds. Pellethane® (PU) was spun simultaneously with poly(ethylene oxide) (PEO, subsequently extracted). Low, medium and high porosity scaffolds and heparinized versions of each were characterized and implanted in vivo for evaluation of cellular infiltration and inflammation subcutaneously in male Wistar rats (7,14 and 28 days, n = 6). Average pore-size for low (76 ± 0.2%), medium (83 ± 0.5%) and high (90 ± 1.0%) porosity scaffolds was 4.0 ± 2.3 µm, 9.9 ± 4.2 µm and 11.1 ± 5.5 µm (p < 0.0001). Heparinization resulted in increased fiber diameter (3.6 ± 1.1 µm vs. 1.8 ± 0.8 µm, p < 0.0001) but influenced neither pore-size (p = 0.67) nor porosity (p = 0.27). Cellular infiltration for low, medium and high porosity scaffolds reached 33 ± 7%, 77 ± 20% and 98 ± 1% of scaffold width, respectively, by day 28 of implantation (p < 0001); heparinization did not affect infiltration (p = 0.89). The ultimate tensile strength (UTS) and Young's modulus (E ) of the constructs increased linearly with increasing PU fiber fraction (UTS: r = 0.97, p < 0.0001, E : r = 0.76, p < 0.0001) and heparinization resulted in decreased strength but increased stiffness compared to non-heparinized scaffolds. Increased PEO to PU fraction in the scaffold resulted in predictable losses to mechanical strength and improvements to cellular infiltration, which could make PEO to PU fraction a useful optimization parameter for small diameter vascular grafts. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1559-1572, 2017.
Echocardiographic determination of multicomponent blood flow dynamics in the left ventricle remains a challenge.In this paper, we compare contrast enhanced, high frame rate (HFR) (1000 frames/s) echo-particle image velocimetry (ePIV) against optical particle image velocimetry (oPIV, gold standard), in a realistic left ventricular (LV) phantom. We find that ePIV compares well to oPIV, even for the high velocity inflow jet (normalized RMSE = 9% ± 1%). In addition, we perform the method of proper orthogonal decomposition, to better qualify and quantify the differences between the two modalities. We show that ePIV and oPIV resolve very similar flow structures, especially for the lowest order mode with a cosine similarity index of 86%. The coarser resolution of ePIV does result in increased variance and blurring of smaller flow structures when compared to oPIV. However, both modalities are in good agreement with each other for the modes that constitute the bulk of the kinetic energy. We conclude that HFR ePIV can accurately estimate the high velocity diastolic inflow jet and the high energy flow structures in an LV setting. Index Terms-Echo-particle image velocimetry (ePIV), echocardiography, high frame rate (HFR) imaging, left ventricular (LV) flow, ultrasound contrast agents (UCAs), ultrasound imaging velocimetry (UIV).
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