X-ray PIV measurement of blood flow in deep vessels of a rat: An in vivo feasibility study

Speckle-Tracking Strain Analysis for Mapping Spatiotemporal Contractility of Induced Pluripotent Stem Cell (iPSC)-Derived Cardiomyocytes

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) hold tremendous potential for cardiovascular disease modeling, drug screening, personalized medicine, and pathophysiology studies. The availability of a robust protocol and functional assay for studying phenotypic behavior of hiPSC-CMs is essential for establishing an in vitro disease model. Many heart diseases manifest due to changes in the mechanical strain of cardiac tissue. Therefore, non-invasive evaluation of the contractility properties of hiPSC-CMs remains crucial to gain an insight into the pathogenesis of cardiac diseases. Speckle tracking-based strain analysis is an efficient non-invasive method that uses video microscopy and image analysis of beating hiPSC-CMs for quantitative evaluation of mechanical contractility properties. This article presents step-by-step protocols for extracting quantitative contractility properties of an hiPSC-CM system obtained from five members of a family, of whom three were affected by DiGeorge syndrome, using speckle tracking-based strain analysis. The hiPSCs from the family members were differentiated and purified into hiPSC-CMs using metabolic selection. Time-lapse images of hiPSC-CMs were acquired using high-spatial-resolution and high-time-resolution phase-contrast video microscopy. Speckled images were characterized by evaluating the cross-correlation coefficient, speckle size, speckle contrast, and speckle quality of the images. The optimum parameters of the speckle tracking algorithm were determined by performing sensitivity analysis concerning computation time, effective mapping area, average contraction velocity, and strain. Furthermore, the hiPSC-CM response to adrenaline was evaluated to validate the sensitivity of the strain analysis algorithm. Then, we applied speckle tracking-based strain analysis to characterize the dynamic behavior of patient-specific hiPSC-CMs from the family members affected/unaffected by DiGeorge syndrome. Here, we report an efficient and manipulation-free method to analyze the contraction displacement vector and velocity field, contraction-relaxation strain rate, and contractile cycles. Implementation of this method allows for quantitative analysis of the contractile phenotype characteristics of hiPSC-CMs to distinguish possible cardiac manifestation of DiGeorge syndrome. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Differentiation of iPSCs into iPSC-derived cardiomyocytes (iPSC-CMs) and metabolic selection of differentiated iPSC-CMs Support Protocol 1: Culture, maintenance, and expansion of human iPSCs Support Protocol 2: Immunohistochemistry of iPSC-CMs Basic Protocol 2: Time-lapse speckle imaging of iPSC-CMs and speckle quality characterization Support Protocol 3: Enhancement of local contrast of videos by applying contrast limited adaptive histogram equalization (CLAHE) to all frames Support Protocol 4: Evaluation of average speckle size Support Protocol 5: Evaluation of average speckle contrast Support Protocol 6: Determination of relative peak height, Pc(x), of consecutive images acquired from video microscopy of iPSC-CMs Basic Protocol 3: Speckle tracking-based analysis of beating iPSC-CMs Support Protocol 7: Validation of sensitivity of the speckle tracking analysis for mapping the contractility of iPSC-CMs Basic Protocol 4: Data extraction, visualization, and mapping of contractile cycles of iPSC-CMs.

Measurement in opaque flows: a review of measurement techniques for dispersed multiphase flows

A review is presented of measurement techniques to characterise dispersed multiphase flows, which are not accessible by means of conventional optical techniques. The main issues that limit the accuracy and effectiveness of optical techniques are briefly discussed: cross-talk, a reduced signal-to-noise ratio, and (biased) data drop-out. Extensions to the standard optical techniques include the use of fluorescent tracers, refractive index matching, ballistic imaging, structured illumination, and optical coherence tomography. As the first non-optical technique, a brief discussion of electrical capacitance tomography is given. While truly non-invasive, it suffers from a low resolving power. Ultrasound-based techniques have rapidly evolved from Doppler-based profiling to recent 2D approaches using feature tracking. The latter is also suitable for time-resolved flow studies. Magnetic resonance velocimetry can provide time-averaged velocity fields in 3D for the continuous phase. Finally, X-ray imaging is demonstrated to be an important tool to quantify local gas fractions. While potentially very powerful, the impact of the techniques will depend on the development of acquisition and measurement protocols for fluid mechanics, rather than for clinical imaging. This requires systematic development, aided by careful validation experiments. As theoretical predictions for multiphase flows are sparse, it is important to formulate standardised 'benchmark' flows to enable this validation.

Detection of arterial wall abnormalities via Bayesian model selection

Patient-specific modelling of haemodynamics in arterial networks has so far relied on parameter estimation for inexpensive or small-scale models. We describe here a Bayesian uncertainty quantification framework which makes two major advances: an efficient parallel implementation, allowing parameter estimation for more complex forward models, and a system for practical model selection, allowing evidence-based comparison between distinct physical models. We demonstrate the proposed methodology by generating simulated noisy flow velocity data from a branching arterial tree model in which a structural defect is introduced at an unknown location; our approach is shown to accurately locate the abnormality and estimate its physical properties even in the presence of significant observational and systemic error. As the method readily admits real data, it shows great potential in patient-specific parameter fitting for haemodynamical flow models.

Polymeric perfluorocarbon nanoemulsions are ultrasound-activated wireless drug infusion catheters

Catheter-based intra-arterial drug therapies have proven effective for a range of oncologic, neurologic, and cardiovascular applications. However, these procedures are limited by their invasiveness and relatively broad drug spatial distribution. The ideal technique for local pharmacotherapy would be noninvasive and would flexibly deliver a given drug to any region of the body with high spatial and temporal precision. Combining polymeric perfluorocarbon nanoemulsions with existent clinical focused ultrasound systems could in principle meet these needs, but it has not been clear whether these nanoparticles could provide the necessary drug loading, stability, and generalizability across a range of drugs, beyond a few niche applications. Here, we develop polymeric perfluorocarbon nanoemulsions into a generalized platform for ultrasound-targeted delivery of hydrophobic drugs with high potential for clinical translation. We demonstrate that a wide variety of drugs may be effectively uncaged with ultrasound using these nanoparticles, with drug loading increasing with hydrophobicity. We also set the stage for clinical translation by delineating production protocols that are scalable and yield sterile, stable, and optimized ultrasound-activated drug-loaded nanoemulsions. Finally, we exhibit a new potential application of these nanoemulsions for local control of vascular tone. This work establishes the power of polymeric perfluorocarbon nanoemulsions as a clinically-translatable platform for efficacious, noninvasive, and localized ultrasonic drug uncaging for myriad targets in the brain and body.

Interdigitated microelectronic bandage augments hemostasis and clot formation at low applied voltage in vitro and in vivo

Hemorrhage or uncontrolled bleeding can arise either due to a medical condition or from a traumatic injury and are typically controlled with the application of a hemostatic agent. Hemostatic agents are currently derived from animal or human products, which carry risks of blood borne infections and immune dysregulation. Therefore, the need exists for novel biomedical therapies not derived from animal or human products to achieve hemostasis. Accordingly, we created an interdigitated microelectronic bandage that applies low voltage electrical stimulation to an injury site, resulting in faster clot formation without excessive heating, accelerated fibrin formation, and hemostasis overall. Our interdigitated microelectronic bandage found fibrin formed 1.5× faster in vitro. In vivo, total cessation of bleeding was 2.5× faster, resulting in 2× less blood loss. Electricity has been used in medical applications such as defibrillation, cauterization, and electrosurgery, but scant research has focused on hemostasis. Here we report a novel surface treatment using an interdigitated microelectronic device that creates rapid hemostasis in both in vitro and in vivo bleeding models with low applied voltages, representing a new and novel class of hemostatic agents that are electrically-based.

Enhancement of measurement accuracy of X-ray PIV in comparison with the micro-PIV technique

The X-ray PIV (particle image velocimetry) technique has been used as a non-invasive measurement modality to investigate the haemodynamic features of blood flow. However, the extraction of two-dimensional velocity field data from the three-dimensional volumetric information contained in X-ray images is technically unclear. In this study, a new two-dimensional velocity field extraction technique is proposed to overcome technological limitations. To resolve the problem of finding a correction coefficient, the velocity field information obtained by X-ray PIV and micro-PIV techniques for disturbed flow in a concentric stenosis with 50% severity was quantitatively compared. Micro-PIV experiments were conducted for single-plane and summation images, which provide similar positional information of particles as X-ray images. The correction coefficient was obtained by establishing the relationship between velocity data obtained from summation images (V_S) and centre-plane images (V_C). The velocity differences between V_S and V_C along the vertical and horizontal directions were quantitatively analysed as a function of the geometric angle of the test model for applying the present two-dimensional velocity field extraction technique to a conduit of arbitrary geometry. Finally, the two-dimensional velocity field information at arbitrary positions could be successfully extracted from X-ray images by using the correction coefficient and several velocity parameters derived from V_S.

Array-source X-ray velocimetry

X-ray velocimetry (XV) has shown promise for investigations into various dynamic biological systems, including the motion of lungs and the flow of blood. Prior research in the field of XV has highlighted the need for both high spatial resolution to resolve features for tracking, and temporal resolution for accurate velocity measurement. In X-ray imaging systems, enhancement of spatial and temporal resolution requires a small focal spot size and high power output respectively, increasing anode power density requirements. In this paper, we present a multi-source XV regime whereby simultaneously illuminating a sample with multiple sources of small focal spot size, overall illumination can be increased whilst maintaining minimal source blurring without increasing power density requirements. Through a series of simulations, we demonstrate the capability for multi-source systems under various practical constraints, such as focal spot size and power density, to provide increased accuracy compared to single source systems.

Divergence Compensatory Optical Flow Method for Blood Velocimetry

Detailed blood velocity map in the vascular system can be obtained by applying the optical flow method (OFM) in processing fluoroscopic digital subtracted catheter angiographic images; however, there are still challenges with the accuracy of this method. In the present study, a divergence compensatory optical flow method (DC-OFM), in which a nonzero divergence of velocity is assumed due to the finite resolution of the image, was explored and applied to the digital subtraction angiography (DSA) images of blood flow. The objective of this study is to examine the applicability and evaluate the accuracy of DC-OFM in assessing the blood flow velocity in vessels. First, an Oseen vortex flow was simulated on the standard particle image to generate an image pair. Then, the DC-OFM was applied on the particle image pair to recover the velocity field for validation. Second, DSA images of intracranial arteries were used to examine the accuracy of the current method. For each set of images, the first image is the in vivo DSA image, and the second image is generated by superimposing a given flow field. The recovered velocity map by DC-OFM agrees well with the exact velocity for both the particle images and the angiographic images. In comparison with the traditional OFM, the present method can provide more accurate velocity estimation. The accuracy of the velocity estimation can also be improved by implementing preprocess techniques including image intensification, Gaussian filtering, and "image-shift."

In vivo measurement of hemodynamic information in stenosed rat blood vessels using X-ray PIV

Measurements of the hemodynamic information of blood flows, especially wall shear stress (WSS), in animal models with circulatory vascular diseases (CVDs) are important to understand the pathological mechanism of CVDs. In this study, X-ray particle image velocimetry (PIV) with high spatial resolution was applied to obtain velocity field information in stenosed blood vessels with high WSS. 3D clips fabricated with a 3D printer were applied to the abdominal aorta of a rat cadaver to induce artificial stenosis in the real blood vessel of an animal model. The velocity and WSS information of blood flows in the stenosed vessel were obtained and compared at various stenosis severities. In vivo measurement was also conducted by fastening a stenotic clip on a live rat model through surgical intervention to reduce the flow rate to match the limited temporal resolution of the present X-ray PIV system. Further improvement of the temporal resolution of the system might be able to provide in vivo measurements of hemodynamic information from animal disease models under physiological conditions. The present results would be helpful for understanding the relation between hemodynamic characteristics and the pathological mechanism in animal CVD models.