Rose Bengal Labeled Bovine Serum Albumin for Protein Transport Imaging in Subcutaneous Tissues Using Computed Tomography and Fluorescence Microscopy.

Subcutaneous (SC) injection of protein-based therapeutics is a convenient and clinically established drug delivery method. However, progress is needed to increase the bioavailability. Transport of low molecular weight (Mw) biotherapeutics such as insulin and small molecule contrast agents such as lipiodol has been studied using X-ray computed tomography (CT). This analysis, however, does not translate to the investigation of higher Mw therapeutics, such as monoclonal antibodies (mAbs), due to differences in molecular and formulation properties. In this study, an iodinated fluorescein analog rose bengal (RB) was used as a radiopaque and fluorescent label to track the distribution of bovine serum albumin (BSA) compared against unconjugated RB and sodium iodide (NaI) via CT and confocal microscopy following injection into ex vivo porcine SC tissue. Importantly, the high concentration BSA-RB exhibited viscosities more like that of viscous biologics than the small molecule contrast agents, suggesting that the labeled protein may serve as a more suitable formulation for the investigation of injection plumes. Three-dimensional (3D) renderings of the injection plumes showed that the BSA-RB distribution was markedly different from unconjugated RB and NaI, indicating the need for direct visualization of large protein therapeutics using conjugated tags rather than using small molecule tracers. Whereas this proof-of-concept study shows the novel use of RB as a label for tracking BSA distribution, our experimental approach may be applied to high Mw biologics, including mAbs. These studies could provide crucial information about diffusion in SC tissue and the influence of injection parameters on distribution, transport, and downstream bioavailability.

Translating proof-of-concept for platelet slip into improved antithrombotic therapeutic regimens.

Platelets are central to thrombosis. Research at the intersection of biological and physical sciences provides proof-of-concept for shear rate-dependent platelet slip at vascular stenosis and near device surfaces. Platelet slip extends the observed biological "slip-bonds" to the boundary of functional gliding without contact. As a result, there is diminished engagement of the coagulation cascade by platelets at these surfaces. Comprehending platelet slip would more precisely direct antithrombotic regimens for different shear environments, including for percutaneous coronary intervention (PCI). In this brief report we promote translation of the proof-of-concept for platelet slip into improved antithrombotic regimens by: (1) reviewing new supporting basic biological science and clinical research for platelet slip; (2) hypothesizing the principal variables that affect platelet slip; (3) applying the consequent construct model in support of-and in some cases to challenge-relevant contemporary guidelines and their foundations (including for urgent, higher-risk PCI); and (4) suggesting future research pathways (both basic and clinical). Should future research demonstrate, explain and control platelet slip, then a paradigm shift for choosing and recommending antithrombotic regimens based on predicted shear rate should follow. Improved clinical outcomes with decreased complications accompanying this paradigm shift for higher-risk PCI would also result in substantive cost savings.

Interpenetrating Networks of Collagen and Hyaluronic Acid That Serve as In Vitro Tissue Models for Assessing Macromolecular Transport.

High-fidelity preclinical in vitro tissue models can reduce the failure rate of drugs entering clinical trials. Collagen and hyaluronic acid (HA) are major components of the extracellular matrix of many native tissues and affect therapeutic macromolecule diffusion and recovery through tissues. Although collagen and HA are commonly used in tissue engineering, the physical and mechanical properties of these materials are variable and depend highly on processing conditions. In this study, HA was chemically modified and crosslinked via hydrazone bonds to form interpenetrating networks of crosslinked HA (HAX) with collagen (Col). These networks enabled a wide range of mechanical properties, including stiffness and swellability, and microstructures, such as pore morphology and size, that can better recapitulate diverse tissues. We utilized these interpenetrating ColHAX hydrogels as in vitro tissue models to examine macromolecular transport and recovery for early-stage drug screening. Hydrogel formulations with varying collagen and HAX concentrations imparted different gel properties based on the ratio of collagen to HAX. These gels were stable and swelled up to 170% of their original mass, and the storage moduli of the ColHAX gels increased over an order of magnitude by increasing collagen and HA concentration. Interestingly, when HAX concentration was constant and collagen concentration increased, both the pore size and spatial colocalization of collagen and HA increased. HA in the system dominated the ζ-potentials of the gels. The hydrogel and macromolecule properties impacted the mass transport and recovery of lysozyme, ß-lactoglobulin, and bovine serum albumin (BSA) from the ColHAX gels─large molecules were largely impacted by mesh size, whereas small molecules were influenced primarily by electrostatic forces. Overall, the tunable properties demonstrated by the ColHAX hydrogels can be used to mimic different tissues for early-stage assays to understand drug transport and its relationship to matrix properties.

Assessment of Cavitation Intensity in Accelerating Syringes of Spring-Driven Autoinjectors.

PURPOSE: Cavitation is an undesired phenomenon that may occur in certain types of autoinjectors (AIs). Cavitation happens because of rapid changes of pressure in a liquid, leading to the formation of small vapor-filled cavities, which upon collapsing, can generate an intense shock wave that may damage the device container and the protein drug molecules. Cavitation occurs in the AI because of the syringe-drug relative displacement as a result of the syringe's sudden acceleration during needle insertion and the ensuing pressure drop at the bottom of the container. Therefore, it's crucial to analyze the potential effect of cavitation on AI. The goal of the current study is to investigate the effects of syringe and AI design parameters such as air gap size, syringe filling volume, fluid viscosity, and drive spring force (syringe acceleration) on the risk and severity of cavitation. METHODS: A model autoinjector platform is built to record the syringe and cavitation dynamics which we use to estimate the cavitation intensity in terms of extension rate and to study the effects of design parameters on the severity of cavitation. RESULTS: Our results show the generation of an intense shock wave and a high extension rate upon cavitation collapse. The induced extension rate increases with syringe acceleration and filling volume and decreases with viscosity and air gap size. CONCLUSION: The most severe cavitation occurred in an AI device with the larger drive spring force and the syringe of a smaller air gap size filled with a less viscous fluid and a larger filling volume.

The aerodynamics of flying snake airfoils in tandem configuration.

Flying snakes flatten their body to form a roughly triangular cross-sectional shape, enabling lift production and horizontal acceleration. While gliding, they also assume an S-shaped posture, which could promote aerodynamic interactions between the fore and the aft body. Such interactions have been studied experimentally; however, very coarse models of the snake's cross-sectional shape were used, and the effects were measured only for the downstream model. In this study, the aerodynamic interactions resulting from the snake's posture were approximated using two-dimensional anatomically accurate airfoils positioned in tandem to mimic the snake's geometry during flight. Load cells were used to measure the lift and drag forces, and flow field data were obtained using digital particle image velocimetry (DPIV). The results showed a strong dependence of the aerodynamic performance on the tandem arrangement, with the lift coefficients being generally more influenced than the drag coefficients. Flow field data revealed that the tandem arrangement modified the separated flow and the wake size, and enhanced the lift in cases in which the wake vortices formed closer to the models, producing suction on the dorsal surface. The downforce created by the flow separation from the ventral surface of the models at 0 deg angle of attack was another significant factor contributing to lift production. A number of cases showing large variations of aerodynamic performance included configurations close to the most probable posture of airborne flying snakes, suggesting that small postural variations could be used to control the glide trajectory.

The Interface Motion and Hydrodynamic Shear of the Liquid Slosh in Syringes.

PURPOSE: Interface motion and hydrodynamic shear of the liquid slosh during the insertion of syringes upon autoinjector activation may damage the protein drug molecules. Experimentally validated computational fluid dynamics simulations are used in this study to investigate the interfacial motion and hydrodynamic shear due to acceleration and deceleration of syringes. The goal is to explore the role of fluid viscosity, air gap size, syringe acceleration, syringe tilt angle, liquid-wall contact angle, surface tension and fill volume on the interface dynamics caused by autoinjector activation. METHODS: A simplified autoinjector platform submerged in water is built to record the syringe and liquid motion without obstruction of view. The syringe kinematics is imported to the simulations based on OpenFOAM InterIsoFoam solver, which is used to study the effects of various physical parameters. RESULTS: The simulations agree with experiments on the air-liquid interface profile and interface area. The interfacial area and the volume of fluid subject to high strain rate decrease with the solution viscosity, increase with the air gap height, syringe velocity, tilt angle and syringe wall hydrophobicity, and hardly change with the surface tension and liquid column height. The hydrodynamic shear mainly occurs near the syringe wall and entrained bubbles. CONCLUSION: For a given dose of drug solution, the syringe with smaller radius and larger length will generate less liquid slosh. Reducing the air volume and syringe wall hydrophobicity are also helpful to reduce interface area and effective shear. The interface motion is reduced when the syringe axis is aligned with the gravitational direction.

Diastolic Intra-Left Ventricular Pressure Difference During Exercise: Strong Determinant and Predictor of Exercise Capacity in Patients With Heart Failure.

BACKGROUND: Although the enhancement of early-diastolic intra-left ventricular pressure difference (IVPD) during exercise is considered to maintain exercise capacity, little is known about their relationship in heart failure (HF). METHODS AND RESULTS: Cardiopulmonary exercise testing and exercise-stress echocardiography were performed in 50 HF patients (left ventricular [LV] ejection fraction 39 ± 15%). Echocardiographic images were obtained at rest and submaximal and peak exercise. Color M-mode Doppler images of LV inflow were used to determine IVPD. Thirty-five patients had preserved exercise capacity (peak oxygen consumption [VO2] ≥14 mL·kg-1·min-1; group 1) and 15 patients had reduced exercise capacity (group 2). During exercise, IVPD increased only in group 1 (group 1: 1.9 ± 0.9 mm Hg at rest, 4.1 ± 2.0 mm Hg at submaximum, 4.7 ± 2.1 mm Hg at peak; group 2: 1.9 ± 0.8 mm Hg at rest, 2.1 ± 0.9 mm Hg at submaximum, 2.1 ± 0.9 mm Hg at peak). Submaximal IVPD (r = 0.54) and peak IVPD (r = 0.69) were significantly correlated with peak VO2. Peak IVPD determined peak VO2 independently of LV ejection fraction. Moreover, submaximal IVPD could well predict the reduced exercise capacity. CONCLUSION: Early-diastolic IVPD during exercise was closely associated with exercise capacity in HF. In addition, submaximal IVPD could be a useful predictor of exercise capacity without peak exercise in HF patients.

Dogs lap using acceleration-driven open pumping.

Dogs lap because they have incomplete cheeks and cannot suck. When lapping, a dog's tongue pulls a liquid column from the bath, suggesting that the hydrodynamics of column formation are critical to understanding how dogs drink. We measured lapping in 19 dogs and used the results to generate a physical model of the tongue's interaction with the air-fluid interface. These experiments help to explain how dogs exploit the fluid dynamics of the generated column. The results demonstrate that effects of acceleration govern lapping frequency, which suggests that dogs curl the tongue to create a larger liquid column. Comparing lapping in dogs and cats reveals that, despite similar morphology, these carnivores lap in different physical regimes: an unsteady inertial regime for dogs and steady inertial regime for cats.

Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance.

A prominent feature of gliding flight in snakes of the genus Chrysopelea is the unique cross-sectional shape of the body, which acts as the lifting surface in the absence of wings. When gliding, the flying snake Chrysopelea paradisi morphs its circular cross-section into a triangular shape by splaying its ribs and flattening its body in the dorsoventral axis, forming a geometry with fore-aft symmetry and a thick profile. Here, we aimed to understand the aerodynamic properties of the snake's cross-sectional shape to determine its contribution to gliding at low Reynolds numbers. We used a straight physical model in a water tunnel to isolate the effects of 2D shape, analogously to studying the profile of an airfoil of a more typical flyer. Force measurements and time-resolved (TR) digital particle image velocimetry (DPIV) were used to determine lift and drag coefficients, wake dynamics and vortex-shedding characteristics of the shape across a behaviorally relevant range of Reynolds numbers and angles of attack. The snake's cross-sectional shape produced a maximum lift coefficient of 1.9 and maximum lift-to-drag ratio of 2.7, maintained increases in lift up to 35 deg, and exhibited two distinctly different vortex-shedding modes. Within the measured Reynolds number regime (Re=3000-15,000), this geometry generated significantly larger maximum lift coefficients than many other shapes including bluff bodies, thick airfoils, symmetric airfoils and circular arc airfoils. In addition, the snake's shape exhibited a gentle stall region that maintained relatively high lift production even up to the highest angle of attack tested (60 deg). Overall, the cross-sectional geometry of the flying snake demonstrated robust aerodynamic behavior by maintaining significant lift production and near-maximum lift-to-drag ratios over a wide range of parameters. These aerodynamic characteristics help to explain how the snake can glide at steep angles and over a wide range of angles of attack, but more complex models that account for 3D effects and the dynamic movements of aerial undulation are required to fully understand the gliding performance of flying snakes.

Modeling drug transport and absorption in subcutaneous injection of monoclonal antibodies: Impact of tissue deformation, devices, and physiology.

The pharmaceutical industry has experienced a remarkable increase in the use of subcutaneous injection of monoclonal antibodies (mAbs), attributed mainly to its advantages in reducing healthcare-related costs and enhancing patient compliance. Despite this growth, there is a limited understanding of how tissue mechanics, physiological parameters, and different injection devices and techniques influence the transport and absorption of the drug. In this work, we propose a high-fidelity computational model to study drug transport and absorption during and after subcutaneous injection of mAbs. Our numerical model includes large-deformation mechanics, fluid flow, drug transport, and blood and lymphatic uptake. Through this computational framework, we analyze the tissue material responses, plume dynamics, and drug absorption. We analyze different devices, injection techniques, and physiological parameters such as BMI, flow rate, and injection depth. Finally, we compare our numerical results against the experimental data from the literature.

An experimentally validated cavitation inception model for spring-driven autoinjectors.

Cavitation, the formation and collapse of vapor-filled bubbles, poses a problem in spring-driven autoinjectors (AIs). It occurs when the syringe accelerates abruptly during activation, causing pressure fluctuations within the liquid. These bubbles expand and then collapse, generating shock waves that can harm both the device and the drug molecules. This issue stems from the syringe's sudden acceleration when the driving rod hits the plunger. To better understand cavitation in AIs, we explore how design factors like drive spring force, air gap size, and fluid viscosity affect its likelihood and severity. We use a dynamic model for spring-driven autoinjectors to predict and analyze the factors contributing to cavitation initiation and severity. This model predicts the motion of AI components, such as the displacement and velocity of the syringe barrel, and allows us to investigate pressure wave propagation and the subsequent dynamics of cavitation under various operating conditions. We investigated different air gap heights (from 1 to 4 mm), drive spring forces (from 8 to 30 N), and drug solution viscosities (from 1 to 18 cp) to assess cavitation inception based on operational parameters. Results reveal that AI dynamics and cavitation onset and severity strongly depend upon AI operating parameters, namely drive spring force and air gap height. The maximum syringe acceleration increases with spring stiffness and decreases with air gap height; increases in air gap height prolong the time interval of syringe acceleration but diminish the maximum syringe acceleration. From actuation to injection, air gap pressure peaks twice, first due to impact with the rod/plunger and secondly due to the deacceleration event upon injection. The maximum air gap pressure increases with spring stiffness and decreases with air gap height. Results show that maximum cavitation bubble radii and collapse-driven extension rates occur with higher driver spring forces, smaller air gap heights, and less viscous solutions. A cavitation criterion is developed for cavitation in autoinjectors that concludes that cavitation in autoinjectors depends on the peak syringe acceleration.

Novel interpretable Feature set extraction and classification for accurate atrial fibrillation detection from ECGs.

OBJECTIVE: We present a novel method for detecting atrial fibrillation (AFib) by analyzing Lead II electrocardiograms (ECGs) using a unique set of features. METHODS: For this purpose, we used specific signal processing techniques, such as proper orthogonal decomposition, continuous wavelet transforms, discrete cosine transform, and standard cross-correlation, to extract 48 features from the ECGs. Thus, our approach aims to more effectively capture AFib signatures, such as beat-to-beat variability and fibrillatory waves, than traditional metrics. Moreover, our features were designed to be physiologically interpretable. Subsequently, we incorporated an XGBoost-based ECG classifier to train and evaluate it using the publicly available 'Training' dataset of the 2017 PhysioNet Challenge, which includes 'Normal,' 'AFib,' 'Other,' and 'Noisy' ECG categories. RESULTS: Our method achieved an accuracy of 96 % and an F1-score of 0.83 for 'AFib' detection and 80 % accuracy and 0.85 F1-score for 'Normal' ECGs. Finally, we compared our method's performance with the top-classifiers from the 2017 PhysioNet Challenge, namely ENCASE, Random Forest, and Cascaded Binary. As reported by Clifford et al., 2017, these three best performing models scored 0.80, 0.83, 0.82, in terms of F1-score for 'AFib' detection, respectively. CONCLUSION: Despite using significantly fewer features than the competition's state-of-the-art ECG detection algorithms (48 vs. 150-622), our model achieved a comparable F1-score of 0.83 for successful 'AFib' detection. SIGNIFICANCE: The interpretable features specifically designed for 'AFib' detection results in our method's adaptability in clinical settings for real-time arrhythmia detection and is even effective with short ECGs (<10 heartbeats).

Evolution of cardiac tissue and flow mechanics in developing Japanese Medaka.

The effects of pressure drop across cardiac valve cushion regions and endocardial wall strain in the early developmental stages of a teleost species heart are poorly understood. In the presented work, we utilize microscale particle image velocimetry (µPIV) flow measurements of developing medaka hearts from 3 to 14 dpf (n = 5 at each dpf) to quantify the pressure field and endocardial wall strain. Peak pressure drop at the atrioventricular canal (ΔPAVC) and outflow tract (ΔPOFT) show a steady increase with fish age progression. Pressure drops when non-dimensionalized with blood viscosity and heart rate at each dpf are comparable with measurements in zebrafish hearts. Retrograde flows captured at these regions display a negative pressure drop. A novel metric, Endocardial Work (EW), is introduced by analyzing the ΔPAVC-strain curves, which is a non-invasive measure of work required for ventricle filling. EW is a metric that can differentiate between the linear heart stage (< 100 Pa-%), cardiac looped chamber stage (< 300 Pa-%), and the fully formed chamber stage (> 300 Pa-%).

Enhanced echocardiographic assessment of intracardiac flow in congenital heart disease.

BACKGROUND: 4D flow magnetic resonance imaging (4D flow MRI) can assess and measure the complex flow patterns of the right ventricle (RV) in congenital heart diseases, but its limited availability makes the broad application of intracardiac flow assessment challenging. Color Doppler imaging velocity reconstruction from conventional echocardiography is an emerging alternative, but its validity against 4D flow MRI needs to be established. OBJECTIVE: To compare intracardiac flow parameters measured by color Doppler velocity reconstruction (DoVeR) against parameters measured from 4D flow MRI. METHODS: We analyzed 20 subjects, including 7 normal RVs and 13 abnormal RVs (10 with repaired Tetralogy of Fallot, and 3 with atrial-level shunts). Intracardiac flow parameters such as relative pressure difference, vortex strength, total kinetic energy, and viscous energy loss were quantified using DoVeR and 4D flow MRI. The agreement between the two methods was determined by comparing the spatial fields and quantifying the cross-correlation and normalized difference between time-series measurements. RESULTS: The hemodynamic parameters obtained from DoVeR and 4D flow MRI showed similar flow characteristics and spatial distributions. The time evolutions of the parameters were also in good agreement between the two methods. The median correlation coefficient between the time-series of any parameter was between 0.87 and 0.92, and the median L2-norm deviation was between 10% to 14%. CONCLUSIONS: Our study shows that DoVeR is a reliable alternative to 4D flow MRI for quantifying intracardiac hemodynamic parameters in the RV.

Structure, sulfatide binding properties, and inhibition of platelet aggregation by a disabled-2 protein-derived peptide.

Disabled-2 (Dab2) targets membranes and triggers a wide range of biological events, including endocytosis and platelet aggregation. Dab2, through its phosphotyrosine-binding (PTB) domain, inhibits platelet aggregation by competing with fibrinogen for α(IIb)ß(3) integrin receptor binding. We have recently shown that the N-terminal region, including the PTB domain (N-PTB), drives Dab2 to the platelet membrane surface by binding to sulfatides through two sulfatide-binding motifs, modulating the extent of platelet aggregation. The three-dimensional structure of a Dab2-derived peptide encompassing the sulfatide-binding motifs has been determined in dodecylphosphocholine micelles using NMR spectroscopy. Dab2 sulfatide-binding motif contains two helices when embedded in micelles, reversibly binds to sulfatides with moderate affinity, lies parallel to the micelle surface, and when added to a platelet mixture, reduces the number and size of sulfatide-induced aggregates. Overall, our findings identify and structurally characterize a minimal region in Dab2 that modulates platelet homotypic interactions, all of which provide the foundation for rational design of a new generation of anti-aggregatory low-molecular mass molecules for therapeutic purposes.

Automated Layer Identification Method for Skin Tissue Histology Images.

We present a novel automated tissue layer identification method for histology images. The method requires a single user input: the number of layers to be identified. The method incorporates a coarse boundary identification step followed by a refinement step. The coarse identification segments the image into 125 × 125 pixel sub-tiles, computes the histogram of each sub-tile, implements K-means clustering to label each sub-tile, and uses Dijkstra's algorithm to form the layer boundary. The refinement step identifies hair follicles, improves the detail and accuracy of the boundary, and segments the epidermis. The method only uses one color channel (blue). We test our proposed method using eight excised porcine tissue samples taken at different anatomical locations. The layer segmentations demonstrated that the dermis thickness increased, and the subcutaneous thickness decreased moving from breast to belly. Minimal variation in the thickness of the epidermis layer across anatomical locations was observed. Overall, these results highlight the importance of quantifying and assessing the tissue environment. Moreover, we demonstrate that our proposed method was robust across different histology stains and did not depend on color-specific information.

Multi-feature-Based Robust Cell Tracking.

Cell tracking algorithms have been used to extract cell counts and motility information from time-lapse images of migrating cells. However, these algorithms often fail when the collected images have cells with spatially and temporally varying features, such as morphology, position, and signal-to-noise ratio. Consequently, state-of-the-art algorithms are not robust or reliable because they require manual inputs to overcome the cell feature changes. To address these issues, we present a fully automated, adaptive, and robust feature-based cell tracking algorithm for the accurate detection and tracking of cells in time-lapse images. Our algorithm tackles measurement limitations twofold. First, we use Hessian filtering and adaptive thresholding to detect the cells in images, overcoming spatial feature variations among the existing cells without manually changing the input thresholds. Second, cell feature parameters are measured, including position, diameter, mean intensity, area, and orientation, and these parameters are simultaneously used to accurately track the cells between subsequent frames, even under poor temporal resolution. Our technique achieved a minimum of 92% detection and tracking accuracy, compared to 16% from Mosaic and Trackmate. Our improved method allows for extended tracking and characterization of heterogeneous cell behavior that are of particular interest for intravital imaging users.

Material properties of skin in the flying snake Chrysopelea ornata.

In snakes, the skin serves for protection, camouflage, visual signaling, locomotion, and its ability to stretch facilitates large prey ingestion. The flying snakes of the genus Chrysopelea are capable of jumping and gliding through the air, requiring additional functional demands: its skin must accommodate stretch in multiple directions during gliding and, perhaps more importantly, during high-speed, direct-impact landing. Is the skin of flying snakes specialized for gliding? Here, we characterized the material properties of the skin of Chrysopelea ornata and compared them with two nongliding species of colubrid snakes, Thamnophis sirtalis and Pantherophis guttatus, as well as with previously published values. The skin was examined using uniaxial tensile testing to measure stresses, and digital image correlation methods to determine strains, yielding metrics of strength, elastic modulus, strain energy, and extensibility. To test for loading orientation effects, specimens were tested from three orientations relative to the snake's long axis: lateral, circumferential, and ventral. Specimens were taken from two regions of the body, pre- and pos-tpyloric, to test for regional effects related to the ingestion of large prey. In comparison with T. sirtalis and P. guttatus, C. ornata exhibited higher post-pyloric and lower pre-pyloric extensibility in circumferential specimens. However, overall there were few differences in skin material properties of C. ornata compared to other species, both within and across studies, suggesting that the skin of flying snakes is not specialized for gliding locomotion. Surprisingly, circumferential specimens demonstrated lower strength and extensibility in pre-pyloric skin, suggesting less regional specialization related to large prey.

Quantifying Numerical Uncertainty in Background-Oriented Schlieren.

Our study presents and evaluates a method for computing the numerical uncertainty in Background Oriented Schlieren (BOS). We use Richardson extrapolation to assess the uncertainty of numerical integration of density gradients, based on residuals of density results across two grid levels. By integrating this numerical uncertainty with the existing random uncertainty, we obtain the final uncertainty of the density field. We assess the method's effectiveness using synthetic fields with artificial noise. Our error analysis shows that the sharpness of the density gradient significantly affects bias error and the prediction of numerical uncertainty. The prediction of numerical uncertainty corresponds to variations in bias error, particularly when the noise level and wavelength of the flow field are altered. By accounting for the numerical uncertainty, our method achieves up to 91% accuracy in predicting total uncertainty, as measured against the root-mean-square of the total error. We further demonstrate the utility of our methodology by applying it to experimental BOS images. Our proposed approach offers a more accurate understanding of uncertainty estimation in the BOS technique, with implications for future experiments.

Automatic 4D Flow MRI Segmentation Using the Standardized Difference of Means Velocity.

We present a method to automatically segment 4D flow magnetic resonance imaging (MRI) by identifying net flow effects using the standardized difference of means (SDM) velocity. The SDM velocity quantifies the ratio between the net flow and observed flow pulsatility in each voxel. Vessel segmentation is performed using an F-test, identifying voxels with significantly higher SDM velocity values than background voxels. We compare the SDM segmentation algorithm against pseudo-complex difference (PCD) intensity segmentation of 4D flow measurements in in vitro cerebral aneurysm models and 10 in vitro Circle of Willis (CoW) datasets. We also compared the SDM algorithm to convolutional neural network (CNN) segmentation in 5 thoracic vasculature datasets. The in vitro flow phantom geometry is known, while the ground truth geometries for the CoW and thoracic aortas are derived from high-resolution time-of-flight (TOF) magnetic resonance angiography and manual segmentation, respectively. The SDM algorithm demonstrates greater robustness than PCD and CNN approaches and can be applied to 4D flow data from other vascular territories. The SDM to PCD comparison demonstrated an approximate 48% increase in sensitivity in vitro and 70% increase in the CoW, respectively; the SDM and CNN sensitivities were similar. The vessel surface derived from the SDM method was 46% closer to the in vitro surfaces and 72% closer to the in vitro TOF surfaces than the PCD approach. The SDM and CNN approaches both accurately identify vessel surfaces. The SDM algorithm is a repeatable segmentation method, enabling reliable computation of hemodynamic metrics associated with cardiovascular disease.