Numerical study for blood flow in pulmonary arteries after repair of tetralogy of Fallot

Morphometrics predicts the differential regurgitant fraction in bilateral pulmonary arteries of patients with repaired tetralogy of fallot

In patients with repaired tetralogy of Fallot (rTOF), the regurgitant fraction (RF) in left pulmonary artery (LPA) and right pulmonary artery (RPA) is usually unequal. The morphometrics may play a crucial role in this RF discrepancy. Cardiovascular MR of 79 rTOF patients and 20 healthy controls were retrospectively enrolled. Forty-four from the 79 patients were matched in age, sex and body surface area to the 20 controls and were investigated for: (1) phase-contrast flow of main pulmonary artery (MPA), LPA, and RPA; (2) vascular angles: the angles between the thoracic anterior-posterior line (TAPL) with MPA (θM-AP), MPA with RPA (θM-R), and MPA with LPA (θM-L); (3) cardiac angle, the angle between TAPL and the interventricular septum; (4) area ratio of bilateral lung and hemithorax regions. Compared with the 20 controls, the 44 rTOF patients exhibited wider θM-AP, sharper θM-L angle, and a smaller θM-L/θM-R ratio. In the 79 rTOF patients, LPA showed lower forward, backward, and net flow, and greater RF as compared with RPA. Multivariate analysis showed that the RF of LPA was negatively associated with the θM-L/θM-R ratio and the age at surgery (R2 = 0.255). Conversely, the RF of RPA was negatively associated with the left lung/left hemithorax area ratio and cross-sectional area (CSA) of LPA, and positively associated with CSA of RPA and MPA (R2 = 0.366). In rTOF patients, the RF of LPA is more severe than that of RPA, which may be related to the vascular morphometrics. Different morphometric parameters are independently associated with the RF of LPA or RPA, which may offer potential insights for surgical strategies.

Hemodynamic-based virtual surgery design of double-patch repair for pulmonary arterioplasty in tetralogy of Fallot

BACKGROUND AND OBJECTIVE

Surgical correction of pulmonary artery stenosis (PAS) is essential to the prognosis of patients with tetralogy of Fallot (TOF). The double-patch method of pulmonary arterioplasty is usually applied in case of multiple stenosis in TOF patients' pulmonary artery (PA) and when PAS cannot be relieved by the single-patch method. The surgical planning for the double-patch design remains challenging. The purpose of this study is to investigate the double-patch design with different angulations between the left pulmonary artery (LPA) and the right pulmonary artery (RPA), and to understand postoperative hemodynamic alterations by the application of computer-aided design (CAD) and computational fluid dynamics (CFD) techniques.

METHODS

The three-dimensional model of the PA was reconstructed based on preoperative computed tomography imaging data obtained from the patient with TOF. Three postoperative models with different designs of double-patch were created by "virtual surgery" using the CAD technique. Double-Patch 120 Model was created with double patches implanted in the main pulmonary artery (MPA) and the PA bifurcation and without changing the spatial position of PA. The angulation between the LPA and the RPA was defined as θ, which equaled to 120° in Pre-Operative Model and Double-Patch 120 Model. Based on Double-Patch 120 Model, Double-Patch 110 Model and Double-Patch 130 Model were generated with θ equaled to 110° and 130°, respectively. Combined with CFD, the differences of velocity streamlines, wall shear stress (WSS), flow distribution ratio (FDR), and energy loss (EL) were compared to analyze postoperative pulmonary flow characteristics.

RESULTS

The values of velocity and WSS decreased significantly after virtual surgery. Obvious vortices and swirling flows were observed downstream of the stenosis of RPA and LPA in Pre-Operative Model, while fewer vortices developed along the anterior wall of the expanded lumens of RPA, especially in Double-Patch 110 Model. With the relief of PAS, two relatively higher WSS regions were observed at the posterior walls of RPA and LPA. The maximum WSS values in these regions of Double-Patch 110 Model were lower than those in Double-Patch 120 Model and Double-Patch 130 Model. Furthermore, the FDRs were elevated and the ELs were greatly reduced. It was found that Double-Patch 110 Model with the angulation between the LPA and the RPA equaled to 110° showed relatively better properties of hemodynamics than other models.

CONCLUSIONS

The angulation between the LPA and the RPA is an important factor that should be integrated in the double-patch design for TOF repair. Virtual surgery based on patient-specific vascular model and computational hemodynamics can be used to provide assistance for individualized surgical planning of double-patch arterioplasty.

Numerical investigation of quantitative pulmonary pressure ratio in different degrees of stenosis

BACKGROUND

Pulmonary artery stenosis endangers people's health. Quantitative pulmonary pressure ratio (QPPR) is very important for clinicians to quickly diagnose diseases and develop treatment plans.

OBJECTIVE

Our purpose of this paper is to investigate the effects of different degrees (50% and 80%) of pulmonary artery stenosis on QPPR.

METHODS

An idealized model is established based on the normal size of human pulmonary artery. The hemodynamic governing equations are solved using fluid-structure interaction.

RESULTS

The results show that the QPPR decreases with the increase of stenosis degree, and it is closely related to the pressure drop at both ends of stenosis. Blood flow velocity and wall shear stress are sensitive to the stenosis degree. When the degree of stenosis is 80%, the amplitude of changes of blood flow velocity and wall shear stress at both ends of stenosis is lower.

CONCLUSIONS

The results suggest that the degree of pulmonary artery stenosis has a significant impact on QPPR and hemodynamic changes. This study lays a theoretical foundation for further study of QPPR.

A Fluid-Structure Interaction Analysis of Blood Clot Motion in a Branch of Pulmonary Arteries

INTRODUCTION

Pulmonary embolism (PE) is one of the most prevalent diseases amid hospitalized patients taking many people's lives annually. This phenomenon, however, has not been investigated via numerical simulations.

METHODS

In this study, an image-based model of pulmonary arteries has been constructed from a 44-year-old man's computed tomography images. The fluid-structure interaction method was used to simulate the motion of the blood clot. In this regard, Navier-Stokes equations, as the governing equations, have been solved in an arbitrary Lagrangian-Eulerian (ALE) formulation.

RESULTS

According to our results, the velocity of visco-hyperelastic model of the emboli was relatively higher than the emboli with hyperelastic model, despite their similar behavioral pattern. The stresses on the clot were also investigated and showed that the blood clot continuously sustained stresses greater than 165 Pa over an about 0.01 s period, which can cause platelets to leak and make the clot grow or tear apart.

CONCLUSIONS

It could be concluded that in silico analysis of the cardiovascular diseases initiated from clot motion in blood flow is a valuable tool for a better understanding of these phenomena.

Characterization of Flow Dynamics in the Pulmonary Bifurcation of Patients With Repaired Tetralogy of Fallot: A Computational Approach

The hemodynamic environment of the pulmonary bifurcation is of great importance for adult patients with repaired tetralogy of Fallot (rTOF) due to possible complications in the pulmonary valve and narrowing of the left pulmonary artery (LPA). The aim of this study was to computationally investigate the effect of geometrical variability and flow split on blood flow characteristics in the pulmonary trunk of patient-specific models. Data from a cohort of seven patients was used retrospectively and the pulmonary hemodynamics was investigated using averaged and MRI-derived patient-specific boundary conditions on the individualized models, as well as a statistical mean geometry. Geometrical analysis showed that curvature and tortuosity are higher in the LPA branch, compared to the right pulmonary artery (RPA), resulting in complex flow patterns in the LPA. The computational analysis also demonstrated high time-averaged wall shear stress (TAWSS) at the outer wall of the LPA and the wall of the RPA proximal to the junction. Similar TAWSS patterns were observed for averaged boundary conditions, except for a significantly modified flow split assigned at the outlets. Overall, this study enhances our understanding about the flow development in the pulmonary bifurcation of rTOF patients and associates some morphological characteristics with hemodynamic parameters, highlighting the importance of patient-specificity in the models. To confirm these findings, further studies are required with a bigger cohort of patients.

Branch Pulmonary Artery Regurgitation in Repaired Tetralogy of Fallot: Correlation with Pulmonary Artery Morphology, Distensibility, and Right Ventricular Function

Background: The aim was to determine the effect of pulmonary artery (PA) morphology on the branch pulmonary artery-regurgitation fraction (BPA-RF), the relationship of pulmonary insufficiency (PI) to BPA-RF and PA-distensibility, and factors (BPA-RF and PA-distensibility) associated with right ventricular function (RVF) in repaired tetralogy of Fallot (rTOF). Methods: A total of 182 rTOF patients (median age 17.1 years) were analyzed for length, angle of PA, BPA-RF, PI, and PA-distensibility, using magnetic resonance imaging. Results: The left PA had a significant greater RF than the right PA (median (interquartile range)): LPA 43.1% (32.6–51.5) and RPA 35.2% (24.7–44.7), p < 0.001. The LPA was shorter with a narrower angle than the RPA (p < 0.001). The anatomy of the branch-PA was not a factor for the greater LPA-RF (odds ratio, 95% confidence interval: CI, p-value): length 0.44 (0.95–2.00), p = 0.28; angle 0.63 (0.13–2.99), p = 0.56. There was a strong positive correlation between PI and BPA-RF-coefficients (95% CI), p-value: LPA 0.78% (0.70–0.86), p < 0.001; RPA 0.78% (0.71–0.84), p < 0.001 and between BPA-RF and distensibility-coefficients (95%CI), p-value: LPA 0.73% (0.37–1.09), p < 0.001; RPA 1.63% (1.22–2.03), p < 0.001, respectively. The adjusted BPA-RF did not predict RVF, RPA (p = 0.434), LPA (p = 0.268). Conclusions: PA morphology is not a significant factor for the differential BPA-RF. The vascular wall in rTOF patients responds to chronic increased intravascular volume by increasing distensibility. BPA-RF is not a determinant of RVF.

The Effect of Geometric and Hemodynamic Parameters on Blood Flow Efficiency in Repaired Tetralogy of Fallot Patients

Surgical repair of Tetralogy of Fallot (TOF) involves a series of steps to remove right ventricular outflow tract and pulmonary artery obstruction. However, the large degree of anatomic variability among preoperative TOF patients may impact the effectiveness of different repair strategies and, subsequently, different geometric modifications for different patients. This study investigates the relationships between geometric and hemodynamic parameters and mechanical energy efficiency for a patient-specific dataset of 16 postoperative TOF repairs, using morphometric and statistical shape analyses, as well as computational fluid dynamics simulations with physiologically-relevant inlet and outlet boundary conditions. Quantitatively, negative correlations were found between the right and left pulmonary artery centerline tract cumulative torsion and energy efficiency (r = - 0.65, p = 0.01, for both). A positive correlation was also found for a statistical shape mode associated with skewing of the geometric sub-regions (r = 0.61, p = 0.01). Qualitatively, medium- and low-efficiency geometries exhibit disturbed flow and much more proximal vortex formation as compared to a high-efficiency geometry. Thus, it is recommended, as much as possible, to both relieve and avoid the introduction of torsion into the patient's anatomy during surgical repair of TOF.

Computational Analysis of the Pulmonary Arteries in Congenital Heart Disease: A Review of the Methods and Results

With the help of computational fluid dynamics (CFD), hemodynamics of the pulmonary arteries (PA's) can be studied in detail and varying physiological circumstances and treatment options can be simulated. This offers the opportunity to improve the diagnostics and treatment of PA stenosis in biventricular congenital heart disease (CHD). The aim of this review was to evaluate the methods of computational studies for PA's in biventricular CHD and the level of validation of the numerical outcomes. A total of 34 original research papers were selected. The literature showed a great variety in the used methods for (re) construction of the geometry as well as definition of the boundary conditions and numerical setup. There were 10 different methods identified to define inlet boundary conditions and 17 for outlet boundary conditions. A total of nine papers verified their CFD outcomes by comparing results to clinical data or by an experimental mock loop. The diversity in used methods and the low level of validation of the outcomes result in uncertainties regarding the reliability of numerical studies. This limits the current clinical utility of CFD for the study of PA flow in CHD. Standardization and validation of the methods are therefore recommended.

Integrative Computational Models of Lung Structure-Function Interactions

Anatomically based integrative models of the lung and their interaction with other key components of the respiratory system provide unique capabilities for investigating both normal and abnormal lung function. There is substantial regional variability in both structure and function within the normal lung, yet it remains capable of relatively efficient gas exchange by providing close matching of air delivery (ventilation) and blood delivery (perfusion) to regions of gas exchange tissue from the scale of the whole organ to the smallest continuous gas exchange units. This is despite remarkably different mechanisms of air and blood delivery, different fluid properties, and unique scale-dependent anatomical structures through which the blood and air are transported. This inherent heterogeneity can be exacerbated in the presence of disease or when the body is under stress. Current computational power and data availability allow for the construction of sophisticated data-driven integrative models that can mimic respiratory system structure, function, and response to intervention. Computational models do not have the same technical and ethical issues that can limit experimental studies and biomedical imaging, and if they are solidly grounded in physiology and physics they facilitate investigation of the underlying interaction between mechanisms that determine respiratory function and dysfunction, and to estimate otherwise difficult-to-access measures. © 2021 American Physiological Society. Compr Physiol 11:1501-1530, 2021.

Common arterial trunk in a cat: a high-resolution morphological analysis with micro-computed tomography

A 6-month-old female cat presented with respiratory distress. Physical examination showed a grade 5/6 holosystolic murmur with prominent precordial impulse over the left cranial chest wall. Echocardiography revealed bilateral hypertrophy of the ventricular walls, a dilated ascending aorta overriding the interventricular septum, a membranous ventricular septal defect and no obvious pulmonary trunk or pulmonary artery branches. Turbulent blood flow was detected around the ventricular septal defect and ascending aorta. Follow-up assessment, 12 months later, revealed marked and progressive biatrial dilation and biventricular hypertrophy. Four months after that, the cat died of severe congestive heart failure. To make a definitive postmortem diagnosis, we performed contrast enhanced micro-computed tomography (CT) on the ex vivo heart with micron-scale spatial resolution imaging and three-dimensional reconstruction. Micro-computed tomography analysis confirmed a common arterial trunk that bifurcated into the left pulmonary artery and aorta 5-mm distally from the truncal valve. The pulmonary trunk was absent. Slightly distal to the first branching, the common arterial trunk further branched into the right pulmonary artery and ascending aorta, indicating the aortic dominant form. Although CT angiography would be a preferred imaging modality for living animals, micro-computed tomography is a valuable tool for the ex vivo diagnosis of complex cardiac anomaly, such as presented in this cat.

Assessing right ventricular systolic function using ultrasonic speckle-tracking imaging in repaired Tetralogy of Fallot with different pulmonary artery branch angles

OBJECTIVE

This study assessed whether ultrasonic speckle-tracking imaging (STI) could help evaluate right ventricular systolic function in repaired Tetralogy of Fallot (TOF) with different pulmonary artery branch angles.

METHODS

We retrospectively evaluated 64 patients who underwent surgery for TOF and 60 normal children. The angle between the left pulmonary artery and main pulmonary artery was measured using echocardiography and computed tomography angiography (CTA). Furthermore, STI was used to record the global longitudinal strain of the four-chamber view (GLS4), the global longitudinal strain of the two-chamber view (GLS2), and the global longitudinal strain of the right ventricle (RVGLS).

RESULTS

The GLS4, GLS2, and RVGLS values in the TOF groups with different pulmonary artery branch angles were significantly lower than those in the control group. Furthermore, the GLS2 and RVGLS values were significantly lower for angles of 90-100° and <90° (vs >100°). Multivariate linear regression analyses revealed that pulmonary regurgitation and the angle between the left and main pulmonary arteries were two important factors affecting RVGLS. The Bland-Altman consistency test revealed good agreement regarding the pulmonary artery branch angles measured using echocardiography and CTA.

CONCLUSION

In patients with TOF, the RVGLS was lower for acute left pulmonary artery angulation than for round and blunt left pulmonary artery angulation. The angle of the pulmonary artery branches was an important factor affecting RVGLS. Echocardiography can be used to measure the angle of the pulmonary artery branches, which provides valuable information for surgical correction of pulmonary artery morphology.

Blood flow simulations in the pulmonary bifurcation in relation to adult patients with repaired tetralogy of Fallot

Understanding the haemodynamic environment of the pulmonary bifurcation is important in adults with repaired conotruncal congenital heart disease. In these patients, dysfunction of the pulmonary valve and narrowing of the branch pulmonary arteries are common and can have serious clinical consequences. The aim of this study was to numerically investigate the underlying blood flow characteristics in the pulmonary trunk under a range of simplified conditions. For that, an in-depth analysis was conducted in idealised two-dimensional geometries that facilitate parametric investigation of healthy and abnormal conditions. Subtle variations in morphology influenced the haemodynamic environment and wall shear stress distribution. The pressure in the left pulmonary artery was generally higher than that in the right and main arteries, but was markedly reduced in the presence of a local stenosis. Different downstream pressure conditions altered the branch flow ratio, from 50:50% to more realistic 60:40% ratios in the right and left pulmonary artery, respectively. Despite some simplifications, this study highlights some previously undocumented aspects of the flow in bifurcating geometries, by clarifying the role of the stagnation point location on wall shear stress and differential branch pressures. In addition, measurements of the mean pressure ratios in the pulmonary bifurcation are discussed in the context of a new haemodynamic index which could potentially contribute to the assessment of left pulmonary artery stenosis in tetralogy of Fallot patients. Further studies are required to confirm the results in patient-specific models with personalised physiological flow conditions.

A Methodology to Assess Subregional Geometric Complexity for Tetralogy of Fallot Patients

During surgical repair of tetralogy of fallot (TOF), pulmonary valve preservation (preservative repair) has demonstrated improved long-term outcomes compared to repairs that incise into the valve annulus (nonpreservative repair). Given the influence of geometry on hemodynamics, the success of preservative repair may be linked to the suitability of the preoperative patient geometry. However, the specific patient anatomies that may be predisposed to successful preservative repair are unknown due to significant interpatient variability in right ventricular outflow tract (RVOT) and pulmonary artery geometries, as well as the limitations in current methods of subregional geometric analysis. As a first step toward understanding the link between geometry and hemodynamics in TOF patients at a subregion level, we characterize the TOF geometry from the right ventricular infundibulum (INF) to the left and right pulmonary arteries. Our process consists of segmentation of magnetic resonance (MR) images and analysis of cross-sectional slices of the geometries along the centerlines. For the INF, main, left, and right pulmonary arteries individually, we quantify geometric parameters important in determining hemodynamic characteristics such as flow separation and recirculation, which can influence the degree of regurgitation. Specifically, we calculate the diameter along the subregion length, the average diameter, length, and tortuosity for each segment, as well as the bifurcation, left pulmonary artery (LPA) and right pulmonary artery (RPA) branch angles. This approach enables direct geometric comparisons within and among patients and allows for observation of the range in anatomic presentation. We have applied this approach to a dataset of 11 postoperative TOF patients, repaired with both preservative and nonpreservative surgical techniques.

Methodology for Hemodynamic Assessment of a Three-Dimensional Printed Patient-Specific Vascular Test Device

Assessing hemodynamics in vasculature is important for the development of cardiovascular diagnostic parameters and evaluation of medical devices. Benchtop experiments are a safe and comprehensive preclinical method for testing new diagnostic endpoints and devices within a controlled environment. Recent advances in three-dimensional (3D) printing have enhanced benchtop tests by allowing generation of patient-specific and pathophysiologic conditions. We used 3D printing, coupled with image processing and computer-aided design (CAD), to develop a patient-specific vascular test device from clinical data. The proximal pulmonary artery (PA) tree including the main, left, and right pulmonary arteries, with a stenosis within the left PA was selected as a representative anatomy for developing the vascular test device. Three test devices representing clinically relevant stenosis severities, 90%, 80%, and 70% area stenosis, were evaluated at different cardiac outputs (COs). A mock circulatory loop (MCL) generating pathophysiologic pulmonary pressure and flow was used to evaluate the hemodynamics within the devices. The dimensionless pressure drop–velocity ratio characteristic curves for the three stenosis severities were obtained. At a fixed CO, the dimensionless pressure drop increased nonlinearly with an increase in (a) the velocity ratio for a fixed stenosis severity and (b) the stenosis severity at a specific velocity ratio. The dimensionless pressure drop observed in vivo was similar (within 1%) to that measured in moderate area stenosis of 70% because both flows were viscous dominated. The hemodynamics of the 3D printed test device can be used for evaluating diagnostic endpoints and medical devices in a preclinical setting under realistic conditions.

Evaluation of pulmonary artery stenosis in congenital heart disease patients using functional diagnostic parameters: An in vitro study

Congenital pulmonary artery (PA) stenosis is often associated with abnormal PA hemodynamics including increased pressure drop (Δp) and reduced asymmetric flow (Q), which may result in right ventricular dysfunction. We propose functional diagnostic parameters, pressure drop coefficient (CDP), energy loss (E_loss), and normalized energy loss (E¯_loss) to characterize pulmonary hemodynamics, and evaluate their efficacy in delineating stenosis severity using in vitro experiments. Subject-specific test sections including the main PA (MPA) bifurcating into left and right PAs (LPA, RPA) with a discrete LPA stenosis were manufactured from cross-sectional imaging and 3D printing. Three clinically-relevant stenosis severities, 90% area stenosis (AS), 80% AS, and 70% AS, were evaluated at different cardiac outputs (COs). A benchtop flow loop simulating pulmonary hemodynamics was used to measure Q and Δp within the test sections. The experimental Δp-Q characteristics along with clinical data were used to obtain pathophysiologic conditions and compute the diagnostic parameters. The pathophysiologic Q_LPA decreased as the stenosis severity increased at a fixed CO. CDP_LPA, E_loss,LPA (absolute), and E¯_loss,LPA (absolute) increased with an increase in LPA stenosis severity at a fixed CO. Importantly, CDP_LPA and E¯_loss,LPA had reduced variability with CO, and distinct values for each LPA stenosis severity. Under variable CO, a) CDP_LPA values were 14.5-21.0 (70% AS), 60.7- 2.2 (80% AS), ≥ 261.6 (90% AS), and b) E¯_loss,LPA values (in mJ per Q_LPA) were -501.9 to -1023.8 (70% AS), -1247.6 to -1773.0 (80% AS), -1934.5 (90% AS). Hence, CDP_LPA and E¯_loss,LPA are expected to assess the true functional severity of PA stenosis.

Quantification of pulmonary regurgitation in patients with repaired Tetralogy of Fallot by 2D phase-contrast MRI: Differences between the standard method of velocity averaging and a pixel-wise analysis

Objectives

To compare the values of pulmonary regurgitation in patients with repaired Tetralogy of Fallot quantified from two-dimensional phase-contrast data, by using a new pixel-wise analysis and the standard velocity-averaging method.

Design

Quantitative in silico and in vivo analysis.

Setting

Hospital Sótero del Río. The magnetic resonance images were acquired using a Philips Achieva 1.5T scanner.

Participants

Twenty-five patients with repaired Tetralogy of Fallot who underwent cardiovascular magnetic resonance imaging requested by their referring physicians were included in this study.

Main outcome measures

Using a computational fluid dynamics simulation, we validated our pixel-wise method, quantifying the error of our method in comparison with the standard method. The patients underwent a standard two-dimensional phase-contrast magnetic resonance imaging acquisition for quantifying pulmonary artery flow. Pulmonary regurgitation fraction was estimated by using our pixel-wise and the standard method. The two-dimensional flow profiles were inspected looking for simultaneous antegrade and retrograde flows in the same cardiac phase. Statistical analysis was performed with t-test for related samples, Bland–Altman plots, and Pearson correlation coefficient.

Results

Estimation of pulmonary regurgitation fraction using the pixel-wise analysis revealed higher values compared with the standard method (39 ± 16% vs. 30 ± 22%, p-value <0.01). Eight patients (32%) had a difference of more than 10% between methods. Analysis of two-dimensional flow profiles in these patients revealed simultaneous antegrade and retrograde flows through the pulmonary artery during systole–early diastole.

Conclusion

Quantification of pulmonary regurgitation fraction in patients with repaired Tetralogy of Fallot through a pixel-wise analysis yields higher values of pulmonary regurgitation compared with the standard velocity-averaging method.

Numerical simulation of particle transport and deposition in the pulmonary vasculature

To quantify the transport and adhesion of drug particles in a complex vascular environment, computational fluid particle dynamics (CFPD) simulations of blood flow and drug particulate were conducted in three different geometries representing the human lung vasculature for steady and pulsatile flow conditions. A fully developed flow profile was assumed as the inlet velocity, and a lumped mathematical model was used for the calculation of the outlet pressure boundary condition. A receptor-ligand model was used to simulate the particle binding probability. The results indicate that bigger particles have lower deposition fraction due to less chance of successful binding. Realistic unsteady flow significantly accelerates the binding activity over a wide range of particle sizes and also improves the particle deposition fraction in bifurcation regions when comparing with steady flow condition. Furthermore, surface imperfections and geometrical complexity coupled with the pulsatility effect can enhance fluid mixing and accordingly particle binding efficiency. The particle binding density at bifurcation regions increases with generation order and drug carriers are washed away faster in steady flow. Thus, when studying drug delivery mechanism in vitro and in vivo, it is important to take into account blood flow pulsatility in realistic geometry. Moreover, tissues close to bifurcations are more susceptible to deterioration due to higher uptake.

Methodology for implementing patient-specific spatial boundary condition during a cardiac cycle from phase-contrast MRI for hemodynamic assessment

Pulmonary insufficiency (PI) can render the right ventricle dysfunctional due to volume overloading and hypertrophy. The treatment requires a pulmonary valve replacement surgery. However, determining the right time for the valve replacement surgery has been difficult with currently employed clinical techniques such as, echocardiography and cardiac MRI. Therefore, there is a clinical need to improve the diagnosis of PI by using patient-specific (PS) hemodynamic endpoints. While there are many reported studies on the use of PS geometry with time varying boundary conditions (BC) for hemodynamic computation, few use spatially varying PS velocity measurement at each time point of the cardiac cycle. In other words, the gap is that, there are limited number of studies which implement both spatially- and time-varying physiologic BC directly with patient specific geometry. The uniqueness of this research is in the incorporation of spatially varying PS velocity data obtained from phase-contrast MRI (PC-MRI) at each time point of the cardiac cycle with PS geometry obtained from angiographic MRI. This methodology was applied to model the complex developing flow in human pulmonary artery (PA) distal to pulmonary valve, in a normal and a subject with PI. To validate the methodology, the flow rates from the proposed method were compared with those obtained using QFlow software, which is a standard of care clinical technique. For the normal subject, the computed time average flow rates from this study differed from those obtained using the standard of care technique (QFlow) by 0.8 ml/s (0.9%) at the main PA, by 2 ml/s (3.4%) at the left PA and by 1.4 ml/s (3.8%) at the right PA. For the subject with PI, the difference was 7 ml/s (12.4%) at the main PA, 5.5 ml/s (22.6%) at the left PA and 4.9 ml/s (18.0%) at the right PA. The higher percentage differences for the subject with PI, was the result of overall lower values of the forward mean flow rate caused by excessive flow regurgitation. This methodology is expected to provide improved computational results when PS geometry from angiographic MRI is used in conjunction with PS PC-MRI data for solving the flow field.