Wouter V. Potters

Volumetric arterial wall shear stress calculation based on cine phase contrast MRI.

To assess the accuracy and precision of a volumetric wall shear stress (WSS) calculation method applied to cine phase contrast magnetic resonance imaging (PC‐MRI) data.

Generalized versus patient-specific inflow boundary conditions in computational fluid dynamics simulations of cerebral aneurysmal hemodynamics.

BACKGROUND AND PURPOSE: Attempts have been made to associate intracranial aneurysmal hemodynamics with aneurysm growth and rupture status. Hemodynamics in aneurysms is traditionally determined with computational fluid dynamics by using generalized inflow boundary conditions in a parent artery. Recently, patient-specific inflow boundary conditions are being implemented more frequently. Our purpose was to compare intracranial aneurysm hemodynamics based on generalized versus patient-specific inflow boundary conditions. MATERIALS AND METHODS: For 36 patients, geometric models of aneurysms were determined by using 3D rotational angiography. 2D phase-contrast MR imaging velocity measurements of the parent artery were performed. Computational fluid dynamics simulations were performed twice: once by using patient-specific phase-contrast MR imaging velocity profiles and once by using generalized Womersley profiles as inflow boundary conditions. Resulting mean and maximum wall shear stress and oscillatory shear index values were analyzed, and hemodynamic characteristics were qualitatively compared. RESULTS: Quantitative analysis showed statistically significant differences for mean and maximum wall shear stress values between both inflow boundary conditions (P < .001). Qualitative assessment of hemodynamic characteristics showed differences in 21 cases: high wall shear stress location (n = 8), deflection location (n = 3), lobulation wall shear stress (n = 12), and/or vortex and inflow jet stability (n = 9). The latter showed more instability for the generalized inflow boundary conditions in 7 of 9 patients. CONCLUSIONS: Using generalized and patient-specific inflow boundary conditions for computational fluid dynamics results in different wall shear stress magnitudes and hemodynamic characteristics. Generalized inflow boundary conditions result in more vortices and inflow jet instabilities. This study emphasizes the necessity of patient-specific inflow boundary conditions for calculation of hemodynamics in cerebral aneurysms by using computational fluid dynamics techniques.

Wall shear stress estimated with phase contrast MRI in an in vitro and in vivo intracranial aneurysm

To evaluate wall shear stress (WSS) estimations in an in vitro and in vivo intracranial aneurysm, WSS was estimated from phase contrast magnetic resonance imaging (PC‐MRI) and compared with computational fluid dynamics (CFD).

Reproducibility and Interobserver Variability of Systolic Blood Flow Velocity and 3D Wall Shear Stress Derived From 4D Flow MRI in the Healthy Aorta

To investigate the reproducibility and interobserver variability of 3D aortic velocity vector fields and wall shear stress (WSS) averaged over five systolic timeframes derived from noncontrast 4D flow magnetic resonance imaging (MRI).

A methodology to detect abnormal relative wall shear stress on the full surface of the thoracic aorta using four-dimensional flow MRI

To compute cohort‐averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS.

In vivo imaging of enhanced leukocyte accumulation in atherosclerotic lesions in humans.

BACKGROUND Understanding how leukocytes impact atherogenesis contributes critically to our concept of atherosclerosis development and the identification of potential therapeutic targets. OBJECTIVES The study evaluates an in vivo imaging approach to visualize peripheral blood mononuclear cell (PBMC) accumulation in atherosclerotic lesions of cardiovascular (CV) patients using hybrid single-photon emission computed tomography/computed tomography (SPECT/CT). METHODS At baseline, CV patients and healthy controls underwent (18)fluorodeoxyglucose positron emission tomography-computed tomography and magnetic resonance imaging to assess arterial wall inflammation and dimensions, respectively. For in vivo trafficking, autologous PBMCs were isolated, labeled with technetium-99m, and visualized 3, 4.5, and 6 h post-infusion with SPECT/CT. RESULTS Ten CV patients and 5 healthy controls were included. Patients had an increased arterial wall inflammation (target-to-background ratio [TBR] right carotid 2.00 ± 0.26 in patients vs. 1.51 ± 0.12 in controls; p = 0.022) and atherosclerotic burden (normalized wall index 0.52 ± 0.09 in patients vs. 0.33 ± 0.02 in controls; p = 0.026). Elevated PBMC accumulation in the arterial wall was observed in patients; for the right carotid, the arterial-wall-to-blood ratio (ABR) 4.5 h post-infusion was 2.13 ± 0.35 in patients versus 1.49 ± 0.40 in controls (p = 0.038). In patients, the ABR correlated with the TBR of the corresponding vessel (for the right carotid: r = 0.88; p < 0.001). CONCLUSIONS PBMC accumulation is markedly enhanced in patients with advanced atherosclerotic lesions and correlates with disease severity. This study provides a noninvasive imaging tool to validate the development and implementation of interventions targeting leukocytes in atherosclerosis.

Age‐related changes in aortic 3D blood flow velocities and wall shear stress: Implications for the identification of altered hemodynamics in patients with aortic valve disease

To investigate age‐related changes in peak systolic aortic 3D velocity and wall shear stress (WSS) in healthy controls and to investigate the importance of age‐matching for 3D mapping of abnormal aortic hemodynamics in bicuspid aortic valve disease (BAV).

Wall shear stress calculations based on 3D cine phase contrast MRI and computational fluid dynamics: a comparison study in healthy carotid arteries

Wall shear stress (WSS) is involved in many pathophysiological processes related to cardiovascular diseases, and knowledge of WSS may provide vital information on disease progression. WSS is generally quantified with computational fluid dynamics (CFD), but can also be calculated using phase contrast MRI (PC‐MRI) measurements. In this study, our objectives were to calculate WSS on the entire luminal surface of human carotid arteries using PC‐MRI velocities (WSSMRI) and to compare it with WSS based on CFD (WSSCFD).

Measuring Wall Shear Stress Using Velocity-Encoded MRI

This study reviews the application of velocity-encoded magnetic resonance imaging (MRI) for the calculation of wall shear stress (WSS). The basics of velocity-encoded MRI and WSS are reviewed and calculation methods for estimation of the WSS from 2D or 3D (cine) velocity-encoded MRI data are presented. In recent years, there has been a trend towards 3D WSS quantification methods. Current clinical applications of WSS are discussed, including an overview of estimated WSS magnitudes in different patient groups at multiple anatomical locations (aorta, carotid arteries, and intracranial aneurysms). A large variation was found between different WSS calculation methods. The future of MRI-based WSS calculations depends on its prognostic and diagnostic value, both of which need to be further explored in clinical studies. In this context, both further improvement of the quality of velocity-encoded MRI data and scan time reduction are pivotal.

Hemodynamic Differences in Intracranial Aneurysms before and after Rupture

BACKGROUND AND PURPOSE: Rupture risk of intracranial aneurysms may depend on hemodynamic characteristics. This has been assessed by comparing hemodynamic data of ruptured and unruptured aneurysms. However, aneurysm geometry may change before, during, or just after rupture; this difference causes potential changes in hemodynamics. We assessed changes in hemodynamics in a series of intracranial aneurysms, by using 3D imaging before and after rupture. MATERIALS AND METHODS: For 9 aneurysms in 9 patients, we used MRA, CTA, and 3D rotational angiography before and after rupture to generate geometric models of the aneurysm and perianeurysmal vasculature. Intra-aneurysmal hemodynamics were simulated by using computational fluid dynamics. Two neuroradiologists qualitatively assessed flow complexity, flow stability, inflow concentration, and flow impingement in consensus, by using flow-velocity streamlines and wall shear stress distributions. RESULTS: Hemodynamics changed in 6 of the 9 aneurysms. The median time between imaging before and after rupture was 678 days (range, 14–1461 days) in these 6 cases, compared with 151 days (range, 34–183 days) in the 3 cases with unaltered hemodynamics. Changes were observed for flow complexity (n = 3), flow stability (n = 3), inflow concentration (n = 2), and region of flow impingement (n = 3). These changes were in all instances associated with aneurysm displacement due to rupture-related hematomas, growth, or newly formed lobulations. CONCLUSIONS: Hemodynamic characteristics of intracranial aneurysms can be altered by geometric changes before, during, or just after rupture. Associations of hemodynamic characteristics with aneurysm rupture obtained from case-control studies comparing ruptured with unruptured aneurysms should therefore be interpreted with caution.