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Platelet Rheology
Published in Gordon D. O. Lowe, Clinical Blood Rheology, 2019
Compared to the red cell, platelets exist in the circulation in very small quantities. A circulating platelet has a discoid (plate-like) appearance with a diameter of approximately 2 to 3 µm in man. The volume fraction of platelets in whole blood is approximately 0.2 to 0.5%, compared to 35 to 45% for red blood cells. Thus, it is not surprising that platelets play no role in the macrorheological determination of blood behavior. Blood either with or without platelets will flow identically through tubes of diameters considerably larger than platelets or in viscometers of various designs.
Perfusion Imaging
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
Prior to discussing methods of estimating physiologically relevant perfusion parameters using DSC, a basic understanding of the significance and normative values of these parameters should be discussed. The simplest perfusion parameter to measure from the DSC concentration curve is that of regional cerebral blood volume (rCBV), which is an estimate of the volume of blood contained in the microvasculature. This may be defined as either a mass or volume fraction reporting the volume of blood in a voxel divided by the mass or volume of the voxel, respectively (40). Typically, the volume fraction is reported as a percentage with normal values determined by H215O positron emission tomography (PET) to be 5.2% ± 1.2% and 2.7% ± 0.5% in gray and white matter, respectively (41).
IVIM Models: Advantages, Disadvantages, and Analysis Pitfalls
Published in Denis Le Bihan, Mami Iima, Christian Federau, Eric E. Sigmund, Intravoxel Incoherent Motion (IVIM) MRI, 2018
Gabrielle Fournet, Luisa Ciobanu, Denis Le Bihan
Using this method, the obtained value for fIVIM does not depend on T2 and the acquisition parameter TE. This method opens the path toward quantitative measurements of the blood volume fraction. The simultaneous measurement of T2 and the diffusion coefficients of the tissue and blood compartments also shows that T2 values can be separated for the two compartments and could also be used as disease biomarkers.
A two-fluid blood stasis model for false lumen thrombosis after type B dissection repair
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Xudong Jiang, Da Li, Peng Wu, Xiaoqiang Li, Tinghui Zheng
A novel two-fluid flow model was introduced to simulate the process of blood washout and stasis. A time point was selected for a fully developed hemodynamic flow field. After this time point, the substance at the inlet was defined as a new fluid (or ‘new blood’) with the same physical properties as the existing blood (or ‘old blood’) in the computational domain, such as density and viscosity. Then the classic two-fluid/phase model can be used to solve the two-fluid flow field. In this work, the volume of fluid (VOF) surface tracking technology was used to solve the two-fluid hemodynamic field (Ferziger and Peric 1999). By solving the volume fraction equation in each computational cell, the position and shape of the new and old blood interface could be tracked in time, the location of the remaining old blood could be obtained, and the area of blood stasis could be determined. In each computational cell, the total volume fraction of the two fluids is 1. Volume fraction of 0 of one fluid indicates that this fluid is empty in this cell, while 1 indicated that the cell is full of this fluid. The interface of the two fluids is determined by the volume fraction of each fluid of 0.5. For the new blood, the volume fraction equation is as follows:
Patient-specific hemodynamic analysis of IVCS-induced DVT
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Xudong Jiang, Xueping Gu, Tianze Xu, Xiaoqiang Li, Peng Wu, Lili Sun
A novel two-fluid flow model was introduced to simulate the process of blood washout and stasis (Dai et al. 2021). A second-order implicit backward Euler scheme was chosen for temporal discretization. The size of time step was set to 10 ms. Maximum 20 sub-iterations were used for each physical time step, and the maximum RMS residual was set to 10−5 as a convergence criterion. First, single-fluid simulations were carried out for 5 seconds to get statistically converged flow field. Then, simulation of blood stasis continued from the converged single-fluid flow field. Both the new and old blood were regarded as incompressible Newtonian fluids, with the same material properties. All the computational setup was the same as the single-fluid run, except that the VOF method was employed to solve the two-fluid flow. The volume fraction of the new blood was set as 1 at the inlet, while that of the old blood was 0 at the inlet. As time evolves, the new blood will gradually replace the old blood. The location of and volume fraction of old blood can be tracked and monitored over time. The convergence criterion for the simulation of blood stasis was that the drop of OBVF is within 1% in one second. Due to the disparity in inlet velocity for different cases, 5–11 seconds were needed to reach convergence.
A joint numerical and experimental study on the self-organization of red blood cells in confined microfluidic channels
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2019
S. Mendez, C. Iss, D. Midou, A. Moreau, D. Held, A. Charrier, A. Viallat, E. Helfer
Numerical simulations are performed with the YALES2BIO (http://imag.umontpellier.fr/∼yales2bio) solver, dedicated to the simulation of blood flows, using the immersed boundary method (Sigüenza et al. 2016). The red blood cell membrane is modelled as an infinitely thin elastic surface resisting shear, area changes and bending (Mendez and Abkarian 2018). The internal viscosity is assumed to be 5 times larger than the suspending viscosity. Simulations are performed in a periodic channel, the organization of the suspension emerging over time instead of space in the experiment. Spherical capsules simulations have also been performed to test the effect of deformability on the behaviour of the suspensions. The volume fraction (haematocrit, Ht) has been varied from 2 to 20%.