On the importance of spiral‐flow inflow boundary conditions when using idealized artery geometries in the analysis of liver radioembolization: A parametric study

Abstract

In the last decades, the numerical studies on hemodynamics have become a valuable explorative scientific tool. The very first studies were done over idealized geometries, but as numerical methods and the power of computers have become more affordable, the studies tend to be patient specific. We apply the study to the numerical analysis of tumor‐targeting during liver radioembolization (RE). RE is a treatment for liver cancer, and is performed by injecting radiolabeled microspheres via a catheter placed in the hepatic artery. The objective of the procedure is to maximize the release of radiolabeled microspheres into the tumor and avoid a healthy tissue damage. Idealized virtual arteries can serve as a generalist approach that permits to separately analyze the effect of a variable in the microsphere distribution with respect to others. However, it is important to use proper physiological boundary conditions (BCs). It is not obvious, the need to account for the effect of tortuosity when using an idealized virtual artery. We study the use of idealized geometry of a hepatic artery as a valid research tool, exploring the importance of using realistic spiral‐flow inflow BC. By using a literature‐based cancer scenario, we vary two parameters to analyze the microsphere distribution through the outlets of the geometry. The parameters varied are the type of microspheres injected and the microsphere injection velocity. The results with realistic inlet velocity profile showed that the particle distribution in the liver segments is not affected by the analyzed injection velocity values neither by the particle density. Novelty Statement In this article, we assessed the use of idealized geometries as a valid research tool and applied the use of an idealized geometry to the case of an idealized hepatic artery to study the particle‐hemodynamics during radioembolization (RE). We studied three different inflow boundary conditions (BCs) to assess the usefulness of the geometry, two types of particle injection velocities and two types of commercially available microspheres for RE treatment. In recent years, the advent in computational resources allowed for more detailed patient‐specific geometry generation and discretization and hemodynamics simulations. However, general studies based on idealized geometries can be performed in order to provide medical doctors with some basic and general guidelines when using a given catheter for a given cancer scenario. Moreover, using an idealized geometry can be a reasonable approach which allows us to isolate a given parameter and control other parameters, so that parameters can be independently assessed. Even though an idealized geometry does not match any patient's geometry, the use of an idealized geometry can be valid when drawing general conclusions that may be useful in patient‐specific cases. However, we believe that even if an idealized hepatic artery geometry is used for the study, it is necessary to account for the upstream and downstream tortuosity of vessels through the BCs. I...

Computational study of a novel catheter for liver radioembolization

“…A three‐dimensional idealised geometry of the hepatic artery was used in this study, as shown in Figure 1. This type of arterial geometry can be used as a generalist approach that allows for the independent analysis of the effect of a variable in the microsphere distribution with respect to others 17 …”

“…To further analyse the particle dispersion on a surface of interest, an index is defined to evaluate the degree to which the particles are spread out in the artery lumen in the simulations, denoted as the coefficient of variation, , as explained in 17 . This index represents the ratio between the standard deviation, σ , and the average, , of the particles located in the cells at a specific cross‐section of the artery and is defined by Equation (16): The particle concentration in a group of cells in a specific cross‐section of the artery is determined by the unsteady statistics variable accumulative particles in cell , ϕ , defined in ANSYS® Fluent 19.2 24…”

“…This type of arterial geometry can be used as a generalist approach that allows for the independent analysis of the effect of a variable in the microsphere distribution with respect to others. 17 …”

“…This type of arterial geometry can be used as a generalist approach that allows for the independent analysis of the effect of a variable in the microsphere distribution with respect to others. 17 This geometrical model, which represents a hepatic artery "type I" according to Hiatt's hepatic artery classification, 18 is built with the following geometric parameters: the daughter-parent branch diameter ratio is 0.8, and the average branch length is 35 mm 19 ; the angle between the flow direction in the parent vessel and the flow direction in the daughter vessel is 30 20,21 ; and a typical diameter of the proper hepatic artery (PHA) of 5 mm 22 is used, ending with an outlet diameter of 3 mm. The hepatic artery consists of two levels of bifurcations with four outlets in total (see the outlet nomenclature in Figure 1D).…”

Computational Fluid Dynamics Modeling of Liver Radioembolization: A Review

“…Blood has been assumed to have a density of 1060 kg/m 3 [ 12 , 18 , 21 – 25 , 27 , 29 – 32 ] or 1050 kg/m 3 [ 10 , 13 – 17 , 20 , 26 , 33 , 34 , 37 ]. Blood densities around 1050 kg/m 3 have been measured in the arterial level, decreasing to a value of 1040 kg/m 3 at the capillary level [ 38 ].…”