The human coronary arteries, which supply the heart muscle with vital oxygen and nutrients, are central to cardiovascular health and function. To better understand the intricate network of these blood vessels and their role in various cardiac conditions, medical professionals and researchers turn to scanned coronary artery imaging. This innovative technique allows us to peer deep into the heart, revealing critical details about the coronary arteries and paving the way for advanced diagnostics and treatment strategies.

CFD allows researchers and medical professionals to study blood flow in coronary arteries without invasive procedures. Some benefits of the CFD analysis are:

• Visualization of blood flow patterns
• Assessment of stenosis severity
• Prediction of hemodynamic changes
• Personalized medicine
• Research and development, and
• Risk prediction

However, how can we make use of the provided scanned geometry, which usually is of poor quality?

Today we’ll concentrate on processing already-reconstructed geometry from scanned images using Siemens NX CAD program to prepare it for the CFD analysis.

Convergent modeling

What do we mean by convergent modeling though?

Convergent modeling is a modeling system that lets you use both features and facet geometry directly with imported modeling data, without requiring you to convert any of the modeling data.

Using convergent models, you can use different types of modeling data from multiple sources to accelerate your concept-to-production and reverse engineering workflow.

Now let’s look at how we can use this tool in our situation!

Workflow in NX

Step 1: Manipulation of convergent model

Firstly, we need to import the scanned and reconstructed geometry as a .stl file into our current model.

After that, from the application toolbar we select the Shape Studio to enter the convergent modeling editor.

Figure 1: Shape Studio Application

In order to modify the convergent model, we select the Polygon Modeling tab.

Figure 2: Polygon Modeling

Now, we can use several tools like Remesh, Cleanup Facet Body, Smooth, Snip and Fill Hole to perform the changes in the part to fit your desired outcome.

We must be very careful while processing the scanned geometry because medical geometry is very complex, and we would like to avoid any significant surface modifications. Therefore, carrying out these steps in this order will enable us to achieve the desired geometry:

1. Remesh the model to add more precise facets.
2. Use Cleanup Facet Body to analyze and fix any geometry errors.
3. Use a modest Smoothing Factor to Smooth the surface.
4. To make changes locally, use Snip and Fill Hole.

Figure 3: Convergent modeling editing tools

We can achieve the desired result shown in Figure 4 by carrying out each of these steps.

Figure 4: Modification of the scanned artery geometry to a solid smoothened part

Step 2: Geometry preparation for Boundary conditions of CFD analysis

Vertical surfaces are crucial for representing the inlet and outflow boundary conditions in CFD analyses. A good practice for the analysis is to create a cylindrical volume in the front of the artery so that the velocity boundary profile can be directly implemented on the entrance of the cylinder. This way, we ensure that the flow is fully developed in the artery. Such modifications can be made in the Modeling editor of NX.

One important step that should not be omitted is the refinement of the artery which is unified with the cylindrical inlet.

Most of the time, there won’t be a seamless transition from the cylinder to the artery’s inlet. These sharp edges should be avoided since they can compromise the accuracy of the CFD analysis.

Figure 5: Geometry of artery with cylindrical volume

Step 3: Refinement of the geometry for final export

To achieve that, we must first export the geometry as an .stl file, then later import it once more. In its place, we now have a single new convergent geometry. In this approach, we can recreate some of our initial steps, but only need to smooth the critical area of connection.

Finally, we have created a geometry for an artery, which is now set up for analysis!

Figure 6: Final geometry of the artery for CFD analysis

Don’t miss the video below for a thorough demonstration of all the processes outlined above.

At FEAC, we trust that this blog post has been informative and beneficial to prepare top-notch Digital Twins. Should you have any inquiries and questions, please don’t hesitate to reach out to us at support@feacomp.com.

Author:

E Elisavet Oursoula Kavoura – CAD Designer at FEAC Engineering Mechanical Engineer M.Sc e-mail: e.kavoura@feacomp.com LinkedIn Profile: Eliza Kavoura