Variable wall parameters based on centerline

[Rodrigo Romarowski]

Hi all,

I would like to assign variable wall parameters to an aorta I imported as a VTP file. However, I can only select the same regions as my fluid boundary conditions (vessel wall as a whole and caps). Is there any way of assigning wall parameters based on the centerline? Or is it possible to split the wall with the SimVascular interface into subdomains with different labels?

Thanks a lot!

Rodrigo

[David Parker]

Hi Rodrigo,

There is currently no functionality in SimVascular to set wall parameters based on center line, this would need to be done externally using custom software.

I believe that there is a Python script used by our lab members that can do this, let me have a look around and see if I can find it.

Cheers,
Dave

[Rodrigo Romarowski]

Thanks a lot, I am looking forward to using it.

I am curious about the tutorial "Example 4" where you use variable wall parameters. What is the goal of setting a specific wall thickness in a boundary which is a "cap" and thus will be spatially fixed in the simulation?

[David Parker]

The wall thickness is interpolated along the mesh using the values set at the caps. If you look at the scale bar in the Variable Wall Thickness in varwallprop.vtp picture in Example 4 you will see that the mesh thickness varies between 0.1 and 0.2. This should be explained in the tutorial, I will fix that.

Cheers,
Dave

[Rodrigo Romarowski]

Thanks again for your advise David.

Did you have any chance of getting that Python script for using the centerline to set the wall parameters? I have a similar one based on VMTK that would write an array with a a radius-dependent value in each triangle of the surface mesh, but I don't think there is any possibility of using that vtk array to indicate the wall properties to the CMM method.

[David Parker]

Hi Rodrigo,

I have not had a chance to work on this, hope to get to it within the next couple of weeks.

The VMTK center line looks interesting, just installed vmtk and had a look. The radius data is not useful for setting material properties though, unless the material properties depended on the radius, like for an aneurysm. What you could do is to somehow set the material property along the center line and then use vmtksurfacecenterlineprojection to project it to a surface mesh.

Cheers,
Dave

[Rodrigo Romarowski]

Thanks David!

In fact the radius of the centerline is not a good indicator itself, but can certainly identify branches automatically . Also, a radius threshold can be set for example to jump from the thoracic aorta, to the abdominal, to the iliacs.

I am looking forward to your answer. It would be nice if the thickness/young modulus could be read from an array in the surface mesh. In the example attached, I added different tags to a surface mesh based on the volume mesh refinement I needed. Would it be possible to do sth like this?

Thanks again,

Rodrigo

[David Parker]

Hi Rodrigo,

Interesting use of the radius data to identify anatomical regions, I will make sure to remember that useful technique, might be useful for our lab.

I've been writing a small VTK app to set material IDs on a centerline and write that to a VTK .vtp file. I can then project the IDs to a surface (I think). I will then write a program to read in that surface and create the information needed by our solvers for multiple material properties. If you tagged the surface mesh another way then you could use the same program to create the solver data files. I'm working on this in my spare time but I hope to finish in a couple of weeks or so.

Cheers,
Dave

[Rodrigo Romarowski]

Thanks a lot, that would be great!

[arash ghorbannia]

Hi all,

I used a trick for local identification of Elastic Modulus across aorta. Please let me know if there are better ways to do this.
I am creating a model for aortic coarctation and need different elastic modulus in 1- ascending , 2- coarctation and 3- descending aorta. so to do this, first I created segments of entire aorta and made two copies of that. I used one of them to create each of the three regions mentioned above. for example, to create ascending aorta, I scales down the segments in coarctation and distal aorta to make it fall inside the final geometry. I did the same for coarctation (i.e. scaled down the segments in ascending and descending aorta) and descending (i.e. scaled down the segments in ascending aorta and coarctation region) using other two copies of the segments. then I created a model using all three segments. each one created a surface in corresponding region and fall inside the model everywhere else. the attached picture is the final model after smoothing. three surfaces in the prescribed location made it possible to locally specify elastic modulus across the aorta. I was not able to find other solutions for this. It did work in my case but if someone is looking for continues variation, variation of wall properties based on centerline would be a better idea.

https://drive.google.com/open?id=1NsyyM ... xD64jXXaFQ