Anatomy of the heart
When we started the project we had very limited knowledge of the anatomy of the human heart. Therefore our first order of business was to learn more about all the different parts of the heart, what their function is and about various congenital heart defects. The cardiologists in Leiden helped us with this by showing us several preserved hearts and explaining the basics of how the heart works. They also provided us with some online courses from which we could learn even more. This took up most of the first week. At the same time we took a look at the segmented CT-scan of a patient’s heart that they had already prepared for us, so we could see if we could work with it.
From CT to CAD
At this point our knowledge of CAD-software and file types that could be used to create a printable model was very limited. Especially working with meshes was something we had little to no experience with. Because the file created with the CT-scan was a mesh, we spent quite some time researching other options. We looked for ways to convert a mesh into a NURBS model, we searched for existing models that we could adjust and change and even tried to model a heart from scratch. All with varying but not very promising results. Converting a mesh didn’t work at all or resulted in a model that was difficult to work with, as were most of the existing models we found. Creating a heart from scratch seemed possible but was very time consuming.
But then we had a breakthrough. We found a piece of software that allowed us to easily adjust the mesh models from the CT-scans. Working with the model from the scan would mean a higher anatomical accuracy. To get the computer model as close to the scanned heart as possible, Leiden scanned one of the preserved hearts for us. Because a preserved heart is not beating and inside a body anymore it is possible to use more radiation and get a higher resolution. However, we could not get everything out of the scan. The valves were too thin to see, so we had to model them ourselves.
Progress in the process
At this point everyone in the group started to get their own place in the process and develop their own specialty. This prevented us from doing any double work and made it possible to learn new software and techniques in a very short time. We had someone who cleaned up the mesh model and made it into a solid, someone who modeled the coronary arteries, someone who modeled the valves and someone who put everything together into a correct, printable model. During this process we also started making our first test prints, which were mostly valves, to see what the materials were really like and how thin, soft or hard we could make everything.
It ended up taking longer than we initially thought and wanted to start printing our first entire heart. This was due to the fact that it took us a long time to find the appropriate software, learn how to use it and also combining all the separate parts we had into one printable solid. However, because we did take our time for this process we ended up with a set of steps that were easy to repeat. So once we had our first printed heart and the cardiologists from LUMC gave us some very useful feedback about the anatomy of it, we were able to improve the heart quite fast. Not only did we adjust it anatomically, we also gave various parts of the heart different colors and material properties. We did this with the purpose of making it easier for patients to understand the model.
In the end we had a printed model of a healthy heart, without defects. The colors of the model were not exactly what we wanted yet, due to it being too late to switch the colors in the printer. However the different colors that we did use gave a good impression of what is possible. The different material settings also turned out well and both could be easily adjusted for a next print if necessary. The valves could anatomically still be located a bit better and maybe the heart could also be cut in a different location, or more than one, to make them more visible. But with the process we created and our skills that we are still developing as we go, this could all be easily changed.
The next step would be to create a model of a heart with a defect. The same methods as we used for a normal heart can be used for this. Fitting in the modeled parts in an anatomically correct way will probably be a bit more challenging, because the defect can make the heart look very different. This makes it more difficult to find the right location of, for instance, the valves. However, with the expertise of the cardiologists at LUMC it is definitely possible.