Monthly Archives: October 2015
Last friday we finally recieved our heart, complete with valves. A nice side product of printing with the connex is that you literally have to unpack your exciting present.
So after some time, the heart slowly appeared out of the solid mass. We were quite satisfied with the result. The valves where looking good and the coronary arteries where quite clear too.
Ofcourse it is not a perfect print, which was confirmed after showing it to the cardiologists. Some valves were not positioned correctly and the coronary arteries were not perfect too.
Since we were using the CT-scans that the LUMC cardiologists provided us with, we had a model of the heart that was more or less anatomically correct. However, the valves were missing from this model. The scan had a resolution with voxels of approximately 1 by 1 millimeter. Because the cusps of the valves and the heart strings are thinner than that, they didn’t show up on the CT-scan. Therefore we had to model them ourselves.
The aortic and pulmonary valves look quite similar. They are both semilunar valves and consist of three leaflets that are shaped like a half full moon, hence the name. These were fairly simple to model in Rhino. We did a test print to see what material combination we could or should use and to show in Leiden. We got some useful feedback. On the first try the connections of the cusps with the artery were located in a single plane, while in reality the leaflets are attached to the arteries in semi-circles. This was quite easily fixed so then the aortic and pulmonary valve could be placed inside the heart. Because the aorta and the pulmonary artery always roughly have the shape of a circle, this model can be used in almost any heart.
The tricuspid and mitral valve were more of a challenge. They are also quite similar, except for one major difference: the tricuspid valve has three cusps and the mitral has two. Therefore the modeling principles could be used for both, but they did result in two separate models. What made it difficult to model were the very thin heart strings that protrude from the edges of the leaflets and connect them with the papillary muscles that are attached to the walls of the ventricles. Every heart is shaped a little differently, especially ones with a cardiac defect. For that reason it was vital that the valve would be easy to adjust and the heart strings could be deformed and their ends dragged to connect to different places. At the same time we had to make sure the cusps and strings were thick enough to print properly. Our test piece showed that the strings and the leaflets required a minimal thickness of 1 millimeter and probably more to increase the durability. Anatomically this would not be entirely correct, but it would still look small in relation to the rest of the heart and show how the connection is made. In Rhino we modeled the leaflets as one piece, because in a real heart they are all connected as well. The strings were created separately and made adjustable with Grasshopper, which we also used to automatically combine all the parts into a closed polysurface so that the valve would be printable.
In the end we had three separate models. One that can be used as the aortic and pulmonary valve, one tricuspid valve and one mitral valve. The semilunar valve can be placed in the heart model by simply scaling and rotating it. The ventricular valves can be put in the right position by deforming the cusps and dragging the heart strings to the right place.
The coronary arteries have a very complex structure and are lying around the myocard of the hearth. The coronary arteries can be split into two parts: the right coronary artery and the left coronary artery. They both begin in the aortic sinuses respectively the left and right aortic sinuses. The middle aortic sinus doesn’t have a connection with a coronary artery.
The right coronary artery is follows the border between the right atrium and right ventricle in the sulci of the hearth. When the sulci is reaching the interventricular septum of the hearth the sulci and the right coronary artery is turning and follows his way on the interventricular septum as the posterior interventricular branch of the right coronary artery.
The left coronary artery splits into two veins: the Circumflex branch of left coronary artery and the anterior interventricular branch. The Circumflex follows the border of the left atrium and the left ventricle in the sulci of the heart. The end of the Circumflex is near the spot were the posterior interventricular branch of right coronary artery at the interventricular septum.
The anterior interventricular branch is following the sulci on the interventricular septum of the hearth. The interventricular branch ends near the end of the posterior interventricular branch of right coronary artery.
These 3 veins are the main veins of the hearth. They split up in multiple branches that are going into the myocard to muscles of the heart of blood. For the printed model it is only necessary to visualize these tree veins, because it is very heart to see which way the branches are following.
After we had made the valves which fitted every heart that could be modelled we faced the next challenge: to print you need a solid. We could place the valves at the right place but the problem was that both the surface of the heart and the surface of the valve were intersecting with each other. When we tried to mesh Boolean in rhino the fan from your laptop creates such a lifting effect that your laptop actually begins to float or it spontaneously combusts. So we came to the conclusion that we needed to search for another solution that using Rhino.
Our friends from Autodesk had the ideal program which we could use to mix the meshes, join them, or Boolean difference them. This program helped us throughout the rest of the project and was our savior. Every patch that needed to be done, every Boolean difference or union, this program would fix everything for us.
Each and every model that is used in anatomy classes uses colours to give a visual representation of the oxygen deprived and enriched parts of the heart. This is also what we wanted to create in our model, give a good representation of which part of the heart does what and which colour fits this. To do so we needed to cut the atria and ventricles from the hearth, give them an offset and make them in to a solid. This sounds like a pretty straight forward job, it turned out the other way. Because of the very complex shape the parts of the heart has creating an offset in Rhino was a hard task. After a lot of tinkering, mending holes and patching stuff finally it was done. An offset ventricle and atrium on the right and left side. Each part was Boolean differenced with the whole heart so there was no overlap and the atria and ventricle where separate layers so they could both be given an individual colour.
To give an accurate representation of the human heart it needs it valves. The hearth has four valves which are in different places and have different sizes. Each of the valves is connected to the hearth or even to each other. Seen the fact that every heart of every human is different we needed to make a system where we modelled the valves and could deform them later without losing their generic shape.
The scans from the LUMC were in, downloaded and ready to work with. To make a printable file the scan needed to be ONE surface, the problem still was that the CT scans gave us an image which consisted out of multiple smaller surfaces. A lot of cleaning needed to be done, but how. Rhino is a beautiful modelling program but when it comes to meshes it offers us not so much, and so the next search for a modelling program which could model meshes in a quick and easy manner began. After downloading multiple trails, and have tried many programs we found the savior, geomagic. Geomagic offers many platforms on which you can work with meshes. This is where we found the program which we use by now. The program deforms the mesh into a clay shape which could be stretched and moulded. We patched the holes in the model, made it a solid and converted into a smooth and beautiful STL file. Now the real work began…….
In last weeks submitted piece you could read for our quest of a remodel able model of the human heart. There were three fields to look in to before making a decision on which path we wanted to choose. After a lot of research, struggling, downloading 100+ trails for programs and 400 liters of coffee the die is casted! Finally the next steps in the search for the ultimate didactical model for the LUMC are made.
The ideas for a NURBS model are cleared out of the way. Why, would you say. Simply because of the fact that a good NURBS model costs a lot of money and there is no certainty that the NURBS could be re modeled the way we needed. The idea for building a NURBS model ourselves was also cleared of the table because it would take too much time to repeat this step for every patient and with every heart.
Then the final big option was the one we started initially with: The scans from the heart. The problem with the scans is that they are grainy, have a lot of noise and you cannot keep track where the heart starts or ends. This thanks to the fact that the heart moves. It also is inside of an human body surrounded by organs and muscles which al have fairly the same density as the heart itself. So therefore only the Lumens (the cavities where the blood rushes through) are really visible in the scans. The challenge was set: How could the scans get better so we could work with a more detailed mesh?
The LUMC has an unique collection of un-operated hearts with an congenital heart disease. Al these hearts are deprived of blood and plasticized. So in deliberation with our client we asked if the plasticized hearts could be scanned, because of the lack of surrounding tissue and blood, maybe this would help bring the noise down and give us an more detailed scan. And so it was that we got a beautiful scan last week from the LUMC.
Our first test prints arrived from the printer today.
The slice of the heart looks pretty neat. We also printed some test structures to see how thin we could print and how it behaves with different materials (different stiffness). Removing the support material becomes the biggests issue with ultra thin rods.
Slice of (baby) heart:
Modelled tricuspidalus (valve between right atrium and right chamber)
Test sample with different thicknesses: