How does Democratize3d know what to print from the CT scan file?

[agoyne]

Does it only print the areas that appear brightly in the scan? We want to 3d print a model of the collecting system of a kidney and were planning on using a ct scan. In order for it to print only the collecting system, would we need to use contrast in it and make sure all of the surroundings are black? What would be the best way to print an isolated organ with democtratize3d?

[Dr. Mike]

Democratiz3D uses a threshold segmentation method. You can adjust the threshold value (in Hounsfield units) to control what structures you want included or excluded, based on their density. This works best for bones. 

 

Since you want to segment only the collecting system, you can give contrast and do a delayed phase CT to show the contrast is the collecting system, but you will still have the issue of the bones being included too. The best way to deal with this is to create a subvolume of your CT scan. That is only include the volume that contains your collecting system and exclude the bones. This tutorial shows you how to use 3D Slicer to create a NRRD file that has a subvolume with the Crop Volume tool. Once you have cropped your volume, upload the subvolume NRRD file to democratiz3D and it will spit out your collecting system. If a few small bone chunks are still present, you can manually delete from from your STL file using Meshmixer, Blender, or some other mesh editing software program. Hope this helps.