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Cranioplasty

Cranioplasty is the surgical fix of a bone imperfection in the skull that is left behind after a past operation or accident. A bone graft from elsewhere in the body or a synthetic material may be used to repair defects or gaps in the cranial (skull) bones.

INPUT: DICOM Images (Brain Plain CT)

OUTPUT: Mould, cavity and missing part

Process Flow:

Steps: https://www.youtube.com/watch?v=ieayuzjayzY

  1.  Open 3DSlicer.

  2. Load data which are dicom images in this case by clicking the button DCM from the toolbar.

  3. Import the file NCCT head file.

  4. Now go to the segment editor module.

  5. Now click on the button ADD which will add a new segment to this volume.

  6. Now click on the threshold button below this section and set it to get the desired section by looking at the right side. Make sure you get the whole section in which you are interested in.

  7. Now click on the button show 3D to see a 3d view of the skull.

  8. To clean it a bit use the Islands tool. Choose keep the largest Island and click Apply.

  9. After this export the file in stl format by clicking on the triangular icon right of the segmentations button.

  10. Now we need to create a mould for the missing part in meshmixer. To do that we need this missing part’s stl file which will be created using solidworks. In this tutorial we will assume that we already have that file.

  11. To make the mould, open meshmixer. 

  12. Import stl file of the missing file (received from designer).

  13. Now go to the edit button and click on generate face groups. This option will divide the whole mesh into different face groups which we will use later. 

  14. Now click on the select button and double click on the part to select it all.

  15. Go to edit option and select offset and set it to 4mm (this operation could take a few minutes but if this option is taking more than 4 to 5 minutes then you can do one thing just import the missing part in another meshmixer menu and sculpt it a bit to smoothen it and make offset process faster: https://drive.google.com/open?id=1vpZJf0hmn4vELAiMBqzjVqlBzH7XNnZx ).

  16. Now rotate the file accordingly so that only the front side is visible and select the front face by choosing select visible operation in the select menu. If the boundary is not smooth click on the smooth boundary option in the select menu.

  17. Now delete this section by pressing the delete button on the keyboard and save this file first with some different name.

  18. Now perform undo operation and select invert connected operation and delete the back face of outer shape. So now we have two files one is for the front face and the other is for the back face. Let’s take the file with a back face and create a mould for it.

  19. After deleting the outer surface you will see the actual part within the thicker part.

  20. Now to create a mould we have to delete the front face of the actual part as well and then connect the remaining two surfaces to make a solid.

  21. To delete that we have to separate the both layers by choosing the option to separate shells from the edit menu.

  22.  

    An object browser will pop up containing the name of both the shells.

  23.  

    Now hide the outer shell by clicking on the eye icon. And delete the front face of the inner shell using the operation expand to groups option from select menu(Note that face groups are in different colours so the selection of one face is easy: https://drive.google.com/open?id=1bG1FwxqaqhqbBq1HcKGJwB96GPwAw3O3 ).
  24. Select the inner layer and flip its normals in the edit option in the select menu.
  25. Now we have 2 layers which we have to connect with each other to make a solid mould.

  26.  

    To do this we will use netfabb’s add triangles repair.

  27.  

    We will import the file in netfabb and click on the + button and then add triangles to fill it: https://drive.google.com/open?id=1w8ZRPBBfyhsoGCtVu3PakaBegQ8BJb0L .

  28. Once we are done with that we will save that file stl format.

  29.  

    Now we have to make the lower part of the mould to print it.

  30.  

    To do that we have to select the lower part and then do transform operation(do it in world frame not local frame) in the deform menu to stretch it out. And then do a plane cut to even out its surface.

  31. Now we have to make the lower part of the mould to print it.

  32.  

    To do that we have to select the lower part and then do transform operation(do it in world frame not local frame) in the deform menu to stretch it out. And then do a plane cut to even out its surface.

  33. Same steps will be followed to make the other part of the mould through the file we saved earlier.

  34.  

    Now we need 2 pins to hold these two moulds together. We have a stl file of pins. We just have to place these in extreme corners using the boolean union option as shown in the picture below.

  35.  We have to place the pins in the lower mould and create holes in the upper mould to hold these. To do that we will use boolean difference operation by choosing pins and upper mould simultaneously.

  36.  

    Now we will put letters on the print using meshmix option in meshmixer. We just need to drag and drop it wherever we want.

    Font size of case number: Letters: 0.06

                                  Numbers: 0.05

    Font size of Aha 3D: Letters: 0.07

                          Numbers: 0.07

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