3D Printing of Preclinical X-ray Computed Tomographic Data Sets

The overall goal of this procedure is to create anatomical models of preclinical X-ray CT data sets using 3D plastic printing technology. This is accomplished by first placing a rat or a mouse into an image station and scanning an x-ray computed tomography mode. Next, the data is reconstructed and formatted for input into a commercial 3D printing device.

In the final step, the printer extrudes a complex physical model of skeletal or soft tissue data in plastic. Ultimately, 3D printing technology is used to take the data off the computer screen and place it in the palm of one's hand. I first had the idea for this method when I was working with x-ray CT data sets in the laboratory, and I became aware of 3D printing technology in my engineering classes here at Notre Dame.

The main advantage of this technique over other existing methods like plastic injection molding, is that 3D printing enables the creation of extremely complex models that otherwise would not be possible to produce. Though this method can be used to print 3D data of skeletal structures, it can also be applied soft tissue systems such as the lungs giving a final product like this. All in vivo and ex vivo imaging performed for this protocol demonstration was acquired using the Albea X-ray computed tomography system images were reconstructed using the filtered back projection algorithm via Albea Suite 5.0 reconstruction for the in vivo images seen in this protocol, one male low bun with star rat of 10 months age was scanned while fully anesthetized using ISO fluorine for ex vivo imaging.

A New Zealand white rabbit skull sample preserved in 10%Formalin was scanned. These combined acquisition and reconstruction settings produce a final image with 0.125 millimeter isotropic voxels, which is considered sufficient for whole animal analysis and 3D printing of anatomical structures. Note that the skeletal features from the CT scans can be printed from the raw data without performing segmentation.

However, segmentation of soft tissues is required prior to processing this data for 3D printing. Here an example with lung tissue can be seen Next, the data must be converted from micro PET into DICOM format. Using PMOD analysis software, the DICOM data contains volumetric density values for each voxel.

Then in order to prepare the DICOM data for printing, the data must be processed as a contiguous surface instead of a volume image, J version 1.43 U software can be used to obtain surface renderings for further processing. Finally, two programs, mesh lab version 1.31 and net fab studio basic 4.9 can be used concurrently to remove any excess mesh, join together, disconnected meshes, repair holes, and then smooth the final mesh. The primary differences between these two programs are the tool sets made available to the user and some aspects of the interface navigation control.

They're both 3D mesh editing software programs and using them together provides the easiest approach to editing the model. Be sure to save the file type as STL when using mesh lab. To print the CT model using the maker bot begin by opening the STL file that was generated in previous steps in replicator G software.

Replicator G is a maker bot industries program used to communicate with the printer in the lower right hand corner of the software menu. Click on the scale option and then select Fill the build space. Next, select rotate, then click lay flat.

Then click on center for models with fine detail. Also select the fill build platform option to scale up the model. Then from the same menu, click move, and then select put on platform.

Once the proper orientation has been achieved, select generate G code from the top menu bar. A window with printing options will now appear on screen. Now select the extruder that will provide the filament to print the object being either left or right.

Also check off. Use raft support from the dropdown menu entitled Use support material. Be sure to select the full support option.

Next, select generate G code, A popup box showing the progress of the G code will now appear. Once the G code has been completed, select build to file for use with an SD card and save drag file generated at this stage onto an SD memory card. For transfer, place this SD card into the maker bot.

Then use the maker bot keypad to select print from SD and select the desired file name. At this point, the maker bot will automatically begin to warm up to print the object. Here we can see a time-lapse video of the maker bot printing the 3D model from a CT dataset To perform printing.

Using the online shapeways service start by creating a free account on the Shapeways website. Then the previously generated STL file can be directly uploaded. Select a title for the uploaded file.

Then select a unit of measure from the dropdown menu that appears. Now select upload model. Once the file is uploaded, the website will take a few minutes to process the file to assure it can be printed.

The model will be available for printing in the My Models page after about 10 minutes. In the example scene here, the white strong flexible selection was used to print skeletal structures and the purple strong flexible selection was used to print the lung tissue. The STL file may also be printed out using a commercial high resolution three dimensional printer, such as the Projet HD 3000.

To use this system, the STL file needs to first be loaded into the 3D system's proprietary format to lay out the job on the platform. This requires changing the orientation of the model around to minimize both the use of wax support and print time. Save this file and send it electronically to the printer and load a platform of aluminum into the printer.

The projet HD 3000 will then begin to print the 3D object as seen here. Once it is printed, remove the model from the platform and place it into an oven at approximately 73 degrees Celsius. This will melt the support wax from the model.

Finally, carefully remove the object from the oven while it is still hot and wipe it down with a Kim wipe. This will remove any remaining wax from the surface of the object. Here we can see the final products for three methods of printing of the same in vivo rat CT dataset.

All three models consist of a cropped skeletal structure and removable lungs, which were printed independently and pieced together. The model seen here is the result of the proje HD 3000 high resolution printer created using translucent acrylic plastic. While this object was produced using a third party company, Shapeways Incorporated, in which the skeletal structure was printed using nylon 12 white plastic, while the respiratory structures were fabricated in purple, these models were printed to scale measuring approximately 11 centimeters in length.

This object was made using the MakerBot due to resolution limits of the MakerBot. This model was scaled up resulting in an object of 21 centimeters in length. Here we see the final products of each method of printing for the ex vivo rabbit skull CT dataset.

All three objects were printed to scale and measure approximately 8.5 centimeters in length, and here we see the final products for two methods of printing. A full in vivo CT dataset of the rat. Both models consists of a complete skeletal structure minus the tail and removable lungs.

These two models were printed to actual scale. Note that due to the intricate detail required, the full skeleton could not be printed with the maker bot replicator. After watching this video, you should have a solid understanding of how to use 3D printing technology to create complex anatomical models derived from X-ray CT data sets.