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Dr. Mike

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Posts posted by Dr. Mike


  1. I agree. Even with polyjet, there is the issue of wall thickness. The leaflets are very thin and thus hard to print with any printing technology. With great difficulty I designed an 3D printed a customized sheep heart for flow testing of TAVR devices using elastic material. 

     

     


  2. I've found that printing anatomic parts with a single extruder is difficult, primarily due to limitations on supports with complex, organic geometries. Dual extruder with soluble interfaces is what I use if FDM is required. Stereolithography is also an option although it is messier and arguably requires more postprocessing. Anyone have success with a regular single extruder (excluding specialized setups like MMU)?

     

    Mike


  3. If you are only interested in bone, the lower dose is probably fine. Make sure you get sequences with soft tissue reconstruction algorithm in addition to the standard bone algorithm. Edge enhancement with the bone algorithm causes speckling, which can make bone segmentation more difficult. See my blog article on selecting a good scan for 3D printing below for details. Look at the section on reconstruction kernel.

     

     


  4. A member recently messaged me a comment. I am posting the response here to help the general community:

    "Regarding democratiz3D, I like that it's simple to use.  Being able to convert to even higher resolution STL files for free would be nice."

     

    My response:

    Do you know about our Ultra quality settings? If you set democratiz3D to use ultra quality, you will get an output STL with about 3 million polygons. That is super high resolution. Files of that resolution are difficult to even open on regular PCs because of the extreme detail. 

     

    Ultra quality STLs take about an hour of server time to generate, and thus we cannot give them away for free. They are available with Premium subscriptions. However, you can still get them for free with our Pay or Share program. If you agree to share your STL with the community, we will pick up the tab for the conversion. It is free for you as our gift because you gave something to the community. 

     

    Hope this helps!

     

    Dr. Mike


  5. A member recently asked the following question:

     

    "Is there a skull that would work for someone who is interested in facial reconstruction sculpting or forensic sculpting? I searched some of the skulls but found most seem to have hollow spaces. "

     

    We have a variety of skulls available for download and 3D print -- several hundred at least. I am sure you can find something representative of what you need. I am not sure what you mean by "hollow spaces." A normal skull has many hollow spaces, including the paranasal sinuses, mastoid air cells, and of course the intracranial portion where the brain sits. Are you seeking something different?

     

    Dr. Mike


  6. A user asked us the following:

    "Is it possible to get kidneys and near by attached vascular and possible tumors cut out of a CT scan? "

    The answer is yes. This will probably require lots of time manually segmenting the various structures, but it is possible. It is easiest of the CT scan is with IV contrast and in thin slices. Attached is a picture of a custom print job we did for a medical device company. 

     

    If you need a custom print print please contact us. If you want to learn more about custom models for medical device testing or other purposes, you can find more info here. 

     

    20190729_012109.jpg


  7. A member asked us the following question:

    "I uploaded a NRRD file and was hoping to be able to download it as an STL - any advice?"

     

    You can use our democratiz3D service to automatically convert an NRRD into a 3D printable bone STL model. You can find more about democratiz3D here. There are many tutorials available here.  Hope this helps.


  8. You are diving into the deep topic of medical imaging scans for 3D printing. I wrote a blog article on how to get the most out of your scan here. Take a look as it is very helpful.

     

    3mm is not bad for a CT scan for 3D printing.  In order to understand why the radiology department created 3 mm slices, you need to understand how CT scans work. Modern CT scanners do not acquire data in slices. Rather, the acquisition is helical. The patient moves in the scanner on the Z axis at a fixed speed, while the x-ray tube spins around that axis during acquisition. As a result, relative to the body, the x-ray tube moves around like a helix, i.e. corkscrew. The raw data from this acquisition is stored in memory in the CT scanner. It is then reconstructed into flat slices that can be of any thickness anywhere from 0.5 mm to 5 mm.

    helical-scan.png

     

    Thinner slices are not always better however. There is a fixed number of x-ray photons that were acquired during the scan. When the slices are created after the fact, the data that those photons created is spread among the slices. If you have a lot of very thin slices then there are few photons per slice. Just like with a handheld camera when you shoot in low light, having a low number of photons results in a grainy image. The exact same things happen with a CT scanner. Thin slices tend to be very grainy and it can be difficult to detect abnormalities when the image quality is poor. Thicker slices on the other hand are fewer in number and have more photons per slice and thus are less grainy. Think of a nice photograph from a handheld camera on a bright sunny day. There are so many photons to make the image, the image is crystal clear. Thicker slices, while giving a higher quality image, are also thicker, and very small structures are harder to see.

     

    Therefore, if you had a CT scan and reconstructed 0.5 mm slices, those images would be much grainier and of lower quality than if you had reconstructed with 5 mm slices. When the scan is being taken the radiologist determines what slice thickness is the best for diagnosing the problem at hand. If you're getting a CT scan of the abdomen for appendicitis, you will get 5 mm slices. If you have a problem with your middle tier and are getting a CT scan of the mastoid, you'll probably get 0.5 mm slices.

     

    It should be noted that the raw data from the scan acquisition takes up a lot of memory. While the reconstructed slices are saved in the hospitals radiology system, the raw data from the scan is stored on the physical scanner itself. Typically after a few days that data is purged to make room for new scan data. So, after a few days it is not possible to generate any new slices from the scan, as the raw data has been purged.

     

    My guess is that 3 mm slices is as good as you are ever going to be able to get from your scan. To reduce the stairstep artifact, run a smoothing algorithm on your model. This should reduce that appearance.

     

    I hope this helps

     

    Dr. Mike

     

     


  9. If you increase the threshold value (150->250 Hounsfield units), that will tend to include less bone in the model. If decrease it, more bone will be included. 

     

    Just want to check -- are you starting with a CT or an MRI. CTs work better.

     

    Hope this helps.

     

    Dr. Mike


  10. I use 3D slicer and the segmentation module. It takes a little time to get familiar with the tools, but they can be pretty powerful.

     

    I just did this kidney yesterday, including the kidney tissue, renal collecting system, artery and vein. 

     

    FYI, we are building the ability to automatically segment organs into democratiz3D. Right now it only supports creation of bone models, but in the future auto segmentation of organs will be a feature. 

     

    Hope this helps,

     

    Dr. Mike

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  11. Try this tutorial. Creating the nrrd is pretty simple and takes about a minute. 

     

     

    If you are trying to create a bone model from a CT scan, try democratized -- embodi3D's cloud service for automatic conversion. 

     

    If you want to do other things, we have a variety of free tutorials online. 

     

    Good luck!


  12. I think flaviu knows what a medical scan is. He is asking for specifics. CT? MRI? with contrast? If MRI what pulse sequence? T1? T2? MRAGE? post con? What body part? What slice thickness? etc etc. 

     

    Hil, I think you may be underestimating the difficulty in printing from a medical scan. How are you going to extract your model data from the medical scan? How are you going to quality control the segmentation? How are you going to print it (size, material, layer thickness, orientation, supports, etc). You have to have this all planned out before you go down this road.

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