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Copyright © 2020, Sebastian Andreß
All rights reserved. Please find the license here.

Please cite the corresponding paper when using this filter for publications:

@article{3DPrintWrapSolidify,
    author      = {Weidert, Simon and Andress, Sebastian and Linhart, Christoph and Suero, Eduardo M. and Greiner, Axel and Böcker, Wolfgang and Kammerlander, Christian and Becker, Christopher A.},
    title       = {3D printing method for next-day acetabular fracture surgery using a surface filtering pipeline: feasibility and 1-year clinical results},
    journal     = {International Journal of Computer Assisted Radiology and Surgery},
    publisher   = {Springer},
    date        = {2020-01-02},
}

For further collaborations, patient studies or any help, do not hesitate to contact Sebastian Andreß. Thanks a lot to Andras Lasso for also contributing and improving the module.

Surface Wrap Solidify

Introduction

This effect was designed for creating fractured bone models for fast 3D printing. Especially in orthopedic trauma surgery, the editing time, as well as the printing time should be as short as possible. Using this effect helps to fulfil both features. Also, by removing inner cancellous structures, it is possible to achieve a fracture reduction on the printed model.

In our use-case, we used this effect after applying a simple threshold operation and separating the bone with simple brushing and island techniques. Please watch the workflow example videos. The effect was tested on more than 30 acetabular fracture models, it reduced the printing time about 70%.

Description

The Wrap Solidify Effect uses the following pipeline:

1. A surface representation of the selected segment is created (segmented model).
   • Smoothing Factor defines smoothing of the input surface representation
2. Around this segmented model a sphere is created (sphere/surface model).
3. Shrinkwrapping (iteratively shrinking and remeshing the sphere model to the segmented model) is used for surface definition.
   • Number of Shrinkwrap Iterations is used to define the number of iterations.
   • Smoothing Factor is used for smoothing between iterations.
   • Spacing is used to define resolution of remesh.
4. (optional) The resulting surface model is converted into a segmentation.

Optional Steps

• Carve out Cavities:

  1. Three initial shrinking and remeshing iterations (Step 1-3).
     • Minimal Cavities Diameter and Minimal Cavities Depth is used to define cavities (like in the example images the acetabular cup)
  2. Vertices of the surface model get projected into cavities.
  3. Final shrinkwrap iterations (Step 3-4).

• Create Shell:

  1. Initial Shrinkwrapping (Step 1-3).
  2. After the shrinkwrapping, all vertices of the surface model, that are not touching the segmented model, are deleted.
     • Shell to Input Distance is used to define maximal allowed distance between the vertices of the surface model and the segmented model.
  3. The surface model gets converted to a solid shell model.
     • Output Shell Thickness is used to define the thickness of this shell.
  4. (optional) Step 4.

Results

To see the creation of the results, please see the Workflow Example section.

Workflow Example

As described in the Introduction, this effect was designed to create fast printable bones as easy and least time consuming as possible. The parameters are especially fitted for hemipelvic bones. The threshold and manual edit takes about 3 minutes, the effect itself another 2 minutes resulting in an printable bone. The effect itself reduces the printing time about 70 percent.

Threshold

A thresholding operation between 300 and the maximal Houndsfiled Unit was performed, using the Threshold effect. By using the sphere brush, first the femoral head, and subsequently connecting parts in the sacroiliac joint were erased. Using the Islands effect, the exempted hemipelvis was added to an own segment.

Filter process

In this example, the processing time was 1:46 min on a Apple MacBook Pro 2017 (3,1 GHz Intel Core i7, Memory 16 GB).

How to install

The Extension is available in the Extension Manager for Slicer Versions greater than 4.11. To install it manually, please follow the description on the official 3D Slicer page.