MUG500+: Database of 500 high-resolution healthy human skulls and 29 craniotomy skulls and implants

In this article, we present a skull database containing 500 healthy skulls segmented from high-resolution head computed-tomography (CT) scans and 29 defective skulls segmented from craniotomy head CTs. Each healthy skull contains the complete anatomical structures of human skulls, including the cranial bones, facial bones and other subtle structures. For each craniotomy skull, a part of the cranial bone is missing, leaving a defect on the skull. The defects have various sizes, shapes and positions, depending on the specific pathological conditions of each patient. Along with each craniotomy skull, a cranial implant, which is designed manually by an expert and can fit with the defect, is provided. Considering the large volume of the healthy skull collection, the dataset can be used to study the geometry/shape variabilities of human skulls and create a robust statistical model of the shape of human skulls, which can be used for various tasks such as cranial implant design. The craniotomy collection can serve as an evaluation set for automatic cranial implant design algorithms.


a b s t r a c t
In this article, we present a skull database containing 500 healthy skulls segmented from high-resolution head computed-tomography (CT) scans and 29 defective skulls segmented from craniotomy head CTs. Each healthy skull contains the complete anatomical structures of human skulls, including the cranial bones, facial bones and other subtle structures. For each craniotomy skull, a part of the cranial bone is missing, leaving a defect on the skull. The defects have various sizes, shapes and positions, depending on the specific pathological conditions of each patient. Along with each craniotomy skull, a cranial implant, which is designed manually by an expert and can fit with the defect, is provided. Considering the large volume of the healthy skull collection, the dataset can be used to study the geometry/shape variabilities of human skulls and create a robust statistical model of the shape of human skulls, which can be used for various tasks such as cranial implant design. The craniotomy collection can serve as an evaluation set for automatic cranial implant design algorithms.
© 2021 The Author(s

Value of the Data
• The 500 healthy skulls can be used to create an statistical shape model (SSM) for cranial implant design [2] , study the geometry variability of human skulls [3,4] , etc. • The 29 craniotomy skulls together with the corresponding manually designed cranial implants can serve as an evaluation set for automatic cranial implant design algorithms. • Researchers can create synthetic cranial defects on the 500 healthy skulls in order to train deep learning algorithms [1,[5][6][7] and host challenges [8] . • The .stl files included in the MUG500+ dataset are 3D printable and can be used for educational purposes.  The folder of the craniotomy skulls are named from B0 0 01 to B0 029 . Under each folder, the .nrrd file is the image data (size: 512 × 512 × Z) of the defective skulls. The .stl files are the meshes of the skull and the manually designed cranial implant. Figs. 2 and 3 show a healthy skull ( A0285 ) and six craniotomy skulls ( B0 0 01, B0 0 02, B0 0 04, B0 0 06, B0 016 and B0019 ) with various defects, respectively. Table 1 shows the meta information (resolution, slice thickness, etc) of the healthy and craniotomy skulls.

Experimental Design, Materials and Methods
Having a uniform collection of medical datasets and a standard operating procedure (SOP) for data processing not only makes the research outcome based on these datasets more reliable but also facilitate reproducibility of the results by other institutions, which is increasingly important

Skull generation from head CT scans
Both the healthy skulls ( .nrrd ) and craniotomy skulls ( .nrrd ) are segmented from head CT scans by medical experts based on a thresholding technique using 3D Slicer ( https://www.slicer. org/ ) [9] . For each head CT, the segmentation threshold is decided specifically by the expert so that the complete cranial and facial bones on the skull can be preserved. The mesh files ( .stl ) of the skulls are extracted from the corresponding segmentation masks.

Computer-aided cranial implant design for the 29 craniotomy skulls
The cranial implants of the 29 craniotomy skulls are designed by an expert using the Geomagic Sculpt software. The software takes as input the .stl version of the craniotomy skulls and the resulting implants can be exported in the same format ( .stl ). Fig. 4 shows an illustration of a craniotomy skull (in gray ) with the corresponding cranial implant (in yellow ). We have also recorded a tutorial video about the semi-automatic cranial implant design workflow with Geomagic Sculpt, which can be viewed at https://www.youtube.com/watch?v=FzaR3ydjaSc .

Ethics Statement
This investigation was approved by the internal review board (IRB) of the Medical University of Graz, Austria (IRB: EK-32-177 ex 19/20).

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. https://www.fwf.ac.at/ ) KLI 678-B31 (enFaced). Last but not least, we want to point out to our medical online framework Studierfenster ( www.studierfenster.at ), where an automatic cranial reconstruction and implant design system has been incorporated [10] .