Ethical clearance was obtained from the local board and,
based on previously given informed consent,
anonymized imaging data was obtained from 10 patients diagnosed with HCC.
Initially,
CT and MRI DICOM sequences were segmented using a semi-automated protocol developed with the free software InVesalius v3.1.1 (Renato Archer Information Technology Center,
Brazil) running on a high performance Microsoft Windows mobile workstation.
This software allowed us to select a region of interest (ROI) in three distinct planes (axial,
sagittal and coronal) under the supervision of a radiologist,
in order to create a 1:1 scale 3D surface of the liver HCC that was exported in a file format type accessible for the 3D printer (.STL file format) [Figure 1].
Fig. 1: InVesalius application – selecting the ROI in three distinct planes in order to generate a 3D surface of the liver HCC.
References: Department of Medical Imaging, University of Medicine and Pharmacy, Craiova, Romania
In some cases,
we selected a second ROI in order to highlight the necrotic area inside the tumor based on UH (on CT images) and signal intensity (on MRI images) [Figure 2].
Fig. 2: A) Tumor located inside the liver parenchyma; B) Central necrotic area within the tumor; C) Necrotic area.
References: Department of Medical Imaging, University of Medicine and Pharmacy, Craiova, Romania
The .STL files were later imported in another free software (MeshMixer v3.5 for Windows,
developed by Autodesk).
This application allowed us to turn the tumor .STL files into hollow shells with a 2mm thick wall.
Additionally,
in order to replicate the tumor elasticity and deformability,
we adjusted the internal structure of the tumor mesh by applying MeshMixer’s built-in lattice hex grid pattern to fill the inside of the tumor [Figure 3].
Fig. 3: The internal structure of the printed tumor represented by the lattice hex grid pattern.
References: Department of Medical Imaging, University of Medicine and Pharmacy, Craiova, Romania
After exporting the final version of the .STL files from MeshMixer,
we were able to import them later into Up Studio software (developed by Beijing Tiertime Technology Co.
Ltd.) for preprocessing.
Regarding the 3D printing of the tumor,
we used an UP BOX+ 3D printer manufactured by Tiertime that features an enclosed cabinet,
allowing us to be completely in control of the printing scan speed and temperature.
We used a 1.75mm diameter nGen_Flex black flexible filament,
a printing speed of 35mm/s and a build platform temperature of 60°C.
The inside matrix that simulated tumor stiffness was printed as a lattice pattern with various apertures,
translating into different degrees of resistance to digital pressure.
The outside of the tumor was deformable and perfectly replicated the topology of the imaging model.
We have obtained a total of 12 tumor reconstruction models from 10 patients diagnosed with HCC [Figure 4 and Figure 5].
Fig. 4: 3D printed tumor – multiple viewing angles.
References: Department of Medical Imaging, University of Medicine and Pharmacy, Craiova, Romania
Fig. 5: 3D printed liver tumors.
References: Department of Medical Imaging, University of Medicine and Pharmacy, Craiova, Romania
After introducing the models to 45 medical students in their 4th year of training and allowed them to interact with the 3D printed tumors for one hour,
we gave them a questionnaire in order to assess the impact this approach may have on the curricula.
The questionnaire revealed that 100% of the subjects found the approach more appealing than interacting only with the image,
44 out of 45 found the model accurate when compared to the 2D sections observed on the CT and MRI scans and all subjects could appreciate the various degrees of stiffness within the tumor model.