A.Medical data collection
As for 3D printing individual physical model, the data source is the patient’s digital image data, such as CT, MRI etc. The imaging data is the 3D model file generated from the computer software, and 3D printer will type the section into an entity in layer by reading the section information of the file. The scanning accuracy of the imaging data will directly influence the authenticity of the 3D printing medical model. Therefore, the standardization of the collection of skeleton imaging data is crucial.
1. CT Data Collection:
CT is the most common medical data source of digital design and has strong analysis capability towards bone tissue and contrast medium. CT data needs to satisfy the following requirements as per 3D printing design demands:
①Equipment option: it is suggested to use the multislice spiral CT with screw pitch, but not the traditional progressive type CT or single-slice helical CT;
②Scanning range: on condition clinical requirements are satisfied;
③Scanning internal: ≤1mm, but not＞2mm at suggestion;
④CT scanning parameter determination: as per clinical needs;
⑤Resolution: it is suggested to use the CT with the pixel matrix of 512x512, and pixel size of 0.5mmx0.5mm;
⑥Scanning position: the correct placement of scanning position is beneficial to the later 3D design and measurement. During CT scanning, it is suggested to place the limbs where the long axis of the limb is in accordance with the scanning demand; in case that there is external fixation or joint deformation in the limb, it is suggested to decrease the angle between the two things. It is suggested to place the two sides of the limbs in symmetry according to the anatomy posture: both the upper limbs should be unbent and placed beside the body; palm forward; the two lower extremities should be drawn close and toe forward.
⑦Contrast medium: it can be used by selection as per clinical requirements;
⑧Metallic foreign body: constructed defect can be generated during the CT scanning, which will result in the error of skeleton imaging accuracy.
2. Data Collection with MRI:
MRI has preferable analysis capability towards soft tissue, however in view of a larger scanning slice of MRI, MRI is rarely used for accurate data collection, but often used in marking the soft tissue and lesion range.
①In the MARI scanning sequence, T1 imaging shows a clear anatomical structure, which is suitable for joint 3D design; MRI enhancement 2D section image is suitable to mark the tumor and its infiltration range.
②MRI data is mainly applied to blend and rectify with CT data, and assist CT image in 3D printing model design and text.
3. Image Data Format, Transfer and Archive:
①As for the medical 2D section image used for reestablishment and archive, it is suggested to use the digital image and communication standard format conforming to Dicom 3.0, but it is not suggested to use the other formats generated from PACS system.
②As for the already reestablished and designed 3D model file, it is suggested to use common STL format, but it is not suggested to use the other file formats.
③As for bundling and minification before the file transfer, it is suggested to use the data storage and archive method combined with mobile storage medium and fixed storage medium, so as to guarantee the safety and inquiry convenience.
B. Digital model design
Design is the soul of 3D printing technology, and also the core step to turn the traditional medical image into 3D printing entity. The design is crucial for 3D printing model. In order to ensure a real, reliable and practical 3D printing medical model, the clinician should involve in the model design in the whole course, and he/she should finally check ad confirm during the design process.
The model dimensions should be designed strictly as per1:1 original proportion.
High biofidelity ensures a small anatomical form error.
Design modelling as per the requirements of the doctor so as to satisfy the clinical practical needs.