Three-dimensional (3D) printing has significant advantages over other imaging techniques because it can represent anatomical structures inside the body. As the complexity of procedures in medicine has increased and become minimally invasive, the need for realistic representations of human anatomy is becoming increasingly important. The heart is a complex organ which has valves, chambers, and vessels of which, especially in congenital heart disease, can be difficult to represent using conventional imaging techniques. 3D printing can be used for surgical planning, patient education, and student teaching.
Creating a 3D printed model first starts with 3D data sets usually obtained by computed tomography (CT), magnetic resonance imaging (MRI) and 3D echocardiography. This initial step called “segmentation” allows specific heart and vascular imaging information to be extracted from the original raw data, which comes in Digital Imaging and Communication in Medicine (DICOM) format. Unfortunately, DICOM files cannot be utilised by 3D printers. Therefore, they have to be converted into Standard Tessellation Language (STL) format and will need further post-processing to optimise the form for printing (Figure 1).
A variety of 3D printing techniques and materials are available, some of which are well suited to the needs of cardiovascular medicine and surgery. The most useful are sterolithography, selective laser sintering, binder jet, poly jet technology, and fused deposition.
- Stereolithography represents an early technique based on a layer by layer photopolymerisation. This technique reveals transparent or non-transparent but rigid printouts and is therefore not ideal for purposes in cardiovascular medicine.
- Selective Laser Sintering (SLS)considered an outclassing technology uses laser as a power source to sinter powdered material. This technique enables 3D printing of delicate cardiac structures, e.g. native valves. Its dissemination is still limited owing to high production costs.
- Binder Jetting is a technique that creates artifacts through inkjet printing of binder into a powder bed of raw material, provides with rigid and non-transparent printouts. It is capable of printing substructures, e.g. ventricles, atria and large vessels in different colours.
- PolyJet Technologyprovides with dual-material printouts combining smooth, soft and transparent material with hard and non-transparent components. The advantage of this technique is its capability of printing pathology or implants being visible through surrounding native tissue.
- Fused Deposition Modeling also known as Fused Filament Fabricationor Plastic Jet Printing utilises melted thermoplastic material being supplied layer by layer as the material hardens immediately after extrusion from a nozzle which can turn the flow on and off.
Similar to printing on paper, 3D printing deposits a small amount of material onto itself, making many passes to grow the form. The time to complete a 3D printing varies from three fours for distinct cardiac or vascular structures to a full day for complete hearts. Because 3D printing is relatively new the costs are still considerable and usually start around $1000 but depend much on the quality of equipment and the institutional volume.
3D printing can be used for preprocedural preparation of complex interventional procedures. Tangible benefits resulting from 3D printing have been shown for transcatheter aortic valve replacement (TAVR), percutaneous mitral valve repair and device closure of interatrial communications. Device selection, sizing of defects and solid structures as well as general 3D conceptualization are clearly shown in the 3D models. Accurate imaging of pathology including its anatomic features and spatial relation to the surrounding structures is critical for selecting optimal approach and evaluation of procedural results. For example, a high-frequency ablation procedure for treatment of atrial fibrillation using 3D printing allows patient specific optimisation (Figure 2) importantly including optimal catheter selection which can be tested in the 3D model prior to the procedure. Similarly, physicians-in-training can also practice and develop adequate skills on dedicated 3D models before translating them into optimal procedural accomplishments.
Through preoperative tactile and visual experience, the opportunities of simulating surgery with 3D models show promise and a vast yet unrealised future of this technology in medicine. More research is needed to demonstrate improved safety and better long-term results, and cost reduction. Nevertheless, even reduction in medical costs from reduction of complications from a surgeon knowing the anatomy precisely before making an incision will likely outweigh the time and expense to prepare the 3D model. Future perspectives of this method derive from standardisation of segmentation of the 3D imaging and optimal printing substrates (i.e. hard vs. soft) 3D printing appears to be most beneficial in highly specific procedures with complex anatomy. Prospective, multicenter clinical trials as well as standardisation of 3D modeling are needed to verify accuracy of this approach and clinical benefits in order to justify insurance reimbursement.
In conclusion, 3D models derived from conventional CT, MRI, and echocardiographic imaging is helpful for individualised treatment of complex cardiovascular anatomy. 3D printing provides users with the ability to manipulate the model and to simulate and test how the procedure will be performed and how a catheter or device responds to the unique cardiovascular anatomy. Although more research is needed, 3D printing has all the necessary elements to provide high quality patient specific treatments, utilising both a visual and tactile experience. As 3D printers become more commonplace, it is anticipated that it will integrate into quality management and payment systems necessary for its continued growth in medicine.
Bartel T, Rivard A, Jimenz A, Mestres CA, Müller S. Medical three-dimensional printing opens up new opportunities in cardiology and cardiac surgery. European Heart Journal 2017, doi:10.1093/eurheart/ehx016
References available on request.
Dr Thomas Bartel speaks on ‘3D printing in cardiology and cardiac surgery: New opportunities’ at the 3D Medical Printing Conference scheduled to be held on 29th January 2018 at the Arab Health Congress.