3D printing in medicine of congenital heart diseases
- 9.2k Downloads
Congenital heart diseases causing significant hemodynamic and functional consequences require surgical repair. Understanding of the precise surgical anatomy is often challenging and can be inadequate or wrong. Modern high resolution imaging techniques and 3D printing technology allow 3D printing of the replicas of the patient’s heart for precise understanding of the complex anatomy, hands-on simulation of surgical and interventional procedures, and morphology teaching of the medical professionals and patients. CT or MR images obtained with ECG-gating and breath-holding or respiration navigation are best suited for 3D printing. 3D echocardiograms are not ideal but can be used for printing limited areas of interest such as cardiac valves and ventricular septum. Although the print materials still require optimization for representation of cardiovascular tissues and valves, the surgeons find the models suitable for practicing closure of the septal defects, application of the baffles within the ventricles, reconstructing the aortic arch, and arterial switch procedure. Hands-on surgical training (HOST) on models may soon become a mandatory component of congenital heart disease surgery program. 3D printing will expand its utilization with further improvement of the use of echocardiographic data and image fusion algorithm across multiple imaging modalities and development of new printing materials. Bioprinting of implants such as stents, patches and artificial valves and tissue engineering of a part of or whole heart using the patient’s own cells will open the door to a new era of personalized medicine.
Keywords3D printing Congenital heart disease Surgical simulation Surgical training
computer aided design
digital Imaging and communication in medicine
hands-on surgical training
steady state free precession
stereolithography or standard tessellation language
Congenital heart diseases are the most common significant birth defects with a live birth prevalence of 7.5 per 1000 . Most congenital heart diseases causing significant hemodynamic and functional consequences require surgical repair. Modern imaging technologies including ultrasound, computed tomography (CT) and magnetic resonance (MR) provide accurate information regarding the anatomy and hemodynamic consequences of congenital heart disease. However, understanding of the surgical anatomy from the provided images requires a complicated process of mental reconstruction and can be often inadequate or wrong. In addition, communication among cardiologists, radiologists and surgeons is often difficult because of complex, diverse and controversial terms used in the description of congenital heart diseases, which may lead to misunderstanding of the surgical anatomy .
Virtual demonstration of the 3D structures on a 2D computer screen facilitates understanding of the complex anatomy. 3D printing takes a closer step toward the reality by providing the physical replicas out of the digital data processed for the virtual models. Medical applications of 3D printing have continuously been expanding [3, 4]. As far as we know, the 1st paper on cardiac application of 3D printing was published in 2000 by Binder et al . In the last 15 years, 3D printing has increasingly been used in the diagnosis, management and education of congenital heart diseases [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34]. This review paper will introduce the applicable imaging techniques, post-processing and printing procedures, current applications and limitations, and future directions of 3D printing in the medicine of congenital heart diseases.
Applicable medical imaging techniques
Imaging techniques applicable for 3D printing of heart models
Computed tomography (CT)
● ECG-gated breath-held contrast-enhanced angiography
● Non-ECG-gated contrast-enhanced angiography
Magnetic resonance (MR)
● Non-contrast 3D SSFP (steady state free precession) imaging
● Non-ECG-gated 3D FLASH (fast low angle shot) angiography using gadolinium-based extracellular contrast agent
● ECG-gated respiration-navigated 3D IR (inversion recovery) FLASH angiography using gadolinium-based blood pool contrast agent (Gadofoveset: ABLAVAR®, Lantheus Medical Imaging, Inc. MA, USA)
● ECG-gated respiration-navigated 4D MUSIC (multiphase steady-state imaging with contrast enhancement) using ultra-small supermagnetic iron oxide (USPIO: Ferumoxyol, AMAG Pharmaceuticals, Lexington, MA, USA)
● 3D grey-scale echocardiography
● 3D color or power Doppler echocardiography
● Rotational CT angiography
ECG-gated CT angiograms provide a spatial resolution of 0.3–0.7 mm and are the most commonly used images among currently applicable imaging modalities in 3D printing of cardiovascular structures. In CT angiography, it is important to time the scanning when all cardiac chambers are homogeneously enhanced. It is also important to inject a generous amount of saline chaser to minimize the artifact from undiluted contrast medium remaining in the superior or inferior vena cava and its tributaries. Although MR angiograms may provide <1 mm spatial resolution, high resolution imaging is at the expense of significant compromise in signal-to-noise ratio. If there is no significant stenotic lesion or valvular regurgitation that cause artifact from turbulent flow, non-contrast 3D SSFP (steady state free precession) imaging provides the images of sufficient quality. However, contrast-enhanced angiography is required in most cases with congenital heart disease. In conventional MR angiography using an extracellular contrast agent, ECG-gating is hardly applicable and a degree of artifact from cardiac motion is unavoidable. ECG-gated and respiration-navigated 3D FLASH (fast low angle shot) angiography using blood-pool contrast agent (Gadofoveset: ABLAVAR®, Lantheus Medical Imaging, Inc. MA, USA) provides excellent images with homogeneous distribution of contrast medium and no significant artifact from turbulent flow . Most recently, ultrasmall superparamagnetic iron oxide (USPIO: Ferumoxyol, AMAG Pharmaceuticals, Lexington, MA, USA) that is used for treatment of iron deficiency anemia has been tried for angiography in children with excellent results , and can certainly be applied for 3D printing.
Ultrasound is not an ideal imaging modality for 3D printing because of the limited access windows for imaging and abundant artifacts from bones and air. However, certain parts of the heart such as atrial and ventricular septa can be imaged appropriately for 3D printing [3, 4, 25, 26, 37]. Although the results are not satisfactory, cardiac valve leaflets can also be imaged and printed with ultrasound data. Lastly, rotational CT angiograms obtained from modern x-ray angiographic equipment can be used for 3D printing .
Postprocessing of image data
3D printing process
The STL files are loaded to the software program of the 3D printer and the materials are assigned to the files for printing. Most commercially available 3D printers are designed for building rigid plastic models, while a few printers are capable of building models with soft rubber-like materials. Ideally, the printing material should have the physical properties such as consistency, elasticity, tensile strength, tear resistance and memory capacity that are similar to those of human soft tissue. Among the existing 3D printers, the printers using polyjet technology and photopolymer resin materials (Objet Connex Series printer and TangoPlus FullCure resin, Stratasys Ltd, Minnesota, USA, and Projet 5500X printer and Visijet CE NT-Elastomeric Natural resin, 3DSystems, Rockhill, USA) provide the physical properties of the printed models closest to those of human soft tissue, allowing simulated surgical and interventional procedures. If the purpose of 3D printing is for demonstration of the anatomy of the heart, any commercially available printer with an acceptable print resolution can be used.
With current 3D printing technology, 3D printing typically takes 3–10 hours to build a single piece of the heart model depending on its size. After the model is completely built, it is harvested and the supporting material and/or the unused print materials are washed out with a waterjet, blown away with an airjet or melted down with chemicals and water. Depending on the materials used and the complexity of the geometry, this cleaning process takes a few minutes to an hour. Powder-based models require curing with chemicals and heat. Although some printers build the models with multiple colors, others provide limited color options. When the printed model is white or faintly colored, one may want to dye the model with a slightly dark color for improved perceptual representation of the complex surface anatomy.
Planning and simulation for surgical and interventional procedures [9, 13, 14, 15, 16, 17, 18, 19, 20, 21, 23, 27, 28, 29, 30, 31]
Preoperative assessment with 3D print models reduces the degree of uncertainty as regards to the patient’s specific anatomy. In selected cases, 3D printing can contribute to an improved outcome as precise preoperative understanding of the complex anatomy may obviate or shorten lengthy exploration, and therefore operation and cardiopulmonary bypass time can be reduced . Surgical procedure on a patient with congenital heart disease is usually performed through a midline sternotomy or lateral thoracotomy and a small incision in the wall of an atrium, an arterial trunk or, rarely, a ventricle. As the patient’s thorax and heart sizes are small in children, the actual surgical scene is difficult to inspect especially from the assistant’s position during the surgery. If the sterilized models showing the important surgical anatomy of the patient’s heart were given to the surgical team, the primary operator’s procedure would be facilitated with precise and streamlined assistance from the assistants . In addition, 3D print models made of flexible material can be used for practice surgery before the real operation.
Indications for 3D printing since 2009 (70 cases)
Congenital heart disease
Double outlet right or left ventricle
Transposition of the great arteries, complete and congenitally corrected
Criss-cross heart or superoinferior ventricles
Heterotaxy with complex heart disease
Complex form of ventricular septal defect
Anomalous pulmonary venous connection
Complex tetralogy of Fallot
Coarctation of the aorta
Traditionally, pathological specimens removed from the patients during autopsy or heart transplantation are used for cardiac morphology teaching. Although the specimens are valuable educational resources, they are scarce and do not represent the whole spectrum of pathology. With improvement of the surgical and medical management of congenital heart diseases and changing concept on human right issues regarding retention of the removed human organs in the pathology laboratory, fewer specimens will be available. On the other hand, the existing specimens are exposed to wear and tear. 3D print models are great educational resources (Figs. 4 and 7) [33, 34]. By using the living patients’ imaging data, almost entire varieties of congenital heart diseases can be covered with 3D print models. The pathological features can be demonstrated in any desired planes or views. Any number of models can be reproduced and shared, and access to the models is not limited. With current technology, however, the valve tissues and myocardial pathology are hardly reproducible. Despite such a limitation, contemporary morphology teaching sessions using 3D printed educational model sets have increasingly been introduced in international and national meetings in the last few years.
3D print models are helpful in education of the patients and their parents . The patient’s cardiovascular pathology and the intended or previously performed surgical or interventional procedures are easy to understand when they are explained using 3D print models.
Learning surgical techniques in congenital heart disease is challenging. As discussed, the size of the heart in children is usually small and the access routes for the procedure are limited for observation. In addition, the rarity of certain congenital heart diseases further limits the opportunity to learn and to improve the surgical skills. 3D printed models are great resources for surgical training (Fig. 6). The supervisors can take unlimited time in showing their procedures. The trainees can take enough time in learning and practicing surgical procedures and repeat the procedures until they feel confident. To the experienced surgeons, 3D print models can be used for development of the new procedures or to improve their surgical skills for rare diseases. In a personal communication, one of our senior surgeons commented that it usually takes a few years for the surgeons to learn how to do the Norwood operation in hypoplastic left heart syndrome and that he should have been able to learn the procedure overnight if 3D print models of a few cases with different pathologic variations would have been available for practice. We organized or supported three HOST courses in the last 12 months. All three courses were successful with high audience satisfaction [Yoo SJ, Spray T, Austine E, van Arsdell GS, et al. Hands-on surgical training (HOST) on congenital heart surgery using 3D print models. In preparation]. We strongly advise the surgeons and trainees to practice their surgical skills on 3D print models first before performing the specific operation on the patients.
The limitations of 3D printing occur in all stages, during imaging, postprocessing and printing. Precise representation of any moving anatomical structures requires high spatial and temporal resolutions. With currently available imaging technologies, it is difficult to image the fine moving structures such as valve leaflets and chordae tendinae with the image quality sufficient enough for 3D printing. These fine structures are important as the abnormalities in these structures are usually associated with significant hemodynamic functional consequences and require delicate surgical repair. As discussed, 3D printing has significant limitations in using the data from ultrasound which is the primary and cheapest imaging technology in cardiac imaging.
Segmentation of the required structures in postprocessing software programs primarily relies on thresholding of signal intensities. When the adjacent structures do not have distinctly different signal intensities allowing automatic boundary detection, extensive time-consuming manual editing is required and the accuracy is significantly compromised.
It is ideal to print the heart using flexible materials with the physical properties similar to that of the human myocardium and valve tissues, especially when practice procedures were to be performed on the models. There are only a few flexible print materials, each of them being able to be used on a specific type of printer only. The surgeons find the models made of flexible material are more difficult to be sewn and easily torn or cut through as compared to real human myocardium or vessels.
The most important limiting factor in applications of 3D printing in patient care and teaching medical professionals is its high cost rather than its utility. The available software programs, printers and printing materials are expensive. Postprocessing is labor-intensive and often requires the hands of experienced imagers. Although 3D printing is also called rapid prototyping, it is fundamentally a time consuming process to build any object by adding numerous layers. The expenses per case can be unbearably high for small programs.
Although most 3D printers are provided with the company’s own specification regarding print resolution, reports on its reproducibility and accuracy in human applications are scarce [9, 19, 31] and prospective studies in larger cohorts are required. Nonetheless, it is of no doubt that 3D models are very helpful in understanding the complex morphology and spatial relationship among the structures. However, the models should be carefully reviewed in conjunction with the standard imaging findings as certain degrees of distortion and abbreviation of the information are inevitable during postprocessing and printing.
As have been the cases for any other procedures in their early developing phases when the objective data are lacking or scarce, it will take time for the insurance and its governing organizations to recognize 3D printing as a standard medical procedure and provide reimbursement for the service. In this respect, prospective clinical trials on use of 3D printing in congenital heart disease surgery and surgical training are crucially important to prove the cost-benefit of this newly developing technology.
Of little doubt, 3D printing will be widely used in the medicine of congenital heart diseases. Hands-on surgical training will gradually become an essential component in the surgical training programs. For rare and complex surgical procedures, hands-on training on the 3D print models will be the prerequisite requirement for performing the procedure on the patients.
As discussed, each imaging modality has its own strengths and weaknesses. Both contrast-enhanced CT and MR are excellent in visualization of the blood pool, while ultrasound is far superior to CT and MR in the demonstration of the anatomy and function of the cardiac valves and chordae tendinae. Image fusion is to improve the image content by combining useful information from multiple imaging modalities . The process requires precise image registration process for spatial coordination between the images from different imaging modalities and mathematical algorithm for combining data from different sources. Image fusion technology will certainly enhance the image quality by compensating the weaknesses of each imaging modality and reduce the extent of artifact.
3D printing can be used for personalized implants such as stents, surgical patches and artificial valves [41, 42]. 3D printing has also been experimentally used for tissue engineering such as cardiac valves. Using 3D printing, a scaffold is printed and the cardiac progenitor cells are laid down with matrix for growth [43, 44, 45]. While a clinically viable product has not yet been fabricated, tissue printing eventually will allow fabrication of the implants made of the patient’s own stem cells and possibly obviate drug testing on animals by testing on bioprinted human tissues or organs .
3D printing has found its niche applications in the medicine of congenital heart diseases. 3D print models allow instantaneous understanding of any complex anatomy and simulation or hands-on training of surgical and interventional procedures. It has made a small revolution in teaching and surgical practice. We expect that Hands-on surgical training (HOST) will soon become a mandatory component of the congenital heart disease surgery programs. 3D printing will expand its utilization with further improvement of imaging and printing technologies and development of new printing materials. Bioprinting and tissue engineering will open the door to the new era of personalized medicine.
- 2.Giroud JM, Jacobs JP, Spicer D, Backer C, Martin GR, Franklin RC, et al. Report from the international society for nomenclature of paediatric and congenital heart disease: creation of a visual encyclopedia illustrating the terms and definitions of the international pediatric and congenital cardiac code. World J Pediatr Congenit Heart Surg. 2010;1(3):300–13. doi: https://doi.org/10.1177/2150135110379622.CrossRefGoogle Scholar
- 8.Noecker AM, Chen JF, Zhou Q, White RD, Kopcak MW, Arruda MJ, et al. Development of patient-specific three-dimensional pediatric cardiac models. ASAIO J. 2006;52(3):349–53. doi: https://doi.org/10.1097/01.mat.0000217962.98619.ab.CrossRefGoogle Scholar
- 18.Sodian R, Weber S, Markert M, Loeff M, Lueth T, Weis FC, et al. Pediatric cardiac transplantation: three dimensional printing of anatomic models for surgical planning of heart transplantation in patients with univentricular heart. J Thorac Cardiovasc Surg. 2008;136(4):1098–9. doi: https://doi.org/10.1016/j.jtcvs.2008.03.055.CrossRefGoogle Scholar
- 21.Farooqi KM, Nielsen JC, Uppu SC, Srivastava S, Parness IA, Sanz J, et al. Use of 3-dimensional printing to demonstrate complex intracardiac relationships in double-outlet right ventricle for surgical planning. Circ Cardiovasc Imaging. 2015;8(5):e003043. doi: https://doi.org/10.1161/CIRCIMAGING.114.003043.CrossRefGoogle Scholar
- 22.Costello JP, Olivieri LJ, Krieger A, Thabit O, Marshall MB, Yoo SJ, et al. Utilizing three-dimensional printing technology to assess the feasibility of high fidelity synthetic ventricular septal defect models for simulation in medical education. World J Pediatr Congenit Heart Surg. 2014;5(3):421–6. doi: https://doi.org/10.1177/2150135114528721.CrossRefGoogle Scholar
- 25.Olivieri LJ, Krieger A, Loke YH, Nath DS, Kim PC, Sable CA. Three-dimensional printing of intracardiac defects from three-dimensional echocardiographic images: feasibility and relative accuracy. J Am Soc Echocardiogr. 2015;28(4):392–7. doi: https://doi.org/10.1016/j.echo.2014.12.016.CrossRefGoogle Scholar
- 27.Costello JP, Olivieri LJ, Su L, Krieger A, Alfares F, Thabit O, et al. Incorporating three-dimensional printing into a simulation-based congenital heart disease and critical care training curriculum for resident physicians. Congenit Heart Dis. 2015;10(2):185–90. doi: https://doi.org/10.1111/chd.12238.CrossRefGoogle Scholar
- 28.Kiraly L, Tofeig M, Jha NK, Talo H. Three-dimensional printed prototypes refine the anatomy of post-modified Norwood-1 complex aortic arch obstruction and allow presurgical simulation of the repair. Interact Cardiovasc Thorac Surg. 2016;22(2):238–40. doi: https://doi.org/10.1093/icvts/ivv320.CrossRefGoogle Scholar
- 31.Ma XJ, Tao L, Chen X, Li W, Peng ZY, Chen Y, et al. Clinical application of three-dimensional reconstruction and rapid prototyping technology of multislice spiral computed tomography angiography for the repair of ventricular septal defect of tetralogy of Fallot. Genet Mol Res. 2015;14(1):1301–9. doi: https://doi.org/10.4238/2015.February.13.9.CrossRefGoogle Scholar
- 32.Biglino G, Capelli C, Wray J, Schievano S, Leaver LK, Khambadkone S, et al. 3D-manufactured patient-specific models of congenital heart defects for communication in clinical practice: feasibility and acceptability. BMJ Open. 2015;5(4):e007165. doi: https://doi.org/10.1136/bmjopen-2014-007165.CrossRefGoogle Scholar
- 33.Yoo SJ, Thabit O, Lee W, Goo HW, van Arsdell GS (2013) Double outlet right ventricle in your hands. Web publication. https://doi.org/imib-chd.com/wp-content/uploads/morphology/1-dorv-in-your-hands/DORV%20IN%20YOUR%20HANDS%2012%20CASE%20SERIES.pdf.
- 34.Yoo SJ, Thabit O, Lee W, Goo HW, Yim D, Ide H, van Arsdell GS (2015) Most peculiar hearts in your hands. Criss-cross, superoinferior, twisted, topsy-turvy, etc. What do they all mean? Web publication. https://doi.org/imib-chd.com/wp-content/uploads/morphology/2-mph-in-your-hands/MOST%20PECULIAR%20HEARTS%20IN%20YOUR%20HANDS%20Full%20Pages.pdf
- 35.Messina M, Rigsby C, Deng J, Bi X, McNeal G (2013) 3D navigator-gated inversion recovery FLASH (Nav_IR_Flash) with blood pool contrast agent. Magnetom Flash 3/2013.Google Scholar
- 36.Han F, Rapacchi S, Khan S, Ayad I, Salusky I, Gabriel S, et al. Four-dimensional, multiphase, steady-state imaging with contrast enhancement (MUSIC) in the heart: a feasibility study in children. Magn Reson Med. 2015;74(4):1042–9. doi: https://doi.org/10.1002/mrm.25491. Epub 2014 Oct 9.CrossRefGoogle Scholar
- 38.Poterucha JT, Foley TA, Taggart NW. Percutaneous pulmonary valve implantation in a native outflow tract: 3-dimensional DynaCT rotational angiographic reconstruction and 3-dimensional printed model. JACC Cardiovasc Interv. 2014;7(10):e151–2. doi: https://doi.org/10.1016/j.jcin.2014.03.015.CrossRefGoogle Scholar
- 42.Giannopouk AA, Chepelev L, Shikh A, Wang A, Dang W, Akyuz E, Hong C, Wake N, Pietila T, Dydynski PB, Mitsouras D, Rybicki FJ (2015) 3D printed ventricular septal defect patch: a primer for the 2015 Radiological Society of North America (RSNA) hands-on course in 3D printing, 3D Printing in Medicine 1:3 doi: https://doi.org/10.1186/s41205-015-0002-4.
- 43.Gaetani R, Doevendans PA, Metz CH, Alblas J, Messina E, Giacomello A, et al. Cardiac tissue engineering using tissue printing technology and human cardiac progenitor cells. Biomaterials. 2012;33(6):1782–90. doi: https://doi.org/10.1016/j.biomaterials.2011.11.003.CrossRefGoogle Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.