In the cardiovascular domain, these imaging technologies that include 3D-echocardiography/ultrasound, 3D-rotational angiography (3DRA), computer-tomography (CT) and magnetic resonance (MR) imaging provide accurate direct information of the anatomy and indirectly of the hemodynamic consequences. 3D-multimodality image integration grossly improves reliability, accuracy and resolution of these modalities, however, as images are not acquired in real-time, three limitations persist: (1) any change in the position of patient or equipment can cause misalignment of the registration; (2) static models do not account for cardiac and respiratory motion; and (3) 3D-models are in projected in two-dimensional plane of the visual screen. 3D-printed anatomical models remain static, but they are different and offer interactivity and hands-on approach. Personalised imaging and modelling of anatomy presents surgeons with a range of advantages, e.g. better understanding of complex anatomy, preoperative planning and virtual surgery, manufacturing of intraoperative aids and prostheses, ability to assess expected result, improved communication within the multidisciplinary team and with patients.
3D-printing processes, manufacturing of patient-specific prototypes
3D-printing consists of consecutive steps of pre-processing (digital data acquisition, segmentation), production (actual stereolithographic printing, a.k.a. additive manufacturing) and post-production (processes similar to chiselling and refinement in sculpture). First, digital data from imaging sources (CT-angio, MRI and echocardiography) are obtained. Most commonly ECG-gated breath-held contrast-enhanced CT-angiography is used that can reach a spatial resolution of 0.3–0.7 mm. Dataset is processed by a special 3D-software [Mimics, Materialise, Leuven, Belgium] and a rotatable digital (virtual) 3D-model is segmented. Accuracy of segmentation depends on the completeness and clarity of raw data and appropriate selection of segmentation values. Areas and structures of interest are exposed while others (temporarily) removed. All this requires intimate knowledge of anatomy. Thus, involvement of the surgeon/morphologist is advised; segmentation is also time-consuming, laborious and – at present – it is not feasible for automation.
The virtual model (stereolithography or ‘.stl’ file) already offers indispensable insight in most instances. The actual printing process involves rapid prototyping and additive manufacturing, building parts layer by layer. In our clinical practice two prototypes are 3D-printed: a real life-sized (blood-volume) solid model provides exact dimensions of the structures; another 1.5-2.5x-magnified (or scaled) hollow model is printed in transparent, flexible material. This allows simulation of the surgical approach and steps of the operation with high-fidelity (virtual surgery). Intraoperative assessment can confirm anatomic accuracy of 3D-models. Prototyping contributes to improved patient safety and shortened operating time, leading to successful outcome.
Among the multiple benefits of 3D-printed models are the improved communication within the multidisciplinary clinical team and patient/family education. Feasibility of new procedures could be experimented with patient-specific morphological characteristics. Besides listed and documented advantages, 3D-printing presents with possible downsides: labour- and technology intensive manufacturing presents with additional costs, need for extra personnel and infrastructure (e.g. 3D-printing facility). It is expected that 3D-printing will have a major role in providing patient-specific (individually customised) implants and prostheses, especially with evolving techniques of bioprinting. Bioscaffolds seeded with progenitor cells of the recipient may develop into complex structures, tissues and ultimately organs. In cardiac surgery, all this could help in fulfilling the ultimate goal to create an ideal cardiac valve implant.
Applications of 3D-modelling and printing in paediatric cardiac surgery
Paediatric cardiac surgery deals with a wide range of patients in view of age (from neonatal to adult-congenital), acuity (from emergencies to elective and/or staged reoperations), and complexities. Most operations are performed with a special attention to the expected growth of structures and assumed transformation of pathophysiology. These aspects mark out our discipline as pioneering in embracing of new modalities, e.g. advances in 3D printing, bioprinting, utilisation of novel methods and materials.
Paediatric cardiac surgery is also a discipline where individual decision-making is key in planning of complex operative plans. Preoperative preparation starts with detailed knowledge of the general patho-morphology before contemplating on an individual surgical procedure. Historically, generations of physicians and surgeons were educated with the help of cardiac specimens that come from individuals with congenital heart disease but they also represent general features of morphology.
Dr Maude Abbott (1869-1940), founder of patho-morphology for congenital heart disease, began ‘museum demonstrations’ in 1904 that had become part of the medical school curriculum. In recent years, however, availability of these specimens has become limited due to stiffened data protection regulations, reduced number of autopsies, natural attrition of specimens and most importantly that patients with congenital heart disease survive. Source of specimens has dramatically dropped.
Transfer of specimens in the morphological archives and from clinical data onto digital platform and creation of a virtual museum could solve the problem. First, specimens are scanned with high-resolution micro-computed tomography (it can achieve a resolution of 10 micrometres). Next, digital information is segmented to create 3D-virtual models and could be 3D-printed in various materials. A virtual museum offers innumerable opportunities for training and education, pre-surgical planning and virtual surgery, patient-family education, etc.
Introduction of 2D-echocardiography enhanced the importance of anatomical knowledge in our discipline that is further emphasised by newer imaging modalities. Interactivity and hands-on approach is key in modern-day medical and postgraduate education, especially in training of the new generations of surgeons. In the meantime, the learning-curve for surgical trainees has become rather steep; no collateral morbidity/mortality is now tolerated. Access to morphological archives – as mentioned – became restricted. Simulation-based methods with 3D (virtual) models and printed prototypes (clinical case scenarios and specimens) could overcome these difficulties and meet the demands of morphological demonstration. Medical education ranges from medical students, trainees, the multidisciplinary clinical team and towards patients/families and the community.
3D-printed prototypes are regularly utilised to improve understanding of the morphology in complex re/operations. 3D-visualisation of the atrial anatomy and connections of the pulmonary and systemic veins in complex atrial baffling procedures offer unique possibility of tailoring geometrically challenging separation patches. Similarly, intraventricular tunnelling and muscle resection can be designed with the help of models. Scaled, transparent hollow-models printed in flexible materials are very suitable in planning intracardiac procedures as segments can be registered with different colours helping identification of the structures. Blood volume models are especially handy for taking measurements and planning procedures on the great vessels and their branches. Actual 3D-printed models are jointly utilized with the 3D-virtual models as these can later be opened, digitally modified, etc. Accuracy of the models is excellent, even after moderate postproduction smoothing. Familiarisation with the expected operative anatomy and planning out alternative surgical scenarios (surgical emulation, virtual surgery) results in improved safety margin. As a critical mass of experience has not yet been accumulated due to the highly individual and variable case-scenarios, no conclusion can be drawn whether 3D-prototypes are effective in saving of time, or other expenses. Personal experience identifies patient-safety and reduced occurrence of complications and ultimately improved quality of care as major advantages.
A National Centre of Excellence (COE) in 3D-printing for healthcare
The vibrant and ever-evolving sociocultural and scientific context of the United Arab Emirates demands the establishment of a Centre of Excellence (COE) in the field of 3D-printed techniques for healthcare. There are five key pillars for the success of such a venture. Most importantly, governmental leadership should embrace and support this rapidly growing and pioneering area by providing transparent legal framework and a spectrum of subsidised programmes. Programmes span from specific clinical applications in orthopaedics, maxillofacial surgery, plastic and reconstructive surgery to cardiovascular surgery to prosthetics and development of bioscaffolds, bioengineered materials, 3D-printed tissues and organs, etc.
Participation of local academic research organisations in biomedical and bioengineering sciences is also key in providing scientific leadership and proper prioritization of viable projects.
The third pillar is the involvement of clinical healthcare (professional and providing institutions) where individual projects can find their realisation, outcome and provide continuous feedback for research. Fourth, healthcare financers should be motivated and involved. Financial cover for 3D-printed models and aids remains unresolved worldwide. At present, there are no internationally established Current Procedural Terminology (CPT) codes available for insurance companies and/or healthcare financial bodies to cover expenses related to 3D-printing.
Finally, the fifth key element is the integration of local 3D-printing companies, who act as an interface with the world of rapidly-evolving technology. They are seminal in adapting new methods from 3D-printing outside of healthcare. Governance of the COE should be based on cooperation and communication among all key participants along a governmental legal framework, established scientific guidelines in research, clinical benefit to the patients, and financial sustainability.
Another direction of 3D-modelling technology is image-guided surgery/augmented reality. With this modality, patient-specific 3D-models or holograms are projected to a fixed point in virtual space or are directly superimposed on structures of the operative area. Thus, key landmarks of the 3D-holographic model are identified and paired with counterparts of the patient’s anatomy. In combination with robotics, optical display could revolutionise surgery: it could allow procedures in the heart with preserved perfusion/organ function while being operated. The operator performs procedures on the holographic model in the 3D-virtual reality and robotic micromanipulators would identically follow the same movements in the patients’ real surgical field. Of course, there are myriads of problems to be solved, e.g. interactivity between the holographic model and real organ – as the latter moves and changes shape and size in time with the cardiac cycle that the virtual model should exactly follow – just to mention one. Nevertheless, such prospects in 3D-technology revive an intellectual excitement comparable to the one that established anatomy as a medical science and paved the way for modern surgical methods five hundred years ago.
Dr Laszlo Kiraly is the Chair of the 3D Medical Printing Conference scheduled to be held from 29-30 January 2018 at the Arab Health Congress.
Profile pic caption:
Dr. Laszlo Kiraly, MD PhD FETCS, is Head of Paediatric Cardiac Surgery at Sheikh Khalifa Medical City in Abu Dhabi
MARK: Following are the captions of the Figures to be used with the article:
Fig 1: 3D-virtual (A,B) and 3D-printed (C,D) models of the aortic arch following modified Norwood-1 arch repair
A: Digital 3D model of the aortic arch, its branches and the pulmonary arteries; left anterior oblique lateral view. B: posterior view. C: 3D-printed prototype of the aortic arch, its branches and the pulmonary arteries, life-size solid model; left anterior oblique lateral view. D: 3D-printed prototype of the aortic arch, its branches and the pulmonary arteries, 3x-magnified size, hollow model; posterior view. Sites of obstruction are denoted by *.
(Abbreviations: DAo: descending aorta; innom: innominate artery; LCA: left common carotid artery; LPA: left pulmonary artery; LSCA: left subclavian artery; neo-Ao(PT): neo-aorta; RCA: right common carotid artery; RMBTS: right modified Blalock-Taussig shunt; RPA: right pulmonary artery; RV/PT: right ventricle to pulmonary trunk junction).
Fig 2: View of the left ventricular outflow tract obstruction (LVOTO) in a 3D-printed model and intraoperatively.
Prominent musculature significantly restricts outflow from the ventricle (black opening). Morphology on the model looks identical to the one confirmed by intraoperative exploration.
Fig 3: 3D-virtual model of tetralogy of Fallot and absent pulmonary valve
The model is opened in a horizontal plane at the level of the aortic root and viewed from above. Orifice of the left coronary artery (LCA) is flattened and obstructed by the grossly dilated right pulmonary artery (RPA). LCA is much smaller than the right coronary artery (RCA). Right-sided structures (superior vena cava: SVC and right ventricle: RV) are blue; left-sided structures (left ventricle: LV; right upper pulmonary vein: RUPV; left upper pulmonary vein: LUPV) are marked in burgundy. The opened and rotated model provides unparalleled insight into the intimate spatial relationship of the structures.