Diagnostic radiology programs currently encompass image-based diagnosis and image-guided therapeutic techniques using multiple available imaging modalities. Three-dimensional (3D) image post-processing of radiologic images routinely uses high-resolution computed tomography (CT) and magnetic resonance imaging (MRI) datasets for diagnostic evaluation and treatment planning. Dedicated training in 3D modeling may be incorporated into some radiology training programs, although it is not required, and formal training programs are limited. In radiology, a comprehensive medical 3D printing training program should prepare radiologists to be knowledgeable and proficient in creating 3D printed medical models from radiological imaging data. This chapter will give background on 3D modeling for medical education and will provide an overview of the fundamentals required for a radiological program that includes medical 3D printing.
Historical Perspective on 3D Modeling for Medical Education
3D modeling in medical education has been used for generations. Together with two-dimensional (2D) drawings, scaled and realistic models have been used to record the discovery of anatomists, record unique and innovative patients and pathologies, and more recently, to widely disseminate both normal and abnormal teaching examples to students of anatomy, physiology, and medicine. 3D models are a staple of medical education; and the use of 3D models in medical schools is being expanded as the use of cadaveric dissection decreases. Surgical training has benefitted greatly from the availability of 3D models to plainly visualize pathology and simulate surgical approaches. The addition of readily available, patient-specific 3D printed models is a further step in the progression toward more personalized medical and surgical care.
One of the earliest existing anatomical models is an Early Classic Mayan head, dated to 300–600 AD. Half of this sculpture shows the head in life and the other half shows the underlying bony skull. In 1027 in China, an imperial physician, Wang Wei-Yi had two life-size bronze statues made for teaching surface anatomy for locating the acupuncture points. Sometime between 400–600 BC, an Indian sage named Sushruta was recorded to have used patient simulators for practice of surgical skills and suggested that such simulation-based education leads to competence and confidence. More recently, the 17th century father and son of the family Grégoire of Paris created obstetrical manikins for teaching midwives. Also, in 17th century, Gaetano Giulio Zummo (1656–1701) a Sicilian abbot created 3D models from wax and recommended them for anatomy training.
Over time, the materials used in creating realistic anatomic models have changed from wax to plaster and plastination. Preparing plastination models is a time-consuming and expensive process, which requires expertise for model preparation. These models are realistic but degrade readily and are easily damaged. More modern static models use plastic materials which rely on premade molds, limiting the flexibility of their application to individual patient care. As a tool for demonstration, however, virtual models and 3D printed models form the historical backbone and future for both hands-on learning and simulation.
3D Printing in Anatomy Education
Anatomy education, a traditional and key element of medical training, has evolved over the past few decades. The gold standard in anatomy education is cadaveric dissection, which is for many students their first encounter with a nonliving body. The process of dissection was traditionally viewed as a right-of-passage for students. Though this passage came with emotional and ethical conflict, dissection helped young physicians form a strong emotional connection to the form of the human body, which they sought to heal. Advances in technology have offered students even greater access to virtual dissection, which also closely mimics the way most nonsurgical physicians view clinical examples of pathology, that is, through imaging.
Anatomical dissection promotes deep anatomical understanding, and because each cadaver represents a unique individual, the process of dissection underscores the breadth of possible anatomical variations. As a 3D hands-on experience, cadaveric dissection offers tactile feedback and enhances manual skill sets. , Moreover, as students work in teams, cadaveric dissection promotes problem-based, team learning.
The total number of hours spent in anatomy teaching labs has decreased over the past 20 years for several reasons: the financial burden of having a fully equipped anatomy laboratory, limited cadaver availability, and the increased availability of e-learning platforms. While e-learning platforms have not fully replaced cadaveric dissection, they have greatly changed the ways students traditionally accessed anatomical information. In addition, these computer-based models are popular with students; however, studies have shown that students who rely solely on computer-based models perform worse compared to students who use traditional resources in learning anatomy.
3D printing as a novel method opens up opportunities to create anatomical models for medical training on an individual scale. Like all printed models, patient-specific 3D printed models allow students at all training levels to review both normal and abnormal anatomical structures outside the cadaveric laboratory. A wide variety of materials can be used to create 3D printed models, which can help accentuate anatomic details. These models are reproducible, safe to handle, and can represent variety of normal and pathologic anatomy.
When combined with cadaveric dissection (as many medical schools now perform CT scans on cadavers prior to dissection), 3D printing expands the possibilities for anatomy students. The creation of anatomical models by students which replicate the body’s form promotes engagement with cadaveric specimens themselves. Prelearning through 3D modeling stimulates anatomical review, forcing students to understand anatomical relationships on a more direct level and facilitates kinesthetic learning by engaging the tactile senses.
Using 3D printing for anatomy training has its limitations. Compared to true anatomical dissection, fine details such as small nerve branches or microstructures, which can be explored in the cadaveric subjects using expert techniques, can be difficult if not impossible to replicate with 3D printing techniques. Whole organ printing with detachable parts requires a tradeoff between precision-printing, and the form and function needed to facilitate active engagement with the printed model.
A further limitation of using 3D printed models as a cadaveric replacement is the model printing time, which may limit the routine use of 3D printing in an ongoing course of study. Industrial 3D printers are better suited to producing multicolored models suitable for visualizing finer structures; however, local efforts to print with such fine detail make routine and on-demand 3D printed models expensive for most training purposes. Additionally, accurate size representation is an important element of student learning, which must be balanced by the time and material cost required for printing; the use of scaled 3D models is discouraged as it may potentially lead to an incomplete understanding of true organ size additional spatial relationships to nearby anatomical structures. The utility of 3D printing for medical education is a growing field of study. One recent systematic review validated the utility of 3D printed models for teaching medical students; and it was postulated that these models positively impacted medical students, especially because of their limited knowledge of anatomy.
3D Printed Models as a Tool in Clinical Radiology Training
Radiology practice, at its core, uses technology to visualize internal structures, assess anatomic relationships, and to infer pathology. These same tools are now used to quantify tissue structure and assess disease progression on a microstructural level. Key to success in radiology training programs is understanding anatomical relationships of increasingly greater complexity than those required of anatomy students, both in normal and in abnormal patients, as well as mastering anatomical description. 3D models can be used in education to visualize and conceptualize complex anatomical structures and are a useful tool for facilitating learning in a range of normal and abnormal patient-focused settings. Models can even include fine detailed structures such as ophthalmology anatomy and can be created based on cadaver prosections. Furthermore, since a catalog of models may not be available in many clinical learning environments, 3D printing allows a resident or student to select a specific area of interest that may be difficult to evaluate, and facilitates using individually printed models to teach these relationships to others.
Normal and Complex Anatomical Relationships
Due to the inherent complexity of normal anatomic structures and the fact that the human body is not made up of straight lines, smooth edges, and 2D interfaces, normal anatomical relationships are often difficult to comprehend. 3D models can be used to visualize and conceptualize complex anatomical structures, and have been shown to be effective tools in medical training. Studies have shown the utility of 3D printed models for teaching complex surface anatomy and as an alternative to traditional didactic instruction.
Beyond identifying key structures on imaging, students often struggle to recognize the relationship between adjacent structures, for example, the ductal anatomy of the pancreas and common duct within the pancreas head. Surface anatomy and its relationship to underlying structures can be difficult to estimate using standard cross-sectional imaging. 3D models, in contrast, more easily demonstrate complex interfaces and allow students to better understand these spatial relationships. 3D printed models have similarly been used to teach complex segmental anatomy of organs such as lungs, liver, and prostate, or branching anatomy of the coronary arteries and circle of Willis.
Another example of using 3D printing to visualize complex anatomical relationships relates to vascular structures in the setting of both common and less common anatomical variants. For example, the left renal vein typically crosses anterior to the aorta when communicating to the IVC. However, important vascular variants including retroaortic and circumaortic renal veins are critical to recognize. The relationship between the aorta, IVC, and renal veins is difficult to conceptualize and students who encounter this variant anatomy benefit from advanced 3D visualization. Similarly, the number and length of the renal veins and arteries is an important consideration that drives presurgical imaging prior to renal transplant surgery and can be difficult to accurately demonstrate to surgeons using 2D sectional anatomy alone ( Fig. 10.1 ) .
There are many common injuries and pathologies which recur in a clinical setting for which trainees rely on representative examples to make diagnoses and highlight contrasts. This occurs most commonly on call, when residents practice with greater independence.
Understanding and referencing classification schemes for abnormal pathologies is a challenging task among radiology trainees for which they typically rely on external reference comparisons including anatomical models, textbooks, and case review examples when making a diagnosis. The opportunity to use patient-specific examples of complex anatomical structures can provide an added benefit in academic hospitals and training environments. Specialty reading rooms such as for musculoskeletal and neurological imaging are well suited to identify and to archive printed examples of these complex cases. Clinical conferences held together with surgeons serve to amplify the benefits to trainees in both diagnostic and procedural subspecialties when 3D models are available as a visual reference during case discussion.
For example, the classification of hip acetabulum fracture types or Le Fort midface fracture classifications can be aided by using printed models as a reference, given the complex anatomy and 3D geometry of these structures. A study on radiology residents showed that residents who received 3D printed models during a didactic lecture regarding acetabular fractures had better learning outcomes compared to control group which only received the didactic presentation. Printed clinical examples move this teaching tool into the clinical learning environment.
Realistic Phantoms for Hardware and Software Evaluation
In radiology departments, phantoms with known material properties and geometries are utilized to properly calibrate imaging equipment and optimize image protocols. Commonly available phantoms are simple geometric phantoms or anthropomorphic phantoms which usually represent typical or average adult or pediatric patients. 3D printing allows for the creation of more realistic models based on patient-specific imaging data, thereby providing more accurate and reliable models for quality assurance (QA) and research investigation. In one example, patient-specific 3D printed phantoms of peripheral and central pulmonary embolism were used to optimize a CT pulmonary artery protocol. Researchers used varying kVp and pitch values and assessed their impact on radiation dose and image quality using 3D printed models of peripheral and central pulmonary embolism, achieving 80% dose reduction. In addition to learning about radiation dosing including “image gently” and “as low as reasonably achievable,” in a simulated environment without exposing a patient to radiation, using 3D printed phantoms gives an opportunity for trainees to experiment with the physics concepts in radiology. More details regarding 3D printed imaging phantoms can be found in Chapter 14 .
3D Printed Models for Radiological Procedural Planning
3D printed models of patient-specific anatomy are being increasingly used for procedural planning and can facilitate understanding of a patient’s complex or unique anatomy, thereby removing diagnostic uncertainty, decreasing procedure times, and potentially improving a patient’s outcome. Surgeons-in-training can use 3D printing techniques, using anatomical or scaled models, to review surgical plans with senior surgeons and simulate their own approach, decreasing diagnostic uncertainty, procedure times, and potentially improving patient outcomes.
A complete description of the advantages and drawbacks of using 3D printed, patient-specific models is beyond the scope of this chapter. However, numerous individual case reports and small studies have highlighted the value of 3D printed models in making patient-specific surgical decisions. 3D printed models have also been shown to help both radiology and surgical trainees better understand anatomical relationships and aid in enhancing surgical technique. Selected clinical case series describing the use of 3D printed models specifically for procedural training of residents in various academic training environments is summarized in Table 10.1 . , In terms of training radiology residents, a recent review noted that available case reports and controlled studies were limited to simpler models and small sample sizes, and therefore could not show true learning benefit with high confidence. This highlights the role for future cooperative research assessing the impact of 3D printing for resident education.
|Specialty||Clinical Entities||Clinical Examples of Complex Anatomy, Delineated for Learners Using 3D Printing Tools|
|Ophthalmology||Orbital decompression training|
|Orthopedic surgery||Spinal surgery training|
|Plastic surgery||Mandible reconstruction|
|Urology||Percutaneous nephrolithotripsy surgery|
|Locating prostate cancer|
|Flexible ureteroscopic training|
Procedure Planning and Simulation for Interventional Radiology Training and Radiological Procedures
Patient-specific 3D printed models present both a clinical benefit and a training aid to both students and junior faculty. Training in and the clinical performance of radiological procedures requires skill, preparation, and experience to develop proficiency and independence. Similar to planning for open surgical procedures, the availability of patient-specific models guides the clinical performance of image-guided procedures.
Use of these models has been shown to improve hand–eye coordination in trainees and optimize their image acquiring quality and positioning. Moreover, as trainees learn to perform minimally invasive procedures, they need to practice using increasingly realistic and challenging simulator tools. Studies have shown benefit to training using realistic phantoms and models. 3D printed models provide even more realistic opportunities to create models and phantoms at patient scale, which can be embedded within other materials such as ballistic gel and used in simulation training for both ultrasound and CT-guided procedures. Presurgical planning and procedure rehearsal can be especially more important in high risk and complicated procedures such as pediatric neurointerventional radiology and can even aid experienced interventional radiologists. For example, in one study, researchers showed that 3D models of pediatric arteriovenous malformations can be printed within 24 hours with a high degree of fidelity and use of these models resulted in a 12% reduction of procedure time.
Introducing Training in 3D Printing to Resident Education
3D printing in medicine is an evolving field, with a wide range of available tools, material, and challenging technical requirements. Moreover, as 3D printed models become further incorporated into clinical workflows and patient-care scenarios, the requirements and degree of oversight needed to oversee and train others in appropriate use increase. Technical descriptions of the image acquisition and processing requirements and regulatory elements regarding 3D printing are covered elsewhere in this book. This section will focus on the advantages of incorporating didactic and hands-on teaching of 3D printing to radiology trainees.
Learning the Process of Obtaining 3D Models and 3D Lab Workflow
Creating anatomically precise models which accurately reflect clinical reality is an arduous process which requires training and expertise to effectively employ in patient care, where both precision and accuracy matter. There are pitfalls specific to each stage, from image acquisition, segmentation, computer-aided design, printing, and postprocessing. Errors at any stage have direct implications for patient care. Physicians who will interpret and report on 3D printed models must learn from case examples—both successful and unsuccessful examples—analogous to the process used in medical QA and morbidity and mortality conferences. In addition, akin to the didactic process used in classroom and patient-care settings, direct training in 3D processing is needed to both generate accurate models and interpret the implications of findings on these models for clinical use.
3D printing is a time-intensive process that uses physical resources and currently carries limited clinical reimbursement. Although Category III Current Procedural Terminology (CPT) codes were introduced by the American Medical Association in July 2019 , reimbursement is extremely limited and many 3D printing labs are funded externally. Rather than generating revenue, these 3D printing labs are typically internally funded and/or draw on donations, research, and educational funding sources. Successful labs employ dedicated managers, specialized technologists, and/or biomedical engineers to segment individual cases for clinical use and manage 3D printing resources. Trainees who receive hands-on experience in a training environment are exposed to the full range of processes and tools, engaging with requesting physicians, interpreting physicians, and technologists. Understanding the fundamental inputs used in running a 3D printing lab allows physicians-in-training to develop a business framework which effectively utilizes resources to balance between the clinical useful 3D printing, cost requirements, and leveraging the nonclinical advantages offered to departments which feature a 3D printing service.
While the reimbursement for medical 3D printing is limited, the opportunity for adding clinical benefit is great. Through engaging with specialty departments, forging effective collaborations, and demonstrating excellence in product and service, interdisciplinary programs are forged and led by those who manage the critical resources. Students in training develop communication and leadership skills by actively participating in these interdepartmental efforts.
In 2013, the Radiological Society of North America (RSNA) launched an educational program on 3D printing. At the time of writing, the RSNA features a dedicated category for scientific presentations and educational exhibits at their annual meeting highlighting advances using 3D Printing . The RSNA 3D Printing Special Interest Group (SIG) has published consensus guidelines for the clinical implementation of 3D printing and offers a venue for scholarly collaboration.
Developing a Research Infrastructure
3D printing has tested use cases not only in clinical practice but also is an evolving field. Using 3D printing tools as part of a research program offers diverse opportunities for residents to be recognized for their contributions to advancing scientific and technical knowledge in the field. New printing technologies, materials, segmentation techniques, and clinical applications require testing to be used effectively in the clinical environment. Both funded and industry-sponsored research opportunities are likely to grow, with opportunities available to programs that can demonstrate effective and efficient use of their available resources, as well as an ability to effectively scale to meet the needs of projects.
There are a range of research avenues using 3D printing which can engage trainees and be used to help build a platform for future academic growth. A major area for investigation includes demonstrating the value-added component of 3D printing in radiological and surgical practices. In addition, studies regarding techniques for improving image acquisition and segmentation protocols and assessing the true accuracy of created models through QA studies provide ample opportunities for radiologists engaged in testing new and evolving technologies.
Sample Curriculum for a Hands-On Resident Minicourse in 3D Printing and Visualization
What should a training course in 3D printing for trainees look like? Structure, didactic education, and hands-on experience are all needed. What follows is a sample curriculum that can be adapted to different training programs, depending on local resources and time availability. Elements of a structured curriculum for trainee education in 3D printing are included in Table 10.2 . Specific elements of the curriculum are discussed in the following section.