We describe a procedure to process computed tomography (CT) scans into high-fidelity, reclaimable, and low-cost procedural task trainers. The CT scan identification processes, export, segmentation, modeling, and 3D printing are all described, along with the issues and lessons learned in the process.
The description of procedural task trainers includes their use as a training tool to hone technical skills through repetition and rehearsal of procedures in a safe environment before ultimately performing the procedure on a patient. Many procedural task trainers available to date suffer from several drawbacks, including unrealistic anatomy and the tendency to develop user-created 'landmarks' after the trainer tissue undergoes repeated manipulations, potentially leading to inappropriate psychomotor skill development. To ameliorate these drawbacks, a process was created to produce a high-fidelity procedural task trainer, created from anatomy obtained from computed tomography (CT) scans, that utilize ubiquitous three-dimensional (3D) printing technology and off-the-shelf commodity supplies.
This method includes creating a 3D printed tissue mold capturing the tissue structure surrounding the skeletal element of interest to encase the bony skeletal structure suspended within the tissue, which is also 3D printed. A tissue medium mixture, which approximates tissue in both high-fidelity geometry and tissue density, is then poured into a mold and allowed to set. After a task trainer has been used to practice a procedure, such as intraosseous line placement, the tissue media, molds, and bones are reclaimable and may be reused to create a fresh task trainer, free of puncture sites and manipulation defects, for use in subsequent training sessions.
Patient care competency of procedural skills is a critical component for developing trainees in civilian and military healthcare1,2 environments. Procedural skills development is particularly important for procedure-intensive specialties such as anesthesiology3 and front-line medical personnel. Task trainers may be used to rehearse numerous procedures with skill levels ranging from those of a first-year medical student or medical technician to a senior resident or fellow. While many medical procedures require significant training to complete, the task presented here-placement of an interosseous (IO) line-is straightforward and requires less technical skill. Successful placement of an IO line can be accomplished after a relatively short period of training. The use of simulation during medical training, which includes the use of task trainers, is recognized as a tool to gain technical procedural skills through the repetition and the rehearsal of a clinical procedure in a safe, low-stress environment, before ultimately performing the procedure on patients2,4,5.
Understandably so, simulation training in medical education environments has become widely accepted and appears to be a mainstay, despite the paucity of data regarding any impact on patient outcomes6,7. Additionally, recent publications demonstrate that simulation improves team performance and patient outcomes as the result of improved team dynamics and decision-making. Still, there is little data to suggest that simulation improves the time or success rate to perform critical, life-saving procedures8,9 suggesting that simulation is complex and multifaceted in the education of health care providers. In patients where standard intravenous access is not possible or indicated, IO line placement may be used to achieve vascular access quickly, requiring minimal skill. Timely and successful performance of this procedure is critical, particularly in the perioperative environment or a trauma scenario10,11,12. Because IO line placement is an infrequently performed procedure in the perioperative area and can be a life-saving procedure, training in a non-clinical environment is critical. An anatomically accurate task trainer specific to IO line placement is an ideal tool for offering predictable training frequency and skills development for this procedure.
Although widely used, currently available commercial task trainers suffer from several significant drawbacks. First, task trainers that allow for multiple attempts of a procedure are costly, not only for the initial purchase of the task trainer but also for replenishing the replaceable parts such as silicone skin patches. The result is often infrequently replaced parts, leaving prominent landmarks that provide the trainee a suboptimal training experience; patients will not come pre-marked where one should do the procedure. Another drawback is that the high cost of traditional task trainers can result in limited access by users when the devices are 'locked up' in protected storage locations to prevent loss or damage to the devices. The result is requiring more rigorously and less available scheduled practice time, limiting their use can certainly make unscheduled training difficult. Finally, most trainers are considered low-fidelity5,13,14 and use only representative anatomy, potentially leading to inappropriate psychomotor skills development or training scars. Low-fidelity trainers also make the thorough assessment of skill acquisition, mastery, and degradation very difficult as training on a low-fidelity device may not adequately mimic the actual real-world procedure.
Representative anatomy also impedes the proper evaluation of the acquisition and mastery of psychomotor skills. Moreover, assessing the transfer of psychomotor skills between simulated medical environments to patient care becomes nearly impossible if some of the psychomotor skills are not reflected in the clinical task. This results in the prevention of consensus on the ability of medical simulation and training to affect patient outcomes. To overcome the challenges of cost, anatomical accuracy, and access, we have developed a low-cost, high-fidelity IO line task trainer. The task trainer is designed from an actual patient's CT scan, resulting in accurate anatomy (Figure 1). The materials used are ubiquitous and easy to obtain, with components that are relatively easy to reclaim. Compared to many other commercially available trainers, the modest cost of the task trainer design described here dramatically reduces the desire to sequester the trainers in a less accessible, protected location and makes multiple repetitions without leading landmarks possible.
NOTE: The University of Nebraska Medical Center Institutional Review Board determined that our study did not constitute human subject research. The local IRB obtained ethical approval and waiver of informed consent. Complete anonymization of imaging data was done before analysis per the hospital de-identification protocol.
1. Data
2. Segmentation
3. 3D Modeling
4. 3D Printing
5. Assembly
6. Task training
Following the protocol, the modeling of the task trainer utilized a CT scan of a de-identified patient. Segmentation of the CT images utilized 3D Slicer software and Auto Meshmixer for 3D modeling. For 3D printing, both 3D Simplify and the Prusa i3 MK3 were used (Figure 1). Subsequently, we completed the assembly of the 3D-printed parts, prepared the tissue media mixture, and poured the media mixture into the assembled task trainer mold. Following a training period with the task trainer, the tissue medium was reclaimed and reused in the assembly of fresh task trainers.
The CT scan of a patient's left knee joint used for the 3D modeling comprised 6-7 cm of tibia and fibula bones below the knee, 2-3 cm of femur bone above the knee, and the patella. During this protocol's execution, the artifacts seen in the CT scan resulting from the overlap between different anatomical segments were manually discarded in Meshmixer after exporting each segment to STLs and performing the 'flip normals' operation. The left tibial bone and tissue STL meshes were modified to reduce the marrow cavity surface's anatomical complexity. Supporting structures were generated to fix the femur, tibia, fibula, and patella to one another. A supporting "brace structure" was added into the Fusion 360 to help booster the thin fibula structure of the bone to the tibia, thus preventing this bone from breaking off.
The mold structure consisted of a rectangular solid, separated into a top and bottom structure, and a 2.5 mm channel to hold the silicone foam cord on the tissue segment's outline perimeter. Supporting pin structures, alignment pin channels, and the bone plug receiver were added to the bone and mold structures by importing their applicable structures into the model (Figure 3). The mold was designed such that two 41 mm Supporting Pin Assembly groups would be sufficient to properly support and suspend the bone structures within the tissue cavity. An opening made to expose the tissue cavity facilitated pouring of the tissue medium by cutting a cylindrical body structure from the mold structure's front.
After finalizing the mold and bone structures in Fusion 360, the following four .STL segments were created by exporting the model: 1) Bones, 2) Bottom mold box, 3) Top mold box, and 4) model hardware (2 x 41 mm Supporting Pins, 2x Supporting Pin Bottoms, and 1x Bone Plug). Next, four STL segments were imported into Simplify 3D, and the representative GCODE files were generated for these segments for printing using a 0.4 mm nozzle and 0.3 mm layer height at a 100 mm/s print rate. Table 1 lists print times and PLA filament material requirement estimates using the settings previously mentioned when all segments were printed on Original Prusa MK3 printers. Rapid incorporation of the tissue medium (gelatin) components is essential to achieve a consistent and homogenous final product. The amount of tissue medium used varies depending on the model of task trainer assembled. An example of the design and actual volumes of tissue medium used in the tibial IO insertion Task Trainer model is shown in Table 2.
To de-mold the task trainer, the compression devices were loosened, the mold top and bottom were separated, and the 2 x 41 mm support pins were rotated and removed from the bones. The bone marrow cavity was then filled with simulated marrow solution, and a bone plug was securely inserted. The final task trainer was then imaged with a CT scan for the measurement of anatomical landmarks and segments. The results demonstrate a high-fidelity task trainer IO line placement (Figure 4). The newly molded task trainer was then placed in a zip lock bag, returned to the refrigerator, and stored for use in a future training session.
Transparent and opaque task trainers were assembled (Figure 5) for IO line placement training sessions. A total of 40 task trainers (20 tibia and 20 humeri) were used during a half-day training of IO line placement offered to the Department of Anesthesiology at our Institution. Both faculty and trainees attended this training. Each attendee had 15 min of hands-on interaction with both task trainers (tibia and humerus) and the equipment necessary to perform the IO line placement. Preliminary data on the task trainers' advantages and disadvantages and task trainer improvements were collected immediately afterward.
Advantages identified by attendees specific to the use of the task trainer included: a) high level of anatomical similarity, b) ability to find anatomical landmarks, c) tactile sensation resembling tissue, d) reproducibility of the practiced procedure, e) ability to aspirate bone marrow to provide task completion feedback, and f) appropriate tactile feedback when drilling into the bone. The ability to reclaim and reuse the task trainer, and the low-cost of the trainer were important features identified by attendees. Further, faculty and trainees suggested adding a skin or fabric layer to more closely resemble the skin's tactile feedback and increasing the limb length. After the training, the tissue medium was reclaimed and reused (Figure 1).
Figure 1: Flow chart depicting the process to create an intraosseous line placement task trainer. Please click here to view a larger version of this figure.
Figure 2: Intraosseous line placement with a tibial task trainer performed using a trainer with opaque tissue medium. (A) Drilling into the bone with a commercially available IO placement drill. (B) Aspiration of marrow upon successful placement of the IO line. Abbreviation: IO = intraosseous. Please click here to view a larger version of this figure.
Figure 3: 3D-designed and 3D printed components that compose the tibial task trainer. (A) 3D designed tibia; (B) 3D printed tibia; (C) 3D designed mold and of the tissue surrounding the tibia and pins; (D) 3D printed mold of the tissue surrounding the tibia and pins. Please click here to view a larger version of this figure.
Figure 4: Opaque and transparent tissue media allows for customization of training. (A) and (C) represent a humerus and tibial task trainer made with opaque tissue medium. (B) and (D) represent a humerus and tibial task trainer made with transparent medium. Note the visibility of skeletal structures with transparent tissue medium. Please click here to view a larger version of this figure.
Figure 5: Anatomical distances are similar between CT scan data used to create the task trainer and from the fully assembled IO line placement humerus task trainer. (A) Bone thickness (mm), (B) skin depth (mm), and (C) the tendon groove (mm) from the CT scan data are anatomically similar to the (D) Bone thickness (mm), (E) skin depth (mm), and (F) tendon groove in CT scan of the fully assembled humerus task trainers. Abbreviations: CT = computed tomography; IO = intraosseous. Please click here to view a larger version of this figure.
Structure | Approximate Print Time (h) | PLA Filament requirements (estimated, in g) | Material Cost (Dollars) |
Box Top | 32 | 800 | 16.00 |
Box Bottom | 17 | 450 | 9.00 |
Bones | 9 | 200 | 4.00 |
Hardware | 2 | 16 | 0.32 |
Table 1:List of time and cost of each component required.
Structure | Volume (L) | Estimated Cost |
Tissue Cavity | 2.06 L | n/a |
Bone Structure | 0.313 L | n/a |
Tissue Cavity – Bone Structure | 1.747 L | $35 (reclaimable) |
Marrow Cavity | 0.075 L | $0.25 |
Table 2: Tissue media volumes.
In this protocol we detail a 3D task trainer’s development process to train the infrequently performed and life-saving procedure of IO line placement. This self-guided protocol uses 3D printing to produce the bulk of the model structures, while the remainder of the components used to assemble the task trainer are ubiquitous, easily obtainable, and non-toxic materials that may be reclaimed and reused. The 3D task trainer is low-cost and requires minimum expertise to create and assemble. We have successfully used our 3D IO line placement task trainer in UNMC Department of Anesthesiology training sessions, which included a demonstration and hands-on practice by faculty and trainees in attendance. The feasibility data collected during the training indicated that attendees agreed that the task trainers had a high degree of anatomical fidelity to actual patient anatomy, and they were further satisfied with the tactile feedback of the device.
Critical steps in the production of a task trainer have been divided into two sections: 3D design and fabrication; task trainer assembly. When creating the 3D models used to form the task trainers, adequate segmentation was critical. Without adherence to anatomic accuracy, the final product may not be correct. Threshold segmentation requires attention to the task trainer’s area of interest to ensure that surface detail is present to give the models the correct shape and thickness. Tibia and humerus thickness are particularly important to provide sufficient tactile feedback during simulated IO line placement. The process for segmenting tissue and bone components can be incredibly time-consuming as CT scans often use iodinated contrast agents, which have overlapping HU ranges with those of bone. Thus, anatomical structures permeated with iodinated contrast may be inappropriately included within bone segments.
Appropriate preparation and storage of the tissue media are critical. Adherence to temperatures stipulated within the protocol is necessary to prevent damage to the 3D printed structures and ensure maximum tissue media longevity. Notably, the tissue media must remain cold or frozen and covered in plastic when not being used to prevent microbial growth and dehydration. The availability and accuracy of patient’s CT scans can impose limitations on creating the IO line task trainer. There appear to be limits on the generation of models regarding the requirements for 3D printing. During the 3D printing process layers of thermoplastic are deposited on top of prior layers or support material. Some models and proposed trainers produced by this process can exceed the size limits of a 3D printer and require modification of the printer size or components to allow printing that retains the trainer’s critical aspects (such as the marrow space for IO models). Other formats suitable for task trainer creation include magnetic resonance imaging. However, the imaging modality displays different data types, requiring modifications to this protocol.
This IO line placement task trainer has several innovative features, including a reduced cost compared to other task trainers, and the ability to customize the task trainer to different anatomic sites (humerus and tibia) and various anatomies, including male or female, and high and low body mass index. Further, the tissue media mixture can be prepared in different opacities, allowing for varying levels of visualization of skeletal structures or landmarks, if desired. Given its anatomical accuracy and reusable nature of its subcomponents, this task trainer provides unique medical procedure training and simulation research opportunities, including the transference of procedural skills from a simulation or training environment to a testing or clinical environment. The high-fidelity and low-cost attributes of this task trainer make it an excellent choice for evaluating procedural skill acquisition and degradation in healthcare trainees and providers. Further, the superior anatomical fidelity of the trainer grants opportunities to evaluate the impact of ergonomics on training scars and degradation of trainer structure, which is a rapidly emerging topic of interest in this field17. Overall, this tool’s use may promote a better understanding of best practices in medical simulation18.
The authors have nothing to disclose.
The funding for this project was provided solely from institutional or departmental resources.
3D printer filament, poly-lactic acid (PLA), 1.75 mm | N/A / Hatchbox | Base for 3D printing molds, bone structures, and bone / mold hardware | |
3D printer, Original Prusa i3 MK3 | Prusa | To print molds, bone structures, and bone / mold hardware | |
bleach, household (6% sodium hypochlorite) | Clorox | Animicrobial additive for tissue media | |
bolts, 1/4”, flat / countersunk or round head, various lengths | N/A | Hardware used to hold mold casing halves together during casting | |
Bucket, 5 gallon, plastic | N/A | To hold tissue media during media preparation | |
chlorhexidine, 4% solution w/v | Animicrobial additive for tissue media | ||
drill, household 3/8’ chuck | N/A | To stir tissue media during media preparation | |
food coloring, red (optional) | N/A | Coloring additive for simulated bone marrow | |
gelatin, unflavored | Knox | Base for tissue media | |
hex nuts, 1/4” | N/A | Hardware used to hold mold casing halves together during casting | |
Non-stick cooking spray | N/A | Mold releasing agent | |
plastic bags, ziplock | Ziplock | To store tissue media | |
psyllium husk fiber, finely ground, orange flavored, sugar free (optional) | Procter & Gamble | Metamucil | Opacity / Echogenicity additive for tissue media |
screwdriver, flat / Phillips (matching bolt hardware) | N/A | To tighten mold casing hardware | |
silicone gasket cord stock, 3mm, round, various lengths | N/A | Gasket media for mold casings | |
spray adhesive, Super 77 (optional) | 3M | Agent used to improve bed adhesion during 3D printing | |
stirring paddle / rod | To stir tissue media during media preparation | ||
turkey baster, household, ## mL | N/A | To inject simulated bone marrow into bone marrow cavity | |
ultrasound gel | Base for simulated bone marrow | ||
water, tap | Used in both tissue media and simulated bone marrow |