Learning objectives
The learning objectives were defined and based on interviews with three IR experts (experts having 6, 16 and 24 years of IR experience). The interviews focused on questions regarding specific steps of an embolization procedure, used instruments, characteristics of embolic agents, and accompanying complications. The answers were collected, and precise learning objectives were defined, forming a foundation for the development and the evaluation of the simulator.
Model construction
The model was sketched, sculpted, and exported as a stereolithography (STL) file using Autodesk Fusion 360 (Autodesk Inc., San Rafael, California) and further modeled in Meshmixer (Autodesk Inc., San Rafael, California). The sculpture was imported to Preform (Formlabs Inc., Somerville, Massachusetts), printed on Formlabs Form 2 (Formlabs Inc., Somerville, Massachusetts), and cured using ultra-violet light with Form cure (Formlabs Inc., Somerville, Massachusetts).
The simulator design purposely depicts abstract targets (chambers) and not specific anatomical regions.
The model consists of four chambers with adjacent collaterals, interconnected between one another by a network of tubes. The chambers are cylindrical segments having a volume of 2 or 3 ml to sensitize trainees to various quantities of an embolic agent. The design incorporating various chambers should mimic vascular pathologies such as arteriovenous malformations or highly vascularized tumors. At the top are cube-shaped blocks filled with a sponge. These act as a filter, blockading the flow of embolic agent outside of the model. The three outflows are united into a single outflow with an additionally printed adapter. After embolization of all the chambers, only the main component needs to be replaced, while the adapter can be reused (Fig. 1).
The model has a size of 149 × 119 × 21 mm and it takes approximately 7 h and 45 min to print. We used “Clear Resin” from Formlabs as the printing material (Formlabs Inc., Somerville, Massachusetts).
Model evaluation
We wanted to evaluate our model by two groups: experts and novices. We have defined experts as fellows in radiology with at least 5 years of work experience. Novices were medical students or radiology residents with no prior experience with embolization. Every participant had to perform four embolizations. Participants should identify the given targeted chamber, place the catheter and guide wire in a controlled manner into the predetermined chamber and adjust the necessary amount of embolic agent. The injected amount should be equal to 2 or 3 ml, depending on the targeted chamber. To approach the chamber a 0,035“ angled guide wire (Terumo, Tokyo, Japan) and a 0,038” angiographic catheter (Cordis, California, USA) were used. The simulator was connected to a flow pump (FlowTek 100, United Biologics Inc., Santa Ana, California). Underneath the simulator, a LED panel was placed to increase the visibility of all materials. A camera above the simulator was used to record the training and connected to a laptop for visual feedback (Figs. 2, 3 and 4).
As a low-cost replacement for the embolization agent, we tested different materials. For this purpose, we used the following selection criteria: 1) the material should behave plastically when applied, 2) it should polymerize after application and form a solid body, 3) the material should be non-toxic, 4) it should be widely available. Based on the selection criteria, we identified superglue as an appropriate agent. By comparing viscosities and densities of selected superglues with n-BCA and considering their availability, we decided to use Pattex superglue liquid (Henkel AG & Co, Düsseldorf, Germany) as our primary agent.
The training area of the simulation was divided into “dry” and “wet” areas. In the dry area, participants prepared an embolic agent, where they mixed Pattex Superglue Liquid with red paint pigment for better visibility. In the wet area, the embolic agent was delivered via 3 ml syringes. To substitute a contrast agent, we chose blue food coloring.
To evaluate participants’ effectiveness and measure the time of procedures, we used two cameras: one directly above the simulator and the second one pointed at the participants. The number of occluded chambers, occurence of backflow, number of successfully performed embolizations and the embolization time were assessed with post hoc video analysis.
The occlusion was defined as success when the chamber was closed, with no observable flow of the contrast agent in the control run. Backflow was defined as reflux of the embolic agent, resulting in a closure of the collateral vessel and blockage of contrast agent’s flow. If the chamber was fully occluded and no backflow was observed, the performed embolization was rated as successful. The time of embolization was measured from the moment of the catheter’s introduction through the sheath until retraction of all materials. After the training all participants filled out a questionnaire evaluating the simulator and the overall training.
Statistical analysis
The number of successfully performed embolizations, closed chambers and backflow occurrences were compared between the novice and the expert group using a chi-quadrat test. The duration of embolizations between the two groups was analyzed using an independent samples Student’s t-test. The changes in proficiency level before and after the training in both groups were compared using a paired samples Student’s t-test. The statistical analysis and figures were performed using R (www.r-project.org).