designing and creating silicone molds and 3d-printed tissue layer models for ultrasound phantom simulation

Building Custom Ballistic Gel Ultrasound Phantoms for Nerve Block Simulations

Ultrasound phantoms - alternatives to live human tissue - give learners the opportunity to practice medical procedures, including ultrasound-guided regional anesthesia (UGRA), without introducing undue risk to patients1. While most commonly manufactured via injection molding of liquid silicone rubber, custom phantoms can be homemade using versatile materials at lower cost. Organic tissues such as tofu, pork, and beef are inexpensive but spoil quickly and are challenging to craft2. Human cadaveric tissue is ideal for anatomic accuracy but is difficult and costly to obtain and preserve1. More recently, virtual reality has been used to provide UGRA training; however, haptic feedback is a key component of procedural learning and is rarely implemented. Even when a hardware-software hybrid model provides high visual fidelity and tactile feedback, the hardware and software required to carry out such training are frequently cost-prohibitive3. Gelatin-based phantoms strike a balance between cost, longevity, and fidelity2.
Ballistic gelatin models are available commercially but are expensive for a perishable resource that is highly utilized in medical simulation centers. Small, simple, gel-based ultrasound phantoms with homogeneous parenchyma and two or three simulated vessels retail for hundreds of dollars. For example, the CAE Blue Phantom basic ultrasound training block costs upwards of $8004. Higher-fidelity phantoms specific to individual nerve block procedures cost thousands of dollars. The CAE Blue Phantom femoral regional anesthesia ultrasound training model costs $5,000 (Table 1)5. To bring down costs, educators have experimented with custom-made phantoms using gelatin or other low-cost or reusable materials6,7,8. Additives such as flour, corn starch, graphite powder, and Metamucil can be used to opacify the gelatin and customize the echogenicity of the phantom, thus increasing its fidelity8,9,10,11,12,13,14.
Previous attempts at homemade gelatin-based nerve block trainers were either unable to adequately recreate the appearance of nerves under ultrasound or utilized perishable items, thus limiting shelf life15,16. Even without these drawbacks, previous iterations did not include relevant anatomical landmarks and fascial planes that would allow trainees to practice specific nerve block procedures. Here, we investigate the production of durable, low-cost, ballistic gel ultrasound phantoms for median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve blocks, as well as a methodology for producing a phantom for any ultrasound-guided nerve block procedure.

Author Spotlight: Developing Cost-Effective and Durable Ultrasound-Guided 3D-Printed Nerve Block Trainers

Building Affordable, Durable, Medium-Fidelity Ballistic Gel Phantoms for Ultrasound-Guided Nerve Block Training

So we leveraged the latest technology such as computer-aided design and 3D printing to make custom, durable, ultrasound-guided nerve block trainers with relatively low cost materials. In doing so, we explored questions relating to the durability and cost effectiveness of nerve block trainers while maximizing the fidelity and accessibility of these trainers. Currently, medical educators and simulation centers must either pay thousands of dollars for hands-on nerve block trainers, or save money using perishable materials that spoil rapidly.Our nerve block trainers use affordable materials that last for months to years, all while simulating anatomy more accurately than other low cost simulators. Other attempts to create homemade nerve block trainers have generally involved perishable materials such as animal meat, which spoils quickly, or homemade gelatin, which grows mold within weeks, even with refrigeration. Our trainers last years with minimal maintenance and cost a fraction of the price of commercial trainers.We're working to develop these nerve block trainers for a variety of other procedures within the operating room in an emergency room. Additionally, we're using infrared tracking in a variety of software options to record metrics about how physicians perform these procedures so that we can analyze the results and try to correlate those to clinical performance.

Designing and Creating Silicone Molds and 3D-Printed Tissue Layer Models for Ultrasound Phantom Simulation

designing-creating-silicone-molds-3d-printed-tissue-layer-models-for

Research

JoVE Journal

Medicine

Ultrasound phantoms - alternatives to live human tissue - give learners the opportunity to practice ultrasound-guided regional anesthesia without introducing undue risk to patients. Gelatin-based phantoms provide educators with durable and reusable task trainers; however, commercially available gel-based phantoms are expensive. Here, we investigate the production of durable, low-cost, ballistic gel-based ultrasound phantoms for median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve blocks, as well as a methodology for producing a phantom for any ultrasound-guided nerve block procedure.
Computer-aided design (CAD) software was utilized to design four phantoms replicating the anatomy of median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve blocks, including relevant landmarks and tissue planes. Plastic models of the desired tissue planes were 3D printed and used to create silicone molds. Ballistic gel was melted and mixed with flour and dye to create a liquid, echogenic ballistic gel, which was poured into the silicone molds. Vessels were simulated by creating negative space in the ballistic gel using metal rods. Nerves were simulated using yarn submerged in ultrasound gel. Simulated bones were designed using CAD and 3D printed.
Ballistic gel is a versatile, durable medium that can be used to simulate a variety of tissues and can be melted and molded into any shape. Under ultrasound, these phantoms provide realistic tissue planes that represent the borders between different layers of skin, muscle, and fascia. The echogenicity of the muscle tissue layers, nerves, vessels, and bones is realistic, and bones have significant posterior shadowing as would be observed in a human subject. These phantoms cost $200 each for the first phantom and $60 for each subsequent phantom. These phantoms require some technical skill to design, but they can be built for just 4% of the cost of their commercial counterparts.

Here, we demonstrate the design and creation of four custom ballistic gelatin ultrasound phantoms for ultrasound-guided regional anesthesia training. We designed the phantoms using computer-aided design software, used 3D-printed models to create silicone molds, and then poured melted ballistic gel into the molds to create custom tissue layers.