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

Summary

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.

Abstract

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.

Introduction

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 recent....

Protocol

For this project, authors JR and PS volunteered as ultrasound subjects, and verbal consent was obtained from both. For those following this protocol, obtain approval from an ethics committee or institutional review board (IRB) prior to using patients or human volunteers as study subjects.

1. Phantom design and silicone mold creation

1. Creation of a reference ultrasound image
   1. For each ultrasound phantom, have a physician with ultrasound sub-specialization .......

Discussion

These custom ballistic gel-based phantoms provide trainees with medium-fidelity median, femoral, suprainguinal fascia iliaca plane, and serratus anterior plane nerve block training for a fraction of the cost of commercially available nerve block phantoms (Table 1). Our first median and femoral nerve block trainers were made in-house for 12% and 9% of the price of the cheapest commercially available median and femoral nerve block trainers, respectively. None of the available femoral nerve block phantoms a.......

Materials

Name	Company	Catalog Number	Comments
ABS Filament - 1.75 m+B+A2:A14	Hatchbox (Pomona, CA)		https://www.hatchbox3d.com/collections/abs-1-75mm
Adobe Photoshop	Adobe (San Jose, CA)		https://www.adobe.com/products/photoshop.html
Amber Tone Dye	Humimic Medical (Greenville, SC)	852844007925	Ballistic gel dye; https://humimic.com/product/amber-tone-dye/
Fusion 360	Autodesk (San Franciso, CA)		Computer-assisted design (CAD) software; https://www.autodesk.com/products/fusion-360/overview?term=1-YEAR&tab=subscription&plc=F360
Gelatin #1 - Medical Gel by the Pound	Humimic Medical (Greenville, SC)	852844007406	Ballistic gel; https://humimic.com/product/gelatin-1-medical-gelatin-by-the-pound/
Gluten-Free All-Purpose Flour	Arrowhead Mills (Hereford, TX)		Flour for echogenicity; https://arrowheadmills.com/products/gluten-free/organic-gluten-free-all-purpose-flour/
Microsoft PowerPoint	Microsoft (Redmond, WA)		https://www.microsoft.com/en-us/microsoft-365/powerpoint
Mold Star 16 FAST Pourable Silicone Rubber	Smooth-On (Macungie, PA)		Pourable silicone rubber; https://www.smooth-on.com/products/mold-star-16-fast/
Peach Tone Dye	Humimic Medical (Greenville, SC)	852844007895	Ballistic gel dye; https://humimic.com/product/peach-tone-dye/
PLA Filament - 1.75 mm	Hatchbox (Pomona, CA)		https://www.hatchbox3d.com/collections/pla-1-75mm
Prusa Original i3 MK3S+ printer	Prusa Research (Prague, Czech Republic)		3D printer; https://www.prusa3d.com/category/original-prusa-i3-mk3s/
Prusa Slicer 2.6.1	Prusa Research (Prague, Czech Republic)		3D printer slicer software; https://www.prusa3d.com/page/prusaslicer_424/
Wool-Ease Thick & Quick Yarn	Lion Brand Yarn (Lyndhurst, NJ)	640-610B	Yarn for simulated nerves; https://www.lionbrand.com/products/wool-ease-thick-and-quick-yarn?variant=32420963516509