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

Published: February 09, 2024

doi:

Brennan P. Marsh-Armstrong*¹, John F. Ryan*¹, David J. Mariano, Preetham J. Suresh, Benjamin Supat

¹University of California, San Diego School of Medicine, ²Department of Anesthesia,University of California, San Diego Health, ³Department of Emergency Medicine,University of California, San Diego Health

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 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.

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

Representative Results

Four ultrasound phantoms were successfully designed and built using the methods described above. An ultrasound cross-section of each model aligned with an ultrasound of equivalent human anatomy is shown in Figure 5. Under ultrasound, these phantoms provide realistic tissue planes, which represent the borders between different layers of skin, muscle, and fascia. The muscle tissue is appropriately and homogeneously echogenic. This echogenicity can be adjusted based on the amount of flour added…

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…

Divulgazioni

The authors have nothing to disclose.

Acknowledgements

This project was funded by the Simulation Training Center (STC) at the University of California, San Diego School of Medicine in La Jolla, CA. We would like to thank Blake Freechtle for his contributions to Figure 5.

Materials

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

Riferimenti

Hocking, G., Hebard, S., Mitchell, C. A review of the benefits and pitfalls of phantoms in ultrasound-guided regional anesthesia. Reg Anesth Pain Med. 36 (2), 162-170 (2011).
Culjat, M. O., Goldenberg, D., Tewari, P., Singh, R. S. A review of tissue substitutes for ultrasound imaging. Ultrasound Med Biol. 36 (6), 861-873 (2010).
Grottke, O. Virtual reality-based simulator for training in regional anaesthesia. Br J Anaesth. 103 (4), 594-600 (2009).
. Regional anesthesia ultrasound training block Available from: https://medicalskillstrainers.cae.com/regional-anesthesia-ultrasound-training-block/p (2023)
CAE Healthcare. . Gen II femoral vascular access & regional anesthesia ultrasound training model. , (2023).
Osmer, C. L. A gelatine-based ultrasound phantom. Anaesthesia. 63 (1), 107 (2008).
Nicholson, R. A., Crofton, M. Training phantom for ultrasound guided biopsy. Br J Radiol. 70, 192-194 (1997).
Bude, R. O., Adler, R. S. An easily made, low-cost, tissue-like ultrasound phantom material. J Clin Ultrasound. 23 (4), 271-273 (1995).
Patel, A. S., Harrington, T. J., Saunt, K. S., Jones, W. K. Construction of an ultrasound biopsy phantom. Australas Radiol. 40 (2), 185-186 (1996).
Culp, W. C. Relative ultrasonographic echogenicity of standard, dimpled, and polymeric-coated needles. J Vasc Interv Radiol. 11 (3), 351-358 (2000).
Morehouse, H., Thaker, H. P., Persaud, C. Addition of Metamucil to gelatin for a realistic breast biopsy phantom. J Ultrasound Med. 26 (8), 1123-1126 (2007).
Phal, P. M., Brooks, D. M., Wolfe, R. Sonographically guided biopsy of focal lesions: a comparison of freehand and probe-guided techniques using a phantom. AJR Am J Roentgenol. 184 (5), 1652-1656 (2005).
McNamara, M. P., McNamara, M. E. Preparation of a homemade ultrasound biopsy phantom. J Clin Ultrasound. 17 (6), 456-458 (1989).
Gibson, R. N., Gibson, K. I. A home-made phantom for learning ultrasound-guided invasive techniques. Australas Radiol. 39 (4), 356-357 (1995).
Lollo, L., Stogicza, A. R. Low-cost, high-fidelity ultrasound phantom gels for regional anesthesia training programs. MedEdPORTAL. 8, (2023).
Rathbun, K. M., Brader, W. T., Norbury, J. W. A simple, realistic, inexpensive nerve phantom. J Ultrasound Med. 38 (8), 2203-2207 (2019).
. Mold Star™ 16 FAST Product Information Available from: https://www.smooth-on.com/products/mold-star-16-fast/ (2023)
Wojtyła, S., Klama, P., Baran, T. Is 3D printing safe? Analysis of the thermal treatment of thermoplastics: ABS, PLA, PET, and nylon. J Occup Environ Hyg. 14 (6), D80-D85 (2017).
. Original Prusa i3 MK3S+ 3D Printer kit Available from: https://www.prusa3d.com/product/original-prusa-i3-mk3s-3d-printer-kit/ (2023)
. Original Prusa MINI+ kit Available from: https://www.prusa3d.com/product/original-prusa-mini-kit-2/ (2023)
. FreeCAD: Your own 3D parametric modeler Available from: https://www.freecad.org/ (2023)
Xu, D., Abbas, S., Chan, V. W. Ultrasound phantom for hands-on practice. Reg Anesth Pain Med. 30 (6), 593-594 (2005).
de Oliveira Filho, G. R., et al. Learning curves and mathematical models for interventional ultrasound basic skills. Anesth Analg. 106 (2), 568-573 (2008).
Koscielniak-Nielsen, Z. J., Rasmussen, H., Hesselbjerg, L. An animal model for teaching ultrasound-guided peripheral nerve blocks. Reg Anesth Pain Med. 34 (4), 379-380 (2009).
Pollard, B. A. New model for learning ultrasound-guided needle to target localization. Reg Anesth Pain Med. 33 (4), 360-362 (2008).
Wells, M., Goldstein, L. The polony phantom: a cost-effective aid for teaching emergency ultrasound procedures. Int J Emerg Med. 3 (2), 115-118 (2010).
van Geffen, G. J., et al. A needle guidance device compared to free hand technique in an ultrasound-guided interventional task using a phantom. Anaesthesia. 63 (9), 986-990 (2008).
Liu, Y., Glass, N. L., Power, R. W. Technical communication: new teaching model for practicing ultrasound-guided regional anesthesia techniques: no perishable food products. Anesth Analg. 110 (4), 1233-1235 (2010).
Sultan, S., Iohom, G., Shorten, G. A novel phantom for teaching and learning ultrasound-guided needle manipulation. J Med Ultrasound. 21 (3), 152-155 (2013).
Micheller, D. A low-fidelity, high-functionality, inexpensive ultrasound-guided nerve block model. CJEM. 19 (1), 58-60 (2017).
Sparks, S., Evans, D., Byars, D. A low cost, high fidelity nerve block model. Crit Ultrasound J. 6 (1), 12 (2014).