A Review of the Benefits and Pitfalls of Phantoms in Ultrasound-Guided Regional Anesthesia

Abstract

With the growth of ultrasound-guided regional anesthesia, so has the requirement for training tools to practice needle guidance skills and evaluate echogenic needles. Ethically, skills in ultrasound-guided needle placement should be gained in a phantom before performance of nerve blocks on patients in clinical practice. However, phantom technology is varied, and critical evaluation of the images is needed to understand their application to clinical use. Needle visibility depends on the echogenicity of the needle relative to the echogenicity of the tissue adjacent the needle. We demonstrate this point using images of echogenic and nonechogenic needles in 5 different phantoms at both shallow angles (20 degrees) and steep angles (45 degrees). The echogenicity of phantoms varies enormously, and this impacts on how needles are visualized. Water is anechoic, making all needles highly visible, but does not fix the needle to allow practice placement. Gelatin phantoms and Blue Phantoms provide tactile feedback but have very low background echogenicity, which greatly exaggerates needle visibility. This makes skill acquisition easier but can lead to false confidence in regard to clinical ability. Fresh-frozen cadavers retain much of the textural feel of live human tissue and are nearly as echogenic. Similar to clinical practice, this makes needles inserted at steep angles practically invisible, unless they are highly echogenic. This review describes the uses and pitfalls of phantoms that have been described or commercially produced.

A Cost‐effective, Gelatin‐Based Phantom Model for Learning Ultrasound‐Guided Fine‐Needle Aspiration Procedures of the Head and Neck

“…Unfortunately, many available instructional models are expensive and impractical for routine use. 1,14 Low-cost gelatin phantoms provide a convenient way to practice invasive procedures before performing them on live patients, and we have developed 2 examples of these easily made models that can be used to teach head and neck fine-needle aspiration. Our phantoms have several advantages over other simple gelatin models.…”

“…The use of other materials such as cornstarch and graphite powder to change gelatin echogenicity has also been described in the literature. 1,33 Psyllium husk powder was selected for our model because of its commercial availability and solubility within the gelatin mixture.…”

“…In the past, items such as olives, hot dog pieces, synthetic beads, balloons, and foam have been used to simulate soft tissue masses. 1 Fresh blueberries provide an advantage over these items in that juice from them can be aspirated during fine-needle aspiration to confirm needle placement (Figure 3).…”

Assessment of a single-operator real-time ultrasound-guided epidural technique in a porcine phantom

“…3,4 Our porcine model provided a high-fidelity inexpensive learning tool in the same way as previously described for practising paravertebral and epidural techniques. 1,2,5 The reality of the model is limited by prone positioning, air tracking, echotexture, and slight anatomical differences. However, the porcine phantom allowed us to demonstrate that our technique is both feasible and highly acceptable to anesthesiologists.…”

Paramedian thoracic epidural training model

“…Phantom models have been developed to allow trainees to refine their needle guidance skills for various procedures throughout their training. 4 Since no phantom model is currently readily available for the paramedian approach to a thoracic epidural, we designed a simple and economical phantom which alerts the trainee immediately when the needle contacts the epidural space.…”