Development of a high-fidelity phantom for training ultrasound-guided radiofrequency ablation of thyroid nodules

Background

Thyroid nodules (TNs) are common solid or fluid-filled lumps in the thyroid gland, often benign but requiring treatment when they grow or cause symptoms. Ultrasound-guided radiofrequency ablation (RFA) has emerged as a minimally invasive alternative to surgery, particularly for benign TNs. However, precise execution is crucial, as the thyroid gland is surrounded by critical structures known as the “dangerous triangle,” including the recurrent laryngeal nerve and blood vessels. Inadequate targeting or excessive heat application during RFA can lead to complications. Currently, alternative training using phantoms can help inexperienced surgeons enhance surgical techniques and procedural safety. However, current phantom models often lack realistic tissue responses, particularly in mimicking protein coagulation, carbonization, and hydrodissection.

Purpose

This study aimed to develop a high-fidelity anthropomorphic neck and thyroid phantom that has similar ultrasound imaging characteristics and RFA response to that of human tissue. The phantom was designed to simulate key procedural steps, including ultrasound-guided hydrodissection and ablation-induced tissue changes, to support training in RFA of TNs.

Methods

The thyroid and neck phantom's anatomical structure was reconstructed using Computed Tomography (CT) imaging to create a 3D-printed mold. It was fabricated using biomimetic dual-network artificial materials (BDAM) through a multi-step molding process. The material characteristics, including the acoustic properties, ultrasound imaging, impedance, electrical conductivity, and thermal ablation response, were systematically evaluated. The phantom underwent ultrasound-guided hydrodissection before RFA, and the resulting ablation zones were compared with those observed in animal tissues.

Results

The phantom's material properties were validated and compared to human muscle and thyroid tissue characteristics from the literature. Additionally, the phantom produced clear ultrasound images during hydrodissection, effectively demonstrating the separation of tissue from the nodule. It also exhibited localized bubbling and coagulative carbonization in response to thermal ablation under ultrasound imaging. The ablation zone closely resembled that observed in pig liver tissues, with a standard deviation (SD) of ≤0.2 cm.

Conclusion

A high-fidelity phantom for training ultrasound-guided RFA of TNs has been presented. The developed phantom demonstrated clear ultrasound imaging and a similar RFA response of biological tissues, particularly pig liver. It provides a realistic and effective platform for training in ultrasound-guided RFA of TNs.