A gel wax phantom for performance evaluation in diagnostic ultrasound: assessment of image uniformity, geometric accuracy, and diameter of a hyperechoic target

Purpose: To develop and validate a phantom for diagnostic ultrasound (US) scanners by embedding targets in gel wax to determine the image uniformity, lateral and axial resolution, and diameter of a stainless-steel disc. Materials and Methods: Acoustic property (AP), which includes the velocity of US (cus), acoustic impedance (Z), and attenuation coefficient in gel wax were determined. The cus, and attenuation coefficient were estimated using the pulse-echo technique. Z was obtained from the product of sample density (\r{ho}) and cus. Two rectangular frames using polytetrafluoroethylene (PTFE) sheets with holes separated by 5, 10, and 20 mm distances were constructed. Nylon filaments and SS-disc (diameter = 16.8 mm) were threaded through the frames and suitably placed in melted gel wax to obtain orthogonal targets. The targets were measured using computerized tomography (CT) and a 2-9 MHz US probe. Results: The AP of gel wax were cus=1418 m/s, \r{ho}= 0.87 g/cm3, Z=1.23 MRayls, attenuation coefficient= 0.88 dB/cm/MHz. The results of US imaging of the targets were compared with their physical sizes and served as baselines for the scanner and probe. The maximum error in distance measurement in the phantom US images was 7.1%, and the phantom volume decreased by 1.8% over 62 weeks. Conclusion: Gel wax can be useful in developing affordable, highly stable, and customizable diagnostic US phantoms that can be implemented widely.