Temperature Distribution of Resonant Cavity Applicator for Thermal Rehabilitation Using 3D Printing

Osteoarthritis (OA) is one of the most common joint diseases. Thermotherapy, such as that using a microwave diathermy applicator, is widely used for OA. The deep tissue of a knee joint should be heated to 36 °C-38 °C for an effective thermotherapy. However, heating this deep region using a microwave diathermy applicator is challenging. Previously, we proposed a resonant cavity applicator to overcome these problems and confirmed its ability (heating experiments on bovine knees) to heat the deep region of a knee joint without physical contact. Furthermore, we proposed a method of temperature measurement using ultrasound images. In this method, the temperature distribution was measured using noninvasive image analysis. In a previous study, we found temperature measurement accuracy of ≤ 1.0 °C. In the present paper, we describe a temperature distribution using a 3D-printed knee model for treating OA. First, we created a 3D finite element model (FEM) of the knee and a 3D-printed knee model from 2D medical images. Second, we calculated temperature distributions in the FEM model and performed a heating experiment with a prototype of the heating system. Third, we performed positioning accuracy experiments to investigate the accuracy of our temperature measurement system comprising a robotic arm, 3D-printed knee model, and ultrasound diagnostics. Finally, we measured the temperature distribution inside the 3D-printed knee model from ultrasound images. The heating experiments confirmed that our proposed method could heat deep regions of a knee joint without any undesirable hotspot. Therefore, our results suggest that this method is useful for effective thermotherapy of OA.