Heating Characteristics of Prototype Knee Rehabilitation System Using Rectangular Resonant Cavity Applicator

: We designed and prototyped a small rectangular resonant cavity applicator system for thermal treatment of knee osteoarthritis, and discussed its usefulness from both results of computer simulations and heating experiments. The authors had proposed a deep knee joint thermal rehabilitation system using a cylindrical resonant cavity, and demonstrated its usefulness from the results of agar phantom heating experiments and clinical heating experiments by volunteers. However, the area of the leg placed inside the cavity was wide when using the cylindrical cavity, so the healthy calf and thigh, which are not the targeted tissues, were also slightly heated. Therefore, in the present study, we clarified the possibility of deep thermal treatment with higher safety by changing the cylindrical shape of the resonant cavity to a compact rectangular shape. First, the dimensions and resonant frequency band of the rectangular cavity applicator were determined using the finite element method (FEM) ． Based on the numerical results, a heating system was prototyped, and heating experiments were conducted on a cylindrical agar phantom and a human leg-shaped agar phantom. Dimensions of the rectangular resonant cavity applicator are 300 mm in height, 350 mm in width and 200 mm in length. Heating experiments were conducted with a heating power of 30 W and a heating time of 10 minutes. As a result, it was confirmed that the central part of the cylindrical agar phantom was locally heated, and the temperature increase value was approximately 8.0 ° C. Furthermore, in the experiment which the leg-shaped agar phantom was heated, it was confirmed that only the knee joint was locally heated and no hot spots were generated in other areas. From these experimental results, it was concluded that the deep part of the knee joint could be safely and locally heated by using the rectangular resonant cavity applicator.