Improvement of resonant cavity applicator for thermotherapy of osteoarthritis

This paper describes heating properties of an improved new resonant cavity applicator for thermotherapy of osteoarthritis in the knee. Thermotherapy is easy, simple and effective in inhibiting osteoarthritis progression in the early stages. However, it is not easy to heat the deep tissue inside a knee. In our previous study, we proposed a new heating system using a resonant cavity applicator for thermotherapy of osteoarthritis. The estimated results of SAR distributions inside a knee using 3D FEM were discussed. With the previous applicator, a human leg was set in the applicator in an extended position. However, it causes pain for patients with osteoarthritis to extend the knee. To overcome this problem, the applicator was improved in this study. In this paper, a new small type resonant cavity applicator with shields was proposed and discussed with estimated results of a 3D anatomical human knee model using FEM. In this applicator, a human leg can be set in the center of the applicator in a bent position. Two cylindrical metal shields are used to focus the heating energy on the diseased joint and the human knee is non-invasively heated. In the present paper, first, estimated SAR distributions using a cylindrical agar phantom are presented. Second, the results of the human knee model reconstructed from 2D MRI images are discussed. From these results, it was found that the improved resonant cavity applicator is of a practical size and is useful for treatment of osteoarthritis inside the knee joint.