Heating characteristic of developed rectangular resonant cavity applicator with ultrasound temperature measurement system

Osteoarthritis (OA) is a common disease that causes pain, stiffness, swelling, and loss of function within the knee joint [1] . In previous studies, we proposed the thermal rehabilitation system using a small rectangular resonant cavity applicator for OA. It could heat and treated the knee joint non-invasively [2] , however, it could not measure the temperature distribution around the heated area. In the present study, we have developed a new treatment system with the function of measuring 2-D temperature distributions from the ultrasound images. This treatment system can non-invasive temperature measurement. For measuring 2-D temperature distributions, it needs ultrasound images at the same position before and after heating. This non-invasive temperature measurement system mainly consists of a manual slider and an ultrasound probe. A jig fixed to the ultrasound probe is attached to the tip of the manual slider. In the heating experiment using the developed system, a human leg-shaped agar phantom with a simulated acrylic bone was used. As an experimental method, first, an ultrasound probe was contacted to the surface of the human leg-shaped agar phantom, and an ultrasound image before heating was captured. Second, the ultrasound image after heating at the same position was captured again. Next, when the probe was moved 5 mm away from the original position using the manual slider, the ultrasound images before and after heating were also captured again. This operation is repeated, and a total of three ultrasound images are captured. The reason is to confirm the result 3-D. By repeating these operations, it is possible to construct a 3-D temperature distribution from the 2-D temperature distributions. Figure 1 shows a resultant temperature distribution from ultrasound images. As shown in Figure 1 , the central part between two acrylics has the highest temperature of the three heated areas. The maximum temperature rise (ΔT) was approximately 7.6 o C. The farther away from the central part of the acrylic, the lower the temperature like Figure 1 (A), (C) . In addition, from Figure 1 (A) and (C) , the temperature increase was warmed within a limited range because no temperature rise was observed except in the central part.