The paper is concerned with the new gel phantoms which can be used to visualize the high temperature region in a three-dimensional way. For the performance test or the maintenance of electromagnetic equipments for hyperthermia, it is desired to examine or check the three-dimensional pattern of the temperature distribution in the human body. In order to visualize the temperature distribution easily, the synthetic paste phantom has been used. The phantom is fabricated by dissolving the Polyvinyl Alcohol (PVA) into water and adding by a small amount of the surface active agent such as polyethylen glycol. The region whose temperature exceeds a certain value (clouding point) becomes white and opaque due to segregation of the agent. Thus the heated region whose temperature exceeds the clouding point can be visualized in the three-dimensional way. But the synthetic paste phantom has a serious problem of convection due to the temperature rise, because the phantom is a viscous fluid.
The new gel phantoms are transparent below the clouding point and the region which exceeds the clouding point becomes white and opaque. But convection due to the temperature rise does not occur in these phantoms. We have examined many kinds of high molecular gels to find suitable ones for the phantom. The materials we have found for the phantom materials are polyacrylamide and gellan gum. They show a good transparency to observe the white and opaque region from the outside and have high melting points. The clouding point can be controlled by changing the kind and concentration of the agent or by adding ionic materials such as a salt. The electrical properties of those phantoms can be adjusted to show the same properties as biological tissues by adding an appropriate amount of ionic material such as a salt. The newly developed phantoms may be quite useful for hyperthermia, because they enable us to observe the temperature region above 42.5°C in a three-dimensional way.
