A tissue-mimicking phantom material has been developed for use with thermal therapy devices and techniques. This material has magnetic resonance properties (primarily T2) which change drastically upon thermal coagulation, enabling its use for device characterization and treatment verification using simple T2-weighted imaging techniques. The coagulation temperature of the phantom can be changed from 50-60 degrees C by adjusting the pH from 4.3 to 4.7. The energy absorption properties can be adjusted to match the acoustical and optical properties of tissues. T2 relaxation measurements are provided as a function of temperature, along with T2-weighted MR images to illustrate the visualization of heating patterns. A complete recipe for fabricating phantoms is provided.