Temperature distribution produced in brain tissue and other media by a radiofrequency hyperthermia generator

The temperature distribution produced in living brain tissue by a radiofrequency, Neuro N-50, hyperthermia probe was measured as a function of probe temperature, heating duration, and distance from the heating probe by a sensor containing five thermocouples for durations up to 2 min. Brain sections were examined to determine the effects of heating at various temperatures. It was found that a simple theoretical conductive heat transfer model predicted the steady-state temperature distributions quite well. At distances up to 7.4 mm from the heating probe, a heating time of 20 s was sufficient to produce about 90% of the temperature rise measured at 120 s. The equilibrium temperature at any distance from the center of the probe was a linear function of the reciprocal of this distance. The time constant for heating was approximately 3 s at 0. 95 mm from the heating probe and about 10 s at 7.4 mm for brain tissue, while these values are about 5-20 s in egg white. For a given probe size, higher probe temperatures increased the size of the region of cell death. According to the heat transfer model, the diameter of the region of tissue that attains a given temperature is proportional to the diameter of the probe. The use of probe temperatures up to 90 degrees C would enable an increase in the volume of the region of cell death, or the use of a smaller diameter probe to produce a lesion of a given size.