What is the formula for temperature increase at 1 MHz?

• A. temp increased = 0.5 x intensity x time
• B. temp increased = intensity x time
• C. temp increased = 0.2 x intensity x time
• D. temp increased = 2 x intensity x time

Answer: (C)

Temperature rise from 1 MHz diathermy is determined by how much energy is delivered to the tissue and for how long. The energy delivered is the product of intensity and time, but the amount of heating per unit energy depends on the frequency. For 1 MHz, an empirical relationship used in practice is that the temperature increase equals 0.2 times intensity times time. The 0.2 factor accounts for tissue absorption and cooling effects at this frequency, so it yields a more moderate temperature rise than higher coefficients would.

For example, with an intensity of 3 W/cm^2 applied for 6 minutes, the temperature increase would be 0.2 × 3 × 6 = 3.6°C. (Keep in mind units: intensity in W/cm^2, time in minutes, result in degrees Celsius.) This is the rationale behind the chosen formula.