4. Formula #1 Thermal effect divided by Heating Rate Per Minute (HRM) = Necessary Treatment Time (TT)
5. Formula #1 Example: Your goal is to achieve a moderate thermal effect (2°C) using 1 MHz ultrasound at an intensity of 2.0 w/cm 2 1 MHz US at intensity of 2.0 w/cm 2 has a predetermined heating rate based on the chart of 0.4°C (.7 °F) Intensity (w/cm 2 ) 1 MHz 3 MHz 0.5 0.04° C (.07°F) 0.3° C (.5 °F) 1.0 0.2° C (.4°F) 0.6° C (1.1 °F) 1.5 0.3° C (.5°F) 0.9° C (1.6 °F) 2.0 0.4° C (.7°F) 1.4° C (2.5 °F) 2°C divided by .4°C = 5 minutes
6.
7. Formula #2 Example: 3 MHz US at intensity of 1.5 w/cm 2 for 5 minutes treatment time 3 MHz US at intensity of 1.5 w/cm 2 has a predetermined heating rate based on chart of 0.9° C (1.6 °F) Intensity (w/cm 2 ) 1 MHz 3 MHz 0.5 0.04° C (.07°F) 0.3° C (.5 °F) 1.0 0.2° C (.4°F) 0.6° C (1.1 °F) 1.5 0.3° C (.5°F) 0.9° C (1.6 °F) 2.0 0.4° C (.7°F) 1.4° C (2.5 °F) 5 min x .9°C = 4.5°C
9. Using fixed heating rate per minute (HRM) values to calculate without the charts 1 MHz ultrasound heats at a rate of 0.2°C (.36°F) per min per w/cm 2 You just need to remember .2 and .6 and you can calculate just about anything without the charts! Example: Treatment time of 6 minutes with intensity set at 1.2 w/cm 2 …
10. Using fixed heating rate per minute (HRM) values to calculate without the charts Then enter this HRM value into the formula you have already used: Treatment Time x Heating Rate Per Minute = Thermal Effect First calculate the Heating Rate Per Min (HRM) by multiplying the heating rate per min per w/cm 2 provided (.2°C) times the intensity (this step is already done for you when using the charts): .2 x 1.2 = .24°C 6 minutes x .24°C = 1.44°C Thermal Effect
11. Using fixed heating rate per minute (HRM) values to calculate without the charts 3 MHz ultrasound heats at a rate of 0.6°C (1.1°F) per min per w/cm 2 Another example, this time with 3 MHZ… Example: Treatment time of 4 minutes with intensity set at 1.4 w/cm 2 …
12. Using fixed heating rate per minute values to calculate without the charts Then enter this HRM value into the formula you have already used: Treatment Time x Heating Rate Per Minute = Thermal Effect First calculate the Heating Rate Per Min (HRM) by multiplying the heating rate per min per w/cm 2 provided (.6°C) times the intensity (this step is already done for you when using the charts): .6 x 1.4 = .84°C 4 minutes x .84°C = 3.36°C Thermal Effect
13. Using fixed heating rate per minute values to calculate without the charts 1 MHz ultrasound heats at a rate of 0.2°C (.36°F) per min per w/cm 2 Doing the reverse…calculating treatment time using .2 and .6 constants Example: 2°C desired thermal effect, 1.7 w/cm 2 used as the intensity …
14. Using fixed heating rate per minute values to calculate without the charts Then enter this HRM value into the formula you have already used: Thermal effect divided by Heating Rate per Min = Treatment Time First calculate the Heating Rate Per Min (HRM) by multiplying the heating rate per min per w/cm 2 provided (.2°C) times the intensity (this step is already done for you when using the charts): .2 x 1.7 = .34°C 2°C divided by .34 °C = 5.88 minutes
15. Using fixed heating rate per minute values to calculate without the charts 3 MHz ultrasound heats at a rate of 0.6°C (1.1°F) per min per w/cm 2 Another example, this time using 3 MHz… Example: 3°C desired thermal effect, 1.2 w/cm 2 used as the intensity …
16. Using fixed heating rate per minute values to calculate without the charts Then enter this HRM value into the formula you have already used: Thermal effect divided by Heating Rate per Min. = Treatment Time First calculate the Heating Rate Per Min (HRM) by multiplying the heating rate per min per w/cm 2 provided (.6°C) times the intensity (this step is already done for you when using the charts): .6 x 1.2 = .72°C 3°C divided by .72 °C = 4.17 minutes
17. Exceptions Using the .2 and .6 constants will be accurate in most situations with the following two exceptions.
18. Exceptions The red numbers below are calculated using the .2 and .6 constants and you can see how they compare side by side with the original chart values.
19. Exceptions The red numbers are calculated by multiplying the .2 or .6 constant times the intensity.
20. Exceptions The first and last values marked with an asterisk are the two exceptions where the calculation is not completely accurate. This includes .5 w/cm 2 intensity using 1 MHz, and 2.0 w/cm 2 intensity using 3 MHz. Otherwise the calculations are identical:
21. Reference: Starkey C. Therapeutic Modalities, 3rd ed . FA Davis: Philadelphia. 2004.
