Which frequencies are used therapeutically?

• A. 1 and 3 MHz
• B. 0.1 and 0.3 MHz
• C. 5 and 10 MHz
• D. 8 and 12 MHz

Answer: (A)

Therapeutic ultrasound relies on specific acoustic frequencies to control how deeply energy penetrates and how much heating occurs. The frequencies routinely used in clinical rehab are 1 MHz and 3 MHz. The lower end, 1 MHz, penetrates deeper into tissue for treating deeper structures, while 3 MHz is absorbed more readily by superficial tissues for quicker heating. Frequencies such as 0.1 or 0.3 MHz are far too low for standard ultrasound therapy and are not used in this modality, as they don’t provide the expected therapeutic heating. Higher frequencies like 5 or 10 MHz, or 8 and 12 MHz, lie outside the typical therapeutic ultrasound range and are associated with imaging or other energy-delivery methods rather than standard deep or superficial heating. Therefore, 1 and 3 MHz are the frequencies used therapeutically.