Which parameter primarily determines depth of penetration in ultrasound?

Which parameter primarily determines depth of penetration in ultrasound?

• A. ERA
• B. Frequency
• C. Time
• D. Power

Answer: (B)

Penetration depth with ultrasound is governed by the frequency. Lower frequencies travel farther because they’re less rapidly attenuated by tissue, so energy reaches deeper structures. Higher frequencies are absorbed more quickly and don’t penetrate as deeply, though they offer better surface resolution. That’s why deeper targets are treated with about 1 MHz, while superficial targets use around 3 MHz. The other parameters—ERA, time, and power—affect the area covered, duration of exposure, and heating intensity, but they don’t set how deep the ultrasound goes.

Penetration depth with ultrasound is governed by the frequency. Lower frequencies travel farther because they’re less rapidly attenuated by tissue, so energy reaches deeper structures. Higher frequencies are absorbed more quickly and don’t penetrate as deeply, though they offer better surface resolution. That’s why deeper targets are treated with about 1 MHz, while superficial targets use around 3 MHz. The other parameters—ERA, time, and power—affect the area covered, duration of exposure, and heating intensity, but they don’t set how deep the ultrasound goes.